Water, despite being one of the most common substances found in nature, turns out to be a very particular substance, anomalous in almost all of its physical-chemical properties, and possibly one of the most complex of all those that are made up of a single chemical compound.
Its uniqueness lies in the ease with which its molecules form large three-dimensional aggregates when it is in a liquid state. This differentiates it from normal fluids and explains the high values of viscosity, surface tension and fusion temperatures "Fusion (change of state)") and boiling.
Its cluster-shaped molecular structure, still not very well known, is due to the fact that the hydrogen atoms are not geometrically aligned with the central oxygen, but rather are folded at an angle of 105°, which gives rise to bipolarity and hydrogen bonds between adjacent molecules. The true water molecule would therefore be (H2O)n, the value of n varying with the conditions of pressure and temperature. Due to the special folded arrangement of the water molecule, it has a great dissolving capacity, this property being precisely what makes its quality more vulnerable.
Another characteristic of water is its great stability, even at high temperatures. At 2,700 °C, only 11% dissociates into hydrogen and oxygen molecules. From this it follows that the total amount of water on earth remains constant for long periods, although its state and situation varies, forming what has been called the hydrological cycle. Under certain circumstances, the water vapor in the atmosphere precipitates in the form of rain or snow.
The hydrological cycle or water cycle is the process of water circulation between the different compartments that make up the hydrosphere. It is a biogeochemical cycle in which there is minimal intervention of chemical reactions, because water moves from one place to another or changes its physical state. The phases of the water cycle are:
• - Evaporation: when water goes from the liquid phase to the gas phase.
• - Condensation: Condensation is a phase change process through which water vapor becomes liquid due to the cooling of the air.
• - Precipitation: is any type of water that falls on the earth's surface. Different forms of precipitation include drizzle, rain, snow, hail, sleet.
• - Infiltration: occurs when water that reaches the soil penetrates the earth through its pores and becomes groundwater.
• - Runoff: is the water that runs through the earth, after precipitation, without penetrating it.
Excessive sedimentation (sewer)
General characteristics of water
Water, despite being one of the most common substances found in nature, turns out to be a very particular substance, anomalous in almost all of its physical-chemical properties, and possibly one of the most complex of all those that are made up of a single chemical compound.
Its uniqueness lies in the ease with which its molecules form large three-dimensional aggregates when it is in a liquid state. This differentiates it from normal fluids and explains the high values of viscosity, surface tension and fusion temperatures "Fusion (change of state)") and boiling.
Its cluster-shaped molecular structure, still not very well known, is due to the fact that the hydrogen atoms are not geometrically aligned with the central oxygen, but rather are folded at an angle of 105°, which gives rise to bipolarity and hydrogen bonds between adjacent molecules. The true water molecule would therefore be (H2O)n, the value of n varying with the conditions of pressure and temperature. Due to the special folded arrangement of the water molecule, it has a great dissolving capacity, this property being precisely what makes its quality more vulnerable.
Another characteristic of water is its great stability, even at high temperatures. At 2,700 °C, only 11% dissociates into hydrogen and oxygen molecules. From this it follows that the total amount of water on earth remains constant for long periods, although its state and situation varies, forming what has been called the hydrological cycle. Under certain circumstances, the water vapor in the atmosphere precipitates in the form of rain or snow.
The hydrological cycle or water cycle is the process of water circulation between the different compartments that make up the hydrosphere. It is a biogeochemical cycle in which there is minimal intervention of chemical reactions, because water moves from one place to another or changes its physical state. The phases of the water cycle are:
• - Evaporation: when water goes from the liquid phase to the gas phase.
• - Condensation: Condensation is a phase change process through which water vapor becomes liquid due to the cooling of the air.
• - Precipitation: is any type of water that falls on the earth's surface. Different forms of precipitation include drizzle, rain, snow, hail, sleet.
• - Underground circulation: it is the circulation of water below the surface. It occurs due to gravity like runoff.
• - Fusion: transition from a solid to a liquid by the action of heat: the fusion of ice in liquid water occurs by the action of heat at 0 °C.
• - Solidification: it is the reverse process of fusion. It consists of the change of state of water from liquid to solid produced by a decrease in temperature.
Some of the water that falls on the earth evaporates directly; On the other hand, it returns to the atmosphere through plant evapotranspiration; The rest reaches, through more or less complex surface or underground paths, the sea, where, by evaporation, it is returned to the atmosphere, thus completing the cycle.
The water sources are:
Meteoric waters: in the case of rural communities or small towns, the collection of rainwater appears as a possible source of supply, which must be collected on adequately prepared land. Regarding the quality of this water, we can mention that it has low quantity dissolved solids, very low turbidity, due to the chemical composition it is considered to have low alkalinity and hardness, and at the same time have a high carbon dioxide content (rainwater when falling dissolves carbon dioxide from the atmosphere which gives it an acidic pH). This is corrected by adding lime. For this type of treatment it is advisable not to use lead pipes due to the aggressiveness of the water.
Surface waters: This is the name given to the waters coming from rivers, streams, lakes, etc. They are generally cloudy and colored waters and, furthermore, because they are superficial, they are subject to contamination. For these reasons, they require purification treatment, including disinfection prior to consumption.
Subalveal waters: these are the waters that run through the subalveo of the river. The subalveo is the area where the filtrate is collected through the ground. They are generally captured through filter wells or filter galleries. They are generally very good quality waters since they have undergone a natural filtration process. The cost of the works to use this water is somewhat high.
Groundwater: are the waters found in the subsoil. We can distinguish three types of different underground sources depending on the position of the water in the ground:
Deep groundwater: deep groundwater captured through semi-urgent wells generally provides drinking water, occupying second place in number of inhabitants served and first in localities served. Groundwater usually lacks turbidity and color, but in some cases of ferruginous groundwater, it becomes colored shortly after extraction due to the oxidation of ferrous compounds contained therein and requires corrective treatment prior to its delivery for consumption. In other cases they may contain excess dissolved solids (high mineralization), chlorides, sulfates, etc., or some toxic elements such as arsenic, vanadium or fluorine in high concentration, resulting in their inappropriate use as a source of supply.
Groundwater or groundwater: they can be used when they constitute the only economically usable source. Its level fluctuates quite a bit and is directly influenced by the rainfall regime. Its quality is variable and although it is physically and chemically acceptable, there is always the danger of microbiological contamination. Therefore, if its use is resolved, it will have to be done through excavated and drilled wells that must be adequately protected against surface contamination, maintaining strict bacteriological control of drinking water.
Spring water: water that springs from the earth. They can constitute a solution in the case of small rural towns, as long as they have sufficient flow and adequate quality. The catchment must be adequately protected. The spring will be safer as its flow rate is less variable, influenced by the rainfall regime, and the less alterable the water quality is.
The uses of water are: sanitation (hygiene and consumption), agriculture (irrigation), livestock (drinking), recreation with and without contact (spa, water sports), protection of aquatic life (fauna and flora), hydroelectric, industrial (process, boilers, refrigeration, concrete).
Throughout the hydrological cycle, the water that, when it passes into the atmosphere through evaporation, is distilled water of maximum purity, is loaded with other substances that determine, at the time of its use, the quality characteristics.
Although in the atmosphere rainwater receives impurities from gases, aerosols, dust and salts, if we limit ourselves to the natural cycle, in the sense of not considering causes of pollution due in one way or another to human activity, most of the impurities come from the geological formations through which it flows or in which it is stored and which, to a greater or lesser extent, it dissolves. Therefore, geology is a determining factor in the composition of water and, ultimately, its natural quality. Thus, on the one hand, water, according to the lithology of the geological formations with which it is in contact, is acidic or alkaline, with high or low content of dissolved salts, with a preponderance of carbonates, sulfates, chlorides, etc. On the other hand, contact with mineral formations can be the occasion for certain elements such as iron, manganese, copper or mercury to be found in the water "Mercury (element)") whose natural origin should be known to differentiate it from subsequent contamination.
The chemical and biological composition that waters have naturally is modified by the reception of effluents, of very different characteristics, caused by human activity. This final composition is what determines the quality of the water at a certain time.
Surface water
This is the name given to the waters that circulate on the surface of the ground.
They can occur in a flowing form as in the case of currents, rivers and streams, or still in the case of lakes, reservoirs, reservoirs and lagoons.
Surface water is produced by runoff generated from precipitation and infiltration of groundwater.
For regulatory purposes, surface water is usually defined as any water open to the atmosphere and subject to surface runoff. Once produced, surface water follows the path of least resistance. A series of streams, creeks, streams and rivers carry water from downsloping areas to a main watercourse. This drainage area is often referred to as a watershed or drainage basin.
A watershed is a basin surrounded by a deep groove, which separates different drainage areas. Water quality is strongly influenced by where in the basin it is diverted for use. The quality of streams, rivers and streams varies according to seasonal flows and can change significantly due to precipitation and accidental spills. Lakes, reservoirs, reservoirs and lagoons generally present a lower amount of sediment than rivers, however they are subject to greater impacts from the point of view of microbiological activity. Still bodies of water, such as lakes and reservoirs, age over a relatively long period as a result of natural processes. This aging process is influenced by microbiological activity that is directly related to nutrient levels in the body of water and can be accelerated by human activity.
Underground Water
Groundwater is defined as the portion of subsurface water that is subject to a pressure greater than atmospheric pressure, so that it flows into open cavities within the earth or moves across its surface in the form of seeps or springs.
Groundwater can enter through several routes: it comes, for example, from the percolation of direct precipitation, infiltration of surface water deposits, and artificial recharge.
There are several exit routes such as the evaporation of free water or soil moisture, evapotranspiration, which is basically due to the use and evaporation of water through vegetation, escapes into rivers or streams or man-made systems such as supply wells.
Groundwater can be generally classified as free and confined layer. In free layer waters, the water table can rise or fall depending on the level of the surface waters, since they act in a similar way to communicating vessels.
The water that penetrates through infiltration can carry different substances in solution depending on its origin. The soil works as a filter for many substances, retaining them, especially organic matter. However, some substances will reach the water table and be carried away by groundwater.
Groundwater acts as a diluent and, since it does not have organisms that transform organic matter, as in surface water, it degrades very slowly under the action of dissolved oxygen. Therefore, any type of organic contamination that originates in groundwater takes many years to be eliminated and inorganic contamination only dilutes and circulates within the underground veins.
Currently, one of the biggest problems with groundwater is contamination by nitrates of agricultural origin, with the addition of toxic and dangerous substances being totally prohibited by any procedure: infiltration, injection, etc., since these do not have any elimination mechanism and can only dilute said substances.
The soil below the earth's surface is made up of two different hydrogeological zones; the unsaturated zone and the saturated zone. The unsaturated zone constitutes a three-phase system: solid, liquid and gas.
• - Solids are generally made up of inorganic and organic materials. Organic matter corresponds to the remains of buried plants and animals that are in different stages of degradation.
• - The liquid phase is made up of water which contains dissolved solids.
• - For its part, the gas phase includes water vapor and other gases present in the atmosphere, although not necessarily in the same proportion. The saturated zone, on the other hand, includes all materials located below the water table.
Pollution concept applied to water
Saying that water is contaminated or not is a concept, somewhat relative, since an absolute classification of the “quality” of the water cannot be made. Distilled water, which, from the point of view of purity, has the highest degree of quality, is not suitable for drinking, this is because the degree of quality of the water must refer to the uses to which it is intended. The determination of the state of water quality will refer to the intended use for it.
In the same way, the concept of pollution must refer to the subsequent uses of water. In this sense, the Water Law (Spanish, Article 85) establishes that pollution is understood as:
Pollution: The action and effect of introducing materials or forms of energy that imply a harmful alteration of the quality of water in relation to subsequent uses or its ecological function.[1][2].
Purification
Contenido
El tratamiento de potabilización comienza en unas rejas que eliminan los sólidos gruesos, luego pasa a un desarenador donde se eliminan los sólidos sedimentables más pesados e inorgánicos, posteriormente ingresa a un sedimentador donde se eliminan los sólidos sedimentables menos pesados y orgánicos. Luego se realiza una coagulación-floculación donde se remueven el resto de los sólidos en suspensión, resto de la materia orgánica, coloración (sólidos disueltos y coloidales), el posterior paso es una decantación donde se eliminan los flocs formados en la etapa anterior, el paso siguiente es una filtración donde se retienen los flocs y micropartículas que no fueron separados en la etapa anterior, luego se alcaliniza porque el pH disminuyó por el agregado de ácidos y finalmente se desinfecta con lo que se eliminan microorganismos patógenos con lo que ya se tiene un efluente apto para el consumo.
Preliminary treatments
Solid particles settle as discrete particles or as flocculated particles due to the action of gravity, forming sludge that must be separated.
Discrete particles are separated in sand traps and problems such as deposition of inert material and damage to electromechanical pumping equipment are avoided.
When the turbidity and suspended solids contain fine particles, mostly non-colloidal, primary sedimentation equipment is placed prior to slow filtration or coagulation-flocculation-sedimentation treatment. If it contains mostly colloidal particles, it is convenient to carry out coagulation-flocculation-sedimentation directly.
The main goals of a sand trap are:
• - Remove discrete particles larger than 0.2 mm.
• - Avoid overloads (higher operating costs).
• - Damage to electromechanical pumping equipment and other installations.
• - Avoid sedimentation problems in the raw water adduction.
Primary sedimentation
Sedimentation serves to separate turbidity and suspended solids, after a time, by the action of gravity. If the suspended material settles quickly, it is considered to have siliceous material of small size but high specific gravity.
Particles larger than 0.2 mm cannot be separated by coagulation.
The units are called settlers or settlers interchangeably and can be circular, rectangular or square.
The retention time must be such that it allows the particles to float (less heavy than water) or the particles to settle (heavier than water).
Solids are considered agglomerable or flocculent when they agglutinate as they descend, changing shape, weight and size with a greater sedimentation speed.
Coagulation, flocculation and decantation
Coagulation and flocculation are part of the processes of a water treatment plant. Coagulation is carried out with rapid stirring and flocculation with slow stirring. The flocs may settle in another chamber or in the same chamber where coagulation occurred. Coagulation is the addition of coagulant so that the particles agglutinate, forming flocs that will then settle in another chamber. Coagulants can be natural or synthetic. The most used is aluminum sulfate and is being displaced by ferric chloride and mainly aluminum chloride. It is common to add polymers and to a lesser extent activated silica and bentonite as flocculants. Adjuvants are polyelectrolytes that improve coagulation and are chains of small subunits that contain ionizable groups such as the amino group, hydroxyl group, and carboxyl group. They improve coagulation because they increase the turbidity of the water, by generating more particles such as impurities, they decrease the dose because they increase the kinetics of the reaction and produce larger flocs faster. Coagulants are aluminum and iron salts that form hydrated oxides (q+) and attract suspended particles (q-) to form flocs. They vary in concentration of useful oxides and optimal pH. pH is a critical parameter in the efficiency of the process. The coagulant dose depends on mixing time (flocculation) - it is lower when the contact area is larger -, injection point (dispersion) - there is a speed at which it is better to inject the coagulant, alkalinity - the higher the alkalinity, the higher the dose -, turbidity - the higher it is, the higher the necessary dose. The optimal conditions of stirring speed, solution concentration, mixing time must be found. To determine these parameters, the JARTEST is carried out, which consists of carrying out agitation tests in the laboratory once a day or more than once (in the case of streams or rivers whose physical characteristics vary greatly). They are marketed in a specific state and have a working pH range.
Dispersion consists of adding coagulant reagents, with stirring. This achieves the destabilization of the colloidal matter. Natural reagents are alumina sulfate, ferric chloride or polymers; all of them available in liquid or solid form. Coagulants vary in concentration of useful oxides and optimal pH. The JARTEST assay allows the coagulant dose to be determined. The greater the turbidity, the greater the dose because the amount of solids in suspension is greater, the more alkaline the greater the dose, the greater the mixing time the better because larger flocs are formed and in greater number, the better the demand point is chosen, the lower the dose, rapid agitation is required for coagulation.
Flocculation is the process of joining previously coagulated or destabilized particles by slow agitation to form "flocs" of greater weight and size, which are separated by filtration, sedimentation or flotation, resulting in the removal of turbidity and color from the water. It starts with mechanical agitation with rotating paddles and motor drive, then moves on to hydraulic agitation where the water rises and falls through dividing plates by hydraulic pressure where the flocs collide with others to become larger. Rapid agitation and pumping break up the flocs that do not reform without the addition of more flocculant.
Filtration
Filtration is a physical process of eliminating microparticles and germs using granular material of different sizes (sand, anthracite and coal). Once it passes through the filter, the water is usually crystal clear. Filters can be gravity (fast or slow) or pressure (vertical or horizontal).
In rapid filtration, the particles are retained throughout the filter mantle, not just a superficial action, where they are only retained on the surface. The components of sand and gravel filters are:.
• - Filtering layer: the basic component is the uniform or stratified graded granular bed of sand and anthracite forming dual and multiple layers. For its design it is essential to know the filtration speed.
• - Support bed: normally made of graded gravel. The granulometry and thickness depend on the drainage system adopted for the washing adopted.
• - Drainage system and false bottom: it consists of the elements that allow the collection of filtered water and the distribution of water over the filtering layer.
Regardless of the type of filtration, filters must be backwashed with water or air at relatively high speed to promote partial fluidization and remove retained solids.
Alkalization
Alkalization consists of adding base because the acidic pH corrodes pipes and generates the release of gases with foam that makes subsequent analysis and treatment difficult. The dose depends on pH and is determined experimentally. Some alkalizers are sodium hydroxide (expensive), calcium carbonate (expensive), and calcium hydroxide (creates scale). The choice depends on costs and the analysis of its disadvantages.
Disinfection
The objective of disinfection of an effluent intended for human consumption and domestic use is the inactivation and destruction of pathogenic microorganisms. Chlorination is an efficient disinfection mechanism. Spores resist disinfectant, these more than protozoan cysts, these more than viruses, these more than vegetative bacteria.
For chlorination, the chlorine dose depends on:.
• - Chlorine demand (oxidizing power of chlorine, varies according to water sources and is determined experimentally because it depends on the concentration of impurities, temperature, time, etc.).
• - Residual chlorine, free plus combined.
• - Concentration of active chlorine.
Residual chlorine is an extra, non-toxic amount of chlorine, which prevents pathogens from entering the water meter from the treatment plant outlet. This point represents the place where water is delivered to customers. Chlorination is carried out in order to satisfy the demand for chlorine and leave a residual of 0.5 mg/L. Efficiency is measured by chlorine analysis and bacteriological analyzes of fecal and total coliforms. There must be an absence of this microorganism to ensure the non-presence of the rest of the pathogens.
If residual chlorine is represented vs. chlorine demand, 3 curves are obtained: no demand, medium demand, high demand. In the curve without chlorine demand, the residual chlorine increases with the chlorine dose, if the demand is medium or high, it grows to a point called breakpoint, where the residual chlorine begins to decrease and by increasing the chlorine dose the curve has the same behavior as the curve without demand.
Fluoridation is primarily used when there is no other source of fluoride for populations. In excess it prevents the fixation of calcium in teeth and bones. Softening is used to decrease the hardness of water. Demanganization and deironization to remove iron and manganese ions that precipitate metals that cause an astringent taste to the water. Dearsenization to eliminate arsenic that is harmful to health. Filtration with activated carbon to eliminate algae so that eutrophication does not occur. Elimination of odor, flavor and colors, for example phenols and organic matter that give it a musty taste. Dechlorination, if intensive use of chlorine has been made and the breakpoint reaction did not occur, allows chlorine levels to be reduced.
Based on the destination of the water, a quality or certain values will be required in the physical-chemical parameters. Drinking water has values recommended by the WHO (international) and the CAA (national).
Softening
It consists of the removal of soluble compounds with calcium and magnesium present in water. These cause the hardness of the water.
Hardness is defined as the propensity to form scale and the precipitating power of the soap solutions used to determine it. Hardness can be temporary (calcium and magnesium carbonates and bicarbonates) or permanent (calcium and magnesium sulfates, nitrates and chloride). The temporary hardness can be separated by heating or boiling them sufficiently. Carbon dioxide is released, precipitating insoluble calcium and magnesium compounds. Hardness is expressed in parts per million calcium carbonate equivalent.
The objective of softening is to remove salts that cause hardness in order to control corrosion, control scale and improve water quality for various uses. The methods used for softening are: decarbonation with lime-soda, ion exchange, membranes through reverse osmosis.
Activated carbon is used to absorb particles that cause taste, odor and color to water. Resins are used for the removal of organic particles. Carbon dioxide is absorbed by calcium hydroxide to form calcium carbonate and magnesium hydroxide. Solvay soda is added to waters with permanent hardness, and allows the decomposition of insoluble calcium sulfate to give rise to insoluble calcium carbonate and soluble sodium sulfate. The addition of lime and soda is applied when the water has a combination of hardness, permanent hardness and temporary hardness. Lime absorbs carbon dioxide, and this is not affected by the soda used to correct permanent hardness.
Ion exchange involves the transfer of ions present in the solution (pollutants) and those present in a zeolite. Chemical substitution reactions occur between a soluble electrolyte and an insoluble one with which it comes into contact. The mechanism is similar to adsorption so it is considered a special case of adsorption. For deionization, a single tank containing the cationic and anionic resins can be used. The cation exchanger is a sulfonated polystyrene hydrogen ion exchanger. The cation exchanger replaces calcium, magnesium, and iron ions with hydrogen ions. The anion exchanger used is a strongly basic amine resin exchanger. The anion exchanger replaces sulfate, carbonate, and bicarbonate ions with hydroxyl ions. Hydrogen ions then combine with hydroxyl ions to give water. The combined operations remove silica, minerals and carbon dioxide to give approximately neutral water. In rectification with the sodium cycle, the sodium ions go to form the solution, while the calcium and magnesium ions go to the solid. Its bases are interchangeable. Sodium ions go on to form sulfates, chlorides and carbonates.
It consists of subjecting a fluid on a membrane to a pressure greater than the osmotic pressure of the solution. Such a membrane is semipermeable and allows the passage of the solvent and not the solutes it contains. The solutes must be of low molecular weight so that they do not clog the membrane. It can be achieved by removing hardness, organic compounds, turbidity, disinfection products and pesticides and other elements present in the water.
Uses of water
Water intended for industrial use is 22%, water intended for agricultural use is 70% and water intended for domestic use is 8%. It is mainly used in heat transfer equipment, cleaning work areas, equipment and instruments and as raw materials. The quantity and quality of water required by an industry will depend on its size and the processes developed. The selection of a treatment system depends on the conditions that ensure sustainability, efficiency over time, raw water quality, required water quality, volumes per stage and treatment costs. The substances contained in water can be dissolved or suspended. The substances in suspension are sludge, organic matter, sand and waste. The dissolved substances are calcium, sodium and magnesium bicarbonates, calcium, sodium and magnesium sulfates, calcium and magnesium nitrates, residues, gases such as carbon dioxide and oxygen.
Effects of impurities
The effects of impurities contained in thermal equipment:
• - Reduction of heat transmitted by increased equipment fouling.
• - Breakdowns in the tubes and plates, due to the reduction of the heat transmitted.
• - Corrosion and fragility of steel.
• - Malfunction of the boiler with foam and water carried over in quantity by the steam.
• - High costs for cleaning, repairs, maintenance, inspection and reserve equipment.
• - Heat losses due to frequent purges.
• - Decrease in the performance of equipment that uses steam due to fouling.
Sampling
It is sampled 5 times, before and after coagulation, before and after filtration and before consumption. For groundwater. It is sampled twice, after extraction and before consumption. In the distribution network, the sampling sites are established at pipe terminal points, sweeping the entire network area and, if applicable, at pumping stations. Samples should be taken from direct entry faucets and not from internal installations.
The control parameters can be physical such as turbidity, pH, temperature, color, odor, conductivity; chemicals such as bicarbonates, sulfates, sulfides, nitrates, nitrites, calcium, magnesium, hardness, alkalinity; bacteriological such as the analysis of total coliforms, fecal coliforms, pseudomonas, enterococci.
It is variable and increases in critical conditions (epidemics, floods, etc.). The most common are: daily (source water), monthly (mains water) and quarterly (decanted, filtered and consumer water from the source).
Effluents
Any liquid, solid or gaseous element or substance that an establishment, property or ship discharges to the receiving body, including all human, animal, natural or synthetic, liquid, solid or gaseous waste or a mixture of them that is thrown with the effluent. The influent enters the process and the effluent leaves the process. The types of effluents are: liquid, gaseous and solid waste. Liquid effluents are supply waters to a population that have been impurified by various uses. They result from the combination of liquids and waste dragged from homes, manufacturing establishments, hospitals plus groundwater, surface water and precipitation that could be added. Gaseous effluents are substances that are discharged into the atmosphere (gases, aerosols, black smoke, mists) through ducts or diffuse emanations. Atmospheric pollution is defined as the atmospheric condition where gases reach concentrations or levels higher than normal, causing risks and damage to ecosystems, goods and people. Pollution comes mainly from automobile traffic, combustion of fossil fuels and activities of chemical industries. A solid waste is any object, substance, solid element from the consumption or use of a good in an industrial, institutional, service activity that the generator abandons, rejects or transfers to another person that can be used to build another good, with economic or final disposal value. Solid waste is divided into usable and non-usable waste. Solid waste is considered waste obtained from sweeping public areas. They are classified as domiciliary and non-domiciliary. Household ones are biodegradable or non-biodegradable. Biodegradable ones are those that degrade easily and in a short period of time such as fruits, fruit peels, vegetables, and non-biodegradable ones are those that do not degrade easily and have very long degradability cycles. Examples are tin, glass and construction elements. They are further classified as recyclable and non-recyclable. In industrial activities, effluents are generated as solid waste, which is why they must be controlled. Household solid waste has various stages: generation, transfer, processing, treatment and final disposal. Generation constitutes the origin of the waste and from there it is moved to other places, the transfer can occur via trucks or water, it includes processes such as compaction or differentiated selection, even from the same place or homes, the processing is carried out to separate the biodegradable material from the non-biodegradable, the treatment makes them harmless or that they do not harm the environment. It is done through biological treatments or landfills. Non-domestic waste can be classified according to its origin: industrial, which can be dangerous, toxic, has a lot of packaging waste, all types of materials; agro-industrial waste that is made up of "stubble" that is the remains of stems and leaves that remain after the harvest and that can be used to extract energy, waste from packaging of pesticides, biocides, fertilizers, they have a special treatment and are not disposed of together with common garbage; miners heavy metal contamination; hospitals that present mainly infectious, toxic, pathological solid waste, have their special legislation for transport, treatment and disposal, pyrolysis treatment is applied in incineration ovens where there must be control of gases, they have a dioxin problem; of construction basically harmless but occupy a large volume, mainly inorganic and can be reused. According to the effects, they are classified as hazardous waste, that waste or waste that, due to its toxic, corrosive, explosive, flammable, reactive characteristics, can cause a risk or damage to health. Containers and packaging that were in contact with them are also considered dangerous; non-hazardous, they are so called because they do not present dangerous characteristics, recipients must verify the type of cargo and classify it as dangerous or not for subsequent treatment; flammable, characteristic of a waste that consists of burning when there is strong ignition under certain conditions of pressure and temperature; toxic, characteristic of a waste that consists of causing adverse biological effects that may cause harm to human health or the environment. For toxic waste, toxicity criteria are defined and control limits are established:
A) Oral median lethal dose (LD50) for rats less than or equal to 200 mg/kg body weight.
B) Dermal mean lethal dose (LD50) for rats less than or equal to 1000 mg/kg body weight.
C) Inhalation mean lethal concentration (LC50) for rats less than or equal to 10 mg/L.
D) High potential for eye irritation, respiratory
Solid waste management is carried out in four stages: avoid, minimize, treat and dispose. Avoiding is the most convenient environmental action, followed by minimizing, which consists of reducing, reusing, recycling and recovering, followed by treating, which consists of physical processes (fractional separation), chemical (calcination), and biological (composting).
Gaseous effluents come mainly from industrial activities and large cities (engine combustion). The main pollutants are: carbon pollutants (carbon dioxide and carbon monoxide); nitrogen pollutants (nitrogen monoxide and nitrogen dioxide); sulfur pollutants (sulfur trioxide and sulfur dioxide); lead, mercury (and other heavy elements) there used to be lead in gasoline and the pollution was very high, low molecular weight organic volatiles (benzene, dioxins, asbestos (no longer used today), CFCs (almost not used today, it was used in refrigeration equipment and aerosols); very small solid particles that form gels, fumes, fogs that not only affect human health but also aesthetics and visibility.
Pollutants can be primary pollutants such as carbon monoxide, ammonia, sulfur dioxide or secondary pollutants that are derived from the above, such as acid rain.
One way to eliminate solid waste is through incineration but the gases must be treated. Filters are used that retain or adsorb dissolved substances (pollutants) in the gas, cyclones where the gas passes through and contaminating particles are separated by centrifugal force, absorption towers where a liquid is brought into contact with the gas and the contaminating particles are transferred to the liquid. Electrostatic precipitators consist of magnets that trap ferromagnetic particles from the gas stream.
Household liquid effluents come from household activities such as washing dishes, washing floors, and evacuating bathrooms. They contain high content of organic matter, detergents, solids, high turbidity, black color due to the presence of metal sulfides. The evacuation of organic matter without prior treatment produces a decrease in dissolved oxygen in the receiving body, which compromises aquatic fauna and flora.
White water comes from rain and contains waste that is dragged from roofs, rooftops, streets, sidewalks, and also contains atmospheric pollutants.
A raw sewage fluid has characteristics:
• - Physical such as variable temperatures, rotten smell (presence of sulfides), grayish-black color (presence of metal sulfides) and high turbidity.
• - Chemicals: presence of calcium and magnesium, phosphates, ammonium ion, nitrates and nitrites, sulfides, sulfites and sulfates, sodium, potassium, proteins, carbohydrates, lipids and detergents.
• - Biological: presence of bacteria, viruses and protozoa.
To measure the characteristics, the following parameters are used:
• - Physical: temperature, color is compared with other standards, odor conductivity (to measure the concentration of inorganic species), solids analysis (to measure the proportions of settleable solids, in suspension and dissolved solids).
• - Chemicals: pH, alkalinity (presence of hydroxyls, carbonates and bicarbonates), hardness (presence of calcium and magnesium), phosphates (phosphorus), ammoniacal nitrogen, nitrites and nitrates (nitrogen), phosphorus (common waste and synthetic detergents), detergents, fats and oils, sulfides, dissolved oxygen (determines presence of aerobic or anaerobic organisms), BOD (cc of biodegradable organic matter), COD (cc of organic matter).
Liquid effluents can also come from special or industrial establishments. In special establishments, the division, handling and cleaning of articles and materials occurs; no transformation occurs in their essence. Examples are: mechanical workshops, analysis laboratories, dry cleaners, pasta factories, hospitals. In industrial establishments, manufacturing, processing and processes occur that produce new products from raw materials or materials used. Examples are: tanneries, meat processing plants, food, chemical, steel, metallurgical, among others.
Industrial drains: together with sewage drains, they constitute the main cause of water pollution. It is difficult to establish the characteristics of industrial wastewater because it depends on the nature and quantity of waste produced, which differs depending on the type of industry, even for those of the same type, since it depends on the manufacturing process developed.
Effluent analytical methods
Un efluente se puede caracterizar según:.
• - Origen: se debe determinar si proviene de una línea o de varias líneas, varías líneas que se unen para luego tratarse o se tratan y luego se unen.
• - Cantidad: relacionado con la masa y el volumen del efluente. Debe conocerse si se evacua en forma continua o no.
• - Calidad: la composición física y química del efluente, que componentes hay y en que concentración, se mide en ppm y si son trazas en ppb.
El muestreo de control consiste en extraer una porción del efluente que sea representativa de la calidad de descarga del efluente en el momento de control, con el propósito de analizar la calidad de la misma. El muestreo tiene como objetivos: controlar la calidad del efluente y proponer un tratamiento en caso de que el mismo sea contaminante, controlar la eficiencia del tratamiento, determinar la factibilidad de reúso o recupero y analizar los efectos del vuelco al cuerpo receptor.
Preservation of samples
Industrial or commercial effluents have an unstable composition due to their varied composition, which forces them to change their composition and concentration. The speed of changes is affected by pH, temperature, concentration and bacterial action. In the same way, the temperature, color and characteristics of oxidizable and reducible substances can change rapidly, so such variables must be analyzed before reaching the laboratory (in situ).
If the nature of the effluent is such that it could decompose rapidly, it should be kept at a low temperature to retard bacterial action and prevent change in characteristics. Temperature control at 4 °C delays bacterial action and suppresses the volatilization of dissolved gases, which affect the physical-chemical characteristics of the samples.
For the analysis, it is recommended to extract a volume of 2 liters of sample, store them correctly in glass or plastic containers that have a wide mouth or a screw-on lid or airtight seal.
Physical parameters
• - Appearance: the term turbid is applied to water that contains suspended matter that intervenes with the passage of light. In lakes, waters with relatively slow flow, turbidity is due to colloidal dispersions and in rivers in overflow conditions it is due to relatively coarse dispersions. Turbidity is an essential consideration in public water supplies for three reasons:.
• - Aesthetics: any turbidity in drinking water is related to possible contamination by wastewater and the dangers associated with it.
• - Filterability: waters with greater turbidity are more difficult to filter because the filter openings become clogged. It becomes more expensive.
• - Disinfection: the solids of municipal wastewater usually encapsulate microorganisms so the disinfectant does not come into contact.
The current standard method for determining turbidity is based on instruments that use the principle of nephelometry. The instrument has a light source that illuminates the sample and photoelectric detectors with an attachment for reading the beam that forms right angles. It is customary to use a formazin polymer suspension or other commercially available preparations as standard. Turbidity data is used to determine whether chemical coagulation and filtration treatment is necessary in water supply plants. The determination of suspended solids is used to verify the removal of turbidity in water. Turbidity is removed by a coagulation-flocculation treatment.
• - Color: indicates the presence of colloidal or suspended substances with which I can intuit the origin of the effluent. Natural color exists in water in the form of negatively charged colloidal particles. Because of this, it can be removed using a salt that contains a trivalent metal ion such as aluminum sulfate or ferric chloride, polyaluminum chloride. The color caused by the suspended matter is the apparent color and the color caused by the organic and plant extracts that are colloidal is the real color. Color intensity increases with pH, which is why it is advisable to measure pH along with color. The suspended matter and coloration (colloidal and dissolved solids) are removed with a coagulation-flocculation treatment. Natural color, like turbidity, is due to a large amount of substances and standard solutions are used to determine color grades. Many samples require pretreatment to detect the true color. Waters that contain natural color have a yellow-brown appearance. Through experience it has been seen that potassium chloroplatinum solutions dyed with cobalt chloride give shades similar to the real colors of water. By varying the amount of cobalt chloride, other colors are obtained. To measure and describe colors that are not in this classification, spectrophotometry must be used.
• - Odor: it is indicative of the old age of the domestic effluent, when it is young it is slightly putrid but when it is old it septizes and acquires a strongly putrid odor due to the development of hydrogen sulfide. The smell can be due to a wide variety of chemical substances, so in its determination its aroma is associated with a known one. For example: onion (acetylene, iodine), hyrcinos (cheese, sweat, etc.), unpleasant (amines, narcotics, animal waste, etc.).
• - Temperature: although domestic sewage liquid has a slightly higher temperature than the supplied water, finding liquids with much higher temperatures indicates that an industrial or commercial discharge is occurring. They cause deterioration of the sewer network and accelerate the biochemical reactions carried out by bacteria, so dissolved oxygen is consumed more quickly and the bacterial population grows.
• - Conductivity: it is related to the total dissolved solids SDT=0.8 k uS/cm and provides a measure of the capacity to transport electric current and varies with the type and number of ions. It can be determined using a conductivity cell linked to a circuit with a Wheatstone Bridge. It gives information about the concentration of ions, that is, the amount of inorganic species that the effluent has. Organic species are difficult to ionize and dissolve. KCl is used to calibrate the conductivity meter.
• - Solids: the term solids refers to matter suspended and dissolved in water. Solids can be settleable, suspended, dissolved and colloidal. Total dissolved solids measures the total filterable solid waste (salts and organic compounds). Excess total dissolved solids generate unpleasant palate and adverse physiological reaction in the consumer. The solids that settle after 10 minutes can destroy pipes and electromechanical equipment and the solids that settle after 2 hours generate environments conducive to anaerobic degradation. They are used to evaluate the treatment carried out. Suspended solids are those that are not dissolved in the body of water and are obtained by evaporating and weighing a filter through which the sample is passed. Dissolved solids cannot be determined directly but must be obtained by difference between total solids and suspended solids. Determination of total solids by evaporation and weighing is performed to determine the concentration of total solids, their fixed and volatile fractions in liquid and semi-solid samples such as river or lake sediments, sludge that is isolated or residual or agglomeration of sludge from vacuum filtration, centrifugation or other dewatering process. Total solids are dried at 103-105 °C. The determination of total solids allows us to estimate the suspended and dissolved matter in the water. Settleable solids indicate the amount of solids that can settle in a given time from a sample volume. Suspended solids are determined by the difference in weight of a filter through which the sample is passed. Colloidal solids are not detected, they are stable, difficult to separate and analyze. Volatile and fixed solids are produced by combustion procedures, in which the organic matter is volatilized and at the same time the temperature is controlled to avoid the volatilization of inorganic substances. The test is compatible with the total oxidation of organic matter. It consists of incinerating the sample at 550 °C.
• - pH: is the logarithm of the hydrogen ion activity. It serves to indicate the alkalinity or acidity of the effluent. An acidic pH corrodes conduction systems and generates gas release. It is determined on site. Aquatic life thrives at a pH between 5 and 10, at other pH levels an imbalance occurs in aquatic life; It determines subsequent treatments because it is a critical factor in softening, corrosion control, coagulation and disinfection. In the biological treatment of wastewater, the pH must be maintained in a favorable range for microorganisms. It can be done in a wide variety of materials and in extreme conditions as long as the appropriate electrode is used. For pH greater than 10 and at high temperatures, it is carried out with a glass electrode designed for this purpose. For semi-solid substances, lance-shaped electrodes are used. The electrodes are standardized with buffer solutions of known pH. Very acidic pHs are corrosive and produce gas evolution.
• - Alkalinity: is the measure of the ability to neutralize acids. It is primarily due to salts of weak acids, although weak and strong bases can also contribute. Bicarbonates are the ones that contribute the most to alkalinity because they are in greater quantity because they arise from the reaction between carbon dioxide and the basic matter of the soil. Under certain conditions, water is alkaline due to the presence of carbonates and hydroxides. This occurs in surface waters with growing algae. Alkalinity is caused by 3 large groups that are classified according to their high pH values: hydroxides, carbonates and bicarbonates. Very alkaline waters have a very unpleasant taste. It is measured volumetrically with 0.02N sulfuric acid and is expressed in calcium carbonate equivalents (or in ppm of CaCO3). This parameter is essential in the processes of coagulation, softening, corrosion control, buffering capacity and in the treatment of industrial waste (because it is prohibited to discharge water with caustic alkalinity).
• - Chlorides: if the concentrations are high, they produce a salty taste that is rejected by many people. Chlorides can be easily measured by volumetric procedures using internal indicators. The most used is the Mohr Method, which uses silver nitrate as a titrant and potassium chromate as an indicator. It is an important consideration in choosing supplies for domestic, agricultural and industrial use. Brackish waters with a high salt content determine the device to be used for the determination. The determination allows regulating the concentration in industrial or domestic effluents to protect the receiving waters. It is a tracer and is very useful because its presence is not visually detectable, it does not have toxic effects, it is a common constituent of water, the chloride ion is not absorbed by the soil, it is not altered or changed by biological processes and it can be easily measured.
• - Dissolved oxygen: performed in situ or fixed using a chemical reagent. It is measured in mg/L. Solubility decreases with temperature and salinity. Nitrogen and oxygen are poorly soluble, and since they do not react chemically with water, their solubility is proportional to the partial pressures of the gases. At a given temperature and under saturation conditions it is estimated using Henry's Law. Its solubility varies with atmospheric pressure at any temperature. Because the rate of biological oxidation increases with temperature and the oxygen demand also increases but the solubility of oxygen decreases, the system must be aerated and this has associated aeration costs. The solubility of oxygen determines the rate of oxygen absorption because the reaction rate depends on the concentration and this determines the costs of aeration. Dissolved oxygen determines whether oxidation occurs by aerobic or anaerobic organisms. Aerobics use oxygen for the oxidation of organic and inorganic compounds to give harmless products and anaerobics carry out oxidation by reduction of inorganic salts such as sulfates and the final products are harmful. Since the two types of microorganisms are propagated, it is important to maintain aerobic conditions, which is why measurements of dissolved oxygen are carried out in the body of water where the effluents are dumped and in the aerobic treatments of wastewater, industrial and domestic. Oxygen causes corrosion of iron and steel in water distribution systems and steam boilers, so oxygen removal is a common practice in the energy industry. The standard volumetric procedures to determine dissolved oxygen if the sample is properly preserved are the Winkler or metric iodine method and its modifications. An oximeter (electrode) can also be used and measurements are made in situ. The electrode can be lowered to various depths of the liquid and readings are made on a connected ammeter located at the surface. A contaminated liquid has zero dissolved oxygen.
• - Oxygen consumed: it is the amount of oxygen necessary to oxidize the substances with reducing properties present in the residual liquid. The most common substances are: ferrous salts, sulfides, lipids, carbohydrates and amino acids. The usual determination is with potassium permanganate as titrant and indicator of the end point. This redox titration is not very precise or reproducible but it gives an idea of the mg/L consumed by the organic matter present in the sample.
• - Biological oxygen demand: it is the amount in mg/L of oxygen necessary to degrade organic matter by the action of aerobic bacteria at 20 °C, in darkness and for 5 days. The importance of its determination lies in the fact that it gives an idea of how contaminated it is with organic matter and the potential consumption of oxygen when it is thrown into the body of water, which compromises the aquatic fauna and flora. It is essentially a bioassay procedure, so it is carried out in conditions that are most similar to nature. Re-aeration of samples should be avoided as the dissolved oxygen level decreases during analysis and during sampling. Due to the limited solubility of oxygen, samples must be diluted to ensure that dissolved oxygen is present in the test. There should be no toxic substances, necessary nutrients, phosphorus, nitrogen and some trace elements. Biological demand is produced by a varied group of microorganisms that carry out oxidation to carbon dioxide and water. Therefore, in the samples there must be a load of "seed" microorganisms necessary for biological oxidation to occur. Oxidative reactions derive from biological action and the speed of these reactions depends on the number of microorganisms and the temperature. The effects of temperature remain constant at 20 °C, which is an average of natural water temperatures. Biological oxidation at a temperature of 20 °C and under other operating conditions (e.g. darkness) is considered complete after 20 days. Since you cannot wait that long for the results, it is analyzed for 5 days. So the measured BOD is only a fraction of the total. The total time for biological oxidation will depend on the seed and the nature of the organic matter, and is only determined experimentally. The BOD test depends on the measurement of dissolved oxygen. It is used to measure the self-purification capacity of the stream and establish the BOD levels for discharge into the body of water. It is an important consideration for the design of treatment equipment, the choice of treatment method, and determining the equipment size of trickling filters and activated sludge units. After treatment plants begin operating, the results are used to evaluate the efficiency of the processes. To summarize the limitations of the BOD: have acclimatized sowing (necessary nutrients, avoid re-aeration, seeds), measurement of only a fraction of what is biodegradable, time (minimum 5 days), pretreatments in case of toxic effluents.
• - Chemical oxygen demand: the advantage is that the analysis time is 3 hours, the disadvantage is that it does not give an idea of biodegradability. BOD/COD data must be available to determine the degree of biodegradability of the sample. It is the amount in mg/L of oxygen necessary to chemically degrade the organic matter contained in the residual liquid at 150 °C for 2 hours and using a strong oxidizing agent such as potassium dichromate. The importance of its determination lies in the fact that the COD levels of the effluent can be known and modified before discharge to the sewer or the receiving body since high COD levels indicate a high presence of organic substances and reducing inorganic substances that consume the oxygen available for aquatic fauna and flora, causing their disappearance. The method allows measuring the organic matter present in the sample because organic compounds are oxidized in the presence of a strong oxidant such as potassium dichromate under acidic conditions. Potassium dichromate degrades biologically oxidizable matter as well as biologically inert organic matter. It does not provide data about the rate at which the biologically active material is stabilized because it degrades both the biologically resistant and the biologically oxidizable material. All oxidizing agents must be placed in excess; it is necessary to measure the excess that remains at the end of the reaction to know the original amount of organic matter. The advantage of dichromate is that the excess can be measured relatively easily. Certain organic compounds such as low molecular weight fatty acids cannot be oxidized by dichromate, which is why a catalyst is used. The results are expressed in mg/L necessary for oxidation. The determination of COD is carried out in a digester and is then determined by titration or colorimetry. For industrial effluents, the regulation is 500<COD<10,000 for contaminated courses and COD<20 for uncontaminated courses. In conjunction with BOD, COD is useful in indicating toxic conditions and the presence of biologically resistant substances. With the BOD and COD data, one of these relationships is obtained:
• - Nitrogen series: colorimetric determinations are carried out, I measure them with the spectrum or comparison of color with standards. The chemistry of nitrogen is complex since it has several oxidation states which can be induced by living organisms. Bacteria can induce positive or negative states and depend on whether they are aerobic or anaerobic organisms. Only a few oxidation states influence water quality. Ammonium nitrogen is measured in spectrum or compared to a standard. To measure nitrite nitrogen and nitrate nitrogen, it is compared with a disk with a color scale. In recently contaminated waters, nitrogen is in the form of organic nitrogen and ammonia. As time passes, nitrogen converts to ammoniacal nitrogen, and if aerobic conditions exist it passes to nitrites and then to nitrates. If an aerobic treatment is to be carried out, there must be sufficient nitrogen since it is a necessary fertilizing element for the growth of algae, otherwise it must be supplied from external sources. But if excess nitrogen, mainly nitrate, is dumped, eutrophication (overpopulation of algae) is generated and the liquid becomes putrid or contaminated, which is why this analysis is so important. The determination of nitrogen is carried out to control the degree of purification in the treatment stages. It is well known that non-ionized ammonia is toxic and the ammonium ion is not. pH is the factor that controls the toxicity of ammonia and is not a problem if the pH is less than 8 and the ammonia concentration is less than 1 mg/L. Ammonia control can be accomplished by effective removal of ammonia or by nitrification (oxidizing it to nitrites and then to nitrates). In some cases, the limitation is the amount of total nitrogen. The techniques for determining nitrites, nitrates and ammoniacal nitrogen vary for each parameter so you can not only quantify it but also identify it. Total nitrogen is determined by the Kjeldahl method. The determination of nitrates is used to know if the establishment complies with the maximum levels of the contaminant. The determination of organic nitrogen and ammonia to know if there is sufficient nitrogen available for biological treatment. If there is not enough amount, it must be provided from external sources.
• - Phosphorus: expressed in mg/L of phosphate phosphorus. The analysis technique is based on a reaction that gives color and is compared with color standards. Polyphosphates are used in public water supplies as a means of corrosion control. They are also used in softened waters to stabilize calcium carbonate and avoid the need for re-carbonization. All surface water supplies are the basis for the growth of aquatic organisms such as algae or cyanobacteria and this growth depends on the amount of fertilizing elements in the water. Nitrogen and phosphorus are the fertilizing elements for the growth of algae and cyanobacteria, so their concentrations limit the growth rate. When there is an abundance of both elements, algal blooms occur and the liquid eventually rots. Domestic water has high levels of phosphorus. Most of the inorganic phosphorus is contributed by human waste, these come from the metabolic degradation of proteins and the elimination of phosphates through urine; in addition to strong synthetic detergents. Phosphate compounds are widely used in steam plants to eliminate boiler scaling. Orthophosphate can be measured from polyphosphates due to their stability under pH, time and temperature conditions. Polyphosphates and organic forms of phosphorus must be converted to orthophosphates which can be determined qualitatively by gravimetric, colorimetric or volumetric methods.
• - Detergents: currently detergents are biodegradable, they have simpler treatments but they have other effects such as foaming that makes treatment and analysis difficult. A colorimetric determination is carried out after prior extraction with chloroform.
• - Fats and oils: they form films and crusts on the surface that clog the pipes, affect the aesthetics of the body of water, they form a film on the surface that prevents the transfer of oxygen from the air to the water, thus compromising the aquatic fauna and flora. They are determined gravimetrically using the method of substances soluble in ethyl ether. They are soluble in ethyl ether and insoluble in water.
• - Phenols: they are pollutants and toxics that impart odor and flavor to the liquid. They are determined by spectrophotometry.
• - Heavy metals: where Cu, Ni, Hg, Cd, Cr, Pb stand out and are determined by atomic absorption spectroscopy. They are generated by metallurgical, steel, and automotive companies that generally recycle them and do not dispose of them.
• - Hydrocarbons: such as gasoline and oil. They are determined by HPLC.
• - Pesticides: they can be chlorinated and phosphorous, they are determined both in water and in sediments. They are very polluting so they are allowed in very low concentrations. They are determined by HPLC and gas chromatography.
• - Sulfide: its presence is due to the decomposition of the organic matter present in the residual liquid. They are generated by the bacterial reduction of sulfates. They are determined by colorimetry and give a blue color. They are toxic and corrosive.
• - Cyanide: cyanides are potentially toxic compounds since a change in pH in the medium can release hydrocyanic acid, a compound associated with maximum toxicity, so it is important to determine the presence as cyanide ion of all cyanide compounds that exist in wastewater, treated wastewater, potable wastewater, natural wastewater. It is determined by potentiometric methods or by spectroscopy. It should be kept at alkaline pH.
These are the most basic and general. Then it will depend on each industry to determine another factor.
Sources of water pollution
The main sources of water pollution are industrial and special establishments. Within the special establishments are the operations of fractionation, handling or cleaning of articles and materials, they do not produce any type of product transformation in essence. Examples are: hospitals, service stations, car washes, hypermarkets and supermarkets. Within industrial establishments there is manufacturing, processing and processes that transform the raw materials or materials used or give rise to new products. Examples are: tanneries, meat processing plants, textiles, paper mills, metallurgical, steel, food (dairy, alcoholic/non-alcoholic beverages, fish), distilleries, sugar mills and chemicals (paints and dyes, fertilizers, pesticides, insecticides, cleaning products).
Industrial drains, together with sewage drains, constitute the predominant cause of water pollution. It is very difficult to define the characteristics of industrial drains, given that they present the particularity of their great variety in terms of nature and quantity of waste produced, with notable differences being verified according to the types of industries, a concept that includes similar ones, since it depends on the modality of the manufacturing process developed. For example, a refrigerator discharges an effluent with organic matter, solids, fats and detergents.
Origin of cloacal fluid
Sewage (wastewater) is mainly composed of waste from three main groups:.
• - Water for domestic use: these are simply those used for personal hygiene, in the kitchen and for cleaning.
• - Human waste: are those used to transport fecal matter and urine to the sewers.
• - Non-domestic waste: from industrial, commercial and service activities. This group usually contains the highest pollution load, which is why pretreatment of the water that is discharged into the sewage network (mainly to industries) is usually required, which in many cases is not fulfilled or is inefficient.
To measure physical contaminants, I would use physical parameters such as turbidity, color (apparently real), odor, temperature, conductivity (to determine what inorganic species the effluent has), solids analysis (to evaluate the percentages of the different types of solids that the water may contain such as suspended, settleable, colloidal and dissolved solids). To measure chemical contaminants, I would use chemical parameters such as pH, alkalinity (to determine the presence of hydroxyls, carbonates and bicarbonates), chlorides, dissolved oxygen (determines aerobic and anaerobic organisms), BOD (to determine the polluting power of waste), COD (to measure the cc of organic matter), phosphorus (common waste, synthetic detergents), detergents, fats and oils, sulfates.
To measure turbidity, a turbidimeter is used; the color is measured with the spectrophotometer; the smell by sensory analysis; the temperature is measured with a thermometer; conductivity with a conductivity meter; dissolved and suspended solids through filtration and gravimetry; settleable solids by sedimentation in an Imhoff cone; Colloidal solids are measured by spectrophotometry. To measure pH, the peachimeter is used; Alkalinity is used to measure hardness; chlorides by titration with silver nitrate; dissolved oxygen using an oximeter; organic matter is measured with BOD, oxygen consumed, COD; phosphorus through phosphates; nitrogen through ammoniacal nitrogen, nitrates, nitrites; detergents using substances reactive to ortho-toluidine blue; fats and oils using substances soluble when cold in ethyl ether.
Environmental impact
Characteristics of cloacal fluid
Knowledge of the nature of sewage water is essential for both treatment and evacuation and environmental quality management. Sewage is characterized by its physical, chemical and microbiological composition. The properties are related to each other, for example temperature affects microbiological activity and the dissolved gases in the water. The physical-chemical characteristics are high alkalinity, high turbidity, large presence of dissolved solids, large presence of suspended solids, high amount of organic matter, detergents, black color due to the presence of metal sulfides. The microbiological characteristics are the presence of viruses, protozoa and bacteria that develop when the liquid is biologically stabilized. The proposed treatment to purify a sewage effluent begins with a grate that retains the largest suspended solids, then has a grit trap that retains the settleable solids after 10 minutes, then contains a settler to retain the settleable solids that were not separated in the grit trap, the next stage is a neutralization where an acid such as hydrochloric or sulfuric acid is added to reduce the pH to neutral pH, then it goes on to a treatment of Activated sludge where the organic matter, suspended solids and coloring are removed, then it goes to adsorption with activated carbon where particles that cause odor and color, the rest of the organic matter, detergents are eliminated.
The most important physical characteristics of wastewater are total solids content, odor, temperature, density, color, turbidity and pH. To evaluate the appearance, turbidity is used with a turbidimeter, the color that is measured is the real apparent color through colorimetry, odor through sensory analysis, temperature through a thermometer, conductivity (to determine how much inorganic species the effluent has) through an electrode, solids analysis (to evaluate the percentages of the different solids that the water may contain, whether in suspension, colloidal, settleable and dissolved).
• - Solids. The solids content is defined as the non-volatile residue after subjecting the water to an evaporation process at 100 °C and drying in an oven at 103-105 °C for one hour. The determination corresponds to the dissolved and suspended solids. Settleable solids are solids that settle to the bottom of a cone-shaped container (Imhoff cone) from one liter of residual liquid over the course of 2 hours. The well-stirred sample is placed in the Imhoff cones. The determination is made in ml/L and mg/L. It allows obtaining an approximate measurement of the amount of sludge that will be obtained in the decantation. Settleable solids give an idea of the organic and inorganic origin of said solids. The solids that settle after 10 minutes correspond to the inorganic solids, which are heavier and then the organic matter begins to settle until the two hours are completed. After 2 hours it is estimated that all the settleable solids were separated. Total solids are also classified as filterable solids or not. This is determined using a fiberglass filter. Filterable solids correspond to dissolved and colloidal solids. Non-filterable solids correspond to suspended matter. Suspended solids may or may not be settleable. The settleable suspended solids are separated in a grit trap (settable solids after 10 minutes) or in a settler (settable solids after 2 hours). The non-sedimentable suspended solids are separated by means of a coagulation-flocculation treatment or by biological oxidation in an activated sludge treatment and in both there is a subsequent decantation. A settler can retain settleable solids after 10 minutes but should not be overloaded. Total solids are classified as volatile and fixed, depending on their volatility at 550 °C, the temperature at which the organic compounds oxidize and form gases and the inorganic fraction remains in the form of ashes. Volatile solids correspond to organic matter and fixed solids correspond to inorganic matter. Filterable solids correspond to total dissolved solids. Water for human consumption with a high content of dissolved solids is unpleasant to the consumer or can induce an adverse physiological reaction in them. Solids analyzes serve as indicators of the effectiveness of biological and physical-chemical treatment. The determination of total solids is a widely used method: determination of total solids and their fixed and volatile fractions in solid or semi-solid samples from river and lake sediments, isolated sludge in wastewater treatments and sludge agglomerations in centrifugation, vacuum filtration and other sludge dehydration processes. Suspended solids are those that are found in water without being dissolved in it, and are calculated mathematically as the difference between total solids and dissolved solids. Total solids can be non-filterable (dissolved) and filterable (undissolved) and are determined by a filter using gravimetry. Volatile and fixed solids are determined by muffle incineration at 550 °C. At this temperature, the oxidation of organic compounds to carbon dioxide and water occurs and the inorganic compounds resist. The determination corresponds to the total oxidation of the organic matter. Colloidal solids are stable and difficult to separate. They are determined by spectrophotometry. For drinking water, a maximum value of 500 ppm of solids is indicated. In boilers, they produce foaming. Due to excessive sedimentation, environments conducive to anaerobic degradation are generated. Suspended solids interfere with the normal development of aquatic life by decreasing the depth to which sunlight passes through. Settleable solids can obstruct pipelines, electromechanical pumping equipment and hinder the operation of the treatment plant.
• - Odors. Normally, odors come from gases released by the decomposition of organic matter. Fresh wastewater has a more tolerable odor than "septic" wastewater. A characteristic odor of septic wastewater comes from hydrogen sulfide, which is generated by the reduction of sulfates by anaerobic bacteria. Industrial wastewater can also contain odorous compounds itself.
Effects of odors: reduce appetite, generate nausea, vomiting, mental disturbances, produce respiratory imbalances. The fishy smell is characteristic of amines, the rotten egg smell is characteristic of hydrogen sulfide, and the smell of fecal matter is characteristic of eskatol.
• - Temperature: water temperature influences the development of aquatic life, chemical reactions and reaction rates, as well as the suitability of water for certain useful uses. The increase in temperature produces an increase in chemical reactions and the speed of chemical reactions, so there is a more rapid decrease in dissolved oxygen, which compromises the development of aquatic fauna and flora. The increase in temperature also causes a decrease in the solubility of oxygen. It causes the deterioration of the sewage network. The determination is made on site. Elevated temperatures are characteristic of a sewage discharge. Elevated temperature effluents are cooled by heat exchangers, cooling towers, ambient contact, or other cooling methods.
• - Density: dense sludge requires greater pumping powers, even if it is very dense it may not move.
• - Color: is the ability it has to absorb certain radiation of the visible spectrum. Pure water is bluish. It cannot be attributed to one component exclusively but the colors are attributed to several contaminants. For example, the grayish-black color is due to the presence of metal sulfides. The water is said to be septized. It serves, together with the smell, to qualitatively determine the age of wastewater. The grayish color is characteristic of recent domestic wastewater. As the time in the sewer networks increases and more anaerobic conditions develop, it becomes darker. The grayish-black color is due to the presence of metal sulfides that are generated by the reaction between the sulfide generated by anaerobic decomposition and the metals present in the water. The water is said to be septic. Some industrial waters can add color to domestic wastewater. It indicates the presence of dissolved or colloidal substances with which the origin of the effluent can be intuited. Natural color is caused by negatively charged colloidal particles. It can be removed by coagulation using a salt containing a trivalent metal ion such as iron or aluminum. The color caused by suspended matter is known as apparent color and can also be removed by coagulation or an activated sludge treatment. Color intensity increases with pH. Therefore, pH is measured together with color. Natural color as well as turbidity is due to a wide variety of substances and an arbitrary standard is adopted for its measurement, this standard is used to directly and indirectly measure color. The suspended matter must be separated before measuring the real color. Waters containing true color have a yellow-brown appearance and can be measured colorimetrically. It has been observed that potassium chloroplatinum solutions dyed with small amounts of cobalt chloride give shades very similar to natural ones. By varying the amounts of cobalt chloride, the degradation of the tones is obtained. To measure and describe colors that are not in this classification, spectrophotometry is used, which consists of measuring the fraction absorbed or transmitted by the sample.
• - Turbidity: is a measure of the sample's ability to transmit light. It is measured in "NTU". It allows estimating the colloidal and suspended matter that is present in the sample.
• - Conductivity: it is related to the dissolved solids through a factor that is the cell constant. It is a measure of the solution's ability to carry electric current. It depends on the number of ions, their nature, their valence, the temperature of the solution. As the temperature increases, the conductivity increases. It is determined by a conductivity cell connected to a circuit through a Wheatstone Bridge. KCl is used to calibrate the conductivity meter. Conductivity and hardness are related because magnesium and calcium salts are the most abundant and contribute the most to conductivity. They reflect the degree of mineralization of the water and its potential productivity. Organic substances dissolve by forming hydrogen bonds, so they are also dissolved substances.
• - pH: the pH range allowed in an effluent is 5.5 to 10. It is optimal for the development of aquatic life forms. It is determined on site. It governs innumerable chemical processes, including some that can generate harmful conditions for humans, such as the contact of an acidic effluent with sodium cyanide, generating hydrogen cyanide, which is a lethal gas. Indicates whether the effluent is acidic or alkaline. An acidic pH corrodes pipes and generates gas release in the form of foam that makes treatment and subsequent analysis difficult. Before biological treatment to prevent microorganisms from developing and biological oxidation from occurring. The optimal pH is 6-8.5. Depending on the concentration of carbon dioxide, this is produced by the mineralization of the salts present in the water. The pH of the water is due to the composition of the land crossed; it is alkaline if the land is limestone and acidic if it is siliceous. Heavy metals dissolve in an acidic medium and precipitate in a basic medium. The electrodes are standardized with buffer solutions of known pHs. It can be measured in a wide variety of materials and under extreme conditions as long as the appropriate electrode is used. For semi-solid substances, the spear-shaped electrode is recommended. For substances with a pH greater than 10 and high temperatures, glass electrodes designed for this purpose are recommended.
To study the chemical characteristics of sewage, the organic matter present, the inorganic matter and dissolved gases must be taken into account. More specifically sulfates, carbonates, bicarbonates, chlorides, nitrates, nitrites, sulfides, phosphates, calcium, magnesium, sodium, potassium, iron, manganese, proteins, carbohydrates, lipids and detergents. The parameters to evaluate the chemical characteristics are pH, alkalinity (to determine the presence of hydroxyls, carbonates and bicarbonates), chlorides, dissolved oxygen (determines aerobic and anaerobic organisms), BOD (to determine the contaminating power of the waste), COD (to measure the cc of organic matter), phosphorus (common waste, synthetic detergents), detergents, fats and oils, sulfides.
• - Organic matter. About 75% of the suspended solids and 40% of the filterable solids in wastewater are organic in nature. They are solids that come from the animal and plant kingdoms, and from human activities related to the synthesis of organic compounds. The main groups of organic substances present in wastewater are proteins (between 40% and 60%), carbohydrates (25%-50%), and fats and oils (approximately 10%). Another compound with an important presence is urea, the main constituent of urine, which due to its rapid decomposition process is rarely present in wastewater that is not very recent. Along with those already mentioned, wastewater contains small quantities of a large number of organic compounds whose structures can be simple or extremely complex. This group includes detergents, priority organic pollutants, volatile organic compounds and pesticides for agricultural use. Due to the increase in the synthesis of organic molecules, the number of them present in wastewater increases every year.
Proteins. The chemical composition of proteins is very complex and unstable, and can adopt many different decomposition mechanisms. Furthermore, as a distinctive characteristic, they contain a high amount of nitrogen and in many cases, they also contain sulfur, phosphorus and iron. Urea and proteins are the main source of nitrogen in wastewater.
Carbohydrates. From the point of view of volume and resistance to decomposition, cellulose is the most important carbohydrate in wastewater. The destruction of cellulose is a process that occurs without difficulty, mainly thanks to the activity of some fungi, whose action is notable in acidic conditions.
Fats and oils. Fats and oils are compounds of alcohol (esters) or glycerol (glycerin) and fatty acids. Chemically they are similar and those that are solid at room temperature are called fats and those that are in a liquid state are called oils. Fats are among the most stable organic compounds and are not easy to degrade biologically. They pollute waterways by forming a film on the surface that prevents the passage of oxygen to the water. They form crusts on the surface of the pipes that prevent the passage of water. It consists of the determination by weight of substances soluble in cold in ethyl ether. From the raw sample, brought to a pH of 4.2 with 2 drops of heliantin, the sample is brought into contact with ethyl ether so that the fats and oils are solubilized in it, and then the ether (low boiling point) of the ether phase is evaporated, so that the amount of fats and oils by weight of the volume used in the sample can be obtained.
• - Biological oxygen demand. is the amount in mg/L of oxygen that is required to decompose the organic matter contained in the residual liquid by aerobic biological action under conditions of 20 °C, in darkness and for 5 days. The importance of its determination lies in the fact that its value gives an idea of how contaminated the liquid is with organic matter and its potential consumption of the oxygen present in water resources, which is detrimental to the development of the fauna and flora present in such resources. It is essentially a bioassay procedure that measures the oxygen consumed by organisms when using the organic matter of a waste, under conditions as similar as possible to nature. To make the sample quantitative, samples must be protected from air by preventing re-aeration as dissolved oxygen decreases. Additionally, due to the limited solubility of oxygen in water, concentrated waste must be diluted to demand levels that maintain this value to ensure that this value of dissolved oxygen is present in the test. Since it is a bioassay procedure, it is of utmost importance that the environmental conditions are appropriate so that the activity of living organisms is carried out without obstacles. This means that there should be no toxic substances, and that the accessory nutrients necessary for bacterial growth, such as nitrogen, phosphorus and trace elements, should be available. Biological demand is produced by a diverse group of organisms that carry out the oxidation of organic matter to almost carbon dioxide and water. Therefore, it is necessary that a group of microorganisms called "seeds" be present in the test. The oxidative reactions that take place in the BOD test are derived from biological activity and the speed of these reactions is given by the population of microorganisms and the temperature. The effects of temperature are kept constant by performing the test at 20 °C, which is more or less the average temperature since minimal cooling is carried out with some other current. The speed of metabolic processes at 20 °C and under test conditions is such that the time must be calculated in days. Theoretically, an infinite time is required for the biological oxidation of organic matter to complete, but for practical purposes, the reaction is complete in 20 days; However, in most cases this period is long and is then reduced to 5 days because it was found that the percentage of BOD obtained is almost the total. Consequently, it must be remembered that the result of the test carried out at this time represents a fraction of the total. The exact amount will depend on the "seed" and the nature of the organic matter, and can only be determined experimentally. The BOD test is based on dissolved oxygen determinations; Therefore, the precision of the result is largely influenced by the care taken in measuring the latter. BOD is the most important criterion used to control pollution of streams where the organic load must be restricted to maintain adequate levels of dissolved oxygen. The determination is used in the study to measure the purification capacity of the streams and allows authorities to set regulated values for discharge into these waters. Furthermore, BOD information allows the design of treatment equipment; It is a factor in the choice of treatment and is used to estimate the size of the units, especially in trickling filters and activated sludge. It is used to evaluate the efficiency of the stages. In summary, the limitations of the BOD test are: having acclimated sowing, pretreatment in case of toxic effluents, measurement of only a fraction of BOD, minimum time of 5 days.
• - Chemical oxygen demand. The advantage of the analysis is that it only lasts 3 hours, the disadvantage is that it does not give an idea of biodegradability. Determinations are made on raw and decanted samples, and COD/BOD data must be available. It is the amount of oxygen necessary in mg/L to chemically degrade the organic matter contained in the residual liquid at 150 °C for 2 hours with an oxidizing agent such as potassium dichromate in an acid medium. The importance of its determination lies in the fact that its value gives an idea of the content of oxygen-consuming substances such as organic substances whose presence in water resources is detrimental to the development of aquatic fauna and flora. It is a way to measure the concentration of organic matter in domestic and industrial waste. This test allows measuring the total amount of oxygen in a waste that is required to oxidize organic matter to carbon dioxide and water. The test is based on the fact that all organic compounds, with a few exceptions, can be oxidized by the action of strong oxidizing agents under acidic conditions. During the COD determination, organic matter is converted to carbon dioxide and water, regardless of the biological capacity of the substances to be assimilated. COD values are higher than BOD values, and can be much higher when significant amounts of biologically resistant organic matter are present. One of the main limitations of the COD test is the impossibility of differentiating between biologically oxidizable matter and biologically inert matter. Furthermore, they do not provide any data on the rate at which the biologically active material stabilizes under the conditions of nature. The main advantage of the COD test is the short time required for the evaluation; The determination is made in 3 hours instead of 5 days as with BOD. It has been observed that potassium dichromate is an excellent oxidizing agent for the determination of this parameter, since it is capable of almost completely oxidizing a wide variety of organic substances to carbon dioxide and water. Because all oxidizing agents must be used in excess, it is necessary to measure the excess that remains at the end of the reaction in order to measure the amount used in the degradation. An important point in favor of dichromate is that the excess can be measured relatively easily. Low molecular weight fatty acids require a catalyst to oxidize. Under COD test conditions, certain reduced inorganic ions can be oxidized and therefore lead to erroneous results. Chlorides cause the biggest problems because their concentration is high in wastewater. This interference is eliminated by adding mercuric sulfate to the sample before adding other reagents. The mercuric ion combines with chloride ions to form a poorly ionized mercuric chloride complex that is not oxidized by the dichromate. The determination of COD is carried out in a digester and is then determined by colorimetry or by titration. For industrial effluents: 500<COD<10000. For uncontaminated courses: COD <20. In conjunction with BOD, COD is useful in indicating toxic conditions and the presence of biologically resistant organic substances. If BOD/COD<0.2 there is mainly non-biodegradable organic matter, BOD/COD=0.4 there is biodegradable and non-biodegradable organic matter in the same proportions, if BOD/COD>0.6 there is mainly biodegradable organic matter.
• - Detergents. They are classified as biodegradable and non-biodegradable. To eliminate the latter, physicochemical methods must be used. Biodegradable detergents generate foams that interfere with the purification process in treatment plants and give a bad appearance to the liquid effluents. Foaming also makes it difficult to carry out analyses. The foam creates a barrier to the passage of oxygen into the liquid. This determination is carried out with a colorimetric kit for detergents. This technique is based on the fact that anionic detergents are combined with o-toluidine blue, obtaining a blue complex which is soluble in chloroform; Then the kit reagent and chloroform are added to the sample, obtaining a colored chloroform phase in such a way that the intensity of the color is proportional to the concentration of detergents that is measured with the kit's comparator.
• - Hydrocarbons: such as gasoline and oil. They are determined by HPLC. They give water an unpleasant odor and taste, which allows them to be identified in amounts of PPB, which is intensified by chlorination. The surface film prevents water-air gas exchange, with the consequent disruption to aquatic life.
• - Pesticides and Chemical Products for Agricultural Use. These compounds are not from wastewater, but are usually incorporated into it, as a result of runoff from parks, agricultural fields and other causes. Most of these products are toxic to most forms of life, which is why they are considered dangerous contaminants of surface waters. Concentrations of these chemicals can cause fish death, contamination of fish meat (reducing its nutritional value), and worsening water quality. They can be chlorinated and phosphorous, and are determined in both waters and sediments. They are very polluting, so they are not suitable in low concentrations (ug/L). It is analyzed with HPLC and gas chromatography.
• - Inorganic matter. There are several inorganic components of wastewater that are important for the determination and control of water quality. Wastewater, except in the case of certain industrial waste, is not usually treated with the aim of eliminating inorganic constituents.
• - Alkalinity. In wastewater, it is caused by the presence of salts of weak acids, weak and strong bases such as hydroxides, carbonates and bicarbonates of calcium, magnesium, sodium, potassium and ammonium. Of all of them, the most common are calcium bicarbonate and magnesium bicarbonate because they are formed in considerable quantities when carbon dioxide reacts with the basic matter of the soil. It is the measure of the ability to neutralize acids. Normally, wastewater is alkaline. It occurs in surface waters with growing algae due to the amount of hydroxides and carbonates. Alkalinity is mainly due to three groups of compounds and according to the high pH values it is classified into: hydroxides, carbonates and bicarbonates. Very alkaline waters have an unpleasant taste for the consumer. Alkalinity is measured volumetrically by titration with N/50 sulfuric acid and is expressed in calcium carbonate equivalents (ppm CaCO3). This parameter is essential for chemical coagulation processes, water softening, corrosion control, buffering capacity and in the treatment of industrial waste, given that it is prohibited to discharge waste with caustic alkalinity into receiving waters and sewers.
• - Nitrogen and phosphorus. These elements are essential for the development of some microorganisms, which is why they are known as nutrients. Traces of other elements, such as iron, are also necessary for biological growth. Since nitrogen is essential for protein synthesis, it is necessary to know its amount in water to assess the possibility of biological wastewater treatment. When the amount of nitrogen is insufficient, it is necessary to add it to make the water treatable. When this is in excess, reducing the amounts of nitrogen may be necessary to avoid excessive algae growth. Phosphorus is also essential for the growth of algae, so it must also be controlled when pouring water into the receiving bodies. The most common forms in which these components can be found are: in the case of nitrogen, organic nitrogen, ammonia, nitrites and nitrates. Phosphorus is normally found as phosphates, polyphosphates and organic phosphates. Those are colorimetric determinations that are made, I measure them with the spectrum. Ammonium nitrogen is measured in spectrum and compared to a standard. The result is expressed in mg/L. Nitrite nitrogen and nitrate nitrogen are measured with a kit and compared to a disk that has a color scale. Initially the nitrogen is as organic nitrogen and ammonia. Organic nitrogen is then gradually converted to ammoniacal nitrogen and later, if aerobic conditions exist, oxidation to nitrates and nitrites occurs. When carrying out the treatment, it is necessary to verify if it has a sufficient amount of nitrogen for the organisms, if not, it must be added, but if it is dumped in excess, especially nitrate (a nutrient), eutrophication (overpopulation of algae) occurs and it eventually rots. It is also used to corroborate the degree of purification obtained with biological treatments. Non-ionized ammonia is toxic but the ammonium ion is not. Ammonia toxicity is not a problem in receiving waters that have a pH less than 8 and an ammoniacal nitrogen concentration less than 1 mg/L. For these reasons, ammonia control can be carried out by nitrification or by effective ammonia removal. In some cases, the limitations apply to the total nitrogen (organic nitrogen plus inorganic nitrogen) that may exist in the effluent. The techniques for determining ammonium, nitrite and nitrate can vary for each parameter, so the type of contaminant can be determined, not just quantified. Total nitrogen can be determined by the Kjeldahl method. The amount of ammoniacal nitrogen present in the water determines the chlorine necessary to obtain chlorine residuals free of chlorination. Nitrate determinations are important to establish whether water supplies meet maximum levels. Ammonia and organic nitrogen analyzes are important to determine if there is sufficient nitrogen for biological treatment. If this is not the case, you must contribute through external sources. The amount of phosphorus is expressed in (mg/L of P-PO4) and is the sum of organic and inorganic phosphorus. The analysis technique is based on a reaction that forms a coloration and is measured in the spectrum. Polyphosphates are used in some public water supplies to control corrosion. They are also used in some softened waters to stabilize calcium carbonate, in order to eliminate the need for recarbonization. Nitrogen and phosphorus are essential for the growth of algae and cyanobacteria, and the limitation of these elements is usually the factor that controls the growth rate. When there is an abundance of both elements, algal blooms occur, producing a variety of nuisance conditions (eutrophication). Domestic wastewater has high amounts of phosphorus compounds. Most of the inorganic phosphorus is contributed by human waste, as a result of the metabolic degradation of proteins and the elimination of phosphates present in the urine, in addition to strong synthetic detergents. Phosphate compounds are used in steam generation plants to eliminate scale. Orthophosphate can be measured without interference under optimal conditions of pH, time and temperature. Organic forms of phosphorus as well as polyphosphates must be transformed into orthophosphates, which can be determined qualitatively by gravimetric, colorimetric and volumetric methods.
• - Ammoniacal nitrogen"). If they are aerated, they should not normally contain ammonia because this is converted into nitrites and then into nitrates. Black water always has ammonia coming from the water sections below human agglomerations. The existence of free ammonia or ammonium ion is proof of recent and dangerous contamination. At high pH, ammonia passes into the state of ammonia, with values lower than 0.025 mg/L being recommended.
• - Nitrites. Nitrites can be found in groundwater as a result of a reducing medium in waters that have already been biologically stabilized. When nitrate is in contact with easily attackable metals, whether at acidic or basic pH, nitrites can be found. The presence of nitrites makes the water undrinkable along with the presence of pathogens because they are toxic.
• - Nitrates. They come from the bacterial oxidation of waste generated by animals. In surface and groundwater there are more nitrates, increasing nitrate levels due to increased use of fertilizers.
A residual effluent with a concentration of 15 mg/L of phosphate (PO4(-3)) is dumped into a lagoon with a flow rate of 30 m3/h. What will be the daily contribution in kg of phosphorus (kg P) to said body?
• - Chlorides. They impart an unpleasant taste to the water. They can corrode pipes and tanks. Furthermore, for agricultural use, the chloride content of water can limit certain crops. Chlorides are very soluble in water, they do not participate in biological processes, they do not play any role in decomposition, and therefore do not undergo modifications.
• - Sulfur. The sulfate ion is found in both supply and waste water. For the synthesis of proteins, it is necessary to have sulfur, which is subsequently released in the degradation process. Sulfates are chemically reduced to sulfides and hydrogen sulfides under bacterial action under anaerobic conditions.
• - Phenols.") are pollutants and toxics that impart flavor and odor to the liquid, analyzed by spectrophotometry. The contribution to natural waters is negligible and biodegradable. They come from industrial effluents but also from the degradation of pesticides.
• - Heavy metals. These include Ni, Mn, Pb, Cr, Cd, Zn, Cu, Fe, Hg, As. Some are essential for the normal development of life and the absence of sufficient quantities could limit the growth of algae, for example. Due to their toxicity, the presence in excessive quantities of any of them will interfere with the use that can be given to the water. That is why it is convenient to control the concentrations of these substances. Some of them are commonly used in agricultural and industrial activity, so their limits are legislated. They are determined by atomic absorption spectroscopy. They are caused by metallurgical, steel, and automotive industries and are generally not replaced but rather recycled.
• - Gases. The gases most frequently found in wastewater are nitrogen, oxygen, carbon dioxide, hydrogen sulfide, ammonia and methane. The first three are gases present in the atmosphere, and are found in all waters in contact with it. The last three are the product of the decomposition (aerobic and anaerobic) of organic matter.
Dissolved oxygen"). It is necessary for the respiration of aerobic microorganisms and other forms of life. It is slightly soluble in water and its presence, like that of the rest of the gases, is conditioned by the partial pressure of the gas in the atmosphere, the temperature, the purity of the water (salinity, suspended solids, etc.). Its solubility is proportional to the partial pressure since they do not react chemically and Henry's law governs the process because it is barely soluble. It is It is modified by the greater or lesser presence of salt and decreases with temperature. Since it prevents the formation of unpleasant odors in wastewater, it is desirable and convenient to have dissolved oxygen. It is measured in situ or fixed by a chemical reagent to be measured in the laboratory. Increasing the temperature does not produce greater biological oxidation unless it is aerated since oxygen has lower solubility. produced by aerobic or anaerobic organisms. Aerobic organisms use free oxygen for the oxidation of organic and inorganic matter and form harmless final products, while anaerobic organisms carry out oxidation by reducing salts such as sulfates and the final products are generally very harmful. Favorable conditions for aerobic microorganisms must be maintained if they are not considered harmful conditions. aerobic, dissolved oxygen measurements must be carried out in aerobic processes and at overturning sites. Oxygen is an important factor in the corrosion of iron and steel, especially in water distribution systems and in steam boilers. Therefore, oxygen removal is a common practice in the energy industry. Standard volumetric procedures for determining dissolved oxygen, if the sample is properly preserved, are the Winkler or metric iodine method. and its modifications. An oximeter (electrode) can also be used that allows in situ measurements of dissolved oxygen. Such electrodes can descend to various depths and dissolved oxygen concentrations can be read on a connected microammeter located at the surface.
Hydrogen Sulfide. As already mentioned, it comes from the anaerobic decomposition of sulfur or the reduction of mineral sulfites and sulfates, first it would pass to sulfite and then to hydrogen sulfide. Its formation is inhibited in the presence of large amounts of oxygen. It is a colorless, flammable gas with a typical odor. The blackening of wastewater is mainly due to the formation of ferrous sulfide and other metal sulfides. They are toxic and corrosive. It is determined by colorimetry, they give a blue color. Waters containing hydrogen sulfide will be very toxic at acidic pHs, even for bacteria. Toxicity will decrease extraordinarily at basic pHs.
Cyanide. Cyanides are potentially toxic compounds since a change in pH in the medium can release hydrocyanic acid, a compound generally associated with the maximum toxicity of these compounds, which is why it is of utmost importance to determine the presence of all cyanide compounds in natural, drinking, residual and treated wastewater as cyanide ion (CN-). They are determined by potentiometric methods or by spectroscopy. It should be kept at alkaline pH.
Methane. It is the main byproduct of the anaerobic decomposition of organic matter. It is not normally found in wastewater because small amounts of oxygen are toxic to the microorganisms responsible for its production.
Oxygen consumed").: measured in (mg/L). It is the amount of oxygen necessary to oxidize substances with reducing properties, present in a waste liquid. Among the most common reducing substances are: ferrous salts, sulfides, lipids, carbohydrates and some amino acids. The usual determination is carried out using potassium permanganate as an oxidant. This redox titration is not very precise or reproducible but it gives an idea of the mg/L consumed per organic matter present in the sample.
Perhaps the most important characteristic of wastewater in this regard is the presence of pathogenic organisms from human waste that are infected or carry a certain disease. The main groups of pathogenic organisms are bacteria, viruses, protozoa and helminths. Pathogenic bacterial organisms that can be excreted by humans cause diseases of the intestinal system such as typhoid and paratyphoid fever, dysentery, diarrhea, and cholera. Due to the high infectiousness of these organisms, each year they are responsible for a large number of deaths in countries with limited health resources.
Effluent treatment
Introduction
As results of the process, sludge and clarified effluent are obtained. The treated effluent is dumped into the receiving body or reused and the sludge is treated and disposed of in landfills or reused (production of biosolids). The series of treatment processes depends on certain factors:.
• - Characteristics of the effluent: pH, toxic products, suspended solids, BOD.
• - Quality of effluent output: it is set taking into account the objectives of the company and the aptitude of the receiving body.
• - Availability of land: the land needed is large and must be low cost.
• - Consider future expansions: expansions will have to be made because stricter limits are required.
Effluent treatment is the set of processes intended to modify the physical, chemical or biological composition of liquid effluents in order to make them harmless for disposal and recovery for other uses.
Coarse suspended solids are separated by filtration with screens, settleable suspended solids by sedimentation, non-settleable fine suspended solids by small opening sieve, biodegradable dissolved or suspended solids by natural biological treatment, biologically persistent suspended solids by adsorption or chemical oxidation, inorganic dissolved solids are separated by reverse osmosis, electrodialysis, ion exchange.
Stages of effluent treatment
For sewage fluid, the treatments applied are primary (physical) or secondary (biological). The primary treatments are sedimentation, filtration and the secondary treatments are Imhoff tank, biodigester, activated sludge. With the primary ones, the settleable solids are removed and part of the suspended matter, the dissolved solids, and the rest of the suspended matter is removed in biological treatments. Treatments are classified according to their degree of purification into primary (they remove more material), secondary and tertiary and according to the physical, chemical and biological phenomena involved. The primary treatments correspond to the physical ones and the secondary treatments correspond to the biological or physical-chemical ones.
Pretreatment
The objective of pretreatment is the elimination of coarse solids such as rags, branches and inert material such as sand and gravel. These cause damage to pipes, electromechanical pumps, and obstructions to the flow of fluid.
This stage of the process can be carried out with the following devices:
• - Grates: They are used to eliminate thick solids such as plastics, wood, rags that cause blockages or damage to pipes, electromechanical pumping equipment, and avoid accumulation in digesters and decanters. They are placed inclined 60-80° with respect to the horizontal. The robotic gates clean themselves. Fines grates are used instead of sedimentation tanks, but these are usually avoided due to stagnation problems and because greater separations are not obtained than settlers.
• - Sieving: They are used to separate finer particles that cause blockages or damage to pipes or electromechanical pumping equipment, accumulation in digesters or decanters. It is usually placed after a sand trap or a grating device. The operation is based on the difference in sizes, as with the bars, only particles smaller than the mesh opening pass through. It can be static or vibratory and rotating. The latter is a wheel that rotates where solids larger than the openings of the wheel mesh are deposited.
• - Desanding: In these sands, gravels, clays that cause blockages, abrasions, accumulations in digesters or decanters are separated. It is based on the separation of particles smaller than a certain size due to the difference in densities between the liquid and the solid. The settleable solids are retained after 10 minutes. The design parameter of a sand trap is the retention time, which is the relationship between the volume of the settler and the inlet flow. Discrete sedimentation occurs where the particles maintain their individuality.
• - Compensation: is used to attenuate variations in flow and the rest of the parameters. This allows a unified system with fewer operating points, which reduces operating costs.
• - Separation of oils and fats: If there is floating material such as bristles, manure, guts, foams, fats and oils, a chamber called an interceptor is used. It has vertical screens that guide the passage of the fluid and horizontal frames to remove the floating material once it reaches the surface. The floating material reaches the surface by natural flotation without the use of any equipment. On the other hand, if the fats and oils are emulsified, a system with air injection is used. The effluent enters a tank through a pressurizing pump where it is saturated with air and then goes to a pressure reducing valve and finally to a chamber where bubbles are released that enclose the dispersed substances and bring them to the surface. The components of an air injection system are: 1) pressurization pump 2) air injector 3) holding tank 4) pressure reducing valve 5) flotation chamber.
• - Neutralization and homogenization: homogenization consists of mixing currents that have varied characteristics of pH, suspended solids, BOD to unify the treatment system and maintain the parameters at few values, this reduces operating costs. Neutralization involves adding acid or alkalis to the alkaline and acidic effluent streams respectively to control pH values. To neutralize acid streams, 1) limestone beds 2) Solvay soda 3) caustic soda 4) lime 5) ammonia are used and the choice is limited to 1) purchase costs 2) reaction speed 3) neutralization capacity 4) storage and discharge of the neutralization products. To neutralize alkaline currents, for economic reasons, sulfuric or hydrochloric acid is used. Neutralization is carried out to maintain the favorable pH for the development of microorganisms (the optimal pH is between 6 and 8.5), acidic pHs corrode the pipes and generate the release of gases such as foam that makes analysis and subsequent treatment difficult, to unify the sewage water treatment system, before discharge to the receiving body because aquatic life is very sensitive to variations in neutral pH.
Primary treatment
The objective of this stage is the physical removal of settleable solids and part of the organic matter, suspended solids. The methods to carry out this stage are:
• - Sedimentation: is used to separate sedimentable suspended solids. They are based on the difference in specific weight between the fluid and the solid. Depending on the nature of the suspended solids, it is classified as:
1.Discreet sedimentation: particles maintain their individuality. For example: deposition of sand, clay, gravel in sand traps. A settler works the same as a sand trap but retains lighter settleable solids for a retention time of 2 hours. They contain a rectangular or circular chamber, a bottom sweeping paddle, an inclined bottom, and a sludge hopper. This is a primary sedimentation equipment.
If you have an effluent with a concentration of solids at 2 hours and 10 minutes, what treatment do you propose if the legislation prohibits settleable solids in the discharge? To eliminate them, a sand trap must be used since it only contains suspended solids that settle after 10 minutes, such as sand, clay, and gravel.
Sedimentation with flocculation. The particles join with others to settle as larger and heavier particles. It is considered secondary sedimentation. It is usually performed after biological treatment.
Sedimentation by zones. The particles fall forming a kind of mantle as a single body.
• - Flotation: separation of dispersed matter. It is used to separate fats and oils that are dispersed. It is also used to thicken biological sludge suspensions. Using a pump, the fluid is propelled so that air is injected into it, which goes to a pressurization tank where saturation with air is achieved. It then goes to a pressure reducing valve to move to a flotation chamber where the bubbles that enclose the dispersed matter such as fats and oils are released and bringing them to the surface. The components of a degreaser are: 1) pressure pump 2) air injection system 3) holding tank 4) pressure reducing valve 5) flotation chamber. If the matter is floating, an interceptor is used.
Both processes can be considered pretreatment in some bibliographies.
Secondary treatment
The objective in this stage is the degradation of the organic matter to stabilize it in a mineral state in a biological reactor, through microbiological activity (generally bacterial) that uses it as a substrate. These reactors are the place where the formation of the mass of microorganisms occurs. Part of this biomass breaks off and is carried away by the effluent, so the reactors are generally followed by settlers. The settled solids are recirculated to the biological reactor but part is discarded, in order to keep the microorganism population under control.
The biological systems used at an industrial level that are generally applied as secondary treatment can be aerobic and anaerobic:
• - Among aerobic procedures there is a diversity of technologies available such as activated sludge, aeration lagoons, percolating beds, etc.
• - Anaerobic processes are fundamentally digestion processes that can be applied to liquid or solid waste and generally include separation and use of the gas produced. The transformation of organic matter into methane and CO2 is carried out in three consecutive stages in which different groups of bacteria intervene with the formation of acetic, propionic, butyric, lactic, formic acid, CO2 and H2 to finally reach methane and C02.
Anaerobic processes are preferred over aerobic processes due to reduced operating costs. In anaerobes, there is the presence of toxic compounds (such as phenol), there are recalcitrant or xenobiotics, which are those whose biodegradability is very difficult. In anaerobic procedures there is less biomass production per unit of substrate reduction so the handling and evacuation of excess sludge is less, there is a lower requirement for nutrients (not organic matter), it is possible to operate at higher loads and methane is produced, which is a gas that can be used as biofuel. In an aerobic treatment, there are longer residence times, there is no emission of bad odors, higher temperatures are not required (around 35 °C), clarification is simpler because larger volumes of sediment are handled, it is easier to control. There are 3 predominant factors to evaluate the biological treatment of an effluent that contains toxic or recalcitrant compounds. Those factors are:
• - The nature of the necessary chemical conversion, for example, halogenated aromatic derivatives are easily attacked by anaerobic communities, while in the case of aerobic communities the compounds tend to polymerize first and are more easily attacked later.
• - The physiology of the microorganisms included, anaerobic degradation is more vulnerable than parallel degradation. Some compounds such as ammonia, sulfites, sulfates can act as inhibitors of methanogenic bacteria. In the nitrogen cycle, nitrogen is gradually converted to ammonia, and if aerobic conditions are present, it is converted to nitrite and then nitrate. If there is excess nitrogen, eutrophication occurs, excessive growth of algae and the liquid eventually rots. Non-ionized ammonia is toxic, so its oxidation to nitrites and then to nitrates is preferred, otherwise ionized ammonia is converted into non-ionized ammonia because it is a reversible reaction. In addition, the amount of N must be controlled because otherwise eutrophication conditions develop.
Tertiary treatment
This type of treatment is carried out after secondary treatment and is carried out to reuse the effluent.
• - Ion exchange: consists of the transfer of the ions that are in the solution to a resin where higher electrostatic forces are maintained. The ions that were part of the resin become part of the solution. It is used to recover precious metals, remove toxic metals and remove hardness. Since complete demineralization can be achieved, the resulting effluent is combined with the feed to generate water that can be used as feed to the boiler. There are a large number of natural substances for exchange such as zeolites, but synthetic resins have greater removal of ions. Resins are insoluble but they manage to adhere acidic and basic groups through chemical reactions. The exchange is reversible so the ions return to the liquid to separate more easily during cleaning. The number of ions determines the exchange capacity and the type of ions determines the ionic selectivity and efficiency of the filter. The material that makes up the resins is styrene or divini-benzene. Ion exchangers can be cationic or anionic. Cation exchangers separate the cations in the solution by hydrogens (hydrogen cycle) or sodium ions (sodium cycle). The exchanger must be regenerated. To remove the solids it carries, water is passed through it in countercurrent and then regenerating solution is passed through it with current, which is brine for the sodium cycle and sulfuric acid for the hydrogen cycle. Water is passed countercurrently to remove the residual regenerant. Cation exchanger resins contain salts of weak or strong acids, but generally contain salts of strong acids. Anion exchangers are used to remove anions from solution with hydroxyl ions. Once the resin is saturated it must be regenerated. To do this, it is cleaned countercurrently with water to remove the solids that remained in the resin. Then the current regenerating solution is placed, which can be ammonium hydroxide or sodium hydroxide. It is washed with countercurrent water to remove the residual regenerant. Anion exchange resins contain weak or strong bases but usually contain salts of strong bases.
• - Adsorption: is the concentration of the solute in a solid, when the solid is brought into contact with the solution. The solid phase is called the adsorbent phase and the solute molecules that are adsorbed are called the adsorbate. The forces responsible for adsorption are the Van Der Waals forces that act between the solute molecules and the surface of the solid. It is the result of the imbalance of surface forces. No force acts inside the molecules because the molecules are surrounded by similar ones. The adsorption capacity is proportional to the adsorption surface, so as the contact area increases, there will be more interaction. Active carbons in the form of grains and powders are used as adsorbents to adsorb detergents, particles that cause bad odor and taste, organic contaminants, and chlorine. They are prepared from raw materials such as lignite, wood, nutshells through dehydration and carbonization procedures, followed by the application of hot steam. It has a great possibility of regeneration, 30 times or more. To regenerate, the carbon is placed at 930 °C in an air-steam atmosphere. Regeneration removes adhering organic material and the carbon returns to its original capacity. The equilibrium relationships between the adsorbent and adsorbate are described by adsorption isotherms. The most used models are BET, Langmuir and Freundlich. The data are obtained in continuous laboratory tests and the effect of pH, temperature and other parameters on the adsorption process is predicted. They are said to be in equilibrium when the concentration of the contaminant in the solution is in dynamic equilibrium with the concentration of the contaminant in the solid. The Langmuir isotherm assumes that the molecules are adsorbed forming a monomolecular layer and the BET isotherm assumes that the molecules bind to previously adsorbed layers and that each layer is adsorbed following the Langmuir model. The desorption operation can be continuous or discontinuous. In batch operation, powdered coal is used, which is mixed with water and then decanted. In continuous operation, a column filled with granular carbon is used through which the fluid percolates. As it descends through the column the contaminants progressively descend. The removal of contaminants in activated carbon columns is carried out by 3 mechanisms: 1) adsorption 2) fixation of large particles 3) deposition of colloidal matter. Sedimentation is by zones, that is, a transition layer is formed where the concentration is maximum at the bottom and minimum at the top. This is the active zone of the spine and the progressive movement can be known by a rupture curve. The ordinates are in mg/L of COD and flow duration or total bed volumes are placed on the abscissa. Normally the columns are arranged in series, when the effluent reached the specified breaking concentration in the first column, it is introduced into the second so that it does not exceed the specified breaking concentration while the first column is regenerated. It is located at the end of the treatment because it is a tertiary treatment. The adsorption processes do not generate undesirable byproducts to the water, the equipment has a compact design so it takes up little space and the operation and maintenance costs are not very high, flexibility in the face of flow and concentration variations.
Disinfection consists of the removal of pathogens and algae by adding physical or chemical disinfectants. The physical ones are high temperatures or radiation such as UV, the chemicals are potassium permanganate, chlorogens and ozone. Among the chlorogens are chloramines, sodium hypochlorite, calcium hypochlorite and chlorine gas. Sodium hypochlorite and chlorine gas are usually used because they leave a residual and because of their low cost. It must be dosed to the filtered water before consumption so that the demand is satisfied and a residual of 2mg/L remains. Disinfection efficiency is measured by the presence of coliforms. Coliforms can be fecal or total. If there are no coliforms then the rest of the pathogens are not found either. It is applied to effluents that have already had primary and secondary treatment, to effluents intended for consumption. Chlorination also reduces BOD because it oxidizes part of the organic compounds, oxidation of metal ions, oxidation of the compounds that generate odor and flavor in the water, oxidation of cyanides to harmless products. It is performed in a contact chamber located at the end of the treatment.
15,000 L/h of an industrial effluent whose chlorine demand is 1 ppm must be disinfected with a NaClO solution whose concentration is 8% w/V. What dose of product in ml/min is required to prolong the disinfection of the liquid?
Working dose to achieve disinfection (q): Q.D.100/C.60=10.1.100/8.60=2.1 ml/min.
Sludge treatment
Sludge that results solely from solid-liquid separation processes (decantation, flotation) is known as primary sludge, and those from biological processes are designated secondary sludge. The primary ones consist of solid particles, basically organic in nature. The secondary ones are fundamentally excess biomass produced in biological processes. In the case of primary sludge, between 30% and 50% of the BOD of the influent is separated in the primary clarifier as insoluble BOD. In the activated sludge plant, around 2/3 of the soluble BOD separated corresponds to oxidized organic compounds to produce maintenance energy, but the remaining 1/3 corresponds to microbial cells found in the sludge in excess of purges. These sludge cannot be evacuated without prior treatment. The amounts of organic and volatile compounds contained are reduced by subjecting the sludge to digestion, both aerobic and anaerobic digestion processes. The sludge resulting from digestion, with a lower organic matter content, is known as stabilized sludge. The main objectives of stabilization are: (1) Reduction or elimination of annoying odors (2) Reduction of the volume of liquid or weight of solids to be treated in successive operations (3) Reduction of pathogenic microorganisms. The solids content in the sludge must be increased, for this purpose thickening and dewatering is carried out. In thickening from 2 to 15% and in drying from 15 to 50%. For sludge that is difficult to dry, special pretreatments are necessary, including chemical coagulation and thermal treatments. Evacuation is then carried out in two ways: dumping and application to the land or incineration.
It is a process of aeration, for a significant period of time, of a mixture of digestible sludge from primary clarification and sludge from aerobic biological treatment, with a decrease in volatile suspended solids (SSV) and the destruction of cells because the bacteria unfold because the substrate is not sufficient. The main objective is to reduce sludge and to do so it transforms organic substances into volatile substances. When the amount of sludge to be digested is small, batch digestion is used, followed by intermittent discharge of digested sludge. The rate of cell destruction decreases when the food/microorganism (A/M) ratio decreases. Consequently, the greater the proportion of primary sludge in the process, the slower the digestion, since the primary sludge has a relatively high BOD (high A) and low SSV (low M), meaning high values of the A/M ratio. The curve for residual BOD becomes almost flat as the MLVSS reaches its maximum. Taking into account that aerobic digestion of sludge takes place in the endogenous respiration phase, there is practically no decrease in soluble BOD. The main objective is the reduction of sludge to be evacuated, rather than the reduction of soluble BOD. In the case of aerobic digestion, residence times are shorter than in anaerobic processes, which means lower investments in digester capacity or volume. On the other hand, however, the energy costs for aeration are usually significant. This means that aerobic digesters are used in small units.
Quality control
Quality control can be internal or external (also called quality evaluation). A good internal quality control program is composed of at least 7 elements: operator competency certification, recovery of known additions, analysis of internally supplied standards, analysis of reagent blanks, analysis of duplicates, calibration by standards, and analysis of control charts.
Quality evaluation consists of the use of internal and external control measures with the intention of evaluating the data obtained in the laboratory. It includes sections such as performance evaluation samples, comparison samples between laboratories and performance verifications in a manner analogous to internal quality control.
I must meet quality standards, the more stages I control, the quality increases but the cost increases. When there is waste or by-products, there is no need to control the quality unless there is one that can be used.
A product or service is the customer's perception of it; it is the ability of a product or service to satisfy needs, a set of inherent characteristics that give it the ability to satisfy implicit and explicit needs. Although quality cannot be easily defined, one knows what it is. It means being held to a higher standard, rather than being satisfied with mediocre one. It could also be defined as an innate quality, an absolute and universally recognized characteristic.
Quality has many definitions that depend on the point of view one considers. A definition from the perspective of the chemistry laboratory is that of ISO 9000: "quality is the degree to which a set of inherent characteristics meet requirements."
From a product perspective: it is the ability to differentiate qualitatively and quantitatively with respect to some required attribute. Amount of a non-monetarily quantifiable attribute that each unit has.
From a user perspective: quality is characterized according to certain parameters, the quality of responding to a need, the quality of adapting to use, the quality of responding to customer preferences.
From a production perspective: quality is the degree to which a product (or service) meets design specifications. It is conformity with specifications.
From a value perspective: quality means exceeding customer expectations in terms of conditions of use and at an appropriate price. Degree to which a product's inherent characteristics satisfy needs.
The factors related to quality have a technical dimension that encompasses the scientific and technical aspects that affect the product or service, a human dimension that seeks to maintain good relationships between clients and companies, and an economic dimension that attempts to minimize costs for both clients and the company. Other factors related to quality are: fair and desired quantity of product to be manufactured and offered, exact price according to supply and demand, speed of product distribution or customer service.
Determinations in the laboratory
The general properties measurable before processing the sample are pH and conductivity.
The pH is the logarithm of the hydrogen ion activity. Indicates at a given temperature whether a substance is acidic or basic. In the potentiometric method, an electrode is used to determine the pH. To measure, the electrode is immersed, resting on its support if available, in the solution where you want to measure the pH. Shake gently to homogenize the sample and prevent the entry of carbon dioxide. It is not affected by oxidants, reducers, turbidity, color. Coatings of fatty material or particles can interfere with the response of the electrode. To clean it, gently rub the electrode with paper or using detergents, then rinse it several times with distilled water. Additionally, it can be rinsed with 0.1N hydrochloric acid and 0.1N sodium hydroxide solutions and then stored in pH 7 buffer solution overnight. It is washed several times before and after use. Be careful not to rest the electrode on the bottom or walls. After use, it is stored in a solution so that its operation is always optimal. pH is affected by temperature through mechanical and chemical effects. It must be measured in situ.
It is directly proportional to the temperature. It is measured through the potentiometric method using an electrode. The conductivity meter is calibrated with KCl solutions of known conductivity. It is not affected by color, turbidity, oxidant, reducer. You have to wash it several times before and after use. For measurements, the electrode is immersed in the solution. The sample is homogenized by stirring during the measurement. During the measurement you should not touch the walls or the bottom. Results are affected by greasy material and particles adhering to the electrode. To clean the electrode, gently rub the electrode with paper or apply a detergent solution, followed by rinsing with distilled water. It must be measured in situ.
• - Use gloves, glasses, overalls, face masks, long pants, closed shoes to avoid contact of the acids or the sample with the skin, eyes and mouth.
• - Do not run in the laboratory.
• - Do not distract others.
• - Each group will be responsible for its work area and material.
• - Do not leave tools on the floor.
• - Know where they are located and how to use chemical protection elements (antiseptics, alcohol, iodine), fire extinguishers, first aid kit, emergency showers, emergency exits.
• - When working with toxic products, work under a hood.
• - Keep reagents in safe places taking into account their compatibility to store them with others.
• - Know the R and S phrases of the reagents. The R phrases are warnings or risks and the S phrases are recommendations or work advice.
• - You cannot eat, drink and smoke inside the laboratory.
Parameter analysis
From the analysis of an effluent from a manufacturing establishment, the following results were obtained:
Oxygen consumed = 950 mg/L.
Total residue at 105 °C = 1720 mg/L.
Total residue at 600 °C = 210 mg/L.
Total settleable solids = 560 mg/L.
With these data, what do you consider would be the main polluting effects if this effluent were thrown into a stream without being previously treated?
The parameters show that there is a large amount of organic matter so if it is dumped without being treated, the dissolved oxygen will decrease because it will be consumed by the organic matter and will compromise the aquatic fauna and flora. Suspended matter affects aquatic life because it does not allow sunlight to pass through them. In addition, it affects the appearance of the receiving body, causing a negative socio-economic impact.
Indicate 3 major contaminants in wastewater from a refrigerator and indicate what parameters you would use to measure each of them.
An effluent from a refrigerator contains solids, fats and oils, detergents and organic matter. Organic matter would be measured with oxygen consumed, solids with total residue due to evaporation, detergents with phosphates or the o-toluidine blue method provides a more direct measurement, fats and oils with substances soluble in cold in ethyl ether.
The following parameters are determined for a textile industry: pH=10.2, T=60 °C, settleable solids at 2 hours=0.8 ml/L. What treatments would you apply to the effluent so that these parameters comply with what is expressed in the regulations?
At first, sedimentation is applied to eliminate settleable matter (settled solids are not allowed after 2 hours), then it is introduced into a contact chamber where it is neutralized with sulfuric or hydrochloric acid (the permitted pH is between 5.5 and 10). It is introduced into a cooling tower so that the working temperature in the biological reactor is correct. Furthermore, the regulated tipping temperature is less than 40°C. Finally, it is introduced into a biological reactor to degrade non-sedimentable organic matter. A more economical option is to let the load cool in an ambient chamber to the target temperature with the disadvantage that it would take longer.
What are the main components of sewage fluid? What treatment do you propose to eliminate them?
The majority components are solids that settle after 10 minutes, fats and oils and organic matter. To separate the fats and oils, a part of the settleable solids would use a grease trap, then a sand trap is placed to separate the rest of the settleable solids after 10 minutes, then a settler is placed where the settleable solids that were not retained in the sand trap, of an organic nature and less heavy, are removed and finally an activated sludge treatment is placed where the rest of the organic matter, the rest of the suspended solids and the coloration are separated.
References
[1] ↑ Agentes Forestales de Extremadura. Segunda Edición, junio de 2003. Editorial MAD, S.L. ISBN 84-665-2654-4.
[2] ↑ Carlos Buxadé Carbó. Genética, Patología, Higiene y Residuos Animales. Junio 1995. Mundi-Prensa Libros. 348 pág.
• - Infiltration: occurs when water that reaches the soil penetrates the earth through its pores and becomes groundwater.
• - Runoff: is the water that runs through the earth, after precipitation, without penetrating it.
• - Underground circulation: it is the circulation of water below the surface. It occurs due to gravity like runoff.
• - Fusion: transition from a solid to a liquid by the action of heat: the fusion of ice in liquid water occurs by the action of heat at 0 °C.
• - Solidification: it is the reverse process of fusion. It consists of the change of state of water from liquid to solid produced by a decrease in temperature.
Some of the water that falls on the earth evaporates directly; On the other hand, it returns to the atmosphere through plant evapotranspiration; The rest reaches, through more or less complex surface or underground paths, the sea, where, by evaporation, it is returned to the atmosphere, thus completing the cycle.
The water sources are:
Meteoric waters: in the case of rural communities or small towns, the collection of rainwater appears as a possible source of supply, which must be collected on adequately prepared land. Regarding the quality of this water, we can mention that it has low quantity dissolved solids, very low turbidity, due to the chemical composition it is considered to have low alkalinity and hardness, and at the same time have a high carbon dioxide content (rainwater when falling dissolves carbon dioxide from the atmosphere which gives it an acidic pH). This is corrected by adding lime. For this type of treatment it is advisable not to use lead pipes due to the aggressiveness of the water.
Surface waters: This is the name given to the waters coming from rivers, streams, lakes, etc. They are generally cloudy and colored waters and, furthermore, because they are superficial, they are subject to contamination. For these reasons, they require purification treatment, including disinfection prior to consumption.
Subalveal waters: these are the waters that run through the subalveo of the river. The subalveo is the area where the filtrate is collected through the ground. They are generally captured through filter wells or filter galleries. They are generally very good quality waters since they have undergone a natural filtration process. The cost of the works to use this water is somewhat high.
Groundwater: are the waters found in the subsoil. We can distinguish three types of different underground sources depending on the position of the water in the ground:
Deep groundwater: deep groundwater captured through semi-urgent wells generally provides drinking water, occupying second place in number of inhabitants served and first in localities served. Groundwater usually lacks turbidity and color, but in some cases of ferruginous groundwater, it becomes colored shortly after extraction due to the oxidation of ferrous compounds contained therein and requires corrective treatment prior to its delivery for consumption. In other cases they may contain excess dissolved solids (high mineralization), chlorides, sulfates, etc., or some toxic elements such as arsenic, vanadium or fluorine in high concentration, resulting in their inappropriate use as a source of supply.
Groundwater or groundwater: they can be used when they constitute the only economically usable source. Its level fluctuates quite a bit and is directly influenced by the rainfall regime. Its quality is variable and although it is physically and chemically acceptable, there is always the danger of microbiological contamination. Therefore, if its use is resolved, it will have to be done through excavated and drilled wells that must be adequately protected against surface contamination, maintaining strict bacteriological control of drinking water.
Spring water: water that springs from the earth. They can constitute a solution in the case of small rural towns, as long as they have sufficient flow and adequate quality. The catchment must be adequately protected. The spring will be safer as its flow rate is less variable, influenced by the rainfall regime, and the less alterable the water quality is.
The uses of water are: sanitation (hygiene and consumption), agriculture (irrigation), livestock (drinking), recreation with and without contact (spa, water sports), protection of aquatic life (fauna and flora), hydroelectric, industrial (process, boilers, refrigeration, concrete).
Throughout the hydrological cycle, the water that, when it passes into the atmosphere through evaporation, is distilled water of maximum purity, is loaded with other substances that determine, at the time of its use, the quality characteristics.
Although in the atmosphere rainwater receives impurities from gases, aerosols, dust and salts, if we limit ourselves to the natural cycle, in the sense of not considering causes of pollution due in one way or another to human activity, most of the impurities come from the geological formations through which it flows or in which it is stored and which, to a greater or lesser extent, it dissolves. Therefore, geology is a determining factor in the composition of water and, ultimately, its natural quality. Thus, on the one hand, water, according to the lithology of the geological formations with which it is in contact, is acidic or alkaline, with high or low content of dissolved salts, with a preponderance of carbonates, sulfates, chlorides, etc. On the other hand, contact with mineral formations can be the occasion for certain elements such as iron, manganese, copper or mercury to be found in the water "Mercury (element)") whose natural origin should be known to differentiate it from subsequent contamination.
The chemical and biological composition that waters have naturally is modified by the reception of effluents, of very different characteristics, caused by human activity. This final composition is what determines the quality of the water at a certain time.
Surface water
This is the name given to the waters that circulate on the surface of the ground.
They can occur in a flowing form as in the case of currents, rivers and streams, or still in the case of lakes, reservoirs, reservoirs and lagoons.
Surface water is produced by runoff generated from precipitation and infiltration of groundwater.
For regulatory purposes, surface water is usually defined as any water open to the atmosphere and subject to surface runoff. Once produced, surface water follows the path of least resistance. A series of streams, creeks, streams and rivers carry water from downsloping areas to a main watercourse. This drainage area is often referred to as a watershed or drainage basin.
A watershed is a basin surrounded by a deep groove, which separates different drainage areas. Water quality is strongly influenced by where in the basin it is diverted for use. The quality of streams, rivers and streams varies according to seasonal flows and can change significantly due to precipitation and accidental spills. Lakes, reservoirs, reservoirs and lagoons generally present a lower amount of sediment than rivers, however they are subject to greater impacts from the point of view of microbiological activity. Still bodies of water, such as lakes and reservoirs, age over a relatively long period as a result of natural processes. This aging process is influenced by microbiological activity that is directly related to nutrient levels in the body of water and can be accelerated by human activity.
Underground Water
Groundwater is defined as the portion of subsurface water that is subject to a pressure greater than atmospheric pressure, so that it flows into open cavities within the earth or moves across its surface in the form of seeps or springs.
Groundwater can enter through several routes: it comes, for example, from the percolation of direct precipitation, infiltration of surface water deposits, and artificial recharge.
There are several exit routes such as the evaporation of free water or soil moisture, evapotranspiration, which is basically due to the use and evaporation of water through vegetation, escapes into rivers or streams or man-made systems such as supply wells.
Groundwater can be generally classified as free and confined layer. In free layer waters, the water table can rise or fall depending on the level of the surface waters, since they act in a similar way to communicating vessels.
The water that penetrates through infiltration can carry different substances in solution depending on its origin. The soil works as a filter for many substances, retaining them, especially organic matter. However, some substances will reach the water table and be carried away by groundwater.
Groundwater acts as a diluent and, since it does not have organisms that transform organic matter, as in surface water, it degrades very slowly under the action of dissolved oxygen. Therefore, any type of organic contamination that originates in groundwater takes many years to be eliminated and inorganic contamination only dilutes and circulates within the underground veins.
Currently, one of the biggest problems with groundwater is contamination by nitrates of agricultural origin, with the addition of toxic and dangerous substances being totally prohibited by any procedure: infiltration, injection, etc., since these do not have any elimination mechanism and can only dilute said substances.
The soil below the earth's surface is made up of two different hydrogeological zones; the unsaturated zone and the saturated zone. The unsaturated zone constitutes a three-phase system: solid, liquid and gas.
• - Solids are generally made up of inorganic and organic materials. Organic matter corresponds to the remains of buried plants and animals that are in different stages of degradation.
• - The liquid phase is made up of water which contains dissolved solids.
• - For its part, the gas phase includes water vapor and other gases present in the atmosphere, although not necessarily in the same proportion. The saturated zone, on the other hand, includes all materials located below the water table.
Pollution concept applied to water
Saying that water is contaminated or not is a concept, somewhat relative, since an absolute classification of the “quality” of the water cannot be made. Distilled water, which, from the point of view of purity, has the highest degree of quality, is not suitable for drinking, this is because the degree of quality of the water must refer to the uses to which it is intended. The determination of the state of water quality will refer to the intended use for it.
In the same way, the concept of pollution must refer to the subsequent uses of water. In this sense, the Water Law (Spanish, Article 85) establishes that pollution is understood as:
Pollution: The action and effect of introducing materials or forms of energy that imply a harmful alteration of the quality of water in relation to subsequent uses or its ecological function.[1][2].
Purification
Contenido
El tratamiento de potabilización comienza en unas rejas que eliminan los sólidos gruesos, luego pasa a un desarenador donde se eliminan los sólidos sedimentables más pesados e inorgánicos, posteriormente ingresa a un sedimentador donde se eliminan los sólidos sedimentables menos pesados y orgánicos. Luego se realiza una coagulación-floculación donde se remueven el resto de los sólidos en suspensión, resto de la materia orgánica, coloración (sólidos disueltos y coloidales), el posterior paso es una decantación donde se eliminan los flocs formados en la etapa anterior, el paso siguiente es una filtración donde se retienen los flocs y micropartículas que no fueron separados en la etapa anterior, luego se alcaliniza porque el pH disminuyó por el agregado de ácidos y finalmente se desinfecta con lo que se eliminan microorganismos patógenos con lo que ya se tiene un efluente apto para el consumo.
Preliminary treatments
Solid particles settle as discrete particles or as flocculated particles due to the action of gravity, forming sludge that must be separated.
Discrete particles are separated in sand traps and problems such as deposition of inert material and damage to electromechanical pumping equipment are avoided.
When the turbidity and suspended solids contain fine particles, mostly non-colloidal, primary sedimentation equipment is placed prior to slow filtration or coagulation-flocculation-sedimentation treatment. If it contains mostly colloidal particles, it is convenient to carry out coagulation-flocculation-sedimentation directly.
The main goals of a sand trap are:
• - Remove discrete particles larger than 0.2 mm.
• - Avoid overloads (higher operating costs).
• - Damage to electromechanical pumping equipment and other installations.
• - Avoid sedimentation problems in the raw water adduction.
Primary sedimentation
Sedimentation serves to separate turbidity and suspended solids, after a time, by the action of gravity. If the suspended material settles quickly, it is considered to have siliceous material of small size but high specific gravity.
Particles larger than 0.2 mm cannot be separated by coagulation.
The units are called settlers or settlers interchangeably and can be circular, rectangular or square.
The retention time must be such that it allows the particles to float (less heavy than water) or the particles to settle (heavier than water).
Solids are considered agglomerable or flocculent when they agglutinate as they descend, changing shape, weight and size with a greater sedimentation speed.
Coagulation, flocculation and decantation
Coagulation and flocculation are part of the processes of a water treatment plant. Coagulation is carried out with rapid stirring and flocculation with slow stirring. The flocs may settle in another chamber or in the same chamber where coagulation occurred. Coagulation is the addition of coagulant so that the particles agglutinate, forming flocs that will then settle in another chamber. Coagulants can be natural or synthetic. The most used is aluminum sulfate and is being displaced by ferric chloride and mainly aluminum chloride. It is common to add polymers and to a lesser extent activated silica and bentonite as flocculants. Adjuvants are polyelectrolytes that improve coagulation and are chains of small subunits that contain ionizable groups such as the amino group, hydroxyl group, and carboxyl group. They improve coagulation because they increase the turbidity of the water, by generating more particles such as impurities, they decrease the dose because they increase the kinetics of the reaction and produce larger flocs faster. Coagulants are aluminum and iron salts that form hydrated oxides (q+) and attract suspended particles (q-) to form flocs. They vary in concentration of useful oxides and optimal pH. pH is a critical parameter in the efficiency of the process. The coagulant dose depends on mixing time (flocculation) - it is lower when the contact area is larger -, injection point (dispersion) - there is a speed at which it is better to inject the coagulant, alkalinity - the higher the alkalinity, the higher the dose -, turbidity - the higher it is, the higher the necessary dose. The optimal conditions of stirring speed, solution concentration, mixing time must be found. To determine these parameters, the JARTEST is carried out, which consists of carrying out agitation tests in the laboratory once a day or more than once (in the case of streams or rivers whose physical characteristics vary greatly). They are marketed in a specific state and have a working pH range.
Dispersion consists of adding coagulant reagents, with stirring. This achieves the destabilization of the colloidal matter. Natural reagents are alumina sulfate, ferric chloride or polymers; all of them available in liquid or solid form. Coagulants vary in concentration of useful oxides and optimal pH. The JARTEST assay allows the coagulant dose to be determined. The greater the turbidity, the greater the dose because the amount of solids in suspension is greater, the more alkaline the greater the dose, the greater the mixing time the better because larger flocs are formed and in greater number, the better the demand point is chosen, the lower the dose, rapid agitation is required for coagulation.
Flocculation is the process of joining previously coagulated or destabilized particles by slow agitation to form "flocs" of greater weight and size, which are separated by filtration, sedimentation or flotation, resulting in the removal of turbidity and color from the water. It starts with mechanical agitation with rotating paddles and motor drive, then moves on to hydraulic agitation where the water rises and falls through dividing plates by hydraulic pressure where the flocs collide with others to become larger. Rapid agitation and pumping break up the flocs that do not reform without the addition of more flocculant.
Filtration
Filtration is a physical process of eliminating microparticles and germs using granular material of different sizes (sand, anthracite and coal). Once it passes through the filter, the water is usually crystal clear. Filters can be gravity (fast or slow) or pressure (vertical or horizontal).
In rapid filtration, the particles are retained throughout the filter mantle, not just a superficial action, where they are only retained on the surface. The components of sand and gravel filters are:.
• - Filtering layer: the basic component is the uniform or stratified graded granular bed of sand and anthracite forming dual and multiple layers. For its design it is essential to know the filtration speed.
• - Support bed: normally made of graded gravel. The granulometry and thickness depend on the drainage system adopted for the washing adopted.
• - Drainage system and false bottom: it consists of the elements that allow the collection of filtered water and the distribution of water over the filtering layer.
Regardless of the type of filtration, filters must be backwashed with water or air at relatively high speed to promote partial fluidization and remove retained solids.
Alkalization
Alkalization consists of adding base because the acidic pH corrodes pipes and generates the release of gases with foam that makes subsequent analysis and treatment difficult. The dose depends on pH and is determined experimentally. Some alkalizers are sodium hydroxide (expensive), calcium carbonate (expensive), and calcium hydroxide (creates scale). The choice depends on costs and the analysis of its disadvantages.
Disinfection
The objective of disinfection of an effluent intended for human consumption and domestic use is the inactivation and destruction of pathogenic microorganisms. Chlorination is an efficient disinfection mechanism. Spores resist disinfectant, these more than protozoan cysts, these more than viruses, these more than vegetative bacteria.
For chlorination, the chlorine dose depends on:.
• - Chlorine demand (oxidizing power of chlorine, varies according to water sources and is determined experimentally because it depends on the concentration of impurities, temperature, time, etc.).
• - Residual chlorine, free plus combined.
• - Concentration of active chlorine.
Residual chlorine is an extra, non-toxic amount of chlorine, which prevents pathogens from entering the water meter from the treatment plant outlet. This point represents the place where water is delivered to customers. Chlorination is carried out in order to satisfy the demand for chlorine and leave a residual of 0.5 mg/L. Efficiency is measured by chlorine analysis and bacteriological analyzes of fecal and total coliforms. There must be an absence of this microorganism to ensure the non-presence of the rest of the pathogens.
If residual chlorine is represented vs. chlorine demand, 3 curves are obtained: no demand, medium demand, high demand. In the curve without chlorine demand, the residual chlorine increases with the chlorine dose, if the demand is medium or high, it grows to a point called breakpoint, where the residual chlorine begins to decrease and by increasing the chlorine dose the curve has the same behavior as the curve without demand.
Fluoridation is primarily used when there is no other source of fluoride for populations. In excess it prevents the fixation of calcium in teeth and bones. Softening is used to decrease the hardness of water. Demanganization and deironization to remove iron and manganese ions that precipitate metals that cause an astringent taste to the water. Dearsenization to eliminate arsenic that is harmful to health. Filtration with activated carbon to eliminate algae so that eutrophication does not occur. Elimination of odor, flavor and colors, for example phenols and organic matter that give it a musty taste. Dechlorination, if intensive use of chlorine has been made and the breakpoint reaction did not occur, allows chlorine levels to be reduced.
Based on the destination of the water, a quality or certain values will be required in the physical-chemical parameters. Drinking water has values recommended by the WHO (international) and the CAA (national).
Softening
It consists of the removal of soluble compounds with calcium and magnesium present in water. These cause the hardness of the water.
Hardness is defined as the propensity to form scale and the precipitating power of the soap solutions used to determine it. Hardness can be temporary (calcium and magnesium carbonates and bicarbonates) or permanent (calcium and magnesium sulfates, nitrates and chloride). The temporary hardness can be separated by heating or boiling them sufficiently. Carbon dioxide is released, precipitating insoluble calcium and magnesium compounds. Hardness is expressed in parts per million calcium carbonate equivalent.
The objective of softening is to remove salts that cause hardness in order to control corrosion, control scale and improve water quality for various uses. The methods used for softening are: decarbonation with lime-soda, ion exchange, membranes through reverse osmosis.
Activated carbon is used to absorb particles that cause taste, odor and color to water. Resins are used for the removal of organic particles. Carbon dioxide is absorbed by calcium hydroxide to form calcium carbonate and magnesium hydroxide. Solvay soda is added to waters with permanent hardness, and allows the decomposition of insoluble calcium sulfate to give rise to insoluble calcium carbonate and soluble sodium sulfate. The addition of lime and soda is applied when the water has a combination of hardness, permanent hardness and temporary hardness. Lime absorbs carbon dioxide, and this is not affected by the soda used to correct permanent hardness.
Ion exchange involves the transfer of ions present in the solution (pollutants) and those present in a zeolite. Chemical substitution reactions occur between a soluble electrolyte and an insoluble one with which it comes into contact. The mechanism is similar to adsorption so it is considered a special case of adsorption. For deionization, a single tank containing the cationic and anionic resins can be used. The cation exchanger is a sulfonated polystyrene hydrogen ion exchanger. The cation exchanger replaces calcium, magnesium, and iron ions with hydrogen ions. The anion exchanger used is a strongly basic amine resin exchanger. The anion exchanger replaces sulfate, carbonate, and bicarbonate ions with hydroxyl ions. Hydrogen ions then combine with hydroxyl ions to give water. The combined operations remove silica, minerals and carbon dioxide to give approximately neutral water. In rectification with the sodium cycle, the sodium ions go to form the solution, while the calcium and magnesium ions go to the solid. Its bases are interchangeable. Sodium ions go on to form sulfates, chlorides and carbonates.
It consists of subjecting a fluid on a membrane to a pressure greater than the osmotic pressure of the solution. Such a membrane is semipermeable and allows the passage of the solvent and not the solutes it contains. The solutes must be of low molecular weight so that they do not clog the membrane. It can be achieved by removing hardness, organic compounds, turbidity, disinfection products and pesticides and other elements present in the water.
Uses of water
Water intended for industrial use is 22%, water intended for agricultural use is 70% and water intended for domestic use is 8%. It is mainly used in heat transfer equipment, cleaning work areas, equipment and instruments and as raw materials. The quantity and quality of water required by an industry will depend on its size and the processes developed. The selection of a treatment system depends on the conditions that ensure sustainability, efficiency over time, raw water quality, required water quality, volumes per stage and treatment costs. The substances contained in water can be dissolved or suspended. The substances in suspension are sludge, organic matter, sand and waste. The dissolved substances are calcium, sodium and magnesium bicarbonates, calcium, sodium and magnesium sulfates, calcium and magnesium nitrates, residues, gases such as carbon dioxide and oxygen.
Effects of impurities
The effects of impurities contained in thermal equipment:
• - Reduction of heat transmitted by increased equipment fouling.
• - Breakdowns in the tubes and plates, due to the reduction of the heat transmitted.
• - Corrosion and fragility of steel.
• - Malfunction of the boiler with foam and water carried over in quantity by the steam.
• - High costs for cleaning, repairs, maintenance, inspection and reserve equipment.
• - Heat losses due to frequent purges.
• - Decrease in the performance of equipment that uses steam due to fouling.
Sampling
It is sampled 5 times, before and after coagulation, before and after filtration and before consumption. For groundwater. It is sampled twice, after extraction and before consumption. In the distribution network, the sampling sites are established at pipe terminal points, sweeping the entire network area and, if applicable, at pumping stations. Samples should be taken from direct entry faucets and not from internal installations.
The control parameters can be physical such as turbidity, pH, temperature, color, odor, conductivity; chemicals such as bicarbonates, sulfates, sulfides, nitrates, nitrites, calcium, magnesium, hardness, alkalinity; bacteriological such as the analysis of total coliforms, fecal coliforms, pseudomonas, enterococci.
It is variable and increases in critical conditions (epidemics, floods, etc.). The most common are: daily (source water), monthly (mains water) and quarterly (decanted, filtered and consumer water from the source).
Effluents
Any liquid, solid or gaseous element or substance that an establishment, property or ship discharges to the receiving body, including all human, animal, natural or synthetic, liquid, solid or gaseous waste or a mixture of them that is thrown with the effluent. The influent enters the process and the effluent leaves the process. The types of effluents are: liquid, gaseous and solid waste. Liquid effluents are supply waters to a population that have been impurified by various uses. They result from the combination of liquids and waste dragged from homes, manufacturing establishments, hospitals plus groundwater, surface water and precipitation that could be added. Gaseous effluents are substances that are discharged into the atmosphere (gases, aerosols, black smoke, mists) through ducts or diffuse emanations. Atmospheric pollution is defined as the atmospheric condition where gases reach concentrations or levels higher than normal, causing risks and damage to ecosystems, goods and people. Pollution comes mainly from automobile traffic, combustion of fossil fuels and activities of chemical industries. A solid waste is any object, substance, solid element from the consumption or use of a good in an industrial, institutional, service activity that the generator abandons, rejects or transfers to another person that can be used to build another good, with economic or final disposal value. Solid waste is divided into usable and non-usable waste. Solid waste is considered waste obtained from sweeping public areas. They are classified as domiciliary and non-domiciliary. Household ones are biodegradable or non-biodegradable. Biodegradable ones are those that degrade easily and in a short period of time such as fruits, fruit peels, vegetables, and non-biodegradable ones are those that do not degrade easily and have very long degradability cycles. Examples are tin, glass and construction elements. They are further classified as recyclable and non-recyclable. In industrial activities, effluents are generated as solid waste, which is why they must be controlled. Household solid waste has various stages: generation, transfer, processing, treatment and final disposal. Generation constitutes the origin of the waste and from there it is moved to other places, the transfer can occur via trucks or water, it includes processes such as compaction or differentiated selection, even from the same place or homes, the processing is carried out to separate the biodegradable material from the non-biodegradable, the treatment makes them harmless or that they do not harm the environment. It is done through biological treatments or landfills. Non-domestic waste can be classified according to its origin: industrial, which can be dangerous, toxic, has a lot of packaging waste, all types of materials; agro-industrial waste that is made up of "stubble" that is the remains of stems and leaves that remain after the harvest and that can be used to extract energy, waste from packaging of pesticides, biocides, fertilizers, they have a special treatment and are not disposed of together with common garbage; miners heavy metal contamination; hospitals that present mainly infectious, toxic, pathological solid waste, have their special legislation for transport, treatment and disposal, pyrolysis treatment is applied in incineration ovens where there must be control of gases, they have a dioxin problem; of construction basically harmless but occupy a large volume, mainly inorganic and can be reused. According to the effects, they are classified as hazardous waste, that waste or waste that, due to its toxic, corrosive, explosive, flammable, reactive characteristics, can cause a risk or damage to health. Containers and packaging that were in contact with them are also considered dangerous; non-hazardous, they are so called because they do not present dangerous characteristics, recipients must verify the type of cargo and classify it as dangerous or not for subsequent treatment; flammable, characteristic of a waste that consists of burning when there is strong ignition under certain conditions of pressure and temperature; toxic, characteristic of a waste that consists of causing adverse biological effects that may cause harm to human health or the environment. For toxic waste, toxicity criteria are defined and control limits are established:
A) Oral median lethal dose (LD50) for rats less than or equal to 200 mg/kg body weight.
B) Dermal mean lethal dose (LD50) for rats less than or equal to 1000 mg/kg body weight.
C) Inhalation mean lethal concentration (LC50) for rats less than or equal to 10 mg/L.
D) High potential for eye irritation, respiratory
Solid waste management is carried out in four stages: avoid, minimize, treat and dispose. Avoiding is the most convenient environmental action, followed by minimizing, which consists of reducing, reusing, recycling and recovering, followed by treating, which consists of physical processes (fractional separation), chemical (calcination), and biological (composting).
Gaseous effluents come mainly from industrial activities and large cities (engine combustion). The main pollutants are: carbon pollutants (carbon dioxide and carbon monoxide); nitrogen pollutants (nitrogen monoxide and nitrogen dioxide); sulfur pollutants (sulfur trioxide and sulfur dioxide); lead, mercury (and other heavy elements) there used to be lead in gasoline and the pollution was very high, low molecular weight organic volatiles (benzene, dioxins, asbestos (no longer used today), CFCs (almost not used today, it was used in refrigeration equipment and aerosols); very small solid particles that form gels, fumes, fogs that not only affect human health but also aesthetics and visibility.
Pollutants can be primary pollutants such as carbon monoxide, ammonia, sulfur dioxide or secondary pollutants that are derived from the above, such as acid rain.
One way to eliminate solid waste is through incineration but the gases must be treated. Filters are used that retain or adsorb dissolved substances (pollutants) in the gas, cyclones where the gas passes through and contaminating particles are separated by centrifugal force, absorption towers where a liquid is brought into contact with the gas and the contaminating particles are transferred to the liquid. Electrostatic precipitators consist of magnets that trap ferromagnetic particles from the gas stream.
Household liquid effluents come from household activities such as washing dishes, washing floors, and evacuating bathrooms. They contain high content of organic matter, detergents, solids, high turbidity, black color due to the presence of metal sulfides. The evacuation of organic matter without prior treatment produces a decrease in dissolved oxygen in the receiving body, which compromises aquatic fauna and flora.
White water comes from rain and contains waste that is dragged from roofs, rooftops, streets, sidewalks, and also contains atmospheric pollutants.
A raw sewage fluid has characteristics:
• - Physical such as variable temperatures, rotten smell (presence of sulfides), grayish-black color (presence of metal sulfides) and high turbidity.
• - Chemicals: presence of calcium and magnesium, phosphates, ammonium ion, nitrates and nitrites, sulfides, sulfites and sulfates, sodium, potassium, proteins, carbohydrates, lipids and detergents.
• - Biological: presence of bacteria, viruses and protozoa.
To measure the characteristics, the following parameters are used:
• - Physical: temperature, color is compared with other standards, odor conductivity (to measure the concentration of inorganic species), solids analysis (to measure the proportions of settleable solids, in suspension and dissolved solids).
• - Chemicals: pH, alkalinity (presence of hydroxyls, carbonates and bicarbonates), hardness (presence of calcium and magnesium), phosphates (phosphorus), ammoniacal nitrogen, nitrites and nitrates (nitrogen), phosphorus (common waste and synthetic detergents), detergents, fats and oils, sulfides, dissolved oxygen (determines presence of aerobic or anaerobic organisms), BOD (cc of biodegradable organic matter), COD (cc of organic matter).
Liquid effluents can also come from special or industrial establishments. In special establishments, the division, handling and cleaning of articles and materials occurs; no transformation occurs in their essence. Examples are: mechanical workshops, analysis laboratories, dry cleaners, pasta factories, hospitals. In industrial establishments, manufacturing, processing and processes occur that produce new products from raw materials or materials used. Examples are: tanneries, meat processing plants, food, chemical, steel, metallurgical, among others.
Industrial drains: together with sewage drains, they constitute the main cause of water pollution. It is difficult to establish the characteristics of industrial wastewater because it depends on the nature and quantity of waste produced, which differs depending on the type of industry, even for those of the same type, since it depends on the manufacturing process developed.
Effluent analytical methods
Un efluente se puede caracterizar según:.
• - Origen: se debe determinar si proviene de una línea o de varias líneas, varías líneas que se unen para luego tratarse o se tratan y luego se unen.
• - Cantidad: relacionado con la masa y el volumen del efluente. Debe conocerse si se evacua en forma continua o no.
• - Calidad: la composición física y química del efluente, que componentes hay y en que concentración, se mide en ppm y si son trazas en ppb.
El muestreo de control consiste en extraer una porción del efluente que sea representativa de la calidad de descarga del efluente en el momento de control, con el propósito de analizar la calidad de la misma. El muestreo tiene como objetivos: controlar la calidad del efluente y proponer un tratamiento en caso de que el mismo sea contaminante, controlar la eficiencia del tratamiento, determinar la factibilidad de reúso o recupero y analizar los efectos del vuelco al cuerpo receptor.
Preservation of samples
Industrial or commercial effluents have an unstable composition due to their varied composition, which forces them to change their composition and concentration. The speed of changes is affected by pH, temperature, concentration and bacterial action. In the same way, the temperature, color and characteristics of oxidizable and reducible substances can change rapidly, so such variables must be analyzed before reaching the laboratory (in situ).
If the nature of the effluent is such that it could decompose rapidly, it should be kept at a low temperature to retard bacterial action and prevent change in characteristics. Temperature control at 4 °C delays bacterial action and suppresses the volatilization of dissolved gases, which affect the physical-chemical characteristics of the samples.
For the analysis, it is recommended to extract a volume of 2 liters of sample, store them correctly in glass or plastic containers that have a wide mouth or a screw-on lid or airtight seal.
Physical parameters
• - Appearance: the term turbid is applied to water that contains suspended matter that intervenes with the passage of light. In lakes, waters with relatively slow flow, turbidity is due to colloidal dispersions and in rivers in overflow conditions it is due to relatively coarse dispersions. Turbidity is an essential consideration in public water supplies for three reasons:.
• - Aesthetics: any turbidity in drinking water is related to possible contamination by wastewater and the dangers associated with it.
• - Filterability: waters with greater turbidity are more difficult to filter because the filter openings become clogged. It becomes more expensive.
• - Disinfection: the solids of municipal wastewater usually encapsulate microorganisms so the disinfectant does not come into contact.
The current standard method for determining turbidity is based on instruments that use the principle of nephelometry. The instrument has a light source that illuminates the sample and photoelectric detectors with an attachment for reading the beam that forms right angles. It is customary to use a formazin polymer suspension or other commercially available preparations as standard. Turbidity data is used to determine whether chemical coagulation and filtration treatment is necessary in water supply plants. The determination of suspended solids is used to verify the removal of turbidity in water. Turbidity is removed by a coagulation-flocculation treatment.
• - Color: indicates the presence of colloidal or suspended substances with which I can intuit the origin of the effluent. Natural color exists in water in the form of negatively charged colloidal particles. Because of this, it can be removed using a salt that contains a trivalent metal ion such as aluminum sulfate or ferric chloride, polyaluminum chloride. The color caused by the suspended matter is the apparent color and the color caused by the organic and plant extracts that are colloidal is the real color. Color intensity increases with pH, which is why it is advisable to measure pH along with color. The suspended matter and coloration (colloidal and dissolved solids) are removed with a coagulation-flocculation treatment. Natural color, like turbidity, is due to a large amount of substances and standard solutions are used to determine color grades. Many samples require pretreatment to detect the true color. Waters that contain natural color have a yellow-brown appearance. Through experience it has been seen that potassium chloroplatinum solutions dyed with cobalt chloride give shades similar to the real colors of water. By varying the amount of cobalt chloride, other colors are obtained. To measure and describe colors that are not in this classification, spectrophotometry must be used.
• - Odor: it is indicative of the old age of the domestic effluent, when it is young it is slightly putrid but when it is old it septizes and acquires a strongly putrid odor due to the development of hydrogen sulfide. The smell can be due to a wide variety of chemical substances, so in its determination its aroma is associated with a known one. For example: onion (acetylene, iodine), hyrcinos (cheese, sweat, etc.), unpleasant (amines, narcotics, animal waste, etc.).
• - Temperature: although domestic sewage liquid has a slightly higher temperature than the supplied water, finding liquids with much higher temperatures indicates that an industrial or commercial discharge is occurring. They cause deterioration of the sewer network and accelerate the biochemical reactions carried out by bacteria, so dissolved oxygen is consumed more quickly and the bacterial population grows.
• - Conductivity: it is related to the total dissolved solids SDT=0.8 k uS/cm and provides a measure of the capacity to transport electric current and varies with the type and number of ions. It can be determined using a conductivity cell linked to a circuit with a Wheatstone Bridge. It gives information about the concentration of ions, that is, the amount of inorganic species that the effluent has. Organic species are difficult to ionize and dissolve. KCl is used to calibrate the conductivity meter.
• - Solids: the term solids refers to matter suspended and dissolved in water. Solids can be settleable, suspended, dissolved and colloidal. Total dissolved solids measures the total filterable solid waste (salts and organic compounds). Excess total dissolved solids generate unpleasant palate and adverse physiological reaction in the consumer. The solids that settle after 10 minutes can destroy pipes and electromechanical equipment and the solids that settle after 2 hours generate environments conducive to anaerobic degradation. They are used to evaluate the treatment carried out. Suspended solids are those that are not dissolved in the body of water and are obtained by evaporating and weighing a filter through which the sample is passed. Dissolved solids cannot be determined directly but must be obtained by difference between total solids and suspended solids. Determination of total solids by evaporation and weighing is performed to determine the concentration of total solids, their fixed and volatile fractions in liquid and semi-solid samples such as river or lake sediments, sludge that is isolated or residual or agglomeration of sludge from vacuum filtration, centrifugation or other dewatering process. Total solids are dried at 103-105 °C. The determination of total solids allows us to estimate the suspended and dissolved matter in the water. Settleable solids indicate the amount of solids that can settle in a given time from a sample volume. Suspended solids are determined by the difference in weight of a filter through which the sample is passed. Colloidal solids are not detected, they are stable, difficult to separate and analyze. Volatile and fixed solids are produced by combustion procedures, in which the organic matter is volatilized and at the same time the temperature is controlled to avoid the volatilization of inorganic substances. The test is compatible with the total oxidation of organic matter. It consists of incinerating the sample at 550 °C.
• - pH: is the logarithm of the hydrogen ion activity. It serves to indicate the alkalinity or acidity of the effluent. An acidic pH corrodes conduction systems and generates gas release. It is determined on site. Aquatic life thrives at a pH between 5 and 10, at other pH levels an imbalance occurs in aquatic life; It determines subsequent treatments because it is a critical factor in softening, corrosion control, coagulation and disinfection. In the biological treatment of wastewater, the pH must be maintained in a favorable range for microorganisms. It can be done in a wide variety of materials and in extreme conditions as long as the appropriate electrode is used. For pH greater than 10 and at high temperatures, it is carried out with a glass electrode designed for this purpose. For semi-solid substances, lance-shaped electrodes are used. The electrodes are standardized with buffer solutions of known pH. Very acidic pHs are corrosive and produce gas evolution.
• - Alkalinity: is the measure of the ability to neutralize acids. It is primarily due to salts of weak acids, although weak and strong bases can also contribute. Bicarbonates are the ones that contribute the most to alkalinity because they are in greater quantity because they arise from the reaction between carbon dioxide and the basic matter of the soil. Under certain conditions, water is alkaline due to the presence of carbonates and hydroxides. This occurs in surface waters with growing algae. Alkalinity is caused by 3 large groups that are classified according to their high pH values: hydroxides, carbonates and bicarbonates. Very alkaline waters have a very unpleasant taste. It is measured volumetrically with 0.02N sulfuric acid and is expressed in calcium carbonate equivalents (or in ppm of CaCO3). This parameter is essential in the processes of coagulation, softening, corrosion control, buffering capacity and in the treatment of industrial waste (because it is prohibited to discharge water with caustic alkalinity).
• - Chlorides: if the concentrations are high, they produce a salty taste that is rejected by many people. Chlorides can be easily measured by volumetric procedures using internal indicators. The most used is the Mohr Method, which uses silver nitrate as a titrant and potassium chromate as an indicator. It is an important consideration in choosing supplies for domestic, agricultural and industrial use. Brackish waters with a high salt content determine the device to be used for the determination. The determination allows regulating the concentration in industrial or domestic effluents to protect the receiving waters. It is a tracer and is very useful because its presence is not visually detectable, it does not have toxic effects, it is a common constituent of water, the chloride ion is not absorbed by the soil, it is not altered or changed by biological processes and it can be easily measured.
• - Dissolved oxygen: performed in situ or fixed using a chemical reagent. It is measured in mg/L. Solubility decreases with temperature and salinity. Nitrogen and oxygen are poorly soluble, and since they do not react chemically with water, their solubility is proportional to the partial pressures of the gases. At a given temperature and under saturation conditions it is estimated using Henry's Law. Its solubility varies with atmospheric pressure at any temperature. Because the rate of biological oxidation increases with temperature and the oxygen demand also increases but the solubility of oxygen decreases, the system must be aerated and this has associated aeration costs. The solubility of oxygen determines the rate of oxygen absorption because the reaction rate depends on the concentration and this determines the costs of aeration. Dissolved oxygen determines whether oxidation occurs by aerobic or anaerobic organisms. Aerobics use oxygen for the oxidation of organic and inorganic compounds to give harmless products and anaerobics carry out oxidation by reduction of inorganic salts such as sulfates and the final products are harmful. Since the two types of microorganisms are propagated, it is important to maintain aerobic conditions, which is why measurements of dissolved oxygen are carried out in the body of water where the effluents are dumped and in the aerobic treatments of wastewater, industrial and domestic. Oxygen causes corrosion of iron and steel in water distribution systems and steam boilers, so oxygen removal is a common practice in the energy industry. The standard volumetric procedures to determine dissolved oxygen if the sample is properly preserved are the Winkler or metric iodine method and its modifications. An oximeter (electrode) can also be used and measurements are made in situ. The electrode can be lowered to various depths of the liquid and readings are made on a connected ammeter located at the surface. A contaminated liquid has zero dissolved oxygen.
• - Oxygen consumed: it is the amount of oxygen necessary to oxidize the substances with reducing properties present in the residual liquid. The most common substances are: ferrous salts, sulfides, lipids, carbohydrates and amino acids. The usual determination is with potassium permanganate as titrant and indicator of the end point. This redox titration is not very precise or reproducible but it gives an idea of the mg/L consumed by the organic matter present in the sample.
• - Biological oxygen demand: it is the amount in mg/L of oxygen necessary to degrade organic matter by the action of aerobic bacteria at 20 °C, in darkness and for 5 days. The importance of its determination lies in the fact that it gives an idea of how contaminated it is with organic matter and the potential consumption of oxygen when it is thrown into the body of water, which compromises the aquatic fauna and flora. It is essentially a bioassay procedure, so it is carried out in conditions that are most similar to nature. Re-aeration of samples should be avoided as the dissolved oxygen level decreases during analysis and during sampling. Due to the limited solubility of oxygen, samples must be diluted to ensure that dissolved oxygen is present in the test. There should be no toxic substances, necessary nutrients, phosphorus, nitrogen and some trace elements. Biological demand is produced by a varied group of microorganisms that carry out oxidation to carbon dioxide and water. Therefore, in the samples there must be a load of "seed" microorganisms necessary for biological oxidation to occur. Oxidative reactions derive from biological action and the speed of these reactions depends on the number of microorganisms and the temperature. The effects of temperature remain constant at 20 °C, which is an average of natural water temperatures. Biological oxidation at a temperature of 20 °C and under other operating conditions (e.g. darkness) is considered complete after 20 days. Since you cannot wait that long for the results, it is analyzed for 5 days. So the measured BOD is only a fraction of the total. The total time for biological oxidation will depend on the seed and the nature of the organic matter, and is only determined experimentally. The BOD test depends on the measurement of dissolved oxygen. It is used to measure the self-purification capacity of the stream and establish the BOD levels for discharge into the body of water. It is an important consideration for the design of treatment equipment, the choice of treatment method, and determining the equipment size of trickling filters and activated sludge units. After treatment plants begin operating, the results are used to evaluate the efficiency of the processes. To summarize the limitations of the BOD: have acclimatized sowing (necessary nutrients, avoid re-aeration, seeds), measurement of only a fraction of what is biodegradable, time (minimum 5 days), pretreatments in case of toxic effluents.
• - Chemical oxygen demand: the advantage is that the analysis time is 3 hours, the disadvantage is that it does not give an idea of biodegradability. BOD/COD data must be available to determine the degree of biodegradability of the sample. It is the amount in mg/L of oxygen necessary to chemically degrade the organic matter contained in the residual liquid at 150 °C for 2 hours and using a strong oxidizing agent such as potassium dichromate. The importance of its determination lies in the fact that the COD levels of the effluent can be known and modified before discharge to the sewer or the receiving body since high COD levels indicate a high presence of organic substances and reducing inorganic substances that consume the oxygen available for aquatic fauna and flora, causing their disappearance. The method allows measuring the organic matter present in the sample because organic compounds are oxidized in the presence of a strong oxidant such as potassium dichromate under acidic conditions. Potassium dichromate degrades biologically oxidizable matter as well as biologically inert organic matter. It does not provide data about the rate at which the biologically active material is stabilized because it degrades both the biologically resistant and the biologically oxidizable material. All oxidizing agents must be placed in excess; it is necessary to measure the excess that remains at the end of the reaction to know the original amount of organic matter. The advantage of dichromate is that the excess can be measured relatively easily. Certain organic compounds such as low molecular weight fatty acids cannot be oxidized by dichromate, which is why a catalyst is used. The results are expressed in mg/L necessary for oxidation. The determination of COD is carried out in a digester and is then determined by titration or colorimetry. For industrial effluents, the regulation is 500<COD<10,000 for contaminated courses and COD<20 for uncontaminated courses. In conjunction with BOD, COD is useful in indicating toxic conditions and the presence of biologically resistant substances. With the BOD and COD data, one of these relationships is obtained:
• - Nitrogen series: colorimetric determinations are carried out, I measure them with the spectrum or comparison of color with standards. The chemistry of nitrogen is complex since it has several oxidation states which can be induced by living organisms. Bacteria can induce positive or negative states and depend on whether they are aerobic or anaerobic organisms. Only a few oxidation states influence water quality. Ammonium nitrogen is measured in spectrum or compared to a standard. To measure nitrite nitrogen and nitrate nitrogen, it is compared with a disk with a color scale. In recently contaminated waters, nitrogen is in the form of organic nitrogen and ammonia. As time passes, nitrogen converts to ammoniacal nitrogen, and if aerobic conditions exist it passes to nitrites and then to nitrates. If an aerobic treatment is to be carried out, there must be sufficient nitrogen since it is a necessary fertilizing element for the growth of algae, otherwise it must be supplied from external sources. But if excess nitrogen, mainly nitrate, is dumped, eutrophication (overpopulation of algae) is generated and the liquid becomes putrid or contaminated, which is why this analysis is so important. The determination of nitrogen is carried out to control the degree of purification in the treatment stages. It is well known that non-ionized ammonia is toxic and the ammonium ion is not. pH is the factor that controls the toxicity of ammonia and is not a problem if the pH is less than 8 and the ammonia concentration is less than 1 mg/L. Ammonia control can be accomplished by effective removal of ammonia or by nitrification (oxidizing it to nitrites and then to nitrates). In some cases, the limitation is the amount of total nitrogen. The techniques for determining nitrites, nitrates and ammoniacal nitrogen vary for each parameter so you can not only quantify it but also identify it. Total nitrogen is determined by the Kjeldahl method. The determination of nitrates is used to know if the establishment complies with the maximum levels of the contaminant. The determination of organic nitrogen and ammonia to know if there is sufficient nitrogen available for biological treatment. If there is not enough amount, it must be provided from external sources.
• - Phosphorus: expressed in mg/L of phosphate phosphorus. The analysis technique is based on a reaction that gives color and is compared with color standards. Polyphosphates are used in public water supplies as a means of corrosion control. They are also used in softened waters to stabilize calcium carbonate and avoid the need for re-carbonization. All surface water supplies are the basis for the growth of aquatic organisms such as algae or cyanobacteria and this growth depends on the amount of fertilizing elements in the water. Nitrogen and phosphorus are the fertilizing elements for the growth of algae and cyanobacteria, so their concentrations limit the growth rate. When there is an abundance of both elements, algal blooms occur and the liquid eventually rots. Domestic water has high levels of phosphorus. Most of the inorganic phosphorus is contributed by human waste, these come from the metabolic degradation of proteins and the elimination of phosphates through urine; in addition to strong synthetic detergents. Phosphate compounds are widely used in steam plants to eliminate boiler scaling. Orthophosphate can be measured from polyphosphates due to their stability under pH, time and temperature conditions. Polyphosphates and organic forms of phosphorus must be converted to orthophosphates which can be determined qualitatively by gravimetric, colorimetric or volumetric methods.
• - Detergents: currently detergents are biodegradable, they have simpler treatments but they have other effects such as foaming that makes treatment and analysis difficult. A colorimetric determination is carried out after prior extraction with chloroform.
• - Fats and oils: they form films and crusts on the surface that clog the pipes, affect the aesthetics of the body of water, they form a film on the surface that prevents the transfer of oxygen from the air to the water, thus compromising the aquatic fauna and flora. They are determined gravimetrically using the method of substances soluble in ethyl ether. They are soluble in ethyl ether and insoluble in water.
• - Phenols: they are pollutants and toxics that impart odor and flavor to the liquid. They are determined by spectrophotometry.
• - Heavy metals: where Cu, Ni, Hg, Cd, Cr, Pb stand out and are determined by atomic absorption spectroscopy. They are generated by metallurgical, steel, and automotive companies that generally recycle them and do not dispose of them.
• - Hydrocarbons: such as gasoline and oil. They are determined by HPLC.
• - Pesticides: they can be chlorinated and phosphorous, they are determined both in water and in sediments. They are very polluting so they are allowed in very low concentrations. They are determined by HPLC and gas chromatography.
• - Sulfide: its presence is due to the decomposition of the organic matter present in the residual liquid. They are generated by the bacterial reduction of sulfates. They are determined by colorimetry and give a blue color. They are toxic and corrosive.
• - Cyanide: cyanides are potentially toxic compounds since a change in pH in the medium can release hydrocyanic acid, a compound associated with maximum toxicity, so it is important to determine the presence as cyanide ion of all cyanide compounds that exist in wastewater, treated wastewater, potable wastewater, natural wastewater. It is determined by potentiometric methods or by spectroscopy. It should be kept at alkaline pH.
These are the most basic and general. Then it will depend on each industry to determine another factor.
Sources of water pollution
The main sources of water pollution are industrial and special establishments. Within the special establishments are the operations of fractionation, handling or cleaning of articles and materials, they do not produce any type of product transformation in essence. Examples are: hospitals, service stations, car washes, hypermarkets and supermarkets. Within industrial establishments there is manufacturing, processing and processes that transform the raw materials or materials used or give rise to new products. Examples are: tanneries, meat processing plants, textiles, paper mills, metallurgical, steel, food (dairy, alcoholic/non-alcoholic beverages, fish), distilleries, sugar mills and chemicals (paints and dyes, fertilizers, pesticides, insecticides, cleaning products).
Industrial drains, together with sewage drains, constitute the predominant cause of water pollution. It is very difficult to define the characteristics of industrial drains, given that they present the particularity of their great variety in terms of nature and quantity of waste produced, with notable differences being verified according to the types of industries, a concept that includes similar ones, since it depends on the modality of the manufacturing process developed. For example, a refrigerator discharges an effluent with organic matter, solids, fats and detergents.
Origin of cloacal fluid
Sewage (wastewater) is mainly composed of waste from three main groups:.
• - Water for domestic use: these are simply those used for personal hygiene, in the kitchen and for cleaning.
• - Human waste: are those used to transport fecal matter and urine to the sewers.
• - Non-domestic waste: from industrial, commercial and service activities. This group usually contains the highest pollution load, which is why pretreatment of the water that is discharged into the sewage network (mainly to industries) is usually required, which in many cases is not fulfilled or is inefficient.
To measure physical contaminants, I would use physical parameters such as turbidity, color (apparently real), odor, temperature, conductivity (to determine what inorganic species the effluent has), solids analysis (to evaluate the percentages of the different types of solids that the water may contain such as suspended, settleable, colloidal and dissolved solids). To measure chemical contaminants, I would use chemical parameters such as pH, alkalinity (to determine the presence of hydroxyls, carbonates and bicarbonates), chlorides, dissolved oxygen (determines aerobic and anaerobic organisms), BOD (to determine the polluting power of waste), COD (to measure the cc of organic matter), phosphorus (common waste, synthetic detergents), detergents, fats and oils, sulfates.
To measure turbidity, a turbidimeter is used; the color is measured with the spectrophotometer; the smell by sensory analysis; the temperature is measured with a thermometer; conductivity with a conductivity meter; dissolved and suspended solids through filtration and gravimetry; settleable solids by sedimentation in an Imhoff cone; Colloidal solids are measured by spectrophotometry. To measure pH, the peachimeter is used; Alkalinity is used to measure hardness; chlorides by titration with silver nitrate; dissolved oxygen using an oximeter; organic matter is measured with BOD, oxygen consumed, COD; phosphorus through phosphates; nitrogen through ammoniacal nitrogen, nitrates, nitrites; detergents using substances reactive to ortho-toluidine blue; fats and oils using substances soluble when cold in ethyl ether.
Environmental impact
Characteristics of cloacal fluid
Knowledge of the nature of sewage water is essential for both treatment and evacuation and environmental quality management. Sewage is characterized by its physical, chemical and microbiological composition. The properties are related to each other, for example temperature affects microbiological activity and the dissolved gases in the water. The physical-chemical characteristics are high alkalinity, high turbidity, large presence of dissolved solids, large presence of suspended solids, high amount of organic matter, detergents, black color due to the presence of metal sulfides. The microbiological characteristics are the presence of viruses, protozoa and bacteria that develop when the liquid is biologically stabilized. The proposed treatment to purify a sewage effluent begins with a grate that retains the largest suspended solids, then has a grit trap that retains the settleable solids after 10 minutes, then contains a settler to retain the settleable solids that were not separated in the grit trap, the next stage is a neutralization where an acid such as hydrochloric or sulfuric acid is added to reduce the pH to neutral pH, then it goes on to a treatment of Activated sludge where the organic matter, suspended solids and coloring are removed, then it goes to adsorption with activated carbon where particles that cause odor and color, the rest of the organic matter, detergents are eliminated.
The most important physical characteristics of wastewater are total solids content, odor, temperature, density, color, turbidity and pH. To evaluate the appearance, turbidity is used with a turbidimeter, the color that is measured is the real apparent color through colorimetry, odor through sensory analysis, temperature through a thermometer, conductivity (to determine how much inorganic species the effluent has) through an electrode, solids analysis (to evaluate the percentages of the different solids that the water may contain, whether in suspension, colloidal, settleable and dissolved).
• - Solids. The solids content is defined as the non-volatile residue after subjecting the water to an evaporation process at 100 °C and drying in an oven at 103-105 °C for one hour. The determination corresponds to the dissolved and suspended solids. Settleable solids are solids that settle to the bottom of a cone-shaped container (Imhoff cone) from one liter of residual liquid over the course of 2 hours. The well-stirred sample is placed in the Imhoff cones. The determination is made in ml/L and mg/L. It allows obtaining an approximate measurement of the amount of sludge that will be obtained in the decantation. Settleable solids give an idea of the organic and inorganic origin of said solids. The solids that settle after 10 minutes correspond to the inorganic solids, which are heavier and then the organic matter begins to settle until the two hours are completed. After 2 hours it is estimated that all the settleable solids were separated. Total solids are also classified as filterable solids or not. This is determined using a fiberglass filter. Filterable solids correspond to dissolved and colloidal solids. Non-filterable solids correspond to suspended matter. Suspended solids may or may not be settleable. The settleable suspended solids are separated in a grit trap (settable solids after 10 minutes) or in a settler (settable solids after 2 hours). The non-sedimentable suspended solids are separated by means of a coagulation-flocculation treatment or by biological oxidation in an activated sludge treatment and in both there is a subsequent decantation. A settler can retain settleable solids after 10 minutes but should not be overloaded. Total solids are classified as volatile and fixed, depending on their volatility at 550 °C, the temperature at which the organic compounds oxidize and form gases and the inorganic fraction remains in the form of ashes. Volatile solids correspond to organic matter and fixed solids correspond to inorganic matter. Filterable solids correspond to total dissolved solids. Water for human consumption with a high content of dissolved solids is unpleasant to the consumer or can induce an adverse physiological reaction in them. Solids analyzes serve as indicators of the effectiveness of biological and physical-chemical treatment. The determination of total solids is a widely used method: determination of total solids and their fixed and volatile fractions in solid or semi-solid samples from river and lake sediments, isolated sludge in wastewater treatments and sludge agglomerations in centrifugation, vacuum filtration and other sludge dehydration processes. Suspended solids are those that are found in water without being dissolved in it, and are calculated mathematically as the difference between total solids and dissolved solids. Total solids can be non-filterable (dissolved) and filterable (undissolved) and are determined by a filter using gravimetry. Volatile and fixed solids are determined by muffle incineration at 550 °C. At this temperature, the oxidation of organic compounds to carbon dioxide and water occurs and the inorganic compounds resist. The determination corresponds to the total oxidation of the organic matter. Colloidal solids are stable and difficult to separate. They are determined by spectrophotometry. For drinking water, a maximum value of 500 ppm of solids is indicated. In boilers, they produce foaming. Due to excessive sedimentation, environments conducive to anaerobic degradation are generated. Suspended solids interfere with the normal development of aquatic life by decreasing the depth to which sunlight passes through. Settleable solids can obstruct pipelines, electromechanical pumping equipment and hinder the operation of the treatment plant.
• - Odors. Normally, odors come from gases released by the decomposition of organic matter. Fresh wastewater has a more tolerable odor than "septic" wastewater. A characteristic odor of septic wastewater comes from hydrogen sulfide, which is generated by the reduction of sulfates by anaerobic bacteria. Industrial wastewater can also contain odorous compounds itself.
Effects of odors: reduce appetite, generate nausea, vomiting, mental disturbances, produce respiratory imbalances. The fishy smell is characteristic of amines, the rotten egg smell is characteristic of hydrogen sulfide, and the smell of fecal matter is characteristic of eskatol.
• - Temperature: water temperature influences the development of aquatic life, chemical reactions and reaction rates, as well as the suitability of water for certain useful uses. The increase in temperature produces an increase in chemical reactions and the speed of chemical reactions, so there is a more rapid decrease in dissolved oxygen, which compromises the development of aquatic fauna and flora. The increase in temperature also causes a decrease in the solubility of oxygen. It causes the deterioration of the sewage network. The determination is made on site. Elevated temperatures are characteristic of a sewage discharge. Elevated temperature effluents are cooled by heat exchangers, cooling towers, ambient contact, or other cooling methods.
• - Density: dense sludge requires greater pumping powers, even if it is very dense it may not move.
• - Color: is the ability it has to absorb certain radiation of the visible spectrum. Pure water is bluish. It cannot be attributed to one component exclusively but the colors are attributed to several contaminants. For example, the grayish-black color is due to the presence of metal sulfides. The water is said to be septized. It serves, together with the smell, to qualitatively determine the age of wastewater. The grayish color is characteristic of recent domestic wastewater. As the time in the sewer networks increases and more anaerobic conditions develop, it becomes darker. The grayish-black color is due to the presence of metal sulfides that are generated by the reaction between the sulfide generated by anaerobic decomposition and the metals present in the water. The water is said to be septic. Some industrial waters can add color to domestic wastewater. It indicates the presence of dissolved or colloidal substances with which the origin of the effluent can be intuited. Natural color is caused by negatively charged colloidal particles. It can be removed by coagulation using a salt containing a trivalent metal ion such as iron or aluminum. The color caused by suspended matter is known as apparent color and can also be removed by coagulation or an activated sludge treatment. Color intensity increases with pH. Therefore, pH is measured together with color. Natural color as well as turbidity is due to a wide variety of substances and an arbitrary standard is adopted for its measurement, this standard is used to directly and indirectly measure color. The suspended matter must be separated before measuring the real color. Waters containing true color have a yellow-brown appearance and can be measured colorimetrically. It has been observed that potassium chloroplatinum solutions dyed with small amounts of cobalt chloride give shades very similar to natural ones. By varying the amounts of cobalt chloride, the degradation of the tones is obtained. To measure and describe colors that are not in this classification, spectrophotometry is used, which consists of measuring the fraction absorbed or transmitted by the sample.
• - Turbidity: is a measure of the sample's ability to transmit light. It is measured in "NTU". It allows estimating the colloidal and suspended matter that is present in the sample.
• - Conductivity: it is related to the dissolved solids through a factor that is the cell constant. It is a measure of the solution's ability to carry electric current. It depends on the number of ions, their nature, their valence, the temperature of the solution. As the temperature increases, the conductivity increases. It is determined by a conductivity cell connected to a circuit through a Wheatstone Bridge. KCl is used to calibrate the conductivity meter. Conductivity and hardness are related because magnesium and calcium salts are the most abundant and contribute the most to conductivity. They reflect the degree of mineralization of the water and its potential productivity. Organic substances dissolve by forming hydrogen bonds, so they are also dissolved substances.
• - pH: the pH range allowed in an effluent is 5.5 to 10. It is optimal for the development of aquatic life forms. It is determined on site. It governs innumerable chemical processes, including some that can generate harmful conditions for humans, such as the contact of an acidic effluent with sodium cyanide, generating hydrogen cyanide, which is a lethal gas. Indicates whether the effluent is acidic or alkaline. An acidic pH corrodes pipes and generates gas release in the form of foam that makes treatment and subsequent analysis difficult. Before biological treatment to prevent microorganisms from developing and biological oxidation from occurring. The optimal pH is 6-8.5. Depending on the concentration of carbon dioxide, this is produced by the mineralization of the salts present in the water. The pH of the water is due to the composition of the land crossed; it is alkaline if the land is limestone and acidic if it is siliceous. Heavy metals dissolve in an acidic medium and precipitate in a basic medium. The electrodes are standardized with buffer solutions of known pHs. It can be measured in a wide variety of materials and under extreme conditions as long as the appropriate electrode is used. For semi-solid substances, the spear-shaped electrode is recommended. For substances with a pH greater than 10 and high temperatures, glass electrodes designed for this purpose are recommended.
To study the chemical characteristics of sewage, the organic matter present, the inorganic matter and dissolved gases must be taken into account. More specifically sulfates, carbonates, bicarbonates, chlorides, nitrates, nitrites, sulfides, phosphates, calcium, magnesium, sodium, potassium, iron, manganese, proteins, carbohydrates, lipids and detergents. The parameters to evaluate the chemical characteristics are pH, alkalinity (to determine the presence of hydroxyls, carbonates and bicarbonates), chlorides, dissolved oxygen (determines aerobic and anaerobic organisms), BOD (to determine the contaminating power of the waste), COD (to measure the cc of organic matter), phosphorus (common waste, synthetic detergents), detergents, fats and oils, sulfides.
• - Organic matter. About 75% of the suspended solids and 40% of the filterable solids in wastewater are organic in nature. They are solids that come from the animal and plant kingdoms, and from human activities related to the synthesis of organic compounds. The main groups of organic substances present in wastewater are proteins (between 40% and 60%), carbohydrates (25%-50%), and fats and oils (approximately 10%). Another compound with an important presence is urea, the main constituent of urine, which due to its rapid decomposition process is rarely present in wastewater that is not very recent. Along with those already mentioned, wastewater contains small quantities of a large number of organic compounds whose structures can be simple or extremely complex. This group includes detergents, priority organic pollutants, volatile organic compounds and pesticides for agricultural use. Due to the increase in the synthesis of organic molecules, the number of them present in wastewater increases every year.
Proteins. The chemical composition of proteins is very complex and unstable, and can adopt many different decomposition mechanisms. Furthermore, as a distinctive characteristic, they contain a high amount of nitrogen and in many cases, they also contain sulfur, phosphorus and iron. Urea and proteins are the main source of nitrogen in wastewater.
Carbohydrates. From the point of view of volume and resistance to decomposition, cellulose is the most important carbohydrate in wastewater. The destruction of cellulose is a process that occurs without difficulty, mainly thanks to the activity of some fungi, whose action is notable in acidic conditions.
Fats and oils. Fats and oils are compounds of alcohol (esters) or glycerol (glycerin) and fatty acids. Chemically they are similar and those that are solid at room temperature are called fats and those that are in a liquid state are called oils. Fats are among the most stable organic compounds and are not easy to degrade biologically. They pollute waterways by forming a film on the surface that prevents the passage of oxygen to the water. They form crusts on the surface of the pipes that prevent the passage of water. It consists of the determination by weight of substances soluble in cold in ethyl ether. From the raw sample, brought to a pH of 4.2 with 2 drops of heliantin, the sample is brought into contact with ethyl ether so that the fats and oils are solubilized in it, and then the ether (low boiling point) of the ether phase is evaporated, so that the amount of fats and oils by weight of the volume used in the sample can be obtained.
• - Biological oxygen demand. is the amount in mg/L of oxygen that is required to decompose the organic matter contained in the residual liquid by aerobic biological action under conditions of 20 °C, in darkness and for 5 days. The importance of its determination lies in the fact that its value gives an idea of how contaminated the liquid is with organic matter and its potential consumption of the oxygen present in water resources, which is detrimental to the development of the fauna and flora present in such resources. It is essentially a bioassay procedure that measures the oxygen consumed by organisms when using the organic matter of a waste, under conditions as similar as possible to nature. To make the sample quantitative, samples must be protected from air by preventing re-aeration as dissolved oxygen decreases. Additionally, due to the limited solubility of oxygen in water, concentrated waste must be diluted to demand levels that maintain this value to ensure that this value of dissolved oxygen is present in the test. Since it is a bioassay procedure, it is of utmost importance that the environmental conditions are appropriate so that the activity of living organisms is carried out without obstacles. This means that there should be no toxic substances, and that the accessory nutrients necessary for bacterial growth, such as nitrogen, phosphorus and trace elements, should be available. Biological demand is produced by a diverse group of organisms that carry out the oxidation of organic matter to almost carbon dioxide and water. Therefore, it is necessary that a group of microorganisms called "seeds" be present in the test. The oxidative reactions that take place in the BOD test are derived from biological activity and the speed of these reactions is given by the population of microorganisms and the temperature. The effects of temperature are kept constant by performing the test at 20 °C, which is more or less the average temperature since minimal cooling is carried out with some other current. The speed of metabolic processes at 20 °C and under test conditions is such that the time must be calculated in days. Theoretically, an infinite time is required for the biological oxidation of organic matter to complete, but for practical purposes, the reaction is complete in 20 days; However, in most cases this period is long and is then reduced to 5 days because it was found that the percentage of BOD obtained is almost the total. Consequently, it must be remembered that the result of the test carried out at this time represents a fraction of the total. The exact amount will depend on the "seed" and the nature of the organic matter, and can only be determined experimentally. The BOD test is based on dissolved oxygen determinations; Therefore, the precision of the result is largely influenced by the care taken in measuring the latter. BOD is the most important criterion used to control pollution of streams where the organic load must be restricted to maintain adequate levels of dissolved oxygen. The determination is used in the study to measure the purification capacity of the streams and allows authorities to set regulated values for discharge into these waters. Furthermore, BOD information allows the design of treatment equipment; It is a factor in the choice of treatment and is used to estimate the size of the units, especially in trickling filters and activated sludge. It is used to evaluate the efficiency of the stages. In summary, the limitations of the BOD test are: having acclimated sowing, pretreatment in case of toxic effluents, measurement of only a fraction of BOD, minimum time of 5 days.
• - Chemical oxygen demand. The advantage of the analysis is that it only lasts 3 hours, the disadvantage is that it does not give an idea of biodegradability. Determinations are made on raw and decanted samples, and COD/BOD data must be available. It is the amount of oxygen necessary in mg/L to chemically degrade the organic matter contained in the residual liquid at 150 °C for 2 hours with an oxidizing agent such as potassium dichromate in an acid medium. The importance of its determination lies in the fact that its value gives an idea of the content of oxygen-consuming substances such as organic substances whose presence in water resources is detrimental to the development of aquatic fauna and flora. It is a way to measure the concentration of organic matter in domestic and industrial waste. This test allows measuring the total amount of oxygen in a waste that is required to oxidize organic matter to carbon dioxide and water. The test is based on the fact that all organic compounds, with a few exceptions, can be oxidized by the action of strong oxidizing agents under acidic conditions. During the COD determination, organic matter is converted to carbon dioxide and water, regardless of the biological capacity of the substances to be assimilated. COD values are higher than BOD values, and can be much higher when significant amounts of biologically resistant organic matter are present. One of the main limitations of the COD test is the impossibility of differentiating between biologically oxidizable matter and biologically inert matter. Furthermore, they do not provide any data on the rate at which the biologically active material stabilizes under the conditions of nature. The main advantage of the COD test is the short time required for the evaluation; The determination is made in 3 hours instead of 5 days as with BOD. It has been observed that potassium dichromate is an excellent oxidizing agent for the determination of this parameter, since it is capable of almost completely oxidizing a wide variety of organic substances to carbon dioxide and water. Because all oxidizing agents must be used in excess, it is necessary to measure the excess that remains at the end of the reaction in order to measure the amount used in the degradation. An important point in favor of dichromate is that the excess can be measured relatively easily. Low molecular weight fatty acids require a catalyst to oxidize. Under COD test conditions, certain reduced inorganic ions can be oxidized and therefore lead to erroneous results. Chlorides cause the biggest problems because their concentration is high in wastewater. This interference is eliminated by adding mercuric sulfate to the sample before adding other reagents. The mercuric ion combines with chloride ions to form a poorly ionized mercuric chloride complex that is not oxidized by the dichromate. The determination of COD is carried out in a digester and is then determined by colorimetry or by titration. For industrial effluents: 500<COD<10000. For uncontaminated courses: COD <20. In conjunction with BOD, COD is useful in indicating toxic conditions and the presence of biologically resistant organic substances. If BOD/COD<0.2 there is mainly non-biodegradable organic matter, BOD/COD=0.4 there is biodegradable and non-biodegradable organic matter in the same proportions, if BOD/COD>0.6 there is mainly biodegradable organic matter.
• - Detergents. They are classified as biodegradable and non-biodegradable. To eliminate the latter, physicochemical methods must be used. Biodegradable detergents generate foams that interfere with the purification process in treatment plants and give a bad appearance to the liquid effluents. Foaming also makes it difficult to carry out analyses. The foam creates a barrier to the passage of oxygen into the liquid. This determination is carried out with a colorimetric kit for detergents. This technique is based on the fact that anionic detergents are combined with o-toluidine blue, obtaining a blue complex which is soluble in chloroform; Then the kit reagent and chloroform are added to the sample, obtaining a colored chloroform phase in such a way that the intensity of the color is proportional to the concentration of detergents that is measured with the kit's comparator.
• - Hydrocarbons: such as gasoline and oil. They are determined by HPLC. They give water an unpleasant odor and taste, which allows them to be identified in amounts of PPB, which is intensified by chlorination. The surface film prevents water-air gas exchange, with the consequent disruption to aquatic life.
• - Pesticides and Chemical Products for Agricultural Use. These compounds are not from wastewater, but are usually incorporated into it, as a result of runoff from parks, agricultural fields and other causes. Most of these products are toxic to most forms of life, which is why they are considered dangerous contaminants of surface waters. Concentrations of these chemicals can cause fish death, contamination of fish meat (reducing its nutritional value), and worsening water quality. They can be chlorinated and phosphorous, and are determined in both waters and sediments. They are very polluting, so they are not suitable in low concentrations (ug/L). It is analyzed with HPLC and gas chromatography.
• - Inorganic matter. There are several inorganic components of wastewater that are important for the determination and control of water quality. Wastewater, except in the case of certain industrial waste, is not usually treated with the aim of eliminating inorganic constituents.
• - Alkalinity. In wastewater, it is caused by the presence of salts of weak acids, weak and strong bases such as hydroxides, carbonates and bicarbonates of calcium, magnesium, sodium, potassium and ammonium. Of all of them, the most common are calcium bicarbonate and magnesium bicarbonate because they are formed in considerable quantities when carbon dioxide reacts with the basic matter of the soil. It is the measure of the ability to neutralize acids. Normally, wastewater is alkaline. It occurs in surface waters with growing algae due to the amount of hydroxides and carbonates. Alkalinity is mainly due to three groups of compounds and according to the high pH values it is classified into: hydroxides, carbonates and bicarbonates. Very alkaline waters have an unpleasant taste for the consumer. Alkalinity is measured volumetrically by titration with N/50 sulfuric acid and is expressed in calcium carbonate equivalents (ppm CaCO3). This parameter is essential for chemical coagulation processes, water softening, corrosion control, buffering capacity and in the treatment of industrial waste, given that it is prohibited to discharge waste with caustic alkalinity into receiving waters and sewers.
• - Nitrogen and phosphorus. These elements are essential for the development of some microorganisms, which is why they are known as nutrients. Traces of other elements, such as iron, are also necessary for biological growth. Since nitrogen is essential for protein synthesis, it is necessary to know its amount in water to assess the possibility of biological wastewater treatment. When the amount of nitrogen is insufficient, it is necessary to add it to make the water treatable. When this is in excess, reducing the amounts of nitrogen may be necessary to avoid excessive algae growth. Phosphorus is also essential for the growth of algae, so it must also be controlled when pouring water into the receiving bodies. The most common forms in which these components can be found are: in the case of nitrogen, organic nitrogen, ammonia, nitrites and nitrates. Phosphorus is normally found as phosphates, polyphosphates and organic phosphates. Those are colorimetric determinations that are made, I measure them with the spectrum. Ammonium nitrogen is measured in spectrum and compared to a standard. The result is expressed in mg/L. Nitrite nitrogen and nitrate nitrogen are measured with a kit and compared to a disk that has a color scale. Initially the nitrogen is as organic nitrogen and ammonia. Organic nitrogen is then gradually converted to ammoniacal nitrogen and later, if aerobic conditions exist, oxidation to nitrates and nitrites occurs. When carrying out the treatment, it is necessary to verify if it has a sufficient amount of nitrogen for the organisms, if not, it must be added, but if it is dumped in excess, especially nitrate (a nutrient), eutrophication (overpopulation of algae) occurs and it eventually rots. It is also used to corroborate the degree of purification obtained with biological treatments. Non-ionized ammonia is toxic but the ammonium ion is not. Ammonia toxicity is not a problem in receiving waters that have a pH less than 8 and an ammoniacal nitrogen concentration less than 1 mg/L. For these reasons, ammonia control can be carried out by nitrification or by effective ammonia removal. In some cases, the limitations apply to the total nitrogen (organic nitrogen plus inorganic nitrogen) that may exist in the effluent. The techniques for determining ammonium, nitrite and nitrate can vary for each parameter, so the type of contaminant can be determined, not just quantified. Total nitrogen can be determined by the Kjeldahl method. The amount of ammoniacal nitrogen present in the water determines the chlorine necessary to obtain chlorine residuals free of chlorination. Nitrate determinations are important to establish whether water supplies meet maximum levels. Ammonia and organic nitrogen analyzes are important to determine if there is sufficient nitrogen for biological treatment. If this is not the case, you must contribute through external sources. The amount of phosphorus is expressed in (mg/L of P-PO4) and is the sum of organic and inorganic phosphorus. The analysis technique is based on a reaction that forms a coloration and is measured in the spectrum. Polyphosphates are used in some public water supplies to control corrosion. They are also used in some softened waters to stabilize calcium carbonate, in order to eliminate the need for recarbonization. Nitrogen and phosphorus are essential for the growth of algae and cyanobacteria, and the limitation of these elements is usually the factor that controls the growth rate. When there is an abundance of both elements, algal blooms occur, producing a variety of nuisance conditions (eutrophication). Domestic wastewater has high amounts of phosphorus compounds. Most of the inorganic phosphorus is contributed by human waste, as a result of the metabolic degradation of proteins and the elimination of phosphates present in the urine, in addition to strong synthetic detergents. Phosphate compounds are used in steam generation plants to eliminate scale. Orthophosphate can be measured without interference under optimal conditions of pH, time and temperature. Organic forms of phosphorus as well as polyphosphates must be transformed into orthophosphates, which can be determined qualitatively by gravimetric, colorimetric and volumetric methods.
• - Ammoniacal nitrogen"). If they are aerated, they should not normally contain ammonia because this is converted into nitrites and then into nitrates. Black water always has ammonia coming from the water sections below human agglomerations. The existence of free ammonia or ammonium ion is proof of recent and dangerous contamination. At high pH, ammonia passes into the state of ammonia, with values lower than 0.025 mg/L being recommended.
• - Nitrites. Nitrites can be found in groundwater as a result of a reducing medium in waters that have already been biologically stabilized. When nitrate is in contact with easily attackable metals, whether at acidic or basic pH, nitrites can be found. The presence of nitrites makes the water undrinkable along with the presence of pathogens because they are toxic.
• - Nitrates. They come from the bacterial oxidation of waste generated by animals. In surface and groundwater there are more nitrates, increasing nitrate levels due to increased use of fertilizers.
A residual effluent with a concentration of 15 mg/L of phosphate (PO4(-3)) is dumped into a lagoon with a flow rate of 30 m3/h. What will be the daily contribution in kg of phosphorus (kg P) to said body?
• - Chlorides. They impart an unpleasant taste to the water. They can corrode pipes and tanks. Furthermore, for agricultural use, the chloride content of water can limit certain crops. Chlorides are very soluble in water, they do not participate in biological processes, they do not play any role in decomposition, and therefore do not undergo modifications.
• - Sulfur. The sulfate ion is found in both supply and waste water. For the synthesis of proteins, it is necessary to have sulfur, which is subsequently released in the degradation process. Sulfates are chemically reduced to sulfides and hydrogen sulfides under bacterial action under anaerobic conditions.
• - Phenols.") are pollutants and toxics that impart flavor and odor to the liquid, analyzed by spectrophotometry. The contribution to natural waters is negligible and biodegradable. They come from industrial effluents but also from the degradation of pesticides.
• - Heavy metals. These include Ni, Mn, Pb, Cr, Cd, Zn, Cu, Fe, Hg, As. Some are essential for the normal development of life and the absence of sufficient quantities could limit the growth of algae, for example. Due to their toxicity, the presence in excessive quantities of any of them will interfere with the use that can be given to the water. That is why it is convenient to control the concentrations of these substances. Some of them are commonly used in agricultural and industrial activity, so their limits are legislated. They are determined by atomic absorption spectroscopy. They are caused by metallurgical, steel, and automotive industries and are generally not replaced but rather recycled.
• - Gases. The gases most frequently found in wastewater are nitrogen, oxygen, carbon dioxide, hydrogen sulfide, ammonia and methane. The first three are gases present in the atmosphere, and are found in all waters in contact with it. The last three are the product of the decomposition (aerobic and anaerobic) of organic matter.
Dissolved oxygen"). It is necessary for the respiration of aerobic microorganisms and other forms of life. It is slightly soluble in water and its presence, like that of the rest of the gases, is conditioned by the partial pressure of the gas in the atmosphere, the temperature, the purity of the water (salinity, suspended solids, etc.). Its solubility is proportional to the partial pressure since they do not react chemically and Henry's law governs the process because it is barely soluble. It is It is modified by the greater or lesser presence of salt and decreases with temperature. Since it prevents the formation of unpleasant odors in wastewater, it is desirable and convenient to have dissolved oxygen. It is measured in situ or fixed by a chemical reagent to be measured in the laboratory. Increasing the temperature does not produce greater biological oxidation unless it is aerated since oxygen has lower solubility. produced by aerobic or anaerobic organisms. Aerobic organisms use free oxygen for the oxidation of organic and inorganic matter and form harmless final products, while anaerobic organisms carry out oxidation by reducing salts such as sulfates and the final products are generally very harmful. Favorable conditions for aerobic microorganisms must be maintained if they are not considered harmful conditions. aerobic, dissolved oxygen measurements must be carried out in aerobic processes and at overturning sites. Oxygen is an important factor in the corrosion of iron and steel, especially in water distribution systems and in steam boilers. Therefore, oxygen removal is a common practice in the energy industry. Standard volumetric procedures for determining dissolved oxygen, if the sample is properly preserved, are the Winkler or metric iodine method. and its modifications. An oximeter (electrode) can also be used that allows in situ measurements of dissolved oxygen. Such electrodes can descend to various depths and dissolved oxygen concentrations can be read on a connected microammeter located at the surface.
Hydrogen Sulfide. As already mentioned, it comes from the anaerobic decomposition of sulfur or the reduction of mineral sulfites and sulfates, first it would pass to sulfite and then to hydrogen sulfide. Its formation is inhibited in the presence of large amounts of oxygen. It is a colorless, flammable gas with a typical odor. The blackening of wastewater is mainly due to the formation of ferrous sulfide and other metal sulfides. They are toxic and corrosive. It is determined by colorimetry, they give a blue color. Waters containing hydrogen sulfide will be very toxic at acidic pHs, even for bacteria. Toxicity will decrease extraordinarily at basic pHs.
Cyanide. Cyanides are potentially toxic compounds since a change in pH in the medium can release hydrocyanic acid, a compound generally associated with the maximum toxicity of these compounds, which is why it is of utmost importance to determine the presence of all cyanide compounds in natural, drinking, residual and treated wastewater as cyanide ion (CN-). They are determined by potentiometric methods or by spectroscopy. It should be kept at alkaline pH.
Methane. It is the main byproduct of the anaerobic decomposition of organic matter. It is not normally found in wastewater because small amounts of oxygen are toxic to the microorganisms responsible for its production.
Oxygen consumed").: measured in (mg/L). It is the amount of oxygen necessary to oxidize substances with reducing properties, present in a waste liquid. Among the most common reducing substances are: ferrous salts, sulfides, lipids, carbohydrates and some amino acids. The usual determination is carried out using potassium permanganate as an oxidant. This redox titration is not very precise or reproducible but it gives an idea of the mg/L consumed per organic matter present in the sample.
Perhaps the most important characteristic of wastewater in this regard is the presence of pathogenic organisms from human waste that are infected or carry a certain disease. The main groups of pathogenic organisms are bacteria, viruses, protozoa and helminths. Pathogenic bacterial organisms that can be excreted by humans cause diseases of the intestinal system such as typhoid and paratyphoid fever, dysentery, diarrhea, and cholera. Due to the high infectiousness of these organisms, each year they are responsible for a large number of deaths in countries with limited health resources.
Effluent treatment
Introduction
As results of the process, sludge and clarified effluent are obtained. The treated effluent is dumped into the receiving body or reused and the sludge is treated and disposed of in landfills or reused (production of biosolids). The series of treatment processes depends on certain factors:.
• - Characteristics of the effluent: pH, toxic products, suspended solids, BOD.
• - Quality of effluent output: it is set taking into account the objectives of the company and the aptitude of the receiving body.
• - Availability of land: the land needed is large and must be low cost.
• - Consider future expansions: expansions will have to be made because stricter limits are required.
Effluent treatment is the set of processes intended to modify the physical, chemical or biological composition of liquid effluents in order to make them harmless for disposal and recovery for other uses.
Coarse suspended solids are separated by filtration with screens, settleable suspended solids by sedimentation, non-settleable fine suspended solids by small opening sieve, biodegradable dissolved or suspended solids by natural biological treatment, biologically persistent suspended solids by adsorption or chemical oxidation, inorganic dissolved solids are separated by reverse osmosis, electrodialysis, ion exchange.
Stages of effluent treatment
For sewage fluid, the treatments applied are primary (physical) or secondary (biological). The primary treatments are sedimentation, filtration and the secondary treatments are Imhoff tank, biodigester, activated sludge. With the primary ones, the settleable solids are removed and part of the suspended matter, the dissolved solids, and the rest of the suspended matter is removed in biological treatments. Treatments are classified according to their degree of purification into primary (they remove more material), secondary and tertiary and according to the physical, chemical and biological phenomena involved. The primary treatments correspond to the physical ones and the secondary treatments correspond to the biological or physical-chemical ones.
Pretreatment
The objective of pretreatment is the elimination of coarse solids such as rags, branches and inert material such as sand and gravel. These cause damage to pipes, electromechanical pumps, and obstructions to the flow of fluid.
This stage of the process can be carried out with the following devices:
• - Grates: They are used to eliminate thick solids such as plastics, wood, rags that cause blockages or damage to pipes, electromechanical pumping equipment, and avoid accumulation in digesters and decanters. They are placed inclined 60-80° with respect to the horizontal. The robotic gates clean themselves. Fines grates are used instead of sedimentation tanks, but these are usually avoided due to stagnation problems and because greater separations are not obtained than settlers.
• - Sieving: They are used to separate finer particles that cause blockages or damage to pipes or electromechanical pumping equipment, accumulation in digesters or decanters. It is usually placed after a sand trap or a grating device. The operation is based on the difference in sizes, as with the bars, only particles smaller than the mesh opening pass through. It can be static or vibratory and rotating. The latter is a wheel that rotates where solids larger than the openings of the wheel mesh are deposited.
• - Desanding: In these sands, gravels, clays that cause blockages, abrasions, accumulations in digesters or decanters are separated. It is based on the separation of particles smaller than a certain size due to the difference in densities between the liquid and the solid. The settleable solids are retained after 10 minutes. The design parameter of a sand trap is the retention time, which is the relationship between the volume of the settler and the inlet flow. Discrete sedimentation occurs where the particles maintain their individuality.
• - Compensation: is used to attenuate variations in flow and the rest of the parameters. This allows a unified system with fewer operating points, which reduces operating costs.
• - Separation of oils and fats: If there is floating material such as bristles, manure, guts, foams, fats and oils, a chamber called an interceptor is used. It has vertical screens that guide the passage of the fluid and horizontal frames to remove the floating material once it reaches the surface. The floating material reaches the surface by natural flotation without the use of any equipment. On the other hand, if the fats and oils are emulsified, a system with air injection is used. The effluent enters a tank through a pressurizing pump where it is saturated with air and then goes to a pressure reducing valve and finally to a chamber where bubbles are released that enclose the dispersed substances and bring them to the surface. The components of an air injection system are: 1) pressurization pump 2) air injector 3) holding tank 4) pressure reducing valve 5) flotation chamber.
• - Neutralization and homogenization: homogenization consists of mixing currents that have varied characteristics of pH, suspended solids, BOD to unify the treatment system and maintain the parameters at few values, this reduces operating costs. Neutralization involves adding acid or alkalis to the alkaline and acidic effluent streams respectively to control pH values. To neutralize acid streams, 1) limestone beds 2) Solvay soda 3) caustic soda 4) lime 5) ammonia are used and the choice is limited to 1) purchase costs 2) reaction speed 3) neutralization capacity 4) storage and discharge of the neutralization products. To neutralize alkaline currents, for economic reasons, sulfuric or hydrochloric acid is used. Neutralization is carried out to maintain the favorable pH for the development of microorganisms (the optimal pH is between 6 and 8.5), acidic pHs corrode the pipes and generate the release of gases such as foam that makes analysis and subsequent treatment difficult, to unify the sewage water treatment system, before discharge to the receiving body because aquatic life is very sensitive to variations in neutral pH.
Primary treatment
The objective of this stage is the physical removal of settleable solids and part of the organic matter, suspended solids. The methods to carry out this stage are:
• - Sedimentation: is used to separate sedimentable suspended solids. They are based on the difference in specific weight between the fluid and the solid. Depending on the nature of the suspended solids, it is classified as:
1.Discreet sedimentation: particles maintain their individuality. For example: deposition of sand, clay, gravel in sand traps. A settler works the same as a sand trap but retains lighter settleable solids for a retention time of 2 hours. They contain a rectangular or circular chamber, a bottom sweeping paddle, an inclined bottom, and a sludge hopper. This is a primary sedimentation equipment.
If you have an effluent with a concentration of solids at 2 hours and 10 minutes, what treatment do you propose if the legislation prohibits settleable solids in the discharge? To eliminate them, a sand trap must be used since it only contains suspended solids that settle after 10 minutes, such as sand, clay, and gravel.
Sedimentation with flocculation. The particles join with others to settle as larger and heavier particles. It is considered secondary sedimentation. It is usually performed after biological treatment.
Sedimentation by zones. The particles fall forming a kind of mantle as a single body.
• - Flotation: separation of dispersed matter. It is used to separate fats and oils that are dispersed. It is also used to thicken biological sludge suspensions. Using a pump, the fluid is propelled so that air is injected into it, which goes to a pressurization tank where saturation with air is achieved. It then goes to a pressure reducing valve to move to a flotation chamber where the bubbles that enclose the dispersed matter such as fats and oils are released and bringing them to the surface. The components of a degreaser are: 1) pressure pump 2) air injection system 3) holding tank 4) pressure reducing valve 5) flotation chamber. If the matter is floating, an interceptor is used.
Both processes can be considered pretreatment in some bibliographies.
Secondary treatment
The objective in this stage is the degradation of the organic matter to stabilize it in a mineral state in a biological reactor, through microbiological activity (generally bacterial) that uses it as a substrate. These reactors are the place where the formation of the mass of microorganisms occurs. Part of this biomass breaks off and is carried away by the effluent, so the reactors are generally followed by settlers. The settled solids are recirculated to the biological reactor but part is discarded, in order to keep the microorganism population under control.
The biological systems used at an industrial level that are generally applied as secondary treatment can be aerobic and anaerobic:
• - Among aerobic procedures there is a diversity of technologies available such as activated sludge, aeration lagoons, percolating beds, etc.
• - Anaerobic processes are fundamentally digestion processes that can be applied to liquid or solid waste and generally include separation and use of the gas produced. The transformation of organic matter into methane and CO2 is carried out in three consecutive stages in which different groups of bacteria intervene with the formation of acetic, propionic, butyric, lactic, formic acid, CO2 and H2 to finally reach methane and C02.
Anaerobic processes are preferred over aerobic processes due to reduced operating costs. In anaerobes, there is the presence of toxic compounds (such as phenol), there are recalcitrant or xenobiotics, which are those whose biodegradability is very difficult. In anaerobic procedures there is less biomass production per unit of substrate reduction so the handling and evacuation of excess sludge is less, there is a lower requirement for nutrients (not organic matter), it is possible to operate at higher loads and methane is produced, which is a gas that can be used as biofuel. In an aerobic treatment, there are longer residence times, there is no emission of bad odors, higher temperatures are not required (around 35 °C), clarification is simpler because larger volumes of sediment are handled, it is easier to control. There are 3 predominant factors to evaluate the biological treatment of an effluent that contains toxic or recalcitrant compounds. Those factors are:
• - The nature of the necessary chemical conversion, for example, halogenated aromatic derivatives are easily attacked by anaerobic communities, while in the case of aerobic communities the compounds tend to polymerize first and are more easily attacked later.
• - The physiology of the microorganisms included, anaerobic degradation is more vulnerable than parallel degradation. Some compounds such as ammonia, sulfites, sulfates can act as inhibitors of methanogenic bacteria. In the nitrogen cycle, nitrogen is gradually converted to ammonia, and if aerobic conditions are present, it is converted to nitrite and then nitrate. If there is excess nitrogen, eutrophication occurs, excessive growth of algae and the liquid eventually rots. Non-ionized ammonia is toxic, so its oxidation to nitrites and then to nitrates is preferred, otherwise ionized ammonia is converted into non-ionized ammonia because it is a reversible reaction. In addition, the amount of N must be controlled because otherwise eutrophication conditions develop.
Tertiary treatment
This type of treatment is carried out after secondary treatment and is carried out to reuse the effluent.
• - Ion exchange: consists of the transfer of the ions that are in the solution to a resin where higher electrostatic forces are maintained. The ions that were part of the resin become part of the solution. It is used to recover precious metals, remove toxic metals and remove hardness. Since complete demineralization can be achieved, the resulting effluent is combined with the feed to generate water that can be used as feed to the boiler. There are a large number of natural substances for exchange such as zeolites, but synthetic resins have greater removal of ions. Resins are insoluble but they manage to adhere acidic and basic groups through chemical reactions. The exchange is reversible so the ions return to the liquid to separate more easily during cleaning. The number of ions determines the exchange capacity and the type of ions determines the ionic selectivity and efficiency of the filter. The material that makes up the resins is styrene or divini-benzene. Ion exchangers can be cationic or anionic. Cation exchangers separate the cations in the solution by hydrogens (hydrogen cycle) or sodium ions (sodium cycle). The exchanger must be regenerated. To remove the solids it carries, water is passed through it in countercurrent and then regenerating solution is passed through it with current, which is brine for the sodium cycle and sulfuric acid for the hydrogen cycle. Water is passed countercurrently to remove the residual regenerant. Cation exchanger resins contain salts of weak or strong acids, but generally contain salts of strong acids. Anion exchangers are used to remove anions from solution with hydroxyl ions. Once the resin is saturated it must be regenerated. To do this, it is cleaned countercurrently with water to remove the solids that remained in the resin. Then the current regenerating solution is placed, which can be ammonium hydroxide or sodium hydroxide. It is washed with countercurrent water to remove the residual regenerant. Anion exchange resins contain weak or strong bases but usually contain salts of strong bases.
• - Adsorption: is the concentration of the solute in a solid, when the solid is brought into contact with the solution. The solid phase is called the adsorbent phase and the solute molecules that are adsorbed are called the adsorbate. The forces responsible for adsorption are the Van Der Waals forces that act between the solute molecules and the surface of the solid. It is the result of the imbalance of surface forces. No force acts inside the molecules because the molecules are surrounded by similar ones. The adsorption capacity is proportional to the adsorption surface, so as the contact area increases, there will be more interaction. Active carbons in the form of grains and powders are used as adsorbents to adsorb detergents, particles that cause bad odor and taste, organic contaminants, and chlorine. They are prepared from raw materials such as lignite, wood, nutshells through dehydration and carbonization procedures, followed by the application of hot steam. It has a great possibility of regeneration, 30 times or more. To regenerate, the carbon is placed at 930 °C in an air-steam atmosphere. Regeneration removes adhering organic material and the carbon returns to its original capacity. The equilibrium relationships between the adsorbent and adsorbate are described by adsorption isotherms. The most used models are BET, Langmuir and Freundlich. The data are obtained in continuous laboratory tests and the effect of pH, temperature and other parameters on the adsorption process is predicted. They are said to be in equilibrium when the concentration of the contaminant in the solution is in dynamic equilibrium with the concentration of the contaminant in the solid. The Langmuir isotherm assumes that the molecules are adsorbed forming a monomolecular layer and the BET isotherm assumes that the molecules bind to previously adsorbed layers and that each layer is adsorbed following the Langmuir model. The desorption operation can be continuous or discontinuous. In batch operation, powdered coal is used, which is mixed with water and then decanted. In continuous operation, a column filled with granular carbon is used through which the fluid percolates. As it descends through the column the contaminants progressively descend. The removal of contaminants in activated carbon columns is carried out by 3 mechanisms: 1) adsorption 2) fixation of large particles 3) deposition of colloidal matter. Sedimentation is by zones, that is, a transition layer is formed where the concentration is maximum at the bottom and minimum at the top. This is the active zone of the spine and the progressive movement can be known by a rupture curve. The ordinates are in mg/L of COD and flow duration or total bed volumes are placed on the abscissa. Normally the columns are arranged in series, when the effluent reached the specified breaking concentration in the first column, it is introduced into the second so that it does not exceed the specified breaking concentration while the first column is regenerated. It is located at the end of the treatment because it is a tertiary treatment. The adsorption processes do not generate undesirable byproducts to the water, the equipment has a compact design so it takes up little space and the operation and maintenance costs are not very high, flexibility in the face of flow and concentration variations.
Disinfection consists of the removal of pathogens and algae by adding physical or chemical disinfectants. The physical ones are high temperatures or radiation such as UV, the chemicals are potassium permanganate, chlorogens and ozone. Among the chlorogens are chloramines, sodium hypochlorite, calcium hypochlorite and chlorine gas. Sodium hypochlorite and chlorine gas are usually used because they leave a residual and because of their low cost. It must be dosed to the filtered water before consumption so that the demand is satisfied and a residual of 2mg/L remains. Disinfection efficiency is measured by the presence of coliforms. Coliforms can be fecal or total. If there are no coliforms then the rest of the pathogens are not found either. It is applied to effluents that have already had primary and secondary treatment, to effluents intended for consumption. Chlorination also reduces BOD because it oxidizes part of the organic compounds, oxidation of metal ions, oxidation of the compounds that generate odor and flavor in the water, oxidation of cyanides to harmless products. It is performed in a contact chamber located at the end of the treatment.
15,000 L/h of an industrial effluent whose chlorine demand is 1 ppm must be disinfected with a NaClO solution whose concentration is 8% w/V. What dose of product in ml/min is required to prolong the disinfection of the liquid?
Working dose to achieve disinfection (q): Q.D.100/C.60=10.1.100/8.60=2.1 ml/min.
Sludge treatment
Sludge that results solely from solid-liquid separation processes (decantation, flotation) is known as primary sludge, and those from biological processes are designated secondary sludge. The primary ones consist of solid particles, basically organic in nature. The secondary ones are fundamentally excess biomass produced in biological processes. In the case of primary sludge, between 30% and 50% of the BOD of the influent is separated in the primary clarifier as insoluble BOD. In the activated sludge plant, around 2/3 of the soluble BOD separated corresponds to oxidized organic compounds to produce maintenance energy, but the remaining 1/3 corresponds to microbial cells found in the sludge in excess of purges. These sludge cannot be evacuated without prior treatment. The amounts of organic and volatile compounds contained are reduced by subjecting the sludge to digestion, both aerobic and anaerobic digestion processes. The sludge resulting from digestion, with a lower organic matter content, is known as stabilized sludge. The main objectives of stabilization are: (1) Reduction or elimination of annoying odors (2) Reduction of the volume of liquid or weight of solids to be treated in successive operations (3) Reduction of pathogenic microorganisms. The solids content in the sludge must be increased, for this purpose thickening and dewatering is carried out. In thickening from 2 to 15% and in drying from 15 to 50%. For sludge that is difficult to dry, special pretreatments are necessary, including chemical coagulation and thermal treatments. Evacuation is then carried out in two ways: dumping and application to the land or incineration.
It is a process of aeration, for a significant period of time, of a mixture of digestible sludge from primary clarification and sludge from aerobic biological treatment, with a decrease in volatile suspended solids (SSV) and the destruction of cells because the bacteria unfold because the substrate is not sufficient. The main objective is to reduce sludge and to do so it transforms organic substances into volatile substances. When the amount of sludge to be digested is small, batch digestion is used, followed by intermittent discharge of digested sludge. The rate of cell destruction decreases when the food/microorganism (A/M) ratio decreases. Consequently, the greater the proportion of primary sludge in the process, the slower the digestion, since the primary sludge has a relatively high BOD (high A) and low SSV (low M), meaning high values of the A/M ratio. The curve for residual BOD becomes almost flat as the MLVSS reaches its maximum. Taking into account that aerobic digestion of sludge takes place in the endogenous respiration phase, there is practically no decrease in soluble BOD. The main objective is the reduction of sludge to be evacuated, rather than the reduction of soluble BOD. In the case of aerobic digestion, residence times are shorter than in anaerobic processes, which means lower investments in digester capacity or volume. On the other hand, however, the energy costs for aeration are usually significant. This means that aerobic digesters are used in small units.
Quality control
Quality control can be internal or external (also called quality evaluation). A good internal quality control program is composed of at least 7 elements: operator competency certification, recovery of known additions, analysis of internally supplied standards, analysis of reagent blanks, analysis of duplicates, calibration by standards, and analysis of control charts.
Quality evaluation consists of the use of internal and external control measures with the intention of evaluating the data obtained in the laboratory. It includes sections such as performance evaluation samples, comparison samples between laboratories and performance verifications in a manner analogous to internal quality control.
I must meet quality standards, the more stages I control, the quality increases but the cost increases. When there is waste or by-products, there is no need to control the quality unless there is one that can be used.
A product or service is the customer's perception of it; it is the ability of a product or service to satisfy needs, a set of inherent characteristics that give it the ability to satisfy implicit and explicit needs. Although quality cannot be easily defined, one knows what it is. It means being held to a higher standard, rather than being satisfied with mediocre one. It could also be defined as an innate quality, an absolute and universally recognized characteristic.
Quality has many definitions that depend on the point of view one considers. A definition from the perspective of the chemistry laboratory is that of ISO 9000: "quality is the degree to which a set of inherent characteristics meet requirements."
From a product perspective: it is the ability to differentiate qualitatively and quantitatively with respect to some required attribute. Amount of a non-monetarily quantifiable attribute that each unit has.
From a user perspective: quality is characterized according to certain parameters, the quality of responding to a need, the quality of adapting to use, the quality of responding to customer preferences.
From a production perspective: quality is the degree to which a product (or service) meets design specifications. It is conformity with specifications.
From a value perspective: quality means exceeding customer expectations in terms of conditions of use and at an appropriate price. Degree to which a product's inherent characteristics satisfy needs.
The factors related to quality have a technical dimension that encompasses the scientific and technical aspects that affect the product or service, a human dimension that seeks to maintain good relationships between clients and companies, and an economic dimension that attempts to minimize costs for both clients and the company. Other factors related to quality are: fair and desired quantity of product to be manufactured and offered, exact price according to supply and demand, speed of product distribution or customer service.
Determinations in the laboratory
The general properties measurable before processing the sample are pH and conductivity.
The pH is the logarithm of the hydrogen ion activity. Indicates at a given temperature whether a substance is acidic or basic. In the potentiometric method, an electrode is used to determine the pH. To measure, the electrode is immersed, resting on its support if available, in the solution where you want to measure the pH. Shake gently to homogenize the sample and prevent the entry of carbon dioxide. It is not affected by oxidants, reducers, turbidity, color. Coatings of fatty material or particles can interfere with the response of the electrode. To clean it, gently rub the electrode with paper or using detergents, then rinse it several times with distilled water. Additionally, it can be rinsed with 0.1N hydrochloric acid and 0.1N sodium hydroxide solutions and then stored in pH 7 buffer solution overnight. It is washed several times before and after use. Be careful not to rest the electrode on the bottom or walls. After use, it is stored in a solution so that its operation is always optimal. pH is affected by temperature through mechanical and chemical effects. It must be measured in situ.
It is directly proportional to the temperature. It is measured through the potentiometric method using an electrode. The conductivity meter is calibrated with KCl solutions of known conductivity. It is not affected by color, turbidity, oxidant, reducer. You have to wash it several times before and after use. For measurements, the electrode is immersed in the solution. The sample is homogenized by stirring during the measurement. During the measurement you should not touch the walls or the bottom. Results are affected by greasy material and particles adhering to the electrode. To clean the electrode, gently rub the electrode with paper or apply a detergent solution, followed by rinsing with distilled water. It must be measured in situ.
• - Use gloves, glasses, overalls, face masks, long pants, closed shoes to avoid contact of the acids or the sample with the skin, eyes and mouth.
• - Do not run in the laboratory.
• - Do not distract others.
• - Each group will be responsible for its work area and material.
• - Do not leave tools on the floor.
• - Know where they are located and how to use chemical protection elements (antiseptics, alcohol, iodine), fire extinguishers, first aid kit, emergency showers, emergency exits.
• - When working with toxic products, work under a hood.
• - Keep reagents in safe places taking into account their compatibility to store them with others.
• - Know the R and S phrases of the reagents. The R phrases are warnings or risks and the S phrases are recommendations or work advice.
• - You cannot eat, drink and smoke inside the laboratory.
Parameter analysis
From the analysis of an effluent from a manufacturing establishment, the following results were obtained:
Oxygen consumed = 950 mg/L.
Total residue at 105 °C = 1720 mg/L.
Total residue at 600 °C = 210 mg/L.
Total settleable solids = 560 mg/L.
With these data, what do you consider would be the main polluting effects if this effluent were thrown into a stream without being previously treated?
The parameters show that there is a large amount of organic matter so if it is dumped without being treated, the dissolved oxygen will decrease because it will be consumed by the organic matter and will compromise the aquatic fauna and flora. Suspended matter affects aquatic life because it does not allow sunlight to pass through them. In addition, it affects the appearance of the receiving body, causing a negative socio-economic impact.
Indicate 3 major contaminants in wastewater from a refrigerator and indicate what parameters you would use to measure each of them.
An effluent from a refrigerator contains solids, fats and oils, detergents and organic matter. Organic matter would be measured with oxygen consumed, solids with total residue due to evaporation, detergents with phosphates or the o-toluidine blue method provides a more direct measurement, fats and oils with substances soluble in cold in ethyl ether.
The following parameters are determined for a textile industry: pH=10.2, T=60 °C, settleable solids at 2 hours=0.8 ml/L. What treatments would you apply to the effluent so that these parameters comply with what is expressed in the regulations?
At first, sedimentation is applied to eliminate settleable matter (settled solids are not allowed after 2 hours), then it is introduced into a contact chamber where it is neutralized with sulfuric or hydrochloric acid (the permitted pH is between 5.5 and 10). It is introduced into a cooling tower so that the working temperature in the biological reactor is correct. Furthermore, the regulated tipping temperature is less than 40°C. Finally, it is introduced into a biological reactor to degrade non-sedimentable organic matter. A more economical option is to let the load cool in an ambient chamber to the target temperature with the disadvantage that it would take longer.
What are the main components of sewage fluid? What treatment do you propose to eliminate them?
The majority components are solids that settle after 10 minutes, fats and oils and organic matter. To separate the fats and oils, a part of the settleable solids would use a grease trap, then a sand trap is placed to separate the rest of the settleable solids after 10 minutes, then a settler is placed where the settleable solids that were not retained in the sand trap, of an organic nature and less heavy, are removed and finally an activated sludge treatment is placed where the rest of the organic matter, the rest of the suspended solids and the coloration are separated.
References
[1] ↑ Agentes Forestales de Extremadura. Segunda Edición, junio de 2003. Editorial MAD, S.L. ISBN 84-665-2654-4.
[2] ↑ Carlos Buxadé Carbó. Genética, Patología, Higiene y Residuos Animales. Junio 1995. Mundi-Prensa Libros. 348 pág.
The next stage is decantation and the flocs formed in the previous stage are separated, these form sludge that is collected using Archimedean screws to be taken to the condensing beach. The clarified effluent is removed above the settler. The chambers can be rectangular or circular, this depends on the type of sludge and the retention time. The retention time is defined as the ratio between the volume of the settler and the inlet flow. It is usually 2 hours.
The rate at which water corrodes pipes depends on pH, temperature, concentration of certain mineral substances, velocity, and dissolved oxygen. Among the parallel treatments, dissolved gases such as carbon dioxide, hydrogen sulfide and oxygen can be eliminated by boiling. Phosphates are dosed that form a protective layer of material, caustic soda that increases the pH and hydrazine as a reducer, which eliminates residual oxygen and releases nitrogen as a residue.
• - Process design and plant operation: although there is widespread and efficient aerobic treatment for effluents that contain toxic compounds (phenols, ammonia and cyanides), it has recently been shown that it can also be treated with anaerobic filter reactors such as activated carbon ones. The modern trend is to use anaerobic and aerobic reactors because anaerobic communities are advantageous at high temperatures and high concentrations of substrates, especially insoluble ones, and aerobic communities for low levels of substrates, different chemicals and variable environmental conditions.
This stage can be carried out through the following aerobic processes:.
• - Suspended culture: the residual load is subjected to aeration for a period of time and as a result the organic load is reduced and a flocculent sludge is formed. This sludge is made up of a heterogeneous population of microorganisms. Through the recycling of biological sludge it has been possible to make it continuous. The initial feed is combined with the biological sludge and enters the reactor. The design of the aerobic tank is made based on the soluble BOD and the clarifier is based on the insoluble BOD. The system consists of a reactor with aeration, a circular settler, a sludge dedenser, a sludge drying beach, a sludge movement device, and a contact chamber for disinfection. Initially, a pretreatment and primary treatment are carried out, then it is entered into the aerated reactor using mechanical aerators where the organic matter is degraded by microorganisms that are in the sludge. The effluent then passes to the settler where the sludge below and the clear effluent above are separated. The sludge passes to the dedenser and a portion is returned to the reactor using a sludge movement device such as an Archimedean screw. The clear effluent goes to the disinfection chamber. If the liquid is still not clear, coagulation-flocculation-filtration is carried out and it is disinfected again. In general, conventional activated mud does not have aeration equipment and is designed with an average cell retention time between 3 and 15 days. This average cellular retention value corresponds to a hydraulic retention time between 4 and 8 hours for domestic sewage liquid if the concentration of suspended solids is around 2000 mg/L. Recirculation ranges between 10 and 30% of the feed flow. With aeration, control of the operation and the volume of sludge generated is reduced. It is characterized by having a prolonged contact between the liquid and the mass of the microorganisms, so that there is oxidation in the endogenous phase and has a high efficiency, until the sludge present can be filtered and settled, without the presence of odor. The sequential batch biological reactor (SBR) carries out the reaction, sedimentation and decantation in the same place. The effluent enters to react with the remaining biomass from the previous cycle, sedimentation of the organic matter occurs, then it is allowed to settle, finally it is decanted to disinfect and part of the biomass is recirculated to the reactor and another part is concentrated in the adenser to keep the concentration of microorganisms under control. They usually have two tanks in parallel so that when one is in the emptying stage, the other is in the filling stage. Aerobic oxidation ditches have longer oxidation periods and extended aeration. In the design of activated sludge, the aim is to determine the size of the biological reactor and the retention time of microorganisms in it. The operation requires that the concentration of microorganisms in the reactor be constant and to develop a design equation, two mass balances are first established and analyzed: solids (biomass) and dissolved organic matter (substrate). This analysis, when combined with the understanding of microbial growth, will allow the volume of the aeration basin to be determined.
• - Fixed film: It is a type of fixed film biological reactor with packed column configuration. The trickling filter is a static biological silt filler over which the liquid percolates. Normally the water is distributed over the filled bed evenly with a rotary flow distributor. The residual water percolates downwards through the fill and is collected at the bottom. If the bed is made of stone, the height is limited to 2 meters and if the bed is made with plastic fillers of lower weight and size, the height can be made higher, which allows the contact time to be increased. A biological film of microorganisms is formed that grows as the organic matter degrades through the percolation of the liquid without flooding the bed. The low load biological bed is the one that does not have recirculation and only the upper part presents considerable biological growth. This occurs because since the quantities are low, the reaction only occurs appreciably at the top. Algae form to break down ammonia into nitrite and then nitrate. High-load percolating beds allow higher organic loads to be treated (the recirculation current is added) and recirculation allows a larger volume of biomass to be dragged, which prevents clogging or flooding and the production of odors and flies. Another modality is rotating biological discs that consist of a series of discs mounted on an axis in parallel. The assembly is placed inside a tank with the axis located slightly above the liquid surface so that it is semi-submerged. The biological film is formed on the rotating wheel, it retains the microorganisms and aerates them when it is submerged thanks to the aeration of the tank and when it emerges due to being in contact with a film of air.
A residual effluent containing 300 mg/L of biodegradable organic matter is processed in a 200 m3/day aerobic treatment plant, achieving a 40% conversion into CO2 and H2O. Calculate the kilos of O2 required daily in the purification process.
If 50 kg of sugar is discharged into a water dam whose dissolved oxygen concentration is 10 mg/L at 25 °C. How many liters of this water will be contaminated to the point of eliminating all dissolved oxygen through biodegradation?
C12H22O11+12O2-->12CO2+11H2O.
342kg-12.32kg.
50kg-x=56.14kg.
56.14kg.1000000mg/kg.1L/10mg=5614035.088L.
For the carbon cycle, the products of anaerobic fermentation are gases such as methane and carbon dioxide. The stages are: (1) acid fermentation (2) methanic fermentation. In acid fermentation, complex organic compounds (proteins, fats and carbohydrates) are first hydrolyzed to produce smaller molecular units, which in turn are subjected to biooxidation, becoming mainly short chain acids such as butyl, propionic, acetic. A heterogeneous population of facultative and anaerobic bacteria is responsible for these hydrolysis and oxidation reactions.
In the methanic fermentation stage, methanogenic microorganisms that are strictly anaerobic convert longer chain acids to methane, carbon dioxide, and short chain acids. Acid molecules are repeatedly broken down to give acetic acid which in turn gives carbon dioxide and methane.
If there are aerobic conditions, carbon dioxide and water are formed from the carbon compounds.
For the nitrogen cycle, organic nitrogen is gradually converted to ammonia, and if there are aerobic conditions, it is converted to nitrite and this to nitrates. Non-ionized ammonia is toxic, so there must be aerobic conditions, so that ammonia in solution does not generate non-ionic ammonia because it is in a reversible reaction, and is oxidized to nitrite and then forms nitrate. The amount of N must be controlled so that it is not in excess because eutrophication of the liquid occurs and eventually putrefaction, and the generation of toxic compounds occurs. Eutrophication is characterized by the generation of water with an unpleasant odor and a high consumption of dissolved oxygen by microorganisms because it can no longer be produced photosynthetically due to the absence of sunlight.
In the presence of oxygen, the reactions that occur are:.
NH4(+1)+3/2O2--Nitrosomonas-->NO2(-1)+2H(+1)+H2O.
NO2(-1)+1/2O2--Nitrobacter-->NO3(-1).
For the sulfur cycle, if the sulfur is under anaerobic conditions, hydrogen sulfide is produced, which has a bad smell, and if the sulfur is under aerobic conditions, sulfites are formed that are then oxidized to sulfates.
The main difference is that in the aerobic case it requires provision to the system and in the anaerobic case it does not. Biogas (methane and carbon dioxide) is generated that can be reused energetically, for example, to heat the effluent at the entrance to the process. Another difference is that the anaerobic does not generate the large amount of sludge that the aerobic does and requires treatment (densation and drying). The anaerobic process admits higher organic loads.
The most used equipment is:
• - Anaerobic digester: the stream to be treated is introduced through the bottom and comes into contact with a mantle of sludge that contains particles and granules that are made up of microorganisms. As a result of the treatment, carbon dioxide and methane are generated, these gases are collected at the top and the clear effluent is collected above thanks to screens that stop the biomass that is carried with the effluent. It is in the absence of oxygen.
• - Anaerobic filter: it is a system in which immobilization occurs on a fixed support medium. The fluid circulates through the interstices of the bed formed by biomass and support material, where the degradation reactions occur. Under favorable conditions, the greater the contact surface per unit volume, the greater the treatment capacity. The favorable conditions are that the bed is not flooded nor are there channeling areas through which the fluid does not circulate. It is done in the absence of oxygen. The mechanism is similar to the low-load trickling bed.
• - Imhoff Tank: is a primary treatment device. The sewage water enters through chamber a (sedimentation chamber) and descends through chamber f where anaerobic reactions occur. The sludge is deposited at the bottom and left for 30 days, or until it is well digested so as not to overload the sedimentation chamber. It is removed through the inclined tube b-c and taken to the sludge drying pool. The gases from the digestion are removed through the gas suction cups and tend to move upwards on the outside of the sedimentation chamber without disturbing the settling action because the settled solids obstruct the passage of the gas. The clarified water leaves through d towards the next stage. Due to its digestion behavior, it must have the capacity for both primary and secondary sludge.
They are the simplest method of water treatment that exists. They are shallow excavations surrounded by earthen slopes. It has a rectangular or square shape. The objectives of the gaps are:
• - Improve the quality of the effluent to give it other uses such as irrigation water in agriculture.
• - Eliminate pathogenic microorganisms.
• - Remove organic matter.
The elimination of organic matter is carried out by different processes in the stabilization lagoons. In an aerobic lagoon, algae are produced photosynthetically and organic matter is decomposed by oxidation with aerobic bacteria. In an anaerobic lagoon, organic matter is decomposed by anaerobic bacteria due to the high organic loads they treat.
Anaerobic lagoons have a gray-black color, high surface area, high depths, low BOD removal, shorter retention times and admit high organic loads. The high organic load and short retention periods suppress the photosynthetic activity of the algae, so there is an absence of oxygen at all levels. Anaerobic bacteria are responsible for the stabilization process of organic matter. The advantage of anaerobic lagoons is the production of methane, which is a gas and biofuel that can be used to heat the inlet effluent or for energy uses, a low rate of cellular synthesis and therefore a lower production of sludge, the sludge produced is reasonably stable and can be dried and disposed of by conventional methods, it admits high organic loads, has low nutritional requirements and the disadvantages are the production of bad odors due to hydrogen sulfide, amides and and fatty acids, formation of toxic products such as hydrogen sulfide, the medium is corrosive, requires a fairly restricted pH range because it requires high concentrations of alkalinity, is sensitive to oxygen contamination and to obtain high degrees of treatment, high temperatures are required.
Facultative lagoons have 3 strata: aerobic zone that is on the surface, anaerobic zone that is at the bottom and facultative zone that is in an intermediate position. The aerobic zone receives sunlight and photosynthesis occurs by algae, which produce oxygen that bacteria consume to degrade organic matter. The products of aerobic degradation are carbon dioxide and water necessary for photosynthesis. In the intermediate zone, the facultative zone, there are facultative anaerobic and aerobic bacteria that degrade organic matter as it settles to the bottom. At the bottom, there are anaerobic bacteria that degrade the organic matter that settles at the bottom. The products of anaerobic degradation are methane and carbon dioxide. Carbon dioxide is used in photosynthesis. It presents retention times, depth, land spaces, BOD removal and color intermediate between aerobic and anaerobic lagoons.
Aerobic lagoons present aerobic organisms and photosynthetic algae that produce dissolved oxygen that bacteria consume for the degradation of organic matter. It has longer retention times, little land area, shallow depth, high percentage of BOD removal and clearer waters than the other lagoons. The advantages of aerobic lagoons are the absence of high temperatures, the mineralization of all biodegradable compounds and the disadvantages are a high rate of cellular synthesis, consequently high sludge production, a large proportion of cells in the sludge that makes its digestion necessary for subsequent drying and storage.
The order of exposure of the lagoons is anaerobic, facultative and aerobic.
The advantages of stabilization ponds are:
• - High stabilization of organic matter.
• - Has higher construction costs but lower maintenance costs.
• - Flexibility in the treatment of tips and flow.
• - Removal of pathogens because the largest microorganisms eat them or settle them.
• - Energy consumption is zero.
• - It can be used in the treatment of water with high BOD content.
• - Presents potentially valorizable biomasses after treatment.
The disadvantages of the stabilization lagoon are:
• - Presence of suspended material if there is no efficient bioflocculation.
• - They occupy large areas of land.
• - Considerable water losses due to evaporation in summer.
Aerated lagoons are ponds that have surface aerators that replace algae that produce oxygen photosynthetically. Aerators can be diffused air units. They have higher operating costs, higher construction costs, reduce the necessary surface area compared to an aerobic lagoon but generate a greater amount of sludge. The fundamental difference with the activated sludge system is that there is no sludge recycling.
Advantages of the aerobic system.
• - There is no formation of bad odors.
• - There is no formation of toxic compounds such as hydrogen sulfide.
• - Longer residence times.
• - Higher temperatures are not required.
Advantages of the anaerobic system.
• - Methane is generated, which is a biogas and is a biofuel; it can be used to heat the effluent at the inlet or for other energy purposes.
• - A lower volume of sludge is generated due to the low rate of cellular synthesis, which reduces costs in sludge treatment and evacuation.
• - It is possible to operate at higher loads.
• - The sludge is reasonably stable so it does not require digestion to dry and dispose.
• - Low nutritional requirements.
• - Precipitation: consists of the elimination of suspended solids by adding coagulants such as aluminum sulfate, ferric sulfate, ferric chloride and adjuvants such as polyelectrolytes. A contact chamber and a settler are used. Although in some systems the settler is not necessary since it is decanted in the same space where it is agitated by turning off the agitator.
• - Chlorination: disinfection occurs so bacteria and algae are destroyed, reduction of BOD because organic compounds are oxidized, oxidation of cyanides to harmless products, oxidation of metal ions, oxidation of compounds that generate odor and color.
• - Ozonation"): reacts easily with unsaturated products, they are easily attackable; they break the aromatic rings and the partial oxidation of the rings contributes to the biological treatment; foam formation is reduced. Ozone when oxidized forms oxygen, while chlorine forms a contaminant.
• - Reverse osmosis. It consists of the elimination of contaminants through membranes that are subjected to pressure. The membrane is semipermeable so it allows the solvent to pass through but not the residues in it. It is effective when the effluent carries soluble but not insoluble residues (suspended solids) because they clog the membranes. It is brought into contact at a pressure higher than the osmotic pressure of the solution. The Van Hoff Equation is not applicable for highly concentrated solutions because the osmotic pressure is not correctly predicted. Synthetic resins are made from cellulose acetate and natural resins are made from animal tissues. The tubular configuration consists of an inner tube that has a semipermeable membrane capable of withstanding elevated pressures greater than the osmotic pressure of the solution. The fluid passes through this tube and moves towards the outer tube, causing separation.
• - Electrodialysis. They are used to separate nitrogen and phosphorus. The basic component of the system is a cell made up of membranes. Membranes can be cationic or anionic. Membranes are specific to a class of ions. Cationic membranes have a fixed negative charge and allow the passage of cations, and anionic membranes have a fixed positive charge and allow the passage of anions. A potential difference is established at the ends of the cell (anode and cathode) to allow the passage of ions. The membranes that allow the passage of cations are placed near the anode and those that allow the passage of cations near the anode. The treated water is removed through the dilution compartments and the residual water is removed through the concentration compartments. Fouling produces an increase in resistance. With a higher resistance, maintaining the voltage, there is a decrease in the current and therefore in the demineralizing capacity. Fouling is produced by large organic ions, colloidal matter, suspended matter that must be previously eliminated. Fouling or clogging of the membrane is the main problem and the following is done: 1) water pretreatment by adsorption with active carbon, filtration with microfilters, coagulation-flocculation 2) operation stops for cleaning 3) current reversal tends to minimize fouling.
• - Stripping: is a physical separation process in which the components of the liquid are separated by putting them in contact with a vapor.
Anaerobic digestion consists of keeping sludge in a closed container so that it achieves a more liquid appearance and generates gases. Digesters are either single stage or two stage. The raw sludge is introduced into the area where there is active digestion and gas is being produced. As the gas rises, it drags sludge particles and other materials (fats, oils, etc.) forming a supernatant that is separated from the digester. The digested sludge is removed from the bottom of the tank. The digestion process is favored by high temperature (typically between 24°C and 40°C), which requires that the digesting sludge be heated by steam coils within the reactor, or by an external sludge heater. The gas is collected at the top of the digester, and is normally used as fuel due to its high methane content. The deposition time is long, on the order of 30-60 days, even for heated digesters. The reason for this long time is that only a small part of the volume is used, so it is not recommended for plants with sludge digestion with a capacity greater than 4000 m3/d. The two-stage arrangement allows for better utilization of the volumetric capacity. The first stage is used only for digestion. The second serves as a solid-liquid separator and allows gas collection. The retention time of the first stage is 10-15 days. Only the first stage is heated. The mixing is done in the first stage by mechanical means or by gas recirculation. There are savings in investment costs, due to the absence of aeration equipment, as well as in energy consumption costs. The operation of anaerobic digesters is more difficult, the process being more sensitive to shock loads. Also the supernatant liquid in the case of anaerobes is richer in nutrients and organic compounds. Considering that this supernatant is recycled to the main stream, this could be a disadvantage in anaerobic processes as it is a byproduct.
It is the normal first step in the sludge evacuation process. It can be achieved: 1) by gravity 2) by flotation with dissolved air. The advantages of thickening are: 1) it improves the operation of the digester and reduces investments if subsequent digestion is used, 2) it reduces the volume of sludge evacuation to the ground or to the sea, 3) it improves the economy of dehydration systems (centrifuges, vacuum filters, pressure filters, etc.). Gravity thickeners are circular section tanks in which a rotating scraping mechanism similar to that of clarifiers is installed. Flotation thickeners are used for any type of sludge, but it is recommended for those with a gelatinous structure such as activated sludge.
The quality parameters are design quality, it is the degree to which a product or service is reflected in its design, conformity quality, it is the degree to which a product or service is reproduced with respect to its design, quality of use, the product is easy to use, safe, reliable.
Quality can be internal or external. Internal quality is that planned and achieved by the laboratory and external quality belongs to the client, is that required or eventually perceived.
Quality is evaluated through results, chemical measurement processes, methodological analytical tools such as calibration and instruments such as materials, work and their organization.
External quality is the fulfillment of the client's requirements for a problem they have and internal quality is how the analyst solves it through the analytical process and analytical properties. An analytical problem has tangible factors such as the object, sample, measurand and analyte and has intangible factors such as planning, design, evaluation and correction.
A quality system set of planned activities to satisfy the customer throughout the entity. For the implementation of a quality system, the ISO 25 guide (IRAM 301) is applicable, currently replaced by ISO 17025, it presents the general requirements that a laboratory must meet to be recognized as competent in the execution of calibration or tests.
The objectives of the quality system are: to raise the overall quality of laboratory performance, implement medium and long-term corrective measures, identify good analytical methods, ensure sample integrity, and provide permanent records of instrument performance.
The job of a laboratory technician is to set tasks, perform tasks, transmit knowledge and obtain recognition. It usually uses analytical tools such as a cause-effect diagram where, based on a problem, main causes and secondary causes are defined and which one to attack first is defined. Flow charts are also used to define what operations and in what order they are performed to solve a problem. They are drawn using standard symbols.
Laboratory accreditation is the formal recognition by an independent, scientifically based organization that a laboratory is competent to perform specific tests.
One of the most frequent problems in the laboratory is the correct follow-up of standardized techniques. This type of error is correctable and makes the product unreproducible over time.
The basic procedures for maintaining quality in the laboratory are simple to carry out as long as you are careful in your work and pay attention to the tasks you are performing. There are tools that facilitate the analyst's work within the laboratory:
Field form: tool that allows you to quickly and concisely visualize the steps to be carried out of the selected technique. It also allows you to write down important data and observations.
Data sheet: it is a tool that allows the annotation of the data collected from a technique in a simple and orderly way. Furthermore, depending on how it is designed, it allows the addition of other data such as materials and reagents used, instruments, observations and diagram.
Schemes: simple graphic representations that allow quick and easy identification of the procedure to follow in the technique.
Block diagram: similar to the schematic, it allows quick identification of the procedure to follow in the technique. It does not include as much information as an outline but is simpler to construct and read.
In addition to this, there are procedures that ensure the quality and reproducibility of the results obtained in the laboratory.
• - Respect safety and hygiene regulations.
• - Use calibrated materials that ensure the accuracy of the measurements.
• - Use calibrated instruments and always use them according to their instructions.
• - Follow the techniques to the letter, do not make any changes.
• - Always use standardized procedures.
• - Use quality reagents that are properly preserved.
Manual: there is an operator who, aided by a device or instrument, can make the measurements he needs.
Automatic: there is no operator. The result is given by the team, it would be ideal.
The advantages of automatic control are: time savings, labor savings, maintenance savings, they have visual and audible alarms, and high precision. The disadvantage is the high cost.
The treated effluent must comply with the Quality Standards for Liquid Dumping, Law No. 11220, Annex B. Based on the destination of the water, certain quality or values in the physical-chemical parameters will be required. Drinking water as a beverage has values established by the WHO and the CAA. Water for different uses has values established by the La Plata Basin.
The objectives of a quality system are: to raise the overall quality of laboratory performance, identify good analytical methods, provide permanent records of instrument performance, ensure sample integrity, and implement medium- and long-term corrective measures.
• - Design quality: it is the degree to which a product or service is reflected in its design.
• - Quality of conformity: it is the degree of fidelity with which a product or service is reproduced with respect to its design.
• - Quality of use: the product must be easy to use, safe and reliable.
The sample is a representative portion that retains the same concentrations of the components of the material under study; it must be a reliable sample.
The objective of taking a sample is to obtain a portion of material whose volume is small enough so that it can be easily transported and manipulated in the laboratory without ceasing to accurately represent the material from which it comes. It must be representative and easily transported.
The requirements are: representative, completely characterizes the effluent from which it comes; size, it should not be large for transportation reasons or small so that it is not enough to make the samples; stability, which does not have important changes from when it was collected until it was analyzed; purpose or objective, what I want to determine.
Sampling is carried out at predetermined points and serves to evaluate the efficiency of the physical-chemical treatment. For example, in a settler, the settleable solids are measured at the inlet and outlet of the settler.
Obtaining a sample that meets the requirements of the collection and handling program implies that it must not deteriorate or become contaminated before reaching the laboratory. The considerations are:
• - Alteration of the sample must be avoided (it should not have external agents that modify it).
• - Conservation of the sample (no loss).
• - Environmental conditions (if it is solid it dissolves with rain).
• - Physical and/or chemical changes (no change in physical state or a chemical reaction).
• - Rules (if you do not comply with them, the result may be invalidated).
• - Avoid abnormal situations (stops or starts, unless the data needs to be known at that moment) and.
• - Hygiene and safety precautions.
The types of samples related to site and time are:.
• - Probing sample, it is done only once because the source is fairly constant in composition over a considerable period or over substantial distances in all directions so it can be said that the sample will represent a longer period of time, a larger volume or both.
• - Compensated sample, refers to a mixture of simple samples collected at the same point at different times. They are the most useful for determining the average concentrations to use. They are applied in industrial sewage effluents because they have very variable characteristics over time.
• - Integrated sample is the analysis of mixtures of individual samples, collected at different points at the same time or with the smallest temporal separation possible (less used, I take a spatial average sample). If there is little time, fewer samples are taken to obtain the average.
• - Manual: it is assumed that no equipment is used, but this procedure may result in excessive costs for routine or large-scale sampling programs. The costs per man hour are due to a greater frequency of errors that are made.
• - Automatic: through automatic taking, human errors can be eliminated, labor costs are reduced and frequency is increased.
Due to the variation in effluent characteristics and random variations in analytical processes, a single sample is insufficient to ensure a good result. Therefore, the number of samples is given by the Student Formula and is a function of Student's t for a given confidence level, global standard deviation and acceptable confidence level.
• - Liquids, there are tables that recommend values, it is preferable that there be a sample and that there is no shortage.
• - Solids, by quartering: the solid sample is mixed well, divided into 4 parts, 1 and 3 are mixed, 2 and 4 are removed. Mixed again and the process is repeated. It ends once there is enough sample. The sample is dissolved for analysis.
Complementary actions consist of operations to maintain the integrity of the sample from its issuance to its analysis. Suggestions for taking samples are to use a clean, wide-mouth, 2-liter glass or plastic container with an airtight seal and screw-on lid to avoid losses due to spillage. Hermetic closure (sealing) to avoid contamination or loss, to detect any falsification of the sample that may be made before analysis. You must also take care that the container is not broken or open. This must be rinsed with the sample liquid and then filled with it, avoiding the presence of an air chamber, it must be refrigerated and kept in the dark until the test is carried out. Supplementary data are all the information pertinent to a field study or sampling that will be recorded in a book: observations of color, odor, temperature, dissolved oxygen, pH, sample status. It is then arranged in the form of tables for better compression. The effluent must be flowing and must not be stagnant. To obtain representative samples, possible floating materials accumulated in corners where the water is partially stagnant must be left aside. Due to the high complexity of the matrices and their rapid alteration in this type of samples, a quick transfer to the laboratory is necessary, as well as speed in the analysis. It is preferable that the sampling site be constantly moving which ensures a constant sample. The sample labeling must contain the type of sample, location of extraction, name of the extractor, type of analysis, destination (if not analyzed on site), date, time and observations (if necessary) and the sample number. Precautionary measures should be taken during the sampling operation, such as the use of gloves, nose and eye protection against possible splashes, and not smoking or eating food simultaneously while taking the sample. Use ice cream freezers to transport the samples if this is not possible. There are chemical sample preservation techniques where chemical substances are incorporated, which are placed first and the samples are placed on top of them so that no part is left without coming into contact.
The packaging material is usually plastic or glass, and depending on the case, one or the other may be preferable. The containers are with or without color, transparent and opaque. If it is plastic it is PVC, PET or PTFE. If it is glass, it is less polluting and can be sterilized and reused.
For sample conservation, the objective is to avoid physical, chemical and biological changes in the original sample from extraction to analysis. The changes that occur are: hydrolysis, absorption, desorption, oxidation-reduction, precipitation, microbial action. Regarding the parameters that can be analyzed in situ: some analyzes can be affected more easily than others by irreversible changes. Some cations are lost by adsorption on the walls of glass containers or by ion exchange with them. The temperature changes rapidly; pH can change significantly in a matter of minutes; dissolved gases can be lost. Therefore, the temperature, pH and dissolved gases must be determined at the time of sampling (in situ). In general, the shorter the time between sample collection and analysis, the more reliable the result will be.
Conservation methods are physical or chemical. Chemical methods consist of adding acid, chlorine inhibitor (sodium thiosulfate or ascorbic acid), oxidant or reducer. The physical methods consist of refrigeration at 4 °C (manage T in the case of microbiological analysis). This is achieved with ice creams with ice when they are just extracted, avoiding freezing. The conservations are maintained until the moment of use. To minimize possible volatilization or biodegradation between the time of collection and the time of analysis, the sample should be kept at the lowest possible temperature without freezing (4 °C) and stored in the dark. Chemical preservatives will only be used when it has been demonstrated that they will not spoil the analysis. It is advisable to use multiple sample portions when added chemicals influence other determinations. If they are used, they must be added to the container before placing the sample, so that all parts of it come into contact with the preservative at the time they are collected. There is no method of preservation that is completely satisfactory. Conservation methods are relatively limited and are designed, in general, to delay the action of microorganisms, delay the hydrolysis of chemical compounds and complexes, reduce the volatility of the components, stop the adsorption of cations on the walls or the ion exchange with them. Preservation methods are limited to pH control, addition of chemicals, use of amber or opaque containers. There are tables that list preservation methods, maximum preservation time, minimum sample size and packaging material depending on the determination.
• - It is advisable that if you have long hair, keep it tied up, not use scarves, pendants or elements that could cause risks during the practice.
• - Keep a notebook where you write down calculations, descriptions of the reagents, and observations.
• - Keep a spreadsheet where the weekly results of the analytical techniques are recorded.
• - Be punctual and not be able to leave the laboratory without authorization from the teacher.
• - Know the contents inherent to the work to be developed.
• - Assist with items for personal use: mesh cloth, hygiene accessories.
• - Before starting the practical work, check that the necessary elements and materials are in correct condition (clean, not broken, etc.).
• - Once the practical is finished, collaborate with the general order and cleanliness of the laboratory.
• - Present a written report consisting of data, observations and conclusions.
• - The container must be airtight, have a wide mouth and be clean.
• - The container must be made of glass or plastic and have a capacity of 2 liters.
• - It must be rinsed with the liquid to be collected, without leaving an air chamber.
• - It should be stored refrigerated at 4 °C and in the dark.
• - A funnel and a bucket will be used as accessories for transferring.
• - Each container must be labeled with a number and must be accompanied by a data sheet containing the date, time, extraction site, and person responsible for the extraction.
• - Data obtained in situ must be recorded on parameters such as odor, color, appearance and, if possible, measurements of dissolved oxygen, pH and temperature. This is recorded in the data sheet.
• - Precautionary measures must be taken such as the use of masks, overalls, glasses, long pants, closed shoes and gloves to avoid contact with the eyes, skin or mouth due to splashes that may occur.
• - You cannot drink, smoke or eat during sampling, this incorporates external agents into the sample.
• - The sampling site must not be sealed but must have constant fluid agitation.
The data sheet must record the macroscopic observations, organoleptic properties and physical determinations that can be carried out in situ. Among the macroscopic observations are the number of phases contained in the sample, existence of macro organisms, existence of large solids, turbidity and foam. Among the physical determinations are temperature, pH, conductivity, turbidity and dissolved oxygen. Within the organoleptic properties, color, smell.
Settleable solids are those that settle in an Imhoff cone for 2 hours from one liter of residual liquid. Fixed settleable solids are those that do not volatilize at 600 °C for 15 minutes and volatile settleable solids are those that volatilize under these conditions. Total settleable solids can be measured in volume (ml/L) and weight (mg/L) but fixed and volatile settleable solids only in weight (mg/L).
Settleable solids in volume.
• - Add 1 liter of residual liquid to an Imhoff cone. Do it through the center, not along the walls because the solid will settle.
• - Take a reading after 10 minutes (settled solids after 10 minutes).
• - Let it decant for 2 hours. Gently stir the sediment to fill any empty spaces.
• - Take a reading (settled solids after two hours).
Settleable solids by weight.
• - Siphon the supernatant liquid and transfer the sediment to a capsule previously weighed to the milligram.
• - Evaporate in a bain-marie, avoiding boiling and splashing until all the surface liquid is removed.
• - Dry in an oven at 103-105 °C for 1 hour.
• - Cool in a desiccator.
• - Weigh to the milligram (P2).
Fixed settleable solids.
• - Calcine the sample at 600 °C for 15 minutes.
• - Cool in a desiccator and weigh to the milligram (P3).
Total settleable solids: P2-P1
Fixed settleable solids: P3-P1
Volatile settleable solids: P2-P3.
Total solids are the weight of non-volatile suspended and dissolved matter at 105 °C of one liter of residual liquid. The fixed solids are the non-volatile part of the residue at 600 °C for 15 minutes and the volatile solids are those that volatilize under these conditions. Total solids, volatile solids and fixed solids are expressed in mg/L. Fixed solids correspond to inorganic matter and volatile solids to organic matter.
Total evaporation residue
1.Shake the sample thoroughly and transfer 25-50 ml to a test tube. Then pour the contents of the test tube into a previously tared porcelain capsule (P1).
2.Use distilled water to wash the test tube and place the contents in the capsule.
3.Evaporate in a bain-marie, avoiding boiling and splashing.
Dry at 150°C for one hour.
Cool in a desiccator.
Weigh to the milligram (P2).
Fixed solids
Calcine the residue obtained at 600 °C for 15 minutes.
Cool in a desiccator and weigh to the milligram (P3).
Total solids: (P2-P1)*1000/V
Volatile solids: (P2-P3)*1000/V
Fixed solids: (P3-P1)*1000/V.
The result is conditioned by the combinations of temperature and time. Waters with calcium and magnesium (hard water) are hygroscopic. Water re-enters the waste when hydrophilic crusts form even after drying; this is characteristic of excessive waste. Samples with fats and oils are difficult to dry. At the temperature at which it is dried, separation of volatile compounds occurs, which generates negative errors in the counting of volatiles. At the calcination temperature, some separations of inorganic compounds occur, so it is not an exact method. There are other methods such as total organic carbon.
The oxygen consumed is the oxygen of the potassium permanganate that a water consumes when it reacts with this reagent under certain conditions. The conditions are heating time, heating temperature and concentration of the reagents, and the technique must be rigorously adjusted to them. The purpose of the test is to measure the cc of organic matter, so if the sample contains permanganate-reducing minerals, the corresponding correction must be made. It provides an index of the degree of contamination of the sample, its concentration or load, which is why it is very useful when the BOD is not performed or even as complementary data to the BOD.
The procedure is:
• - Add 100 ml of sample or a dilution of the sample (the maximum dilution allowed is 1/500) to a 250 ml Erlenmeyer flask. Add 10 ml of sulfuric acid (1+3) and 10 ml of 0.0125N potassium permanganate. The sample and sulfuric acid are added with a pipette and potassium permanganate with a burette.
• - Heat to a boil in a pot for 30 minutes. Be careful not to spill the contents of the Erlenmeyer flask into the pot and that the water covers the surface of the liquid contained in the erlenmeyer.
• - After 30 minutes, a purplish color should remain. If the sample is not colored, then perform a higher dilution. If it does not color even with the maximum dilution, stop making dilutions and calculate the oxygen consumed with the maximum volume of permanganate and expressing "greater than" the value obtained. The permanganate oxidizes the organic matter, leaving it in excess.
• - Decolorize with 10 ml of 0.0125N oxalic acid (the oxalic acid remains in excess and the excess amount is equal to the original amount of organic matter that the sample had) and add potassium permanganate drop by drop until a weak pink color is present but persistent for 3 minutes (the excess oxalic acid is neutralized with potassium permanganate). The maximum volume of potassium permanganate for titration is 5 ml. So if more is spent, another dilution is made. This procedure is repeated until the maximum dilution. If the sample is not colored for the maximum volume of titrant and carrying out the maximum dilution, dilutions should be stopped and the oxygen consumed should be calculated using the maximum volume of permanganate and expressing "greater than" the value obtained.
• - Make a target. To do this, instead of using 100 ml of sample, use 100 ml of distilled water and repeat the hot titration procedure.
• - Carry out the cold assessment. It is carried out to determine if there are permanganate-reducing minerals and consists of: adding 100 ml of sample or a dilution (the dilution must be the one that gave positive results in the hot titration).
• - Add 10 ml of sulfuric acid (1+3).
• - Titrate with potassium permanganate drop by drop until a faint pink color persists for 3 minutes.
Calculation of oxygen consumed.
(N-Nb-Nf)*100*f/V.
where N: volume of titrant spent in hot titration.
Nb: volume of titrant spent in the assessment of the blank.
Nf: volume of titrant spent in cold titration.
f: permanganate correction factor.
V: sample volume.
The higher the salinity, the lower the solubility. Salts dissolved in water reduce the intermolecular spaces available for oxygen dissolution. The percentage of saturation is measured as the quotient between the dissolved oxygen measured in the field and the theoretical dissolved oxygen multiplied by 100.
Direct method.
It is carried out with an electrode on the body of water. The percentage of saturation is also obtained. The measurement is obtained once the display stops flashing. The oximeter consists of a platinum cathode and a reference silver/silver chloride anode.
Winkler method.
It is the indirect method of measuring dissolved oxygen. The sample is taken taking care not to leave air bubbles inside the Winkler bottle. The temperature is noted to obtain the theoretical dissolved oxygen in order to express the dissolved oxygen in percentage of saturation.
The Winkler method is applied to waters that do not contain more than 0.1 mg/L of nitrogen in the nitrite state or appreciable quantities of iron, sulfites and thiosulfates, polythionates, free chlorine or hypochlorites and unstable forms of organic matter. In all other cases it is necessary to carry out previous treatments such as Rideal-Stewart or alkaline hypochlorite.
It is the amount of oxygen required by bacteria during the stabilization of organic matter susceptible to degradation by aerobic microorganisms at a temperature of 20 °C, for 5 days and in darkness. It is used to determine the polluting power of domestic and industrial waste.
From organic matter and nutrients, bacteria break down organic matter into carbon dioxide, water, inorganic compounds, new cells and energy. The disadvantage with COD is that it lasts longer and the advantage is that it gives an idea of the biodegradability of the sample. It is used to measure efficiency in wastewater treatment plants. The BOD5 at the inlet and the BOD5 at the outlet are calculated, thereby obtaining the removal percentage.
The temperature is 20 °C because it is an average of natural water temperatures and the speed of biochemical reactions depends on temperature. Theoretically, an infinite amount of time is required for the biological action of organic matter to complete, but for practical purposes the reaction is completed in 20 days. In domestic wastewater, the BOD value at 5 days represents 65 to 80% of the total oxidizable organic matter. As this is a bioassay there is a large margin of error and it is of utmost importance that the environmental conditions are appropriate so that the activity of the microorganisms remains unhindered:
• - Should not make toxic substances.
• - There must be availability of nutrients.
• - Variable species of microorganisms and in large quantities. If there is a normal initial population of microorganisms, the degradation curve gives a normal BOD value, but if the initial population is lower, it gives a lower BOD value because the adaptation phase is longer. The same thing happens if the seed is not acclimatized because they seek to acclimatize to the new compound. Nitrification results in higher BOD values because oxygen is used to oxidize ammonium ions instead of degrading organic matter. This is observed in effluents due to the presence of nitrifying bacteria. Nitrification can be inhibited by the addition of Thiourea.
• - Sufficient oxygen.
Sampling.
The measurement of BOD is carried out in the laboratory. It is kept in a plastic or glass container. It is preserved at 4 °C to avoid the degradation of organic matter and for no more than 24 hours.
Laboratory determination.
The Winkler method or the costometric method is used. The Respirometric method is the most precise but the least developed. In the Winkler method, the Winkler bottle is used, the same as for dissolved oxygen, the lid has an airtight seal and what it basically does is prepare a culture medium, where bacteria, nutrients, and inhibitors are placed. Dissolved oxygen is measured on day 1 and then dissolved oxygen is measured on day 5 and the difference is the BOD5. In the costometric method, pressure differences are measured using a pressure transducer and the result is multiplied by a factor that depends on the sample volume. It has the advantage of not having to measure dissolved oxygen, it is more automatic.
The biochemical oxygen demand of a contaminated liquid is called the oxygen expressed in mg/L, which it consumes in the decomposition of organic matter, by aerobic microbial action. As the decomposition process takes several months to complete and its speed varies with temperature, in practice BOD is measured corresponding to a period of 5 days and a temperature of 20 °C.
From this definition it results that the measurement of BOD of a liquid requires the simultaneous presence in it of:.
a) Organic matter on which decomposition occurs.
b) Aerobic or facultative microorganisms that carry out decomposition.
c) Dissolved oxygen so that the decomposition of organic matter can take place in aerobiosis.
This test was originally conceived by the United Kingdom Royal Commission on Sewage Disposal, as a measure to assess the degree of biochemical oxidation that would occur in a natural water body to which polluting effluents were discharged.
However, the actual conditions of the environment, temperature, water movement, lighting, oxygen concentration, biological population, including planktonic algae and rooted plants, the effect of sediment deposition, photosynthetic action of green plants, presence of nitrogen and ammonia, action of nitrifying bacteria, etc. They cannot be reproduced in the laboratory. Consequently, predictions of the pollution effect of a course are not achieved by direct means, and require the consideration of many factors not involved in the determination of BOD such as water movement, the effect of sediment deposition, among others.
For example, suspended matter in an effluent is often deposited a short distance, immediately downstream of the drain, where it can exert a fairly considerable effect on the concentration of dissolved oxygen (DO).
The BOD determined by dark incubation includes oxygen consumed by algal respiration. The polluting effect of a watercourse effluent can be considerably affected by the photosynthetic action of green plants present, but it is impossible to determine this effect qualitatively in 5-day BOD experiments, so there are no general rules that can be given for BOD of samples containing algae, and each case must be considered according to its characteristics.
A complication of the BOD test is that most of the oxygen consumption of the samples may be due to ammonia and organic nitrogen, which can eventually be oxidized to nitrites and nitrates by nitrifying bacteria, if present. Additionally, ammonium added to the dilution water can also nitrify, and therefore the BOD value is not representative of the sample alone.
Furthermore, due to the low growth of nitrifying bacteria, the degree of nitrification will depend on the number of bacteria initially present, nitrification does not occur to a detectable extent during the 5-day period of raw and settled sewage liquids and in almost all industrial effluents. The BOD test is therefore useful in determining the relative load from the drain to the treatment plant, and the degree of oxygen demand removed by primary treatment.
Nitrification during the 5-day incubation is almost always limited to treated effluents and river waters, which would already be partially nitrified. Only these cases need special attention and the question arises from the use (or not) of the method incorporating a nitrification inhibitor. Determining the degree of nitrification is tedious but, unless known, BOD values can be misleading when evaluating plant performance or calculating effects on a river.
The BOD determined by the dilution method is used as an approximate measure of the amount of biodegradable matter in a sample. For this purpose the dilution test has been successfully applied in practice to samples in which nitrification does not occur, and remains probably the simplest and most suitable test, although in some cases the manometric method can be used. It is optimal in samples where nitrification does not occur because nitrogen and ammonia consume oxygen by nitrifying bacteria and the behavior of nitrifying bacteria is not understood.
The analyst will also consider whether the information he needs can be obtained in some way.
For example, the chemical oxygen test will effect virtually complete oxidation of most organic substances, and thus indicate the amount of oxygen required for complete oxidation of the sample. In other circumstances, and particularly in research work, the determination of organic carbon is more appropriate. In some cases, the results obtained by the BOD test should never be considered separately but in the context of local conditions and with results from other tests.
Complete oxidation of a given drain may require an incubation period that is too long for practical purposes, taking several months to complete. In practice oxidation is considered complete in 20 days. For this reason, the period of 5 days at 20 °C has been accepted as standard.
However, for certain industrial drains and for water contaminated by them, it may be advisable to determine an oxidation curve.
Ultimate BOD calculations from 5-day BOD values (based on calculations using first order exponentials) are not correct. Conversion of data from one incubation period to another can be done only if the oxidation curve has been determined for this individual case, for a series of BOD tests carried out at different incubation periods.
Dilution method.
The dilution method of BOD determination is generally the most widely used. The OD of the sample is determined before and after incubation for 5 days at 20 °C. The difference is the BOD of the same sample after taking into account the dilution carried out.
Precautions.
• - The BOD test should be carried out as quickly as possible once the sample has been taken. This makes it possible to repeat the determination if the results obtained are not satisfactory.
• - If samples are kept at room temperature for several hours, an appreciable change in BOD may occur, depending on the character of the sample. In some cases it may decrease and in others it may increase. The decrease at room temperature is 40% during the first 8 hours of parking.
• - Samples must be free of preservatives and packaged in glass bottles. If samples cannot be processed immediately, they should be kept at a temperature of 5 °C. In the case of individual samples collected over a long period, it is desirable to maintain all samples at temperatures of 5 °C until the compensated sample can be prepared for BOD determination.
• - It is necessary that there be excess dissolved oxygen during the incubation period and it is desirable that it reaches at least 30% of the saturation value after 5 days. Since the solubility of oxygen at the incubation temperature is only 9 mg/L, samples that absorb more than 6 mg/L during incubation for 5 days do not meet this condition. This is the case with sewage liquids and many other contaminated liquids.
• - Additional oxygen is added by diluting the sample with clean, well-aerated water; The dilution depends on the nature of the sample.
Interferences and deficiencies.
• - If the pH of the sample is not in the range 6.5-8.5, it is necessary to add enough alkali or acid to ensure this range. To do this, on a portion of the sample the amount of acid and alkali that is going to be added to neutralize is determined using a suitable indicator such as bromothymol blue or a peachimeter. Then the volume of the calculated aliquot of acid or alkali is added to the sample whose BOD is to be determined.
• - Some samples may be sterile and must be seeded. The purpose of this seeding is to introduce a biological population capable of oxidizing organic matter into the sample. Household waters, non-chlorinated effluents and surface waters that have these microorganisms do not need this seeding.
• - When the sample is known to contain very few microorganisms, as a result, for example, of coloration, high temperature, extreme pH, or specific compositions of some industrial waters, the dilution water should be seeded. For sowing, to each liter of dilution water add 5 ml of raw sewage liquid obtained from the settlers subsequent to aerobic biological purification processes. If necessary, settle the effluent by leaving it in a cylinder for approximately 30 minutes. To sow, add 1-2 ml of the supernatant to each liter of dilution water.
• - Some samples may be supersaturated with dissolved oxygen, especially water contaminated with algae. If such samples are incubated without dilution, the dissolved oxygen concentration should be decreased to saturation to prevent oxygen depletion during incubation. Samples should be kept at 20 °C in partially filled bottles and well shaken.
• - A few sewage effluents and certain industrial effluents contain residual chlorine or products of the action of chlorine on certain constituents. Such liquids cannot be used for the determination of BOD because of the bactericidal effect of chlorine and its byproducts, and also because chlorine introduces an error in the determination of DO. If samples are allowed to sit for 1 to 2 hours, residual chlorine may dissipate. Dilutions for BOD can be separated with standard seeded dilution water. This procedure gives good results for household effluents that have been chlorinated, since chlorine can combine with organic compounds present, producing substances that, although they do not give the iodine-starch reaction for chlorine, inhibit biochemical oxidation or are bactericidal. The BOD determined by these circumstances is generally lower than expected, in relation to organic content, than the BOD measured by other tests.
Sowing of industrial effluents.
• - Sewage effluent seeding, such as those described above, is satisfactory for many industrial effluents. However, the BOD of such effluents determined by standard tests is significantly lower than the chemical oxygen demand, because:
a) samples may contain compounds resistant to biochemical degradation.
b) the organisms planted may be of inappropriate type or require acclimatization, which is why they do not degrade organic matter.
c) there are toxic or bacteriostatic compounds such as chlorine.
Compounds resistant to degradation do not exert an oxygen demand on the received waters, but degradable substances generally contribute to the pollutant load if the BOD test is affected for reasons b) and c) mentioned above.
If the difficulty is due to condition c, it is possible to obtain reliable BOD values only by increasing the dilution of the toxic constituents of the sample to concentration values lower than those that cause inhibition.
Incubation bottles.
• - The use of incubation bottles with a capacity of 250 ml, with a frosted glass stopper, with a narrow mouth is recommended and it is essential that they be very clean. New bottles should be treated with 5N hydrochloric acid and rinsed appropriately.
• - During use, the bottles are kept clean by the acid iodide solution of the Winkler Method, and do not require treatment except rinsing with tap water and distilled water. Special washes are necessary in some cases, but the use of chromic acid is not recommended because traces of chromium may remain in the bottles.
• - Some analysts prefer to use 125 ml capacity bottles, to reduce the space required in the incubator. It is evident that with samples of this type, the size of the bottles can influence the result.
• - Care must be taken so that air does not enter the bottles during incubation, which is obtained by hydraulic closure of the bottles specially designed for BOD.
Incubation.
• - The incubation temperature should be 20 °C+/-0.5 °C, in darkness, because some samples containing algae produce oxygen through photosynthesis, and this interferes with the determination of BOD.
Dilution water.
• - The logical diluent for sewage effluent is the river water into which it is discharged, but this method can only be adopted in special cases, and obviously fails where effluents from very distant locations are processed by the same laboratory because the dilution water should be only one. Furthermore, river water alone can have a considerable BOD.
• - Distillation water is not satisfactory as a diluent and water distilled in copper stills is recommended since copper inhibits the biochemical action, with the maximum tolerated concentration being 0.01 mg/L. The deionized water produced in some commercial units is satisfactory, but the deionized column produced in hard areas requires frequent regenerations.
• - Pretreatment of water by sowing is sometimes necessary.
• - Sample pretreatment is necessary if the sample is supersaturated with oxygen or if the sample contains residual chlorine. If the pH of the sample is not between 6.5 and 8.5, it must be maintained in that range by adding alkali or acid.
• - A dilution water when incubated, with or without seeding, in standard condition should not absorb more than 0.2 mg/L of oxygen and in some cases no more than 0.5 mg/L. A greater oxygen expenditure must be associated with the presence of water-soluble organic vapors in the laboratory atmosphere.
• - Samples kept in the refrigerator should be brought to room temperature before diluting and shaking.
• - Suspended solids in some liquids can cause difficulty if their distribution is not uniform when making dilutions. This may cause discrepancies in the results of different dilutions or duplicate dilutions. It is not advisable to mechanically homogenize them as it can increase their oxygen demand.
• - Sometimes the BOD of the settled or filtered liquid is required. In such cases, the most commonly applied sedimentation time is 30 minutes. For the BOD of filterable substances, membrane filters, glass filters or filter paper are used.
• - Unless the approximate BOD of the sample is known, the degree of dilution required is not and therefore more than one dilution must be made. The lowest dilution should be the one that has a remaining oxygen of 30% in 5 days.
• - It should be noted that some metals such as Cu, Cr, Pb partially inhibit oxygen consumption.
Technique check.
• - From time to time it is desirable to check the entire procedure, including the quality of the dilution water, the effectiveness of sowing and the analyst's technique. For this purpose, pure organic compounds whose BOD is known or determinable are used, such as glucose or glutamic acid. The mixture of glutamic and glutamic acid has certain advantages. Glucose has a high oxidation rate and variables with relatively simple sowing when used with glutamic acid, the oxidation rate is stabilized and is similar to that obtained in many domestic waters.
• - For the checkup, the following procedure is recommended: dissolve 150 mg of glucose and 150 mg of glutamic acid (dried, both previously at 103 °C for 1 hour) in a liter of water; This dilution must be recently prepared. Use dilutions from 1 to 50, with dilution and sowing water and determine BOD by the usual means. The BOD will be approximately 220 mg/L. If the result obtained is greater than 200 mg/L or greater than 240 mg/L, defects in sowing, dilution water or experimental phase should be suspected.
The determination of BOD by this method consists of measuring the decrease in dissolved oxygen that occurs in the liquid to be analyzed, when it is incubated under certain conditions. As the dissolved oxygen concentration of water in equilibrium with air is normally small (at 20 °C and 760 mm Hg it is 7.19 mg of oxygen per liter of water), it is generally necessary to dilute the samples with oxygen-saturated water to ensure its presence for the duration of the incubation.
The model recommended by the APHA is used as a bottle with the following specifications: volume (250-300 ml), shape (cylindrical with an external diameter of approximately 6.5 cm); Frosted cap with a pointed end that closes perfectly, and hydraulic closure to prevent air entry during incubation. The latter can be obtained by placing a rubber collar on the neck of the bottle that slightly extends beyond the upper end of the stopper and fits well.
The free space between the rubber tube and the plug is filled with water. You can also use a jar with the upper end of the neck widened, so that when you place the cap, a hole similar to that of a plate is left, which is filled with water.
With any of these procedures it may happen that before the end of the incubation period, the water in the hydraulic seal completely evaporates. This often occurs in incubators with air renewal and can be avoided by placing a rubber cap for closure, otherwise it must be inspected daily, replacing the evaporated water.
Cleaning the bottles: practiced with the sulfochromic mixture, rinsing them carefully before using them.
Jars with a capacity of 10-20 liters are used to conserve the dilution water. Siphons and pipettes are used, these should be full spill. Air or thermostat incubators with water are used: it must be maintained at 20 °C +/- 1 °C.
The BOD (5 days at 20 °C) of the dilution water cannot be greater than 0.2 mg/L. The concentration of dissolved oxygen should not be greater (supersaturation) or much lower than that corresponding to equilibrium at 20 °C and normal pressure; That is, its dissolved oxygen content must range between 8 and 9 mg/L. Its temperature should be approximately 20 °C. The dilution water must not contain substances that interfere with the recovery of dissolved oxygen, such as iron and nitrite salts, nor substances that inhibit biological growth, such as free chlorine, chloramines, copper salts, etc. Both the pH and the mineral salt content of the dilution water must be favorable to biological growth.
The distilled water used to prepare the dilution water must contain less than 0.05 mg/L of copper, for which it is advisable to use a distiller made entirely of glass. When distilled water has been disinfected with chloramines, these must be removed before distillation, by filtration through carbon, as they are volatile.
Once the water is distilled, it is saturated with oxygen by circulating a current of air through it; But if the distillation is regulated in such a way that the water is collected drop by drop and very cold, aeration becomes unnecessary and sometimes harmful. When aerating, the water tends to become supersaturated with oxygen (especially in winter), remaining in these conditions even after being parked for several days at 20 °C. This requires subtracting part of the DO in the water, to eliminate supersaturation, which complicates the technique.
Finally, the water is kept at 20 °C (temperature at which the BOD is carried out) until the time of use, and only then are the reagents added, stirring gently to avoid aeration.
The dilution water adopted for all BOD tests is Theriault-Nichols, as it has been proven to be the most convenient for liquids that lack essential elements, and its use is also satisfactory because they do not suffer from this deficiency.
To prepare it, the following reagents must be added to the distilled water obtained under the specified conditions:
a) Phosphate buffer solution with added ammonium sulfate: 1.25 ml/L of distilled water.
b) Calcium chloride 0.1 M: 2.5 ml/L of distilled water.
c) Magnesium sulfate 0.04 M: 2.5 ml/L of distilled water.
d) Iron chloride 0.001 M: 0.5 ml/L of distilled water.
The phosphate buffer solution with added ammonium sulfate is prepared by dissolving 34 g of potassium acid phosphate in about 500 ml of distilled water, and then adding NaOH N until a pH of 7.2 is obtained (approximately 175 ml of the NaOH N solution are required). Once the pH has been adjusted, 1.5 g of ammonium sulfate is added and the volume of the solution is finally brought to one liter.
The 0.1 M calcium chloride solution contains 18.3 g of calcium chloride tetrahydrate in one liter; the 0.04 M magnesium sulfate solution contains 9.9 g of magnesium sulfate heptahydrate per liter; The 0.001 M iron chloride solution contains 0.27 g of iron chloride hexahydrate per liter.
pH adjustment: Caustic alkalinity or acidity of the sample can inhibit biological activity. If the pH is less than 5.5, the 0.2 M solution of sodium carbonate (21.2 g of this salt per liter) is added to a portion of the sample until an alkaline reaction with bromothymol blue is obtained; If, on the other hand, the sample is alkaline (pH greater than 8.5), 0.02 M HCl solution is added (17 ml of HCl, specific weight of 1.19, per liter of solution) until the reaction is acidic to cresol red.
In both cases, once the volume of alkali or acid needed is known, another portion of the sample can be neutralized to calculate the BOD without using the indicator, and calculate the corresponding dilution factor.
The neutralization of acid samples that contain iron or aluminum salts in solution produces a precipitate that carries the suspended matter, obtaining lower BOD values in the neutralized sample than in the untreated sample.
A method is currently being studied to overcome this drawback.
The BOD must be determined, the regulatory action of the dilution water may make pH adjustment unnecessary.
The determination of substances soluble in ethyl ether includes fats and oils and the sum of hydrocarbons, fatty acids, waxes and any other substance extractable in ethyl ether from a sample acidified to pH 4.2 and not volatile at 70 °C. The decomposition of plankton and other higher forms of aquatic life gives rise to fats and oils. Most heavy oils and fats are insoluble in water but some can form emulsions by the addition of alkalis, detergents and other chemicals.
Emulsified or dissolved fats and oils are extracted from acidulated water at pH 4.2 and by contact with organic solvents that also extract other substances. There is no selective solvent for fats and oils only. Some low-boiling fractions evaporate during performance of the method and other fractions when the last traces of ether are separated. Naphtha and kerosene are so volatile that they cannot be determined by this method. This method is applicable to wastewater and treated with the above limitations.
Saponified oils and fats tend to remain in emulsion and acidifying the sample to pH 4.2 or adding sodium chloride helps to break this emulsion. Organic substances soluble in ethyl ether in a sample acidified to pH 4.2 and that are not volatile at 70 °C interfere. The maximum sensitivity achieved by the technique is 2 mg/L of substances soluble in ethyl ether.
The sample must be representative, so it is collected from a place that is not watertight, but rather has permanent agitation. When collecting, the sampling container should not be filled because by closing it the floating substances will be lost. To preserve the sample, it should be acidified with diluted hydrochloric acid to pH 4.2.
Work instructions.
• - Homogenize the sample by stirring.
• - Measure 50 ml of sample with a test tube. Transfer to a beaker.
• - Acidify to pH 4.2 with diluted hydrochloric acid.
The only treatment prior to extraction is acidification to pH 4.2 to help break the emulsion of saponified oils and fats.
• - Add 2 drops of heliantine.
Heliantin allows the presence of acids to be evident because it turns from yellow-orange (higher than 4.4) to red (lower than 3.1). It also allows evidence of the formation of two phases: ethereal phase (transparent phase) and aqueous phase (red phase) that separate in the ampoule.
• - Assemble the extraction device with the support and the ampoule under the hood.
• - Add 50 ml of ether using a test tube (makes handling of the ether easier) to the separating ampoule.
It is carried out under a hood because the ether is toxic and proper ventilation and perfect closure must be verified. It is also flammable and explosive so it can be exposed to heat sources such as lighters. This means that it is not performed in conjunction with the consumed oxygen technique. Gloves, overalls, glasses, closed shoes, long pants and a face mask should be used when handling ethyl ether to avoid contact with the skin, eyes, and mouth.
• - Cover, shake (it should not be too soft so that interaction does not occur nor too strong so that the glass does not break) and open the valve in a position so that the liquid does not fall, successive times, to release the gases that exert pressure.
• - Place it back on the support, uncover it and wait for the two phases to settle. The aqueous phase is collected in a beaker and the ethereal phase is collected in a pre-tared crystallizer (P1).
• - Place the contents of the beaker and 20 ml of ether into the ampoule. Cover, shake and open the valve in a position where the liquid does not fall, successive times, to release the gases that exert pressure.
• - Place on the ampoule, uncover and wait for the phases to decant. The red phase is collected in the beaker and the ethereal phase is collected in the crystallizer.
• - Wash the ampoule with 10 ml of ether and place the washing liquid in the crystallizer. Discard the contents of the beaker.
• - Evaporate the ether at a temperature of 60-70 °C.
• - Cool the residue in a desiccator and weigh to the milligram (P2).
• - Make a blank, use 50 ml of distilled water instead of sample and repeat the procedure mentioned so far. Record the weight of the residue (P3).
Calculation of fats and oils.
(P2-P3)*1000/50.
The result is in mg/L if the measurements are recorded in milligrams.
If the target was not made then it is calculated as follows:.
(P2-P1)*1000/50.
The result is in mg/L if the measurements are recorded in milligrams.
Pretreatment is carried out because turbidity and coloration must be removed prior to colorimetric determinations.
The procedure is:
• - Measure 300 ml of sample or a dilution in a 500 ml Erlenmeyer flask.
• - Add 3 ml of 14%W/V aluminum sulfate and 3 drops of 50%W/P sodium hydroxide.
Aluminum sulfate is the coagulant agent and produces colloidal destabilization, which allows the formation of flocs, and sodium hydroxide allows the solution to reach optimal pH and the formation of aluminum hydroxide that precipitates together with the flocs, dragging them along.
• - Cover and shake gently in a circular motion.
• - Verify that the pH of the solution is between 6.5 and 7.5. Add diluted acid and base to correct the pH if necessary. If flocculation is evident, bringing the pH to pH is not necessary.
• - Let it decant (30 min minimum and 24 hours maximum) in the refrigerator. Use the supernatant solution for colorimetric determinations.
If flocculation is not noticeable, the pretreatment is carried out again on the same sample or another sample is used or 20 ml of the supernatant is taken. If sedimentation is not noticeable, then centrifugation is performed.
In samples with high ammoniacal nitrogen content, direct nesslerization should be used instead of distillation. Pretreatment with zinc or aluminum sulfate in an alkaline medium allows the Ca(+2), Mg(+2), S(-2) and Fe(3+) ions to precipitate, which cause turbidity in the presence of the Nessler reagent. Organic matter or coloration also precipitates. The addition of EDTA or Rochelle Salt prevents the precipitation of Ca and Mg ions that react with Nessler's reagent to give color.
Aromatic and aliphatic amines, ketones, aldehydes and alcohols produce a color that varies from yellow to green and turbidity in the presence of Nessler's reagent. Distillation must be resorted to when these interferences cannot be avoided.
The correctly prepared reagent makes it possible to detect 1 mg of ammoniacal nitrogen in 50 ml of solution. Reproducibility below mg is often erratic.
The procedure for determining ammoniacal nitrogen in the sample is as follows:
• - Measure 50 ml of sample or a dilution of it in a 50 ml volumetric flask.
• - Add 1 ml of Nessler's reagent and 2 drops of Seignette's salt.
• - Leave protected from light for 10 minutes.
• - Measure the %T in the spectrophotometer at 420 nm, previously adjusting with the blank.
• - With the value of %T enter the curve and obtain the corresponding concentration. Then the following formula is applied:
mg/L of ammoniacal nitrogen: mg/L read on the curve X 50/sample volume.
The procedure for preparing the blank is:.
• - Measure 50 ml of distilled water into a 50 ml volumetric flask.
• - Add 1 ml of Nessler's reagent and 2 drops of Seignette's Salt.
• - Leave protected from light for 10 minutes.
• - Add 100% T to the reagent blank.
The procedure to prepare the ammoniacal nitrogen curve:.
• - Place aliquots of 1, 2, 5 ml of standard ammonia solution in 50 ml volumetric flasks.
• - Dilute with distilled water up to the volume.
• - Add 1 ml of Nessler's reagent and 2 drops of Seignette's salt.
• - Leave protected from light for 10 minutes.
• - Measure the %T in the spectrophotometer at 420 nm and graph as a function of the concentration of the solutions.
The determination is carried out using a colorimetric kit that uses the cadmium reduction method. In the presence of cadmium, nitrates are converted to nitrites almost quantitatively. The nitrite ions produced undergo diazotization and coupling reactions to form an amber-colored azo dye that can be measured colorimetrically.
Work instructions
Fill the two work tubes up to the mark (5 ml) with pretreated sample or a dilution thereof.
Place one of the tubes in the left position of the color comparator.
Add one reagent sachet, Nitraver 5, to the second tube.
Shake vigorously for 1 minute.
Wait 1 minute for color development.
Place the tube in the right position of the color comparator.
Place in front of a light source and rotate the colored disc until the colors match. If it is very colored, make a greater dilution because the concentration of nitrates is high. Read the result in mg/L of N of NO3.
The result corresponds to the concentration of nitrates and nitrites. Therefore, to measure the nitrate concentration, you must subtract the nitrite concentration obtained by the following method. The results must be affected by the dilution factor if dilution was performed.
The determination of nitrites is carried out using a colorimetric kit that uses the ferrous sulfate method. In an acidic environment, ferrous sulfate reduces nitrite ions to nitrous oxide. Ferrous ions react with nitrous oxide to form a brown complex that can be measured colorimetrically because its color is proportional to the concentration of nitrites in the sample.
Work instructions
Fill both tubes of the kit with 5 ml (up to the first mark) of pretreated sample or a dilution thereof.
Add a reagent sachet to one of the tubes. Cover and shake.
If nitrites are present then a greenish brown color is produced. Allow 5 minutes for color development.
Place the tube with reagent in the upper right opening of the comparator and the tube without reagent in the upper left opening of the comparator.
Expose in front of a light source and rotate until the colors match. If the color does not fit the scale, carry out a greater dilution because the nitrates are in such an amount that the color does not fit into the scale.
Read the value on the mg/L scale of NO2(-). Affect the value read by the dilution factor.
The determination is carried out using a colorimetric kit by reduction with cadmium. Nitrate ions are quantitatively reduced to nitrite in the presence of cadmium. The nitrite ions then undergo diazotization and coupling reactions to form an amber-colored azo dye that can be measured colorimetrically.
The determination is carried out using a colorimetric kit that uses the ferrous sulfate method. In an acidic environment, ferrous sulfate reduces nitrites to nitrous oxide. Ferrous ions react with nitrous oxide to give a brown complex that can be measured colorimetrically because color intensity is proportional to concentration.
Anionic detergents combine with o-toluidine blue to give a chloroform-soluble blue complex. The intensity of the color is proportional to the concentration of detergents.
The organic matter gives a violet color with o-toluidine blue. Therefore, if the liquid contains organic matter, it is determined colorimetrically through a reddish substance soluble in chloroform. To eliminate organic matter, arsenite is added, which eliminates up to 1 mg/L. Interference from hydrogen sulfide can be eliminated by acidification and aeration.
The determination is made using the Murphy-Riley method. The phosphate ion reacts with ammonium molybdate, which when reduced with ascorbic acid gives a blue complex that is molybdenum blue. The phosphorus content in the form of phosphates is determined using a colorimetric kit. The pH does not intervene, the oxidants and reducers do not seriously disturb the accuracy of the method, arsenic does not interfere up to 0.05 mg/L, copper does not interfere up to 5 mg/L and if it is less than 10 mg/L it does not interfere. The total phosphate content expressed as phosphorus corresponds to the sum of concentrations of PO4(-1) and PO4(-2).
Work instructions.
• - Fill both tubes with 5 ml of pretreated sample.
• - Place one of the tubes in position A of the comparator.
• - Add 6 drops of reagent for determination of PO4(-1). Close the tube and shake.
• - Add 6 drops of reagent for determination of PO4(-2). Close the tube and shake.
• - Wait 10 minutes for color development and place in position B of the color comparator.
• - With both tubes uncovered, move them across the scale until they match.
• - Read the value in mg/L of phosphorus in the form of phosphates. If there are intermediate colors, the values can be interpolated. Apply the dilution factor.
• - After use, clean the measuring tubes very well and close them.
The color does not fit into the scale because the concentration of phosphates is very high and the reaction that generates the color occurs appreciably. A higher dilution must be used so that the color developed is smaller and within the scale. The color does not enter the scale because the reagent is in excess, so a minor dilution must be made so that the reagent reacts completely without leaving an excess.
Anionic detergents react with o-toluidine blue to give a blue complex that can be measured colorimetrically and is soluble in chloroform. The organic matter interferes with the determination, giving a violet color when in contact with the o-toluidine blue. Therefore, if one seeks to determine detergents in an effluent with organic matter, it is by giving a red color soluble in chloroform. Sodium arsenite removes up to 1 mg/L. Interference from hydrogen sulfide can be eliminated with acidification and aeration.
Work instructions.
• - Take 10 ml of the pretreated sample and place in a long test tube.
• - Add 6 drops of the reagent for determination of detergents. Cover and shake for 30 seconds.
• - Add 2.5 ml of chloroform. Cover and shake for 30 seconds. Wait 1 minute for phase separation to occur.
• - Uncover and separate the phase with sample using an emptying pipette.
• - Add buffer. Cover and shake for 30 seconds. Wait 1 minute for phase separation to occur.
• - Separate the phase with sample using an emptying pipette.
• - Add buffer solution again. Cover and shake for 30 seconds. Wait 1 minute for phase separation to occur.
• - Separate the phase with sample using an emptying pipette.
• - Place a tube with distilled water in the right compartment of the comparator and place it in the left compartment of the comparator.
• - Place in front of a light source and rotate the color disc until you find a match.
• - Read the value in ppm. Affect by the corresponding dilution.
If the color does not fit into the scale, it happens that the concentration of detergents is higher than what can be read in this method and a greater dilution must be made and affected by the dilution. If the color does not fit into the scale, the reagent is in excess and a minor dilution must be made so that the reagent reacts completely and no excess remains.
The determination is carried out using a colorimetric kit that uses the ferrous sulfate method. In an acidic environment, ferrous sulfate reduces nitrite ions to nitrous oxide. Ferrous ions combine with nitrous oxide to form a brown complex ion and the color intensity is directly proportional to the nitrite concentration in the sample.
Anionic detergents combine with o-toluidine blue, giving rise to a blue substance soluble in chloroform. The color intensity is proportional to the concentration of detergents.
The organic matter gives a violet color with o-toluidine blue, interfering with the determination. Therefore, if it is about determining detergents in sewage liquids, industrial waste or any type of liquid that contains organic matter, it is giving a red color soluble in chloroform. For this reason, sodium arsenite is added to the reagent, which removes up to 1 mg/L. Interference from hydrogen sulfide can be eliminated by acidification and aeration.
It is the most widely used organic contamination parameter. Its determination is related to the measurement of dissolved oxygen consumed by microorganisms in the biochemical oxidation process of biodegradable organic matter.
This test consists of sowing a portion of the water sample (generally diluted), where the initial oxygen concentration is measured and incubated at a certain temperature for a certain period of time.
In order to ensure the reliability of the results obtained, it is necessary to dilute the sample with a specially prepared solution so as to ensure the availability of nutrients and oxygen. The dilution water consists of double-distilled or higher quality water with an amount of oxygen preferably greater than 8mg/l and among the most common nutrients, sodium and potassium phosphates and ammonium and ferric chloride. If necessary, the dilution water should also contain an inoculum of microorganisms (in disinfected effluents, for example). If dilutions have to be made, a blank of the dilution water must also be incubated in parallel, in which the dissolved oxygen must not decrease more than 0.2 mg/l to be considered of good quality.
The standard incubation period is 5 days at 20 °C and without nitrification.
BOD5 Without Nitrification
It is the one taken as a reference for effluent control.
In waste liquids, in addition to carbonaceous organic matter, there are other compounds that consume oxygen. These compounds are mainly oxidizable nitrogen and reducing chemical compounds (ferrous ion, sulfites, sulfides). Among them, the main cause of interference is nitrogen, so an inhibitor is added (the most widely used is 2-chloro-6-(trichloro methi)pyridine).
The BOD (5 days, 20 °C) simulates the first stage of the natural biodegradation process. During this time, only about 60-70% of the most easily biodegradable substances (carbohydrates) are decomposed.
Sampling and storage
Samples for BOD analysis can degrade significantly while in storage between collection and analysis, resulting in low BOD values. If analysis will not be performed within the first two hours, samples should be stored below 4°C. The analysis is no longer representative 24 hours after taking the sample.
Measurement of Initial and Final Oxygen Concentration
The determination of oxygen can be done by iodometry, manometric methods, or with the use of oxygen-permeable membrane electrodes.
COD, like BOD, is a measure of the organic content of wastewater. The difference is that in COD not only biodegradable organic matter is oxidized, but also all organic matter that can be chemically oxidized. This is why the COD value is always higher than the BOD. It is the amount of oxygen required for the oxidation of organic matter by a strong chemical agent to carbon dioxide and water. All organic compounds with a few exceptions can be oxidized to carbon dioxide and water under acidic conditions by strong oxidants.
To achieve the oxidation of organic matter, a powerful oxidant (generally potassium dichromate, occasionally potassium permanganate) is used in a strongly acidic medium (sulfuric acid).
To facilitate oxidation, a catalyst (silver sulfate) is used and the test is carried out at high temperatures for a certain time.
Because chlorides interfere in the test (they oxidize, reducing part of the Cr), it is necessary to inhibit them. This is done by adding mercuric sulfate, which captures the chlorine, forming HgCl2.
2h, 150 °C are taken as standard analysis conditions. The advantage it has with respect to BOD5 is its shorter analysis time, which is carried out in 5 days.
There are 2 laboratory methods to analyze COD. The open reflux or macro COD method, in which a large amount of sample and reagents are used, as the added reagents are toxic and are used in large quantities, is the least used due to the impact it generates on the environment. The closed reflux or micro COD method, the most widely used, uses small concentrations of sample and reagents, which leads to reduced costs and analysis times and generates less impact on the environment. The final reading is carried out by titration or by spectrophotometer.
The procedure is:
• - Add 2.5 ml of sample, 1.5 ml of digester solution (mercuric sulfate and potassium chromate), 3.5 ml of contaminated sulfuric acid (sulfuric acid and small amounts of silver sulfate). The toxic metals are chromium (+6), Ag and Hg.
• - The tube is placed in the thermoreactor at 150 °C for 2 hours.
Choose either of the two:.
• - After digestion, the remaining unreduced potassium dichromate is titrated with ammoniacal ferrous sulfate using ferroin as an indicator. This contains 1,10-phenanthroline that forms a colored complex with ferrous ions. At the point after potassium dichromate (yellow) has been reduced to green Cr(+3), the free Fe(+2) ion complexes the ferroin indicator to form a reddish brown color.
• - After digestion, the amount of chromium that reacts or the excess (according to the working range) is measured colorimetrically at 600 nm. To do this, a calibration curve must be created with standards of known concentration and then, with the absorbance of the sample, determine its concentration.
METHOD INTERFERENCES.
Chlorides, nitrites and other inorganic ions susceptible to oxidation by dichromate. Chlorides constitute the most important interference since they introduce an error due to excess in the COD. In addition, chlorides generate turbidity in the sample when reading in the spectrophotometer. Mercuric sulfate, which is added to the sample before adding the other reagents, avoids the interference caused by chlorides.
SAMPLING.
Like BOD, the COD test is affected if it is not done immediately. It is recommended to extract the sample in glass or plastic containers. If the test cannot be performed immediately, the sample should be acidified to pH<2 with sulfuric acid and kept refrigerated at 4 °C. An analyte stability of 20 days is achieved.
The suspended solids test is carried out by filtering a determined volume of the sample with a standard porosity membrane. The porosity is 1.2 um. The membrane is placed in a capsule and placed in an oven and dried at a predetermined temperature until constant weight (P2). Previously, the same procedure was carried out with the capsule without the filter (P1). The difference in weight, together with the volume of sample that was taken, gives us the amount of TSS.
The sample should be collected in glass or plastic bottles of 1l capacity. Refrigerate samples at 4 °C. Analyze within 24 hours preferably, a maximum of 7 days after sampling.
If the suspended material gets stuck in the filter, the filtration volume must be reduced or the pore size increased.
The dissolved solids test is carried out by filtering a determined volume of the sample with a standard porosity membrane. The porosity is 1.2 um. The filtrate is collected and placed on a previously tared capsule (P1), heated in an oven until constant weight at 180 °C (P2). The difference in weight, together with the volume of sample that was taken, gives us the amount of TSS.
TSS (mg/l) = (P2 – P1) x 1000 / Sample Vol. (ml).
Where:.
• - P1 = capsule weight (mg).
• - P2 = capsule weight + dry filtrate (mg).
The sum of the suspended solids with the dissolved solids gives the total solids which are determined by the total residue due to evaporation.
The sample should be collected in glass or plastic bottles of 1l capacity. Refrigerate samples at 4 °C. Analyze within 24 hours preferably, a maximum of 7 days after sampling.
The pH or the activity of the hydrogen ion indicates, at a given temperature, whether the water is acidic or basic. The pH is defined as the logarithm of the activity of hydrogen ions.
pH = - log [H+].
[H+] = activity of hydrogen ions in mol/l.
Electrometric method.
The method consists of determining the activity of hydrogen ions by potentiometric measurements using a pH electrode. The measurement is carried out with moderate agitation to homogenize the sample. Stirring must be gentle to avoid the entry of carbon dioxide. The electrode is generally not subject to interferences such as color, turbidity, colloidal matter, oxidants, reducers or high salinity. Coatings of fatty material or particles can hinder the response of the electrode. These coatings can be removed by very gentle rubbing with paper or using detergents, followed by rinsing with distilled water. An additional treatment is to use hydrochloric acid (0.1N) and sodium hydroxide (0.1N) to remove any remaining film and then leave them immersed overnight in buffer at pH=7. In any case, the electrode is washed several times before use and after use. Care must be taken not to rest the electrode on the bottom or walls. It rests on its support if it has one to carry out the measurement. Once the measurement is finished, the electrode is stored in a solution so that its operation is always optimal. The pH is affected by temperature due to mechanical and chemical effects, so it must always be indicated at what temperature the measurement was carried out. Samples should be stored for the next day. The pH is preferably determined in-situ.
Color refers to the "true color" it has once its haze has been removed. The "apparent color" not only encompasses the color it has due to dissolved matter but also to suspended matter before filtering or centrifuging it. It is determined by spectrophotometry or visual comparison. The standardized method uses platinum-cobalt standards and the color unit (UC) is that produced by 1 mg/L of platinum in the form of chloroplatinate ion.
Turbidity interferes, which can be eliminated by filtration through a 0.45 um membrane. Another option is centrifugation, which avoids interactions with the filter materials but the results vary with the nature of the sample, the time and speed of centrifugation.
There is no preservation method. It should be analyzed without delay because it is susceptible to pH change. The color intensity increases with increasing pH. It should be between 4 and 10. If storage is required in the dark and <6 °C for a maximum of 48 hours.
The odor must be determined on site. There is no preservation method. It should be analyzed without delay and avoiding modifying the pH.
Before carrying out the test, it is prohibited to eat or smoke:
-If the sample is not at room temperature, temper it.
-Transfer a portion of no less than 50 ml to a 100-400 ml glass bottle or beaker.
-Shake the sample.
-Sniff it lightly.
The phenol standard solution is prepared and standardized to make the calibration curve. The sample is pretreated by adding coagulants, a preliminary distillation is done and then it is reacted with 4-aminoantipyrine and chloroform extraction. This is done to the sample, to a blank and for the preparation of standard solutions. Adjust to pH 4 with buffer solution, add 4-aminoantipyrine and potassium ferricyanide, extract with chloroform, read absorbance at 460 nm, perform calculations and graph the calibration curve.
• - Titulometric Method. This technique is applicable for the determination of cyanide in water and industrial effluents for concentrations greater than 1 mg/L. For the determination of free cyanide as total, for total cyanide it must be distilled from the sample prior to determination. The cyanide ion is titrated with a standard solution of silver nitrate to form the soluble Ag(CN)2 complex. After all the cyanide ion has been complexed, the excess silver ion is detected by a silver-sensitive indicator, p-dimethylamino-benzalrhodanine.
• - Colorimetric Method. To determine cyanide colorimetrically, it is done with a spectrophotometer at 580 nm. It begins with an alkaline treatment of the sample, which is subsequently distilled to transform all the cyanide in the sample into sodium cyanide. It is reacted with chloramine – T at a pH lower than 8 and converted into chlorocyanide, which subsequently forms a bluish-red solution with the addition of barbituric acid – pyridine reagent.
It can be performed by Atomic Absorption Spectrophotometry by Continuous Hydride Generation, or directly. The sample must be digested to reduce interference by organic matter and convert all metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) at 193.7nm.
Flame Atomic Absorption Spectrophotometry Method
The sample must be digested to reduce interference by organic matter and convert all metal to a free form determinable by flame Atomic Absorption Spectrophotometry (AAS) at 228.8 nm. The cadmium content is determined using a calibration curve.
• - Flame Atomic Absorption Spectrophotometry Method. Total chromium is the total content of chromium in its oxidation states III and VI. The sample must be digested to reduce interference by organic matter and convert all metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) with a flame at 357.9 nm. The chromium content is determined using a calibration curve.
• - Sampling and preservation. The sample must be collected in a 1l high-density polyethylene bottle with an airtight seal capacity. The pH should be adjusted to <2 with nitric acid. Analyze before 6 months.
• - Cold vapor atomic absorption spectrophotometry method. The sample must be digested to reduce interference by organic matter and convert all the metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) at 253.7 nm. Mercury is measured after converting it to its free metal form (Hg0) by reduction with stannous chloride in acid solution. This vapor (cold vapor) is transported to a quartz cell where it is measured. The mercury content is determined using a calibration curve.
• - Sampling and preservation. The sample must be collected in a 1l high-density polyethylene bottle with an airtight seal capacity. The pH should be adjusted to <2 with nitric acid. It is advisable to analyze within 28 days.
• - Flame Atomic Absorption Spectrophotometry Method. The sample must be digested to reduce interference by organic matter and convert all the metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) with a flame at 217 nm. The lead content is determined using a calibration curve.
• - Sampling and preservation. The sample must be collected in a high-density polyethylene bottle with a 1l capacity and an airtight seal. The pH should be <2 and is adjusted with nitric acid. It must be analyzed within 6 months.
• - Methylene blue method. This method is based on the reaction of sulfides with ferric chloride and dimethyl-p-phenylenediamine, to produce methylene blue. Ammonium phosphate is then used to eliminate the interference caused by the ferric chloride color. The procedure is applicable for concentrations between 0.1 mg/l and 20 mg/l and is read with a spectrophotometer at 664 nm.
• - Cancellation separation. The cancellation process isolates the detergent from the aqueous solution and produces a relatively pure dry residue. It is achieved by bubbling a stream of nitrogen into a column containing the diluted sample and a layer of ethyl cecate. The detergent is absorbed into the water-nitrogen interface and transported to ethyl acetate. The solvent is separated and evaporated, leaving the detergent as a residue ready for analysis.
• - Detection as Methylene Blue Active Substances (SAAM). Methylene blue active substances transfer the indicator from an aqueous solution to an immiscible organic liquid (chloroform) until equilibrium. This is due to the formation of an ion pair between the SAAM anion and the methylene blue cation.
It is then compared with a calibration curve with a spectrophotometer at 652nm.
• - Interferences. All other SAAMs, such as carboxylates, organic phenols, cyanates, nitrates, etc.
Titremetric method
For this analysis, it must first be brought to a pH close to 9.5 with an adequate buffer to avoid the hydrolysis of cyanates and organic nitrogenous compounds. The ammonia is distilled and collected in a boric acid solution. The titrant is standardized sulfuric acid and a mixed indicator of methyl red and methylene blue is used.
For phosphorus analysis, all forms present must be converted to dissolved phosphate. For this it can be oxidized with a mixture of nitric acid and sulfuric acid.
• - Ascorbic acid method. It is based on the reaction of ammonium molybdate and potassium antimonyl tartrate with phosphate in an acid medium giving a blue color.
• - Interferences. Arsenates produce a similar coloration.
• - Membrane Filtration Technique. The group of fecal coliform bacteria for the membrane filtration technique is defined as all gram-negative, aerobic and some facultative anaerobic, non-endospore-forming bacilli, which when incubated with lactose for 24 hours at 44.5 ± 0.2 °C develop blue colonies. The principle of this technique consists of filtering a measured volume of sample through a cellulose nitrate membrane and incubating it in a selective culture medium at 44.5 °C. This selective medium and incubation temperature decrease the development of non-coliform bacteria that would negatively affect the growth of fecal coliforms.
• - Interferences. Waters with great turbidity and low density of total coliforms; with organic toxins such as phenols, or when there is a very large non-coliform bacterial load.
• - Sampling and preservation. The sample must be collected in sterile, wide-mouth autoclavable glass or polypropylene bottles. The bottle should not be filled completely, there should be an air chamber to homogenize the sample before processing it. It should be stored at 4 °C until analyzed. The maximum cold storage period for the sample is 6 - 8 h.
• - Membrane Filtration Technique. The group of coliform bacteria for the membrane filtration technique are defined as all gram-negative, aerobic and some facultative anaerobic, non-endospore-forming bacilli, which when incubated with lactose for 24 h at 35 °C ± 0.5 °C, develop red colonies with a metallic green sheen. The principle of this technique consists of filtering a measured volume of the sample through a cellulose nitrate membrane and incubating it in selective culture medium at 35 °C. The incorporation of certain dyes into the culture media allows the production of acid and aldehyde due to lactose fermentation to be visualized by the formation of red colonies with a metallic green shine, typical of total coliforms.
• - Interferences. Waters with great turbidity and low density of total coliforms; with organic toxins such as phenols; or when there is a very large non-coliform bacterial load.
• - Sampling and preservation. The procedure is the same as for fecal coliforms.
Determination of coliforms by the multiple tube fermentation technique. The standard technique for the coliform group is multiple tube fermentation. It consists of placing a battery of tubes with four rows with five tubes each. Each tube contains a glass bell inside that is placed upside down. The tubes are then filled with the culture medium and sterilized in an autoclave. Once sterile, the samples are sown. In the first row, the undiluted sample is placed in each tube. In the next row, a 1:10 dilution of the first row is made. In the third row, a 1:10 dilution of the second row is made and in the last row, another 1:10 dilution of the third row. Subsequently, it is taken to an incubator oven, where it is maintained at a temperature of 37 °C for 24 hours.
After cultivation, it is observed how many of the tubes per row test positive, from the lowest to the highest dilution. A test is positive when an air bubble is observed in the glass bell, corresponding to the consumption of the bacteria from the culture medium and production of carbon dioxide, and when turbidity is observed in the solution.
The results are reported as the most probable number of bacteria (nmp), a number based on probability formulas, where the calculation of the average density of coliforms in the sample is estimated.
When adding silver ions to a solution with a pH between 7 and 10 (neutral or slightly alkaline pH) that contains chloride and chromate ions, silver chromate begins to precipitate when the precipitation of silver chloride (white precipitate) is almost complete, that is, when the concentration of chloride ions is negligible from an analytical point of view because the silver chloride disappears from the solution as it precipitates. This allows the appearance of the red precipitate of silver chromate to be considered as an indication of the end point of the reaction between chloride ions and silver.
2Ag(+)+CrO4(-2)-->AgCrO4(s).
It is one of the ions that contribute to the salinity of waters. It is mainly due to the dissolution of the gypsum, its concentration depending on the drained land. It is dissolved due to its stability and resistance to reduction. The presence of other salts increases its solubility. It tends to form salts with dissolved heavy metals, and because the solubility product is very low, it contributes to reducing its toxicity. An increase in sulfates present in the medium is an indicator of an upcoming spill. It is called the sulfate turbidimetric method. The sulfates react with barium to give barium sulfate, which is a white precipitate. The latter is determined photometrically. To do this, a calibration curve must be created with barium sulfate. The barium is supplied by solid barium chloride and is carried out in an acidic medium provided by hydrochloric acid.
What are the main contaminants in wastewater from the food industry? What treatment would you propose to purify them?
The main components are: solids, fats and oils, organic matter and detergents. Initially, to remove the coarsest solids, use a filter, then to remove the fats and oils and part of the settleable solids use an interceptor, later to remove the rest of the settleable solids after 10 minutes use a sand trap, then to remove the remaining settleable solids use a settler, subsequently to eliminate the remaining organic matter, the remaining suspended solids and the coloration carry out a coagulation-flocculation-decantation treatment, finally perform an adsorption with activated carbon to eliminate detergents, particles that cause color and odor, organic matter that has not been separated in the previous process.
What are the major components contained in sewage water and what parameters would you use to measure each of them?
The main contaminants in water are: high pH values, high content of suspended solids, high content of settleable solids, high content of organic matter, coloration, high content of dissolved solids, fats and oils, hardness. To measure pH I would use the potentiometric method, to measure suspended solids I would filter the sample and what remains in the filter is dried and weighed, to measure detergents I would use the ortho-toluidine blue method, settleable solids using an Imhoff cone, organic matter is measured through the oxygen consumed, fats and oils through substances soluble in ethyl ether, hardness through alkalinity, solids dissolved through conductivity, coloration by comparison with standards.
• - Wikilibros hosts a book or manual on Wastewater Engineering.
• - Energy from wastewater.
The next stage is decantation and the flocs formed in the previous stage are separated, these form sludge that is collected using Archimedean screws to be taken to the condensing beach. The clarified effluent is removed above the settler. The chambers can be rectangular or circular, this depends on the type of sludge and the retention time. The retention time is defined as the ratio between the volume of the settler and the inlet flow. It is usually 2 hours.
The rate at which water corrodes pipes depends on pH, temperature, concentration of certain mineral substances, velocity, and dissolved oxygen. Among the parallel treatments, dissolved gases such as carbon dioxide, hydrogen sulfide and oxygen can be eliminated by boiling. Phosphates are dosed that form a protective layer of material, caustic soda that increases the pH and hydrazine as a reducer, which eliminates residual oxygen and releases nitrogen as a residue.
• - Process design and plant operation: although there is widespread and efficient aerobic treatment for effluents that contain toxic compounds (phenols, ammonia and cyanides), it has recently been shown that it can also be treated with anaerobic filter reactors such as activated carbon ones. The modern trend is to use anaerobic and aerobic reactors because anaerobic communities are advantageous at high temperatures and high concentrations of substrates, especially insoluble ones, and aerobic communities for low levels of substrates, different chemicals and variable environmental conditions.
This stage can be carried out through the following aerobic processes:.
• - Suspended culture: the residual load is subjected to aeration for a period of time and as a result the organic load is reduced and a flocculent sludge is formed. This sludge is made up of a heterogeneous population of microorganisms. Through the recycling of biological sludge it has been possible to make it continuous. The initial feed is combined with the biological sludge and enters the reactor. The design of the aerobic tank is made based on the soluble BOD and the clarifier is based on the insoluble BOD. The system consists of a reactor with aeration, a circular settler, a sludge dedenser, a sludge drying beach, a sludge movement device, and a contact chamber for disinfection. Initially, a pretreatment and primary treatment are carried out, then it is entered into the aerated reactor using mechanical aerators where the organic matter is degraded by microorganisms that are in the sludge. The effluent then passes to the settler where the sludge below and the clear effluent above are separated. The sludge passes to the dedenser and a portion is returned to the reactor using a sludge movement device such as an Archimedean screw. The clear effluent goes to the disinfection chamber. If the liquid is still not clear, coagulation-flocculation-filtration is carried out and it is disinfected again. In general, conventional activated mud does not have aeration equipment and is designed with an average cell retention time between 3 and 15 days. This average cellular retention value corresponds to a hydraulic retention time between 4 and 8 hours for domestic sewage liquid if the concentration of suspended solids is around 2000 mg/L. Recirculation ranges between 10 and 30% of the feed flow. With aeration, control of the operation and the volume of sludge generated is reduced. It is characterized by having a prolonged contact between the liquid and the mass of the microorganisms, so that there is oxidation in the endogenous phase and has a high efficiency, until the sludge present can be filtered and settled, without the presence of odor. The sequential batch biological reactor (SBR) carries out the reaction, sedimentation and decantation in the same place. The effluent enters to react with the remaining biomass from the previous cycle, sedimentation of the organic matter occurs, then it is allowed to settle, finally it is decanted to disinfect and part of the biomass is recirculated to the reactor and another part is concentrated in the adenser to keep the concentration of microorganisms under control. They usually have two tanks in parallel so that when one is in the emptying stage, the other is in the filling stage. Aerobic oxidation ditches have longer oxidation periods and extended aeration. In the design of activated sludge, the aim is to determine the size of the biological reactor and the retention time of microorganisms in it. The operation requires that the concentration of microorganisms in the reactor be constant and to develop a design equation, two mass balances are first established and analyzed: solids (biomass) and dissolved organic matter (substrate). This analysis, when combined with the understanding of microbial growth, will allow the volume of the aeration basin to be determined.
• - Fixed film: It is a type of fixed film biological reactor with packed column configuration. The trickling filter is a static biological silt filler over which the liquid percolates. Normally the water is distributed over the filled bed evenly with a rotary flow distributor. The residual water percolates downwards through the fill and is collected at the bottom. If the bed is made of stone, the height is limited to 2 meters and if the bed is made with plastic fillers of lower weight and size, the height can be made higher, which allows the contact time to be increased. A biological film of microorganisms is formed that grows as the organic matter degrades through the percolation of the liquid without flooding the bed. The low load biological bed is the one that does not have recirculation and only the upper part presents considerable biological growth. This occurs because since the quantities are low, the reaction only occurs appreciably at the top. Algae form to break down ammonia into nitrite and then nitrate. High-load percolating beds allow higher organic loads to be treated (the recirculation current is added) and recirculation allows a larger volume of biomass to be dragged, which prevents clogging or flooding and the production of odors and flies. Another modality is rotating biological discs that consist of a series of discs mounted on an axis in parallel. The assembly is placed inside a tank with the axis located slightly above the liquid surface so that it is semi-submerged. The biological film is formed on the rotating wheel, it retains the microorganisms and aerates them when it is submerged thanks to the aeration of the tank and when it emerges due to being in contact with a film of air.
A residual effluent containing 300 mg/L of biodegradable organic matter is processed in a 200 m3/day aerobic treatment plant, achieving a 40% conversion into CO2 and H2O. Calculate the kilos of O2 required daily in the purification process.
If 50 kg of sugar is discharged into a water dam whose dissolved oxygen concentration is 10 mg/L at 25 °C. How many liters of this water will be contaminated to the point of eliminating all dissolved oxygen through biodegradation?
C12H22O11+12O2-->12CO2+11H2O.
342kg-12.32kg.
50kg-x=56.14kg.
56.14kg.1000000mg/kg.1L/10mg=5614035.088L.
For the carbon cycle, the products of anaerobic fermentation are gases such as methane and carbon dioxide. The stages are: (1) acid fermentation (2) methanic fermentation. In acid fermentation, complex organic compounds (proteins, fats and carbohydrates) are first hydrolyzed to produce smaller molecular units, which in turn are subjected to biooxidation, becoming mainly short chain acids such as butyl, propionic, acetic. A heterogeneous population of facultative and anaerobic bacteria is responsible for these hydrolysis and oxidation reactions.
In the methanic fermentation stage, methanogenic microorganisms that are strictly anaerobic convert longer chain acids to methane, carbon dioxide, and short chain acids. Acid molecules are repeatedly broken down to give acetic acid which in turn gives carbon dioxide and methane.
If there are aerobic conditions, carbon dioxide and water are formed from the carbon compounds.
For the nitrogen cycle, organic nitrogen is gradually converted to ammonia, and if there are aerobic conditions, it is converted to nitrite and this to nitrates. Non-ionized ammonia is toxic, so there must be aerobic conditions, so that ammonia in solution does not generate non-ionic ammonia because it is in a reversible reaction, and is oxidized to nitrite and then forms nitrate. The amount of N must be controlled so that it is not in excess because eutrophication of the liquid occurs and eventually putrefaction, and the generation of toxic compounds occurs. Eutrophication is characterized by the generation of water with an unpleasant odor and a high consumption of dissolved oxygen by microorganisms because it can no longer be produced photosynthetically due to the absence of sunlight.
In the presence of oxygen, the reactions that occur are:.
NH4(+1)+3/2O2--Nitrosomonas-->NO2(-1)+2H(+1)+H2O.
NO2(-1)+1/2O2--Nitrobacter-->NO3(-1).
For the sulfur cycle, if the sulfur is under anaerobic conditions, hydrogen sulfide is produced, which has a bad smell, and if the sulfur is under aerobic conditions, sulfites are formed that are then oxidized to sulfates.
The main difference is that in the aerobic case it requires provision to the system and in the anaerobic case it does not. Biogas (methane and carbon dioxide) is generated that can be reused energetically, for example, to heat the effluent at the entrance to the process. Another difference is that the anaerobic does not generate the large amount of sludge that the aerobic does and requires treatment (densation and drying). The anaerobic process admits higher organic loads.
The most used equipment is:
• - Anaerobic digester: the stream to be treated is introduced through the bottom and comes into contact with a mantle of sludge that contains particles and granules that are made up of microorganisms. As a result of the treatment, carbon dioxide and methane are generated, these gases are collected at the top and the clear effluent is collected above thanks to screens that stop the biomass that is carried with the effluent. It is in the absence of oxygen.
• - Anaerobic filter: it is a system in which immobilization occurs on a fixed support medium. The fluid circulates through the interstices of the bed formed by biomass and support material, where the degradation reactions occur. Under favorable conditions, the greater the contact surface per unit volume, the greater the treatment capacity. The favorable conditions are that the bed is not flooded nor are there channeling areas through which the fluid does not circulate. It is done in the absence of oxygen. The mechanism is similar to the low-load trickling bed.
• - Imhoff Tank: is a primary treatment device. The sewage water enters through chamber a (sedimentation chamber) and descends through chamber f where anaerobic reactions occur. The sludge is deposited at the bottom and left for 30 days, or until it is well digested so as not to overload the sedimentation chamber. It is removed through the inclined tube b-c and taken to the sludge drying pool. The gases from the digestion are removed through the gas suction cups and tend to move upwards on the outside of the sedimentation chamber without disturbing the settling action because the settled solids obstruct the passage of the gas. The clarified water leaves through d towards the next stage. Due to its digestion behavior, it must have the capacity for both primary and secondary sludge.
They are the simplest method of water treatment that exists. They are shallow excavations surrounded by earthen slopes. It has a rectangular or square shape. The objectives of the gaps are:
• - Improve the quality of the effluent to give it other uses such as irrigation water in agriculture.
• - Eliminate pathogenic microorganisms.
• - Remove organic matter.
The elimination of organic matter is carried out by different processes in the stabilization lagoons. In an aerobic lagoon, algae are produced photosynthetically and organic matter is decomposed by oxidation with aerobic bacteria. In an anaerobic lagoon, organic matter is decomposed by anaerobic bacteria due to the high organic loads they treat.
Anaerobic lagoons have a gray-black color, high surface area, high depths, low BOD removal, shorter retention times and admit high organic loads. The high organic load and short retention periods suppress the photosynthetic activity of the algae, so there is an absence of oxygen at all levels. Anaerobic bacteria are responsible for the stabilization process of organic matter. The advantage of anaerobic lagoons is the production of methane, which is a gas and biofuel that can be used to heat the inlet effluent or for energy uses, a low rate of cellular synthesis and therefore a lower production of sludge, the sludge produced is reasonably stable and can be dried and disposed of by conventional methods, it admits high organic loads, has low nutritional requirements and the disadvantages are the production of bad odors due to hydrogen sulfide, amides and and fatty acids, formation of toxic products such as hydrogen sulfide, the medium is corrosive, requires a fairly restricted pH range because it requires high concentrations of alkalinity, is sensitive to oxygen contamination and to obtain high degrees of treatment, high temperatures are required.
Facultative lagoons have 3 strata: aerobic zone that is on the surface, anaerobic zone that is at the bottom and facultative zone that is in an intermediate position. The aerobic zone receives sunlight and photosynthesis occurs by algae, which produce oxygen that bacteria consume to degrade organic matter. The products of aerobic degradation are carbon dioxide and water necessary for photosynthesis. In the intermediate zone, the facultative zone, there are facultative anaerobic and aerobic bacteria that degrade organic matter as it settles to the bottom. At the bottom, there are anaerobic bacteria that degrade the organic matter that settles at the bottom. The products of anaerobic degradation are methane and carbon dioxide. Carbon dioxide is used in photosynthesis. It presents retention times, depth, land spaces, BOD removal and color intermediate between aerobic and anaerobic lagoons.
Aerobic lagoons present aerobic organisms and photosynthetic algae that produce dissolved oxygen that bacteria consume for the degradation of organic matter. It has longer retention times, little land area, shallow depth, high percentage of BOD removal and clearer waters than the other lagoons. The advantages of aerobic lagoons are the absence of high temperatures, the mineralization of all biodegradable compounds and the disadvantages are a high rate of cellular synthesis, consequently high sludge production, a large proportion of cells in the sludge that makes its digestion necessary for subsequent drying and storage.
The order of exposure of the lagoons is anaerobic, facultative and aerobic.
The advantages of stabilization ponds are:
• - High stabilization of organic matter.
• - Has higher construction costs but lower maintenance costs.
• - Flexibility in the treatment of tips and flow.
• - Removal of pathogens because the largest microorganisms eat them or settle them.
• - Energy consumption is zero.
• - It can be used in the treatment of water with high BOD content.
• - Presents potentially valorizable biomasses after treatment.
The disadvantages of the stabilization lagoon are:
• - Presence of suspended material if there is no efficient bioflocculation.
• - They occupy large areas of land.
• - Considerable water losses due to evaporation in summer.
Aerated lagoons are ponds that have surface aerators that replace algae that produce oxygen photosynthetically. Aerators can be diffused air units. They have higher operating costs, higher construction costs, reduce the necessary surface area compared to an aerobic lagoon but generate a greater amount of sludge. The fundamental difference with the activated sludge system is that there is no sludge recycling.
Advantages of the aerobic system.
• - There is no formation of bad odors.
• - There is no formation of toxic compounds such as hydrogen sulfide.
• - Longer residence times.
• - Higher temperatures are not required.
Advantages of the anaerobic system.
• - Methane is generated, which is a biogas and is a biofuel; it can be used to heat the effluent at the inlet or for other energy purposes.
• - A lower volume of sludge is generated due to the low rate of cellular synthesis, which reduces costs in sludge treatment and evacuation.
• - It is possible to operate at higher loads.
• - The sludge is reasonably stable so it does not require digestion to dry and dispose.
• - Low nutritional requirements.
• - Precipitation: consists of the elimination of suspended solids by adding coagulants such as aluminum sulfate, ferric sulfate, ferric chloride and adjuvants such as polyelectrolytes. A contact chamber and a settler are used. Although in some systems the settler is not necessary since it is decanted in the same space where it is agitated by turning off the agitator.
• - Chlorination: disinfection occurs so bacteria and algae are destroyed, reduction of BOD because organic compounds are oxidized, oxidation of cyanides to harmless products, oxidation of metal ions, oxidation of compounds that generate odor and color.
• - Ozonation"): reacts easily with unsaturated products, they are easily attackable; they break the aromatic rings and the partial oxidation of the rings contributes to the biological treatment; foam formation is reduced. Ozone when oxidized forms oxygen, while chlorine forms a contaminant.
• - Reverse osmosis. It consists of the elimination of contaminants through membranes that are subjected to pressure. The membrane is semipermeable so it allows the solvent to pass through but not the residues in it. It is effective when the effluent carries soluble but not insoluble residues (suspended solids) because they clog the membranes. It is brought into contact at a pressure higher than the osmotic pressure of the solution. The Van Hoff Equation is not applicable for highly concentrated solutions because the osmotic pressure is not correctly predicted. Synthetic resins are made from cellulose acetate and natural resins are made from animal tissues. The tubular configuration consists of an inner tube that has a semipermeable membrane capable of withstanding elevated pressures greater than the osmotic pressure of the solution. The fluid passes through this tube and moves towards the outer tube, causing separation.
• - Electrodialysis. They are used to separate nitrogen and phosphorus. The basic component of the system is a cell made up of membranes. Membranes can be cationic or anionic. Membranes are specific to a class of ions. Cationic membranes have a fixed negative charge and allow the passage of cations, and anionic membranes have a fixed positive charge and allow the passage of anions. A potential difference is established at the ends of the cell (anode and cathode) to allow the passage of ions. The membranes that allow the passage of cations are placed near the anode and those that allow the passage of cations near the anode. The treated water is removed through the dilution compartments and the residual water is removed through the concentration compartments. Fouling produces an increase in resistance. With a higher resistance, maintaining the voltage, there is a decrease in the current and therefore in the demineralizing capacity. Fouling is produced by large organic ions, colloidal matter, suspended matter that must be previously eliminated. Fouling or clogging of the membrane is the main problem and the following is done: 1) water pretreatment by adsorption with active carbon, filtration with microfilters, coagulation-flocculation 2) operation stops for cleaning 3) current reversal tends to minimize fouling.
• - Stripping: is a physical separation process in which the components of the liquid are separated by putting them in contact with a vapor.
Anaerobic digestion consists of keeping sludge in a closed container so that it achieves a more liquid appearance and generates gases. Digesters are either single stage or two stage. The raw sludge is introduced into the area where there is active digestion and gas is being produced. As the gas rises, it drags sludge particles and other materials (fats, oils, etc.) forming a supernatant that is separated from the digester. The digested sludge is removed from the bottom of the tank. The digestion process is favored by high temperature (typically between 24°C and 40°C), which requires that the digesting sludge be heated by steam coils within the reactor, or by an external sludge heater. The gas is collected at the top of the digester, and is normally used as fuel due to its high methane content. The deposition time is long, on the order of 30-60 days, even for heated digesters. The reason for this long time is that only a small part of the volume is used, so it is not recommended for plants with sludge digestion with a capacity greater than 4000 m3/d. The two-stage arrangement allows for better utilization of the volumetric capacity. The first stage is used only for digestion. The second serves as a solid-liquid separator and allows gas collection. The retention time of the first stage is 10-15 days. Only the first stage is heated. The mixing is done in the first stage by mechanical means or by gas recirculation. There are savings in investment costs, due to the absence of aeration equipment, as well as in energy consumption costs. The operation of anaerobic digesters is more difficult, the process being more sensitive to shock loads. Also the supernatant liquid in the case of anaerobes is richer in nutrients and organic compounds. Considering that this supernatant is recycled to the main stream, this could be a disadvantage in anaerobic processes as it is a byproduct.
It is the normal first step in the sludge evacuation process. It can be achieved: 1) by gravity 2) by flotation with dissolved air. The advantages of thickening are: 1) it improves the operation of the digester and reduces investments if subsequent digestion is used, 2) it reduces the volume of sludge evacuation to the ground or to the sea, 3) it improves the economy of dehydration systems (centrifuges, vacuum filters, pressure filters, etc.). Gravity thickeners are circular section tanks in which a rotating scraping mechanism similar to that of clarifiers is installed. Flotation thickeners are used for any type of sludge, but it is recommended for those with a gelatinous structure such as activated sludge.
The quality parameters are design quality, it is the degree to which a product or service is reflected in its design, conformity quality, it is the degree to which a product or service is reproduced with respect to its design, quality of use, the product is easy to use, safe, reliable.
Quality can be internal or external. Internal quality is that planned and achieved by the laboratory and external quality belongs to the client, is that required or eventually perceived.
Quality is evaluated through results, chemical measurement processes, methodological analytical tools such as calibration and instruments such as materials, work and their organization.
External quality is the fulfillment of the client's requirements for a problem they have and internal quality is how the analyst solves it through the analytical process and analytical properties. An analytical problem has tangible factors such as the object, sample, measurand and analyte and has intangible factors such as planning, design, evaluation and correction.
A quality system set of planned activities to satisfy the customer throughout the entity. For the implementation of a quality system, the ISO 25 guide (IRAM 301) is applicable, currently replaced by ISO 17025, it presents the general requirements that a laboratory must meet to be recognized as competent in the execution of calibration or tests.
The objectives of the quality system are: to raise the overall quality of laboratory performance, implement medium and long-term corrective measures, identify good analytical methods, ensure sample integrity, and provide permanent records of instrument performance.
The job of a laboratory technician is to set tasks, perform tasks, transmit knowledge and obtain recognition. It usually uses analytical tools such as a cause-effect diagram where, based on a problem, main causes and secondary causes are defined and which one to attack first is defined. Flow charts are also used to define what operations and in what order they are performed to solve a problem. They are drawn using standard symbols.
Laboratory accreditation is the formal recognition by an independent, scientifically based organization that a laboratory is competent to perform specific tests.
One of the most frequent problems in the laboratory is the correct follow-up of standardized techniques. This type of error is correctable and makes the product unreproducible over time.
The basic procedures for maintaining quality in the laboratory are simple to carry out as long as you are careful in your work and pay attention to the tasks you are performing. There are tools that facilitate the analyst's work within the laboratory:
Field form: tool that allows you to quickly and concisely visualize the steps to be carried out of the selected technique. It also allows you to write down important data and observations.
Data sheet: it is a tool that allows the annotation of the data collected from a technique in a simple and orderly way. Furthermore, depending on how it is designed, it allows the addition of other data such as materials and reagents used, instruments, observations and diagram.
Schemes: simple graphic representations that allow quick and easy identification of the procedure to follow in the technique.
Block diagram: similar to the schematic, it allows quick identification of the procedure to follow in the technique. It does not include as much information as an outline but is simpler to construct and read.
In addition to this, there are procedures that ensure the quality and reproducibility of the results obtained in the laboratory.
• - Respect safety and hygiene regulations.
• - Use calibrated materials that ensure the accuracy of the measurements.
• - Use calibrated instruments and always use them according to their instructions.
• - Follow the techniques to the letter, do not make any changes.
• - Always use standardized procedures.
• - Use quality reagents that are properly preserved.
Manual: there is an operator who, aided by a device or instrument, can make the measurements he needs.
Automatic: there is no operator. The result is given by the team, it would be ideal.
The advantages of automatic control are: time savings, labor savings, maintenance savings, they have visual and audible alarms, and high precision. The disadvantage is the high cost.
The treated effluent must comply with the Quality Standards for Liquid Dumping, Law No. 11220, Annex B. Based on the destination of the water, certain quality or values in the physical-chemical parameters will be required. Drinking water as a beverage has values established by the WHO and the CAA. Water for different uses has values established by the La Plata Basin.
The objectives of a quality system are: to raise the overall quality of laboratory performance, identify good analytical methods, provide permanent records of instrument performance, ensure sample integrity, and implement medium- and long-term corrective measures.
• - Design quality: it is the degree to which a product or service is reflected in its design.
• - Quality of conformity: it is the degree of fidelity with which a product or service is reproduced with respect to its design.
• - Quality of use: the product must be easy to use, safe and reliable.
The sample is a representative portion that retains the same concentrations of the components of the material under study; it must be a reliable sample.
The objective of taking a sample is to obtain a portion of material whose volume is small enough so that it can be easily transported and manipulated in the laboratory without ceasing to accurately represent the material from which it comes. It must be representative and easily transported.
The requirements are: representative, completely characterizes the effluent from which it comes; size, it should not be large for transportation reasons or small so that it is not enough to make the samples; stability, which does not have important changes from when it was collected until it was analyzed; purpose or objective, what I want to determine.
Sampling is carried out at predetermined points and serves to evaluate the efficiency of the physical-chemical treatment. For example, in a settler, the settleable solids are measured at the inlet and outlet of the settler.
Obtaining a sample that meets the requirements of the collection and handling program implies that it must not deteriorate or become contaminated before reaching the laboratory. The considerations are:
• - Alteration of the sample must be avoided (it should not have external agents that modify it).
• - Conservation of the sample (no loss).
• - Environmental conditions (if it is solid it dissolves with rain).
• - Physical and/or chemical changes (no change in physical state or a chemical reaction).
• - Rules (if you do not comply with them, the result may be invalidated).
• - Avoid abnormal situations (stops or starts, unless the data needs to be known at that moment) and.
• - Hygiene and safety precautions.
The types of samples related to site and time are:.
• - Probing sample, it is done only once because the source is fairly constant in composition over a considerable period or over substantial distances in all directions so it can be said that the sample will represent a longer period of time, a larger volume or both.
• - Compensated sample, refers to a mixture of simple samples collected at the same point at different times. They are the most useful for determining the average concentrations to use. They are applied in industrial sewage effluents because they have very variable characteristics over time.
• - Integrated sample is the analysis of mixtures of individual samples, collected at different points at the same time or with the smallest temporal separation possible (less used, I take a spatial average sample). If there is little time, fewer samples are taken to obtain the average.
• - Manual: it is assumed that no equipment is used, but this procedure may result in excessive costs for routine or large-scale sampling programs. The costs per man hour are due to a greater frequency of errors that are made.
• - Automatic: through automatic taking, human errors can be eliminated, labor costs are reduced and frequency is increased.
Due to the variation in effluent characteristics and random variations in analytical processes, a single sample is insufficient to ensure a good result. Therefore, the number of samples is given by the Student Formula and is a function of Student's t for a given confidence level, global standard deviation and acceptable confidence level.
• - Liquids, there are tables that recommend values, it is preferable that there be a sample and that there is no shortage.
• - Solids, by quartering: the solid sample is mixed well, divided into 4 parts, 1 and 3 are mixed, 2 and 4 are removed. Mixed again and the process is repeated. It ends once there is enough sample. The sample is dissolved for analysis.
Complementary actions consist of operations to maintain the integrity of the sample from its issuance to its analysis. Suggestions for taking samples are to use a clean, wide-mouth, 2-liter glass or plastic container with an airtight seal and screw-on lid to avoid losses due to spillage. Hermetic closure (sealing) to avoid contamination or loss, to detect any falsification of the sample that may be made before analysis. You must also take care that the container is not broken or open. This must be rinsed with the sample liquid and then filled with it, avoiding the presence of an air chamber, it must be refrigerated and kept in the dark until the test is carried out. Supplementary data are all the information pertinent to a field study or sampling that will be recorded in a book: observations of color, odor, temperature, dissolved oxygen, pH, sample status. It is then arranged in the form of tables for better compression. The effluent must be flowing and must not be stagnant. To obtain representative samples, possible floating materials accumulated in corners where the water is partially stagnant must be left aside. Due to the high complexity of the matrices and their rapid alteration in this type of samples, a quick transfer to the laboratory is necessary, as well as speed in the analysis. It is preferable that the sampling site be constantly moving which ensures a constant sample. The sample labeling must contain the type of sample, location of extraction, name of the extractor, type of analysis, destination (if not analyzed on site), date, time and observations (if necessary) and the sample number. Precautionary measures should be taken during the sampling operation, such as the use of gloves, nose and eye protection against possible splashes, and not smoking or eating food simultaneously while taking the sample. Use ice cream freezers to transport the samples if this is not possible. There are chemical sample preservation techniques where chemical substances are incorporated, which are placed first and the samples are placed on top of them so that no part is left without coming into contact.
The packaging material is usually plastic or glass, and depending on the case, one or the other may be preferable. The containers are with or without color, transparent and opaque. If it is plastic it is PVC, PET or PTFE. If it is glass, it is less polluting and can be sterilized and reused.
For sample conservation, the objective is to avoid physical, chemical and biological changes in the original sample from extraction to analysis. The changes that occur are: hydrolysis, absorption, desorption, oxidation-reduction, precipitation, microbial action. Regarding the parameters that can be analyzed in situ: some analyzes can be affected more easily than others by irreversible changes. Some cations are lost by adsorption on the walls of glass containers or by ion exchange with them. The temperature changes rapidly; pH can change significantly in a matter of minutes; dissolved gases can be lost. Therefore, the temperature, pH and dissolved gases must be determined at the time of sampling (in situ). In general, the shorter the time between sample collection and analysis, the more reliable the result will be.
Conservation methods are physical or chemical. Chemical methods consist of adding acid, chlorine inhibitor (sodium thiosulfate or ascorbic acid), oxidant or reducer. The physical methods consist of refrigeration at 4 °C (manage T in the case of microbiological analysis). This is achieved with ice creams with ice when they are just extracted, avoiding freezing. The conservations are maintained until the moment of use. To minimize possible volatilization or biodegradation between the time of collection and the time of analysis, the sample should be kept at the lowest possible temperature without freezing (4 °C) and stored in the dark. Chemical preservatives will only be used when it has been demonstrated that they will not spoil the analysis. It is advisable to use multiple sample portions when added chemicals influence other determinations. If they are used, they must be added to the container before placing the sample, so that all parts of it come into contact with the preservative at the time they are collected. There is no method of preservation that is completely satisfactory. Conservation methods are relatively limited and are designed, in general, to delay the action of microorganisms, delay the hydrolysis of chemical compounds and complexes, reduce the volatility of the components, stop the adsorption of cations on the walls or the ion exchange with them. Preservation methods are limited to pH control, addition of chemicals, use of amber or opaque containers. There are tables that list preservation methods, maximum preservation time, minimum sample size and packaging material depending on the determination.
• - It is advisable that if you have long hair, keep it tied up, not use scarves, pendants or elements that could cause risks during the practice.
• - Keep a notebook where you write down calculations, descriptions of the reagents, and observations.
• - Keep a spreadsheet where the weekly results of the analytical techniques are recorded.
• - Be punctual and not be able to leave the laboratory without authorization from the teacher.
• - Know the contents inherent to the work to be developed.
• - Assist with items for personal use: mesh cloth, hygiene accessories.
• - Before starting the practical work, check that the necessary elements and materials are in correct condition (clean, not broken, etc.).
• - Once the practical is finished, collaborate with the general order and cleanliness of the laboratory.
• - Present a written report consisting of data, observations and conclusions.
• - The container must be airtight, have a wide mouth and be clean.
• - The container must be made of glass or plastic and have a capacity of 2 liters.
• - It must be rinsed with the liquid to be collected, without leaving an air chamber.
• - It should be stored refrigerated at 4 °C and in the dark.
• - A funnel and a bucket will be used as accessories for transferring.
• - Each container must be labeled with a number and must be accompanied by a data sheet containing the date, time, extraction site, and person responsible for the extraction.
• - Data obtained in situ must be recorded on parameters such as odor, color, appearance and, if possible, measurements of dissolved oxygen, pH and temperature. This is recorded in the data sheet.
• - Precautionary measures must be taken such as the use of masks, overalls, glasses, long pants, closed shoes and gloves to avoid contact with the eyes, skin or mouth due to splashes that may occur.
• - You cannot drink, smoke or eat during sampling, this incorporates external agents into the sample.
• - The sampling site must not be sealed but must have constant fluid agitation.
The data sheet must record the macroscopic observations, organoleptic properties and physical determinations that can be carried out in situ. Among the macroscopic observations are the number of phases contained in the sample, existence of macro organisms, existence of large solids, turbidity and foam. Among the physical determinations are temperature, pH, conductivity, turbidity and dissolved oxygen. Within the organoleptic properties, color, smell.
Settleable solids are those that settle in an Imhoff cone for 2 hours from one liter of residual liquid. Fixed settleable solids are those that do not volatilize at 600 °C for 15 minutes and volatile settleable solids are those that volatilize under these conditions. Total settleable solids can be measured in volume (ml/L) and weight (mg/L) but fixed and volatile settleable solids only in weight (mg/L).
Settleable solids in volume.
• - Add 1 liter of residual liquid to an Imhoff cone. Do it through the center, not along the walls because the solid will settle.
• - Take a reading after 10 minutes (settled solids after 10 minutes).
• - Let it decant for 2 hours. Gently stir the sediment to fill any empty spaces.
• - Take a reading (settled solids after two hours).
Settleable solids by weight.
• - Siphon the supernatant liquid and transfer the sediment to a capsule previously weighed to the milligram.
• - Evaporate in a bain-marie, avoiding boiling and splashing until all the surface liquid is removed.
• - Dry in an oven at 103-105 °C for 1 hour.
• - Cool in a desiccator.
• - Weigh to the milligram (P2).
Fixed settleable solids.
• - Calcine the sample at 600 °C for 15 minutes.
• - Cool in a desiccator and weigh to the milligram (P3).
Total settleable solids: P2-P1
Fixed settleable solids: P3-P1
Volatile settleable solids: P2-P3.
Total solids are the weight of non-volatile suspended and dissolved matter at 105 °C of one liter of residual liquid. The fixed solids are the non-volatile part of the residue at 600 °C for 15 minutes and the volatile solids are those that volatilize under these conditions. Total solids, volatile solids and fixed solids are expressed in mg/L. Fixed solids correspond to inorganic matter and volatile solids to organic matter.
Total evaporation residue
1.Shake the sample thoroughly and transfer 25-50 ml to a test tube. Then pour the contents of the test tube into a previously tared porcelain capsule (P1).
2.Use distilled water to wash the test tube and place the contents in the capsule.
3.Evaporate in a bain-marie, avoiding boiling and splashing.
Dry at 150°C for one hour.
Cool in a desiccator.
Weigh to the milligram (P2).
Fixed solids
Calcine the residue obtained at 600 °C for 15 minutes.
Cool in a desiccator and weigh to the milligram (P3).
Total solids: (P2-P1)*1000/V
Volatile solids: (P2-P3)*1000/V
Fixed solids: (P3-P1)*1000/V.
The result is conditioned by the combinations of temperature and time. Waters with calcium and magnesium (hard water) are hygroscopic. Water re-enters the waste when hydrophilic crusts form even after drying; this is characteristic of excessive waste. Samples with fats and oils are difficult to dry. At the temperature at which it is dried, separation of volatile compounds occurs, which generates negative errors in the counting of volatiles. At the calcination temperature, some separations of inorganic compounds occur, so it is not an exact method. There are other methods such as total organic carbon.
The oxygen consumed is the oxygen of the potassium permanganate that a water consumes when it reacts with this reagent under certain conditions. The conditions are heating time, heating temperature and concentration of the reagents, and the technique must be rigorously adjusted to them. The purpose of the test is to measure the cc of organic matter, so if the sample contains permanganate-reducing minerals, the corresponding correction must be made. It provides an index of the degree of contamination of the sample, its concentration or load, which is why it is very useful when the BOD is not performed or even as complementary data to the BOD.
The procedure is:
• - Add 100 ml of sample or a dilution of the sample (the maximum dilution allowed is 1/500) to a 250 ml Erlenmeyer flask. Add 10 ml of sulfuric acid (1+3) and 10 ml of 0.0125N potassium permanganate. The sample and sulfuric acid are added with a pipette and potassium permanganate with a burette.
• - Heat to a boil in a pot for 30 minutes. Be careful not to spill the contents of the Erlenmeyer flask into the pot and that the water covers the surface of the liquid contained in the erlenmeyer.
• - After 30 minutes, a purplish color should remain. If the sample is not colored, then perform a higher dilution. If it does not color even with the maximum dilution, stop making dilutions and calculate the oxygen consumed with the maximum volume of permanganate and expressing "greater than" the value obtained. The permanganate oxidizes the organic matter, leaving it in excess.
• - Decolorize with 10 ml of 0.0125N oxalic acid (the oxalic acid remains in excess and the excess amount is equal to the original amount of organic matter that the sample had) and add potassium permanganate drop by drop until a weak pink color is present but persistent for 3 minutes (the excess oxalic acid is neutralized with potassium permanganate). The maximum volume of potassium permanganate for titration is 5 ml. So if more is spent, another dilution is made. This procedure is repeated until the maximum dilution. If the sample is not colored for the maximum volume of titrant and carrying out the maximum dilution, dilutions should be stopped and the oxygen consumed should be calculated using the maximum volume of permanganate and expressing "greater than" the value obtained.
• - Make a target. To do this, instead of using 100 ml of sample, use 100 ml of distilled water and repeat the hot titration procedure.
• - Carry out the cold assessment. It is carried out to determine if there are permanganate-reducing minerals and consists of: adding 100 ml of sample or a dilution (the dilution must be the one that gave positive results in the hot titration).
• - Add 10 ml of sulfuric acid (1+3).
• - Titrate with potassium permanganate drop by drop until a faint pink color persists for 3 minutes.
Calculation of oxygen consumed.
(N-Nb-Nf)*100*f/V.
where N: volume of titrant spent in hot titration.
Nb: volume of titrant spent in the assessment of the blank.
Nf: volume of titrant spent in cold titration.
f: permanganate correction factor.
V: sample volume.
The higher the salinity, the lower the solubility. Salts dissolved in water reduce the intermolecular spaces available for oxygen dissolution. The percentage of saturation is measured as the quotient between the dissolved oxygen measured in the field and the theoretical dissolved oxygen multiplied by 100.
Direct method.
It is carried out with an electrode on the body of water. The percentage of saturation is also obtained. The measurement is obtained once the display stops flashing. The oximeter consists of a platinum cathode and a reference silver/silver chloride anode.
Winkler method.
It is the indirect method of measuring dissolved oxygen. The sample is taken taking care not to leave air bubbles inside the Winkler bottle. The temperature is noted to obtain the theoretical dissolved oxygen in order to express the dissolved oxygen in percentage of saturation.
The Winkler method is applied to waters that do not contain more than 0.1 mg/L of nitrogen in the nitrite state or appreciable quantities of iron, sulfites and thiosulfates, polythionates, free chlorine or hypochlorites and unstable forms of organic matter. In all other cases it is necessary to carry out previous treatments such as Rideal-Stewart or alkaline hypochlorite.
It is the amount of oxygen required by bacteria during the stabilization of organic matter susceptible to degradation by aerobic microorganisms at a temperature of 20 °C, for 5 days and in darkness. It is used to determine the polluting power of domestic and industrial waste.
From organic matter and nutrients, bacteria break down organic matter into carbon dioxide, water, inorganic compounds, new cells and energy. The disadvantage with COD is that it lasts longer and the advantage is that it gives an idea of the biodegradability of the sample. It is used to measure efficiency in wastewater treatment plants. The BOD5 at the inlet and the BOD5 at the outlet are calculated, thereby obtaining the removal percentage.
The temperature is 20 °C because it is an average of natural water temperatures and the speed of biochemical reactions depends on temperature. Theoretically, an infinite amount of time is required for the biological action of organic matter to complete, but for practical purposes the reaction is completed in 20 days. In domestic wastewater, the BOD value at 5 days represents 65 to 80% of the total oxidizable organic matter. As this is a bioassay there is a large margin of error and it is of utmost importance that the environmental conditions are appropriate so that the activity of the microorganisms remains unhindered:
• - Should not make toxic substances.
• - There must be availability of nutrients.
• - Variable species of microorganisms and in large quantities. If there is a normal initial population of microorganisms, the degradation curve gives a normal BOD value, but if the initial population is lower, it gives a lower BOD value because the adaptation phase is longer. The same thing happens if the seed is not acclimatized because they seek to acclimatize to the new compound. Nitrification results in higher BOD values because oxygen is used to oxidize ammonium ions instead of degrading organic matter. This is observed in effluents due to the presence of nitrifying bacteria. Nitrification can be inhibited by the addition of Thiourea.
• - Sufficient oxygen.
Sampling.
The measurement of BOD is carried out in the laboratory. It is kept in a plastic or glass container. It is preserved at 4 °C to avoid the degradation of organic matter and for no more than 24 hours.
Laboratory determination.
The Winkler method or the costometric method is used. The Respirometric method is the most precise but the least developed. In the Winkler method, the Winkler bottle is used, the same as for dissolved oxygen, the lid has an airtight seal and what it basically does is prepare a culture medium, where bacteria, nutrients, and inhibitors are placed. Dissolved oxygen is measured on day 1 and then dissolved oxygen is measured on day 5 and the difference is the BOD5. In the costometric method, pressure differences are measured using a pressure transducer and the result is multiplied by a factor that depends on the sample volume. It has the advantage of not having to measure dissolved oxygen, it is more automatic.
The biochemical oxygen demand of a contaminated liquid is called the oxygen expressed in mg/L, which it consumes in the decomposition of organic matter, by aerobic microbial action. As the decomposition process takes several months to complete and its speed varies with temperature, in practice BOD is measured corresponding to a period of 5 days and a temperature of 20 °C.
From this definition it results that the measurement of BOD of a liquid requires the simultaneous presence in it of:.
a) Organic matter on which decomposition occurs.
b) Aerobic or facultative microorganisms that carry out decomposition.
c) Dissolved oxygen so that the decomposition of organic matter can take place in aerobiosis.
This test was originally conceived by the United Kingdom Royal Commission on Sewage Disposal, as a measure to assess the degree of biochemical oxidation that would occur in a natural water body to which polluting effluents were discharged.
However, the actual conditions of the environment, temperature, water movement, lighting, oxygen concentration, biological population, including planktonic algae and rooted plants, the effect of sediment deposition, photosynthetic action of green plants, presence of nitrogen and ammonia, action of nitrifying bacteria, etc. They cannot be reproduced in the laboratory. Consequently, predictions of the pollution effect of a course are not achieved by direct means, and require the consideration of many factors not involved in the determination of BOD such as water movement, the effect of sediment deposition, among others.
For example, suspended matter in an effluent is often deposited a short distance, immediately downstream of the drain, where it can exert a fairly considerable effect on the concentration of dissolved oxygen (DO).
The BOD determined by dark incubation includes oxygen consumed by algal respiration. The polluting effect of a watercourse effluent can be considerably affected by the photosynthetic action of green plants present, but it is impossible to determine this effect qualitatively in 5-day BOD experiments, so there are no general rules that can be given for BOD of samples containing algae, and each case must be considered according to its characteristics.
A complication of the BOD test is that most of the oxygen consumption of the samples may be due to ammonia and organic nitrogen, which can eventually be oxidized to nitrites and nitrates by nitrifying bacteria, if present. Additionally, ammonium added to the dilution water can also nitrify, and therefore the BOD value is not representative of the sample alone.
Furthermore, due to the low growth of nitrifying bacteria, the degree of nitrification will depend on the number of bacteria initially present, nitrification does not occur to a detectable extent during the 5-day period of raw and settled sewage liquids and in almost all industrial effluents. The BOD test is therefore useful in determining the relative load from the drain to the treatment plant, and the degree of oxygen demand removed by primary treatment.
Nitrification during the 5-day incubation is almost always limited to treated effluents and river waters, which would already be partially nitrified. Only these cases need special attention and the question arises from the use (or not) of the method incorporating a nitrification inhibitor. Determining the degree of nitrification is tedious but, unless known, BOD values can be misleading when evaluating plant performance or calculating effects on a river.
The BOD determined by the dilution method is used as an approximate measure of the amount of biodegradable matter in a sample. For this purpose the dilution test has been successfully applied in practice to samples in which nitrification does not occur, and remains probably the simplest and most suitable test, although in some cases the manometric method can be used. It is optimal in samples where nitrification does not occur because nitrogen and ammonia consume oxygen by nitrifying bacteria and the behavior of nitrifying bacteria is not understood.
The analyst will also consider whether the information he needs can be obtained in some way.
For example, the chemical oxygen test will effect virtually complete oxidation of most organic substances, and thus indicate the amount of oxygen required for complete oxidation of the sample. In other circumstances, and particularly in research work, the determination of organic carbon is more appropriate. In some cases, the results obtained by the BOD test should never be considered separately but in the context of local conditions and with results from other tests.
Complete oxidation of a given drain may require an incubation period that is too long for practical purposes, taking several months to complete. In practice oxidation is considered complete in 20 days. For this reason, the period of 5 days at 20 °C has been accepted as standard.
However, for certain industrial drains and for water contaminated by them, it may be advisable to determine an oxidation curve.
Ultimate BOD calculations from 5-day BOD values (based on calculations using first order exponentials) are not correct. Conversion of data from one incubation period to another can be done only if the oxidation curve has been determined for this individual case, for a series of BOD tests carried out at different incubation periods.
Dilution method.
The dilution method of BOD determination is generally the most widely used. The OD of the sample is determined before and after incubation for 5 days at 20 °C. The difference is the BOD of the same sample after taking into account the dilution carried out.
Precautions.
• - The BOD test should be carried out as quickly as possible once the sample has been taken. This makes it possible to repeat the determination if the results obtained are not satisfactory.
• - If samples are kept at room temperature for several hours, an appreciable change in BOD may occur, depending on the character of the sample. In some cases it may decrease and in others it may increase. The decrease at room temperature is 40% during the first 8 hours of parking.
• - Samples must be free of preservatives and packaged in glass bottles. If samples cannot be processed immediately, they should be kept at a temperature of 5 °C. In the case of individual samples collected over a long period, it is desirable to maintain all samples at temperatures of 5 °C until the compensated sample can be prepared for BOD determination.
• - It is necessary that there be excess dissolved oxygen during the incubation period and it is desirable that it reaches at least 30% of the saturation value after 5 days. Since the solubility of oxygen at the incubation temperature is only 9 mg/L, samples that absorb more than 6 mg/L during incubation for 5 days do not meet this condition. This is the case with sewage liquids and many other contaminated liquids.
• - Additional oxygen is added by diluting the sample with clean, well-aerated water; The dilution depends on the nature of the sample.
Interferences and deficiencies.
• - If the pH of the sample is not in the range 6.5-8.5, it is necessary to add enough alkali or acid to ensure this range. To do this, on a portion of the sample the amount of acid and alkali that is going to be added to neutralize is determined using a suitable indicator such as bromothymol blue or a peachimeter. Then the volume of the calculated aliquot of acid or alkali is added to the sample whose BOD is to be determined.
• - Some samples may be sterile and must be seeded. The purpose of this seeding is to introduce a biological population capable of oxidizing organic matter into the sample. Household waters, non-chlorinated effluents and surface waters that have these microorganisms do not need this seeding.
• - When the sample is known to contain very few microorganisms, as a result, for example, of coloration, high temperature, extreme pH, or specific compositions of some industrial waters, the dilution water should be seeded. For sowing, to each liter of dilution water add 5 ml of raw sewage liquid obtained from the settlers subsequent to aerobic biological purification processes. If necessary, settle the effluent by leaving it in a cylinder for approximately 30 minutes. To sow, add 1-2 ml of the supernatant to each liter of dilution water.
• - Some samples may be supersaturated with dissolved oxygen, especially water contaminated with algae. If such samples are incubated without dilution, the dissolved oxygen concentration should be decreased to saturation to prevent oxygen depletion during incubation. Samples should be kept at 20 °C in partially filled bottles and well shaken.
• - A few sewage effluents and certain industrial effluents contain residual chlorine or products of the action of chlorine on certain constituents. Such liquids cannot be used for the determination of BOD because of the bactericidal effect of chlorine and its byproducts, and also because chlorine introduces an error in the determination of DO. If samples are allowed to sit for 1 to 2 hours, residual chlorine may dissipate. Dilutions for BOD can be separated with standard seeded dilution water. This procedure gives good results for household effluents that have been chlorinated, since chlorine can combine with organic compounds present, producing substances that, although they do not give the iodine-starch reaction for chlorine, inhibit biochemical oxidation or are bactericidal. The BOD determined by these circumstances is generally lower than expected, in relation to organic content, than the BOD measured by other tests.
Sowing of industrial effluents.
• - Sewage effluent seeding, such as those described above, is satisfactory for many industrial effluents. However, the BOD of such effluents determined by standard tests is significantly lower than the chemical oxygen demand, because:
a) samples may contain compounds resistant to biochemical degradation.
b) the organisms planted may be of inappropriate type or require acclimatization, which is why they do not degrade organic matter.
c) there are toxic or bacteriostatic compounds such as chlorine.
Compounds resistant to degradation do not exert an oxygen demand on the received waters, but degradable substances generally contribute to the pollutant load if the BOD test is affected for reasons b) and c) mentioned above.
If the difficulty is due to condition c, it is possible to obtain reliable BOD values only by increasing the dilution of the toxic constituents of the sample to concentration values lower than those that cause inhibition.
Incubation bottles.
• - The use of incubation bottles with a capacity of 250 ml, with a frosted glass stopper, with a narrow mouth is recommended and it is essential that they be very clean. New bottles should be treated with 5N hydrochloric acid and rinsed appropriately.
• - During use, the bottles are kept clean by the acid iodide solution of the Winkler Method, and do not require treatment except rinsing with tap water and distilled water. Special washes are necessary in some cases, but the use of chromic acid is not recommended because traces of chromium may remain in the bottles.
• - Some analysts prefer to use 125 ml capacity bottles, to reduce the space required in the incubator. It is evident that with samples of this type, the size of the bottles can influence the result.
• - Care must be taken so that air does not enter the bottles during incubation, which is obtained by hydraulic closure of the bottles specially designed for BOD.
Incubation.
• - The incubation temperature should be 20 °C+/-0.5 °C, in darkness, because some samples containing algae produce oxygen through photosynthesis, and this interferes with the determination of BOD.
Dilution water.
• - The logical diluent for sewage effluent is the river water into which it is discharged, but this method can only be adopted in special cases, and obviously fails where effluents from very distant locations are processed by the same laboratory because the dilution water should be only one. Furthermore, river water alone can have a considerable BOD.
• - Distillation water is not satisfactory as a diluent and water distilled in copper stills is recommended since copper inhibits the biochemical action, with the maximum tolerated concentration being 0.01 mg/L. The deionized water produced in some commercial units is satisfactory, but the deionized column produced in hard areas requires frequent regenerations.
• - Pretreatment of water by sowing is sometimes necessary.
• - Sample pretreatment is necessary if the sample is supersaturated with oxygen or if the sample contains residual chlorine. If the pH of the sample is not between 6.5 and 8.5, it must be maintained in that range by adding alkali or acid.
• - A dilution water when incubated, with or without seeding, in standard condition should not absorb more than 0.2 mg/L of oxygen and in some cases no more than 0.5 mg/L. A greater oxygen expenditure must be associated with the presence of water-soluble organic vapors in the laboratory atmosphere.
• - Samples kept in the refrigerator should be brought to room temperature before diluting and shaking.
• - Suspended solids in some liquids can cause difficulty if their distribution is not uniform when making dilutions. This may cause discrepancies in the results of different dilutions or duplicate dilutions. It is not advisable to mechanically homogenize them as it can increase their oxygen demand.
• - Sometimes the BOD of the settled or filtered liquid is required. In such cases, the most commonly applied sedimentation time is 30 minutes. For the BOD of filterable substances, membrane filters, glass filters or filter paper are used.
• - Unless the approximate BOD of the sample is known, the degree of dilution required is not and therefore more than one dilution must be made. The lowest dilution should be the one that has a remaining oxygen of 30% in 5 days.
• - It should be noted that some metals such as Cu, Cr, Pb partially inhibit oxygen consumption.
Technique check.
• - From time to time it is desirable to check the entire procedure, including the quality of the dilution water, the effectiveness of sowing and the analyst's technique. For this purpose, pure organic compounds whose BOD is known or determinable are used, such as glucose or glutamic acid. The mixture of glutamic and glutamic acid has certain advantages. Glucose has a high oxidation rate and variables with relatively simple sowing when used with glutamic acid, the oxidation rate is stabilized and is similar to that obtained in many domestic waters.
• - For the checkup, the following procedure is recommended: dissolve 150 mg of glucose and 150 mg of glutamic acid (dried, both previously at 103 °C for 1 hour) in a liter of water; This dilution must be recently prepared. Use dilutions from 1 to 50, with dilution and sowing water and determine BOD by the usual means. The BOD will be approximately 220 mg/L. If the result obtained is greater than 200 mg/L or greater than 240 mg/L, defects in sowing, dilution water or experimental phase should be suspected.
The determination of BOD by this method consists of measuring the decrease in dissolved oxygen that occurs in the liquid to be analyzed, when it is incubated under certain conditions. As the dissolved oxygen concentration of water in equilibrium with air is normally small (at 20 °C and 760 mm Hg it is 7.19 mg of oxygen per liter of water), it is generally necessary to dilute the samples with oxygen-saturated water to ensure its presence for the duration of the incubation.
The model recommended by the APHA is used as a bottle with the following specifications: volume (250-300 ml), shape (cylindrical with an external diameter of approximately 6.5 cm); Frosted cap with a pointed end that closes perfectly, and hydraulic closure to prevent air entry during incubation. The latter can be obtained by placing a rubber collar on the neck of the bottle that slightly extends beyond the upper end of the stopper and fits well.
The free space between the rubber tube and the plug is filled with water. You can also use a jar with the upper end of the neck widened, so that when you place the cap, a hole similar to that of a plate is left, which is filled with water.
With any of these procedures it may happen that before the end of the incubation period, the water in the hydraulic seal completely evaporates. This often occurs in incubators with air renewal and can be avoided by placing a rubber cap for closure, otherwise it must be inspected daily, replacing the evaporated water.
Cleaning the bottles: practiced with the sulfochromic mixture, rinsing them carefully before using them.
Jars with a capacity of 10-20 liters are used to conserve the dilution water. Siphons and pipettes are used, these should be full spill. Air or thermostat incubators with water are used: it must be maintained at 20 °C +/- 1 °C.
The BOD (5 days at 20 °C) of the dilution water cannot be greater than 0.2 mg/L. The concentration of dissolved oxygen should not be greater (supersaturation) or much lower than that corresponding to equilibrium at 20 °C and normal pressure; That is, its dissolved oxygen content must range between 8 and 9 mg/L. Its temperature should be approximately 20 °C. The dilution water must not contain substances that interfere with the recovery of dissolved oxygen, such as iron and nitrite salts, nor substances that inhibit biological growth, such as free chlorine, chloramines, copper salts, etc. Both the pH and the mineral salt content of the dilution water must be favorable to biological growth.
The distilled water used to prepare the dilution water must contain less than 0.05 mg/L of copper, for which it is advisable to use a distiller made entirely of glass. When distilled water has been disinfected with chloramines, these must be removed before distillation, by filtration through carbon, as they are volatile.
Once the water is distilled, it is saturated with oxygen by circulating a current of air through it; But if the distillation is regulated in such a way that the water is collected drop by drop and very cold, aeration becomes unnecessary and sometimes harmful. When aerating, the water tends to become supersaturated with oxygen (especially in winter), remaining in these conditions even after being parked for several days at 20 °C. This requires subtracting part of the DO in the water, to eliminate supersaturation, which complicates the technique.
Finally, the water is kept at 20 °C (temperature at which the BOD is carried out) until the time of use, and only then are the reagents added, stirring gently to avoid aeration.
The dilution water adopted for all BOD tests is Theriault-Nichols, as it has been proven to be the most convenient for liquids that lack essential elements, and its use is also satisfactory because they do not suffer from this deficiency.
To prepare it, the following reagents must be added to the distilled water obtained under the specified conditions:
a) Phosphate buffer solution with added ammonium sulfate: 1.25 ml/L of distilled water.
b) Calcium chloride 0.1 M: 2.5 ml/L of distilled water.
c) Magnesium sulfate 0.04 M: 2.5 ml/L of distilled water.
d) Iron chloride 0.001 M: 0.5 ml/L of distilled water.
The phosphate buffer solution with added ammonium sulfate is prepared by dissolving 34 g of potassium acid phosphate in about 500 ml of distilled water, and then adding NaOH N until a pH of 7.2 is obtained (approximately 175 ml of the NaOH N solution are required). Once the pH has been adjusted, 1.5 g of ammonium sulfate is added and the volume of the solution is finally brought to one liter.
The 0.1 M calcium chloride solution contains 18.3 g of calcium chloride tetrahydrate in one liter; the 0.04 M magnesium sulfate solution contains 9.9 g of magnesium sulfate heptahydrate per liter; The 0.001 M iron chloride solution contains 0.27 g of iron chloride hexahydrate per liter.
pH adjustment: Caustic alkalinity or acidity of the sample can inhibit biological activity. If the pH is less than 5.5, the 0.2 M solution of sodium carbonate (21.2 g of this salt per liter) is added to a portion of the sample until an alkaline reaction with bromothymol blue is obtained; If, on the other hand, the sample is alkaline (pH greater than 8.5), 0.02 M HCl solution is added (17 ml of HCl, specific weight of 1.19, per liter of solution) until the reaction is acidic to cresol red.
In both cases, once the volume of alkali or acid needed is known, another portion of the sample can be neutralized to calculate the BOD without using the indicator, and calculate the corresponding dilution factor.
The neutralization of acid samples that contain iron or aluminum salts in solution produces a precipitate that carries the suspended matter, obtaining lower BOD values in the neutralized sample than in the untreated sample.
A method is currently being studied to overcome this drawback.
The BOD must be determined, the regulatory action of the dilution water may make pH adjustment unnecessary.
The determination of substances soluble in ethyl ether includes fats and oils and the sum of hydrocarbons, fatty acids, waxes and any other substance extractable in ethyl ether from a sample acidified to pH 4.2 and not volatile at 70 °C. The decomposition of plankton and other higher forms of aquatic life gives rise to fats and oils. Most heavy oils and fats are insoluble in water but some can form emulsions by the addition of alkalis, detergents and other chemicals.
Emulsified or dissolved fats and oils are extracted from acidulated water at pH 4.2 and by contact with organic solvents that also extract other substances. There is no selective solvent for fats and oils only. Some low-boiling fractions evaporate during performance of the method and other fractions when the last traces of ether are separated. Naphtha and kerosene are so volatile that they cannot be determined by this method. This method is applicable to wastewater and treated with the above limitations.
Saponified oils and fats tend to remain in emulsion and acidifying the sample to pH 4.2 or adding sodium chloride helps to break this emulsion. Organic substances soluble in ethyl ether in a sample acidified to pH 4.2 and that are not volatile at 70 °C interfere. The maximum sensitivity achieved by the technique is 2 mg/L of substances soluble in ethyl ether.
The sample must be representative, so it is collected from a place that is not watertight, but rather has permanent agitation. When collecting, the sampling container should not be filled because by closing it the floating substances will be lost. To preserve the sample, it should be acidified with diluted hydrochloric acid to pH 4.2.
Work instructions.
• - Homogenize the sample by stirring.
• - Measure 50 ml of sample with a test tube. Transfer to a beaker.
• - Acidify to pH 4.2 with diluted hydrochloric acid.
The only treatment prior to extraction is acidification to pH 4.2 to help break the emulsion of saponified oils and fats.
• - Add 2 drops of heliantine.
Heliantin allows the presence of acids to be evident because it turns from yellow-orange (higher than 4.4) to red (lower than 3.1). It also allows evidence of the formation of two phases: ethereal phase (transparent phase) and aqueous phase (red phase) that separate in the ampoule.
• - Assemble the extraction device with the support and the ampoule under the hood.
• - Add 50 ml of ether using a test tube (makes handling of the ether easier) to the separating ampoule.
It is carried out under a hood because the ether is toxic and proper ventilation and perfect closure must be verified. It is also flammable and explosive so it can be exposed to heat sources such as lighters. This means that it is not performed in conjunction with the consumed oxygen technique. Gloves, overalls, glasses, closed shoes, long pants and a face mask should be used when handling ethyl ether to avoid contact with the skin, eyes, and mouth.
• - Cover, shake (it should not be too soft so that interaction does not occur nor too strong so that the glass does not break) and open the valve in a position so that the liquid does not fall, successive times, to release the gases that exert pressure.
• - Place it back on the support, uncover it and wait for the two phases to settle. The aqueous phase is collected in a beaker and the ethereal phase is collected in a pre-tared crystallizer (P1).
• - Place the contents of the beaker and 20 ml of ether into the ampoule. Cover, shake and open the valve in a position where the liquid does not fall, successive times, to release the gases that exert pressure.
• - Place on the ampoule, uncover and wait for the phases to decant. The red phase is collected in the beaker and the ethereal phase is collected in the crystallizer.
• - Wash the ampoule with 10 ml of ether and place the washing liquid in the crystallizer. Discard the contents of the beaker.
• - Evaporate the ether at a temperature of 60-70 °C.
• - Cool the residue in a desiccator and weigh to the milligram (P2).
• - Make a blank, use 50 ml of distilled water instead of sample and repeat the procedure mentioned so far. Record the weight of the residue (P3).
Calculation of fats and oils.
(P2-P3)*1000/50.
The result is in mg/L if the measurements are recorded in milligrams.
If the target was not made then it is calculated as follows:.
(P2-P1)*1000/50.
The result is in mg/L if the measurements are recorded in milligrams.
Pretreatment is carried out because turbidity and coloration must be removed prior to colorimetric determinations.
The procedure is:
• - Measure 300 ml of sample or a dilution in a 500 ml Erlenmeyer flask.
• - Add 3 ml of 14%W/V aluminum sulfate and 3 drops of 50%W/P sodium hydroxide.
Aluminum sulfate is the coagulant agent and produces colloidal destabilization, which allows the formation of flocs, and sodium hydroxide allows the solution to reach optimal pH and the formation of aluminum hydroxide that precipitates together with the flocs, dragging them along.
• - Cover and shake gently in a circular motion.
• - Verify that the pH of the solution is between 6.5 and 7.5. Add diluted acid and base to correct the pH if necessary. If flocculation is evident, bringing the pH to pH is not necessary.
• - Let it decant (30 min minimum and 24 hours maximum) in the refrigerator. Use the supernatant solution for colorimetric determinations.
If flocculation is not noticeable, the pretreatment is carried out again on the same sample or another sample is used or 20 ml of the supernatant is taken. If sedimentation is not noticeable, then centrifugation is performed.
In samples with high ammoniacal nitrogen content, direct nesslerization should be used instead of distillation. Pretreatment with zinc or aluminum sulfate in an alkaline medium allows the Ca(+2), Mg(+2), S(-2) and Fe(3+) ions to precipitate, which cause turbidity in the presence of the Nessler reagent. Organic matter or coloration also precipitates. The addition of EDTA or Rochelle Salt prevents the precipitation of Ca and Mg ions that react with Nessler's reagent to give color.
Aromatic and aliphatic amines, ketones, aldehydes and alcohols produce a color that varies from yellow to green and turbidity in the presence of Nessler's reagent. Distillation must be resorted to when these interferences cannot be avoided.
The correctly prepared reagent makes it possible to detect 1 mg of ammoniacal nitrogen in 50 ml of solution. Reproducibility below mg is often erratic.
The procedure for determining ammoniacal nitrogen in the sample is as follows:
• - Measure 50 ml of sample or a dilution of it in a 50 ml volumetric flask.
• - Add 1 ml of Nessler's reagent and 2 drops of Seignette's salt.
• - Leave protected from light for 10 minutes.
• - Measure the %T in the spectrophotometer at 420 nm, previously adjusting with the blank.
• - With the value of %T enter the curve and obtain the corresponding concentration. Then the following formula is applied:
mg/L of ammoniacal nitrogen: mg/L read on the curve X 50/sample volume.
The procedure for preparing the blank is:.
• - Measure 50 ml of distilled water into a 50 ml volumetric flask.
• - Add 1 ml of Nessler's reagent and 2 drops of Seignette's Salt.
• - Leave protected from light for 10 minutes.
• - Add 100% T to the reagent blank.
The procedure to prepare the ammoniacal nitrogen curve:.
• - Place aliquots of 1, 2, 5 ml of standard ammonia solution in 50 ml volumetric flasks.
• - Dilute with distilled water up to the volume.
• - Add 1 ml of Nessler's reagent and 2 drops of Seignette's salt.
• - Leave protected from light for 10 minutes.
• - Measure the %T in the spectrophotometer at 420 nm and graph as a function of the concentration of the solutions.
The determination is carried out using a colorimetric kit that uses the cadmium reduction method. In the presence of cadmium, nitrates are converted to nitrites almost quantitatively. The nitrite ions produced undergo diazotization and coupling reactions to form an amber-colored azo dye that can be measured colorimetrically.
Work instructions
Fill the two work tubes up to the mark (5 ml) with pretreated sample or a dilution thereof.
Place one of the tubes in the left position of the color comparator.
Add one reagent sachet, Nitraver 5, to the second tube.
Shake vigorously for 1 minute.
Wait 1 minute for color development.
Place the tube in the right position of the color comparator.
Place in front of a light source and rotate the colored disc until the colors match. If it is very colored, make a greater dilution because the concentration of nitrates is high. Read the result in mg/L of N of NO3.
The result corresponds to the concentration of nitrates and nitrites. Therefore, to measure the nitrate concentration, you must subtract the nitrite concentration obtained by the following method. The results must be affected by the dilution factor if dilution was performed.
The determination of nitrites is carried out using a colorimetric kit that uses the ferrous sulfate method. In an acidic environment, ferrous sulfate reduces nitrite ions to nitrous oxide. Ferrous ions react with nitrous oxide to form a brown complex that can be measured colorimetrically because its color is proportional to the concentration of nitrites in the sample.
Work instructions
Fill both tubes of the kit with 5 ml (up to the first mark) of pretreated sample or a dilution thereof.
Add a reagent sachet to one of the tubes. Cover and shake.
If nitrites are present then a greenish brown color is produced. Allow 5 minutes for color development.
Place the tube with reagent in the upper right opening of the comparator and the tube without reagent in the upper left opening of the comparator.
Expose in front of a light source and rotate until the colors match. If the color does not fit the scale, carry out a greater dilution because the nitrates are in such an amount that the color does not fit into the scale.
Read the value on the mg/L scale of NO2(-). Affect the value read by the dilution factor.
The determination is carried out using a colorimetric kit by reduction with cadmium. Nitrate ions are quantitatively reduced to nitrite in the presence of cadmium. The nitrite ions then undergo diazotization and coupling reactions to form an amber-colored azo dye that can be measured colorimetrically.
The determination is carried out using a colorimetric kit that uses the ferrous sulfate method. In an acidic environment, ferrous sulfate reduces nitrites to nitrous oxide. Ferrous ions react with nitrous oxide to give a brown complex that can be measured colorimetrically because color intensity is proportional to concentration.
Anionic detergents combine with o-toluidine blue to give a chloroform-soluble blue complex. The intensity of the color is proportional to the concentration of detergents.
The organic matter gives a violet color with o-toluidine blue. Therefore, if the liquid contains organic matter, it is determined colorimetrically through a reddish substance soluble in chloroform. To eliminate organic matter, arsenite is added, which eliminates up to 1 mg/L. Interference from hydrogen sulfide can be eliminated by acidification and aeration.
The determination is made using the Murphy-Riley method. The phosphate ion reacts with ammonium molybdate, which when reduced with ascorbic acid gives a blue complex that is molybdenum blue. The phosphorus content in the form of phosphates is determined using a colorimetric kit. The pH does not intervene, the oxidants and reducers do not seriously disturb the accuracy of the method, arsenic does not interfere up to 0.05 mg/L, copper does not interfere up to 5 mg/L and if it is less than 10 mg/L it does not interfere. The total phosphate content expressed as phosphorus corresponds to the sum of concentrations of PO4(-1) and PO4(-2).
Work instructions.
• - Fill both tubes with 5 ml of pretreated sample.
• - Place one of the tubes in position A of the comparator.
• - Add 6 drops of reagent for determination of PO4(-1). Close the tube and shake.
• - Add 6 drops of reagent for determination of PO4(-2). Close the tube and shake.
• - Wait 10 minutes for color development and place in position B of the color comparator.
• - With both tubes uncovered, move them across the scale until they match.
• - Read the value in mg/L of phosphorus in the form of phosphates. If there are intermediate colors, the values can be interpolated. Apply the dilution factor.
• - After use, clean the measuring tubes very well and close them.
The color does not fit into the scale because the concentration of phosphates is very high and the reaction that generates the color occurs appreciably. A higher dilution must be used so that the color developed is smaller and within the scale. The color does not enter the scale because the reagent is in excess, so a minor dilution must be made so that the reagent reacts completely without leaving an excess.
Anionic detergents react with o-toluidine blue to give a blue complex that can be measured colorimetrically and is soluble in chloroform. The organic matter interferes with the determination, giving a violet color when in contact with the o-toluidine blue. Therefore, if one seeks to determine detergents in an effluent with organic matter, it is by giving a red color soluble in chloroform. Sodium arsenite removes up to 1 mg/L. Interference from hydrogen sulfide can be eliminated with acidification and aeration.
Work instructions.
• - Take 10 ml of the pretreated sample and place in a long test tube.
• - Add 6 drops of the reagent for determination of detergents. Cover and shake for 30 seconds.
• - Add 2.5 ml of chloroform. Cover and shake for 30 seconds. Wait 1 minute for phase separation to occur.
• - Uncover and separate the phase with sample using an emptying pipette.
• - Add buffer. Cover and shake for 30 seconds. Wait 1 minute for phase separation to occur.
• - Separate the phase with sample using an emptying pipette.
• - Add buffer solution again. Cover and shake for 30 seconds. Wait 1 minute for phase separation to occur.
• - Separate the phase with sample using an emptying pipette.
• - Place a tube with distilled water in the right compartment of the comparator and place it in the left compartment of the comparator.
• - Place in front of a light source and rotate the color disc until you find a match.
• - Read the value in ppm. Affect by the corresponding dilution.
If the color does not fit into the scale, it happens that the concentration of detergents is higher than what can be read in this method and a greater dilution must be made and affected by the dilution. If the color does not fit into the scale, the reagent is in excess and a minor dilution must be made so that the reagent reacts completely and no excess remains.
The determination is carried out using a colorimetric kit that uses the ferrous sulfate method. In an acidic environment, ferrous sulfate reduces nitrite ions to nitrous oxide. Ferrous ions combine with nitrous oxide to form a brown complex ion and the color intensity is directly proportional to the nitrite concentration in the sample.
Anionic detergents combine with o-toluidine blue, giving rise to a blue substance soluble in chloroform. The color intensity is proportional to the concentration of detergents.
The organic matter gives a violet color with o-toluidine blue, interfering with the determination. Therefore, if it is about determining detergents in sewage liquids, industrial waste or any type of liquid that contains organic matter, it is giving a red color soluble in chloroform. For this reason, sodium arsenite is added to the reagent, which removes up to 1 mg/L. Interference from hydrogen sulfide can be eliminated by acidification and aeration.
It is the most widely used organic contamination parameter. Its determination is related to the measurement of dissolved oxygen consumed by microorganisms in the biochemical oxidation process of biodegradable organic matter.
This test consists of sowing a portion of the water sample (generally diluted), where the initial oxygen concentration is measured and incubated at a certain temperature for a certain period of time.
In order to ensure the reliability of the results obtained, it is necessary to dilute the sample with a specially prepared solution so as to ensure the availability of nutrients and oxygen. The dilution water consists of double-distilled or higher quality water with an amount of oxygen preferably greater than 8mg/l and among the most common nutrients, sodium and potassium phosphates and ammonium and ferric chloride. If necessary, the dilution water should also contain an inoculum of microorganisms (in disinfected effluents, for example). If dilutions have to be made, a blank of the dilution water must also be incubated in parallel, in which the dissolved oxygen must not decrease more than 0.2 mg/l to be considered of good quality.
The standard incubation period is 5 days at 20 °C and without nitrification.
BOD5 Without Nitrification
It is the one taken as a reference for effluent control.
In waste liquids, in addition to carbonaceous organic matter, there are other compounds that consume oxygen. These compounds are mainly oxidizable nitrogen and reducing chemical compounds (ferrous ion, sulfites, sulfides). Among them, the main cause of interference is nitrogen, so an inhibitor is added (the most widely used is 2-chloro-6-(trichloro methi)pyridine).
The BOD (5 days, 20 °C) simulates the first stage of the natural biodegradation process. During this time, only about 60-70% of the most easily biodegradable substances (carbohydrates) are decomposed.
Sampling and storage
Samples for BOD analysis can degrade significantly while in storage between collection and analysis, resulting in low BOD values. If analysis will not be performed within the first two hours, samples should be stored below 4°C. The analysis is no longer representative 24 hours after taking the sample.
Measurement of Initial and Final Oxygen Concentration
The determination of oxygen can be done by iodometry, manometric methods, or with the use of oxygen-permeable membrane electrodes.
COD, like BOD, is a measure of the organic content of wastewater. The difference is that in COD not only biodegradable organic matter is oxidized, but also all organic matter that can be chemically oxidized. This is why the COD value is always higher than the BOD. It is the amount of oxygen required for the oxidation of organic matter by a strong chemical agent to carbon dioxide and water. All organic compounds with a few exceptions can be oxidized to carbon dioxide and water under acidic conditions by strong oxidants.
To achieve the oxidation of organic matter, a powerful oxidant (generally potassium dichromate, occasionally potassium permanganate) is used in a strongly acidic medium (sulfuric acid).
To facilitate oxidation, a catalyst (silver sulfate) is used and the test is carried out at high temperatures for a certain time.
Because chlorides interfere in the test (they oxidize, reducing part of the Cr), it is necessary to inhibit them. This is done by adding mercuric sulfate, which captures the chlorine, forming HgCl2.
2h, 150 °C are taken as standard analysis conditions. The advantage it has with respect to BOD5 is its shorter analysis time, which is carried out in 5 days.
There are 2 laboratory methods to analyze COD. The open reflux or macro COD method, in which a large amount of sample and reagents are used, as the added reagents are toxic and are used in large quantities, is the least used due to the impact it generates on the environment. The closed reflux or micro COD method, the most widely used, uses small concentrations of sample and reagents, which leads to reduced costs and analysis times and generates less impact on the environment. The final reading is carried out by titration or by spectrophotometer.
The procedure is:
• - Add 2.5 ml of sample, 1.5 ml of digester solution (mercuric sulfate and potassium chromate), 3.5 ml of contaminated sulfuric acid (sulfuric acid and small amounts of silver sulfate). The toxic metals are chromium (+6), Ag and Hg.
• - The tube is placed in the thermoreactor at 150 °C for 2 hours.
Choose either of the two:.
• - After digestion, the remaining unreduced potassium dichromate is titrated with ammoniacal ferrous sulfate using ferroin as an indicator. This contains 1,10-phenanthroline that forms a colored complex with ferrous ions. At the point after potassium dichromate (yellow) has been reduced to green Cr(+3), the free Fe(+2) ion complexes the ferroin indicator to form a reddish brown color.
• - After digestion, the amount of chromium that reacts or the excess (according to the working range) is measured colorimetrically at 600 nm. To do this, a calibration curve must be created with standards of known concentration and then, with the absorbance of the sample, determine its concentration.
METHOD INTERFERENCES.
Chlorides, nitrites and other inorganic ions susceptible to oxidation by dichromate. Chlorides constitute the most important interference since they introduce an error due to excess in the COD. In addition, chlorides generate turbidity in the sample when reading in the spectrophotometer. Mercuric sulfate, which is added to the sample before adding the other reagents, avoids the interference caused by chlorides.
SAMPLING.
Like BOD, the COD test is affected if it is not done immediately. It is recommended to extract the sample in glass or plastic containers. If the test cannot be performed immediately, the sample should be acidified to pH<2 with sulfuric acid and kept refrigerated at 4 °C. An analyte stability of 20 days is achieved.
The suspended solids test is carried out by filtering a determined volume of the sample with a standard porosity membrane. The porosity is 1.2 um. The membrane is placed in a capsule and placed in an oven and dried at a predetermined temperature until constant weight (P2). Previously, the same procedure was carried out with the capsule without the filter (P1). The difference in weight, together with the volume of sample that was taken, gives us the amount of TSS.
The sample should be collected in glass or plastic bottles of 1l capacity. Refrigerate samples at 4 °C. Analyze within 24 hours preferably, a maximum of 7 days after sampling.
If the suspended material gets stuck in the filter, the filtration volume must be reduced or the pore size increased.
The dissolved solids test is carried out by filtering a determined volume of the sample with a standard porosity membrane. The porosity is 1.2 um. The filtrate is collected and placed on a previously tared capsule (P1), heated in an oven until constant weight at 180 °C (P2). The difference in weight, together with the volume of sample that was taken, gives us the amount of TSS.
TSS (mg/l) = (P2 – P1) x 1000 / Sample Vol. (ml).
Where:.
• - P1 = capsule weight (mg).
• - P2 = capsule weight + dry filtrate (mg).
The sum of the suspended solids with the dissolved solids gives the total solids which are determined by the total residue due to evaporation.
The sample should be collected in glass or plastic bottles of 1l capacity. Refrigerate samples at 4 °C. Analyze within 24 hours preferably, a maximum of 7 days after sampling.
The pH or the activity of the hydrogen ion indicates, at a given temperature, whether the water is acidic or basic. The pH is defined as the logarithm of the activity of hydrogen ions.
pH = - log [H+].
[H+] = activity of hydrogen ions in mol/l.
Electrometric method.
The method consists of determining the activity of hydrogen ions by potentiometric measurements using a pH electrode. The measurement is carried out with moderate agitation to homogenize the sample. Stirring must be gentle to avoid the entry of carbon dioxide. The electrode is generally not subject to interferences such as color, turbidity, colloidal matter, oxidants, reducers or high salinity. Coatings of fatty material or particles can hinder the response of the electrode. These coatings can be removed by very gentle rubbing with paper or using detergents, followed by rinsing with distilled water. An additional treatment is to use hydrochloric acid (0.1N) and sodium hydroxide (0.1N) to remove any remaining film and then leave them immersed overnight in buffer at pH=7. In any case, the electrode is washed several times before use and after use. Care must be taken not to rest the electrode on the bottom or walls. It rests on its support if it has one to carry out the measurement. Once the measurement is finished, the electrode is stored in a solution so that its operation is always optimal. The pH is affected by temperature due to mechanical and chemical effects, so it must always be indicated at what temperature the measurement was carried out. Samples should be stored for the next day. The pH is preferably determined in-situ.
Color refers to the "true color" it has once its haze has been removed. The "apparent color" not only encompasses the color it has due to dissolved matter but also to suspended matter before filtering or centrifuging it. It is determined by spectrophotometry or visual comparison. The standardized method uses platinum-cobalt standards and the color unit (UC) is that produced by 1 mg/L of platinum in the form of chloroplatinate ion.
Turbidity interferes, which can be eliminated by filtration through a 0.45 um membrane. Another option is centrifugation, which avoids interactions with the filter materials but the results vary with the nature of the sample, the time and speed of centrifugation.
There is no preservation method. It should be analyzed without delay because it is susceptible to pH change. The color intensity increases with increasing pH. It should be between 4 and 10. If storage is required in the dark and <6 °C for a maximum of 48 hours.
The odor must be determined on site. There is no preservation method. It should be analyzed without delay and avoiding modifying the pH.
Before carrying out the test, it is prohibited to eat or smoke:
-If the sample is not at room temperature, temper it.
-Transfer a portion of no less than 50 ml to a 100-400 ml glass bottle or beaker.
-Shake the sample.
-Sniff it lightly.
The phenol standard solution is prepared and standardized to make the calibration curve. The sample is pretreated by adding coagulants, a preliminary distillation is done and then it is reacted with 4-aminoantipyrine and chloroform extraction. This is done to the sample, to a blank and for the preparation of standard solutions. Adjust to pH 4 with buffer solution, add 4-aminoantipyrine and potassium ferricyanide, extract with chloroform, read absorbance at 460 nm, perform calculations and graph the calibration curve.
• - Titulometric Method. This technique is applicable for the determination of cyanide in water and industrial effluents for concentrations greater than 1 mg/L. For the determination of free cyanide as total, for total cyanide it must be distilled from the sample prior to determination. The cyanide ion is titrated with a standard solution of silver nitrate to form the soluble Ag(CN)2 complex. After all the cyanide ion has been complexed, the excess silver ion is detected by a silver-sensitive indicator, p-dimethylamino-benzalrhodanine.
• - Colorimetric Method. To determine cyanide colorimetrically, it is done with a spectrophotometer at 580 nm. It begins with an alkaline treatment of the sample, which is subsequently distilled to transform all the cyanide in the sample into sodium cyanide. It is reacted with chloramine – T at a pH lower than 8 and converted into chlorocyanide, which subsequently forms a bluish-red solution with the addition of barbituric acid – pyridine reagent.
It can be performed by Atomic Absorption Spectrophotometry by Continuous Hydride Generation, or directly. The sample must be digested to reduce interference by organic matter and convert all metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) at 193.7nm.
Flame Atomic Absorption Spectrophotometry Method
The sample must be digested to reduce interference by organic matter and convert all metal to a free form determinable by flame Atomic Absorption Spectrophotometry (AAS) at 228.8 nm. The cadmium content is determined using a calibration curve.
• - Flame Atomic Absorption Spectrophotometry Method. Total chromium is the total content of chromium in its oxidation states III and VI. The sample must be digested to reduce interference by organic matter and convert all metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) with a flame at 357.9 nm. The chromium content is determined using a calibration curve.
• - Sampling and preservation. The sample must be collected in a 1l high-density polyethylene bottle with an airtight seal capacity. The pH should be adjusted to <2 with nitric acid. Analyze before 6 months.
• - Cold vapor atomic absorption spectrophotometry method. The sample must be digested to reduce interference by organic matter and convert all the metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) at 253.7 nm. Mercury is measured after converting it to its free metal form (Hg0) by reduction with stannous chloride in acid solution. This vapor (cold vapor) is transported to a quartz cell where it is measured. The mercury content is determined using a calibration curve.
• - Sampling and preservation. The sample must be collected in a 1l high-density polyethylene bottle with an airtight seal capacity. The pH should be adjusted to <2 with nitric acid. It is advisable to analyze within 28 days.
• - Flame Atomic Absorption Spectrophotometry Method. The sample must be digested to reduce interference by organic matter and convert all the metal to a free form determinable by Atomic Absorption Spectrophotometry (AAS) with a flame at 217 nm. The lead content is determined using a calibration curve.
• - Sampling and preservation. The sample must be collected in a high-density polyethylene bottle with a 1l capacity and an airtight seal. The pH should be <2 and is adjusted with nitric acid. It must be analyzed within 6 months.
• - Methylene blue method. This method is based on the reaction of sulfides with ferric chloride and dimethyl-p-phenylenediamine, to produce methylene blue. Ammonium phosphate is then used to eliminate the interference caused by the ferric chloride color. The procedure is applicable for concentrations between 0.1 mg/l and 20 mg/l and is read with a spectrophotometer at 664 nm.
• - Cancellation separation. The cancellation process isolates the detergent from the aqueous solution and produces a relatively pure dry residue. It is achieved by bubbling a stream of nitrogen into a column containing the diluted sample and a layer of ethyl cecate. The detergent is absorbed into the water-nitrogen interface and transported to ethyl acetate. The solvent is separated and evaporated, leaving the detergent as a residue ready for analysis.
• - Detection as Methylene Blue Active Substances (SAAM). Methylene blue active substances transfer the indicator from an aqueous solution to an immiscible organic liquid (chloroform) until equilibrium. This is due to the formation of an ion pair between the SAAM anion and the methylene blue cation.
It is then compared with a calibration curve with a spectrophotometer at 652nm.
• - Interferences. All other SAAMs, such as carboxylates, organic phenols, cyanates, nitrates, etc.
Titremetric method
For this analysis, it must first be brought to a pH close to 9.5 with an adequate buffer to avoid the hydrolysis of cyanates and organic nitrogenous compounds. The ammonia is distilled and collected in a boric acid solution. The titrant is standardized sulfuric acid and a mixed indicator of methyl red and methylene blue is used.
For phosphorus analysis, all forms present must be converted to dissolved phosphate. For this it can be oxidized with a mixture of nitric acid and sulfuric acid.
• - Ascorbic acid method. It is based on the reaction of ammonium molybdate and potassium antimonyl tartrate with phosphate in an acid medium giving a blue color.
• - Interferences. Arsenates produce a similar coloration.
• - Membrane Filtration Technique. The group of fecal coliform bacteria for the membrane filtration technique is defined as all gram-negative, aerobic and some facultative anaerobic, non-endospore-forming bacilli, which when incubated with lactose for 24 hours at 44.5 ± 0.2 °C develop blue colonies. The principle of this technique consists of filtering a measured volume of sample through a cellulose nitrate membrane and incubating it in a selective culture medium at 44.5 °C. This selective medium and incubation temperature decrease the development of non-coliform bacteria that would negatively affect the growth of fecal coliforms.
• - Interferences. Waters with great turbidity and low density of total coliforms; with organic toxins such as phenols, or when there is a very large non-coliform bacterial load.
• - Sampling and preservation. The sample must be collected in sterile, wide-mouth autoclavable glass or polypropylene bottles. The bottle should not be filled completely, there should be an air chamber to homogenize the sample before processing it. It should be stored at 4 °C until analyzed. The maximum cold storage period for the sample is 6 - 8 h.
• - Membrane Filtration Technique. The group of coliform bacteria for the membrane filtration technique are defined as all gram-negative, aerobic and some facultative anaerobic, non-endospore-forming bacilli, which when incubated with lactose for 24 h at 35 °C ± 0.5 °C, develop red colonies with a metallic green sheen. The principle of this technique consists of filtering a measured volume of the sample through a cellulose nitrate membrane and incubating it in selective culture medium at 35 °C. The incorporation of certain dyes into the culture media allows the production of acid and aldehyde due to lactose fermentation to be visualized by the formation of red colonies with a metallic green shine, typical of total coliforms.
• - Interferences. Waters with great turbidity and low density of total coliforms; with organic toxins such as phenols; or when there is a very large non-coliform bacterial load.
• - Sampling and preservation. The procedure is the same as for fecal coliforms.
Determination of coliforms by the multiple tube fermentation technique. The standard technique for the coliform group is multiple tube fermentation. It consists of placing a battery of tubes with four rows with five tubes each. Each tube contains a glass bell inside that is placed upside down. The tubes are then filled with the culture medium and sterilized in an autoclave. Once sterile, the samples are sown. In the first row, the undiluted sample is placed in each tube. In the next row, a 1:10 dilution of the first row is made. In the third row, a 1:10 dilution of the second row is made and in the last row, another 1:10 dilution of the third row. Subsequently, it is taken to an incubator oven, where it is maintained at a temperature of 37 °C for 24 hours.
After cultivation, it is observed how many of the tubes per row test positive, from the lowest to the highest dilution. A test is positive when an air bubble is observed in the glass bell, corresponding to the consumption of the bacteria from the culture medium and production of carbon dioxide, and when turbidity is observed in the solution.
The results are reported as the most probable number of bacteria (nmp), a number based on probability formulas, where the calculation of the average density of coliforms in the sample is estimated.
When adding silver ions to a solution with a pH between 7 and 10 (neutral or slightly alkaline pH) that contains chloride and chromate ions, silver chromate begins to precipitate when the precipitation of silver chloride (white precipitate) is almost complete, that is, when the concentration of chloride ions is negligible from an analytical point of view because the silver chloride disappears from the solution as it precipitates. This allows the appearance of the red precipitate of silver chromate to be considered as an indication of the end point of the reaction between chloride ions and silver.
2Ag(+)+CrO4(-2)-->AgCrO4(s).
It is one of the ions that contribute to the salinity of waters. It is mainly due to the dissolution of the gypsum, its concentration depending on the drained land. It is dissolved due to its stability and resistance to reduction. The presence of other salts increases its solubility. It tends to form salts with dissolved heavy metals, and because the solubility product is very low, it contributes to reducing its toxicity. An increase in sulfates present in the medium is an indicator of an upcoming spill. It is called the sulfate turbidimetric method. The sulfates react with barium to give barium sulfate, which is a white precipitate. The latter is determined photometrically. To do this, a calibration curve must be created with barium sulfate. The barium is supplied by solid barium chloride and is carried out in an acidic medium provided by hydrochloric acid.
What are the main contaminants in wastewater from the food industry? What treatment would you propose to purify them?
The main components are: solids, fats and oils, organic matter and detergents. Initially, to remove the coarsest solids, use a filter, then to remove the fats and oils and part of the settleable solids use an interceptor, later to remove the rest of the settleable solids after 10 minutes use a sand trap, then to remove the remaining settleable solids use a settler, subsequently to eliminate the remaining organic matter, the remaining suspended solids and the coloration carry out a coagulation-flocculation-decantation treatment, finally perform an adsorption with activated carbon to eliminate detergents, particles that cause color and odor, organic matter that has not been separated in the previous process.
What are the major components contained in sewage water and what parameters would you use to measure each of them?
The main contaminants in water are: high pH values, high content of suspended solids, high content of settleable solids, high content of organic matter, coloration, high content of dissolved solids, fats and oils, hardness. To measure pH I would use the potentiometric method, to measure suspended solids I would filter the sample and what remains in the filter is dried and weighed, to measure detergents I would use the ortho-toluidine blue method, settleable solids using an Imhoff cone, organic matter is measured through the oxygen consumed, fats and oils through substances soluble in ethyl ether, hardness through alkalinity, solids dissolved through conductivity, coloration by comparison with standards.
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