wastewater treatment or wastewater purification consists of a series of physical, chemical and biological processes that aim to eliminate contaminants present in water, effluent from human use or other uses.
The most widespread solution for controlling wastewater pollution is to treat it in plants where most of the contaminant separation process is done, thus leaving a small part that will be completed by nature in the receiving body. For this, the level of treatment required is a function of the natural self-purification capacity of the receiving body. At the same time, the natural self-purification capacity is a function, mainly, of the flow rate of the receiving body, its oxygen content, and its ability to reoxygenate.[1] Therefore, the objective of wastewater treatment is to produce a reusable effluent in the environment and a solid waste or sludge (also called biosolid or sludge) suitable for disposal or reuse.
Wastewater is generated in residences, institutions and commercial, industrial or agricultural premises. These can be treated at the site where they are generated (for example, septic tanks or other purification means) or they can be collected and taken through a network of pipes – and eventually pumps – to a municipal treatment plant. Efforts to collect and treat discharged domestic wastewater are typically subject to local, state, and federal regulations and standards (regulations and controls). Certain contaminants of industrial origin present in wastewater often require specialized treatment processes.
Wastewater treatment begins with the physical separation of large solids (garbage) from the wastewater stream, using a system of grates (meshes), although said waste can also be crushed by special equipment; Subsequently, desanding is applied (separation of small, very dense solids such as sand) followed by primary sedimentation (or similar treatment) that separates the suspended solids existing in the wastewater. To remove dissolved metals, precipitation reactions are used, which are used to remove lead and phosphorus, mainly, in addition to experimental procedures.[2] This is followed by the progressive conversion of the dissolved biological matter into a solid biological mass using suitable bacteria, generally present in these waters. Once the biological mass is separated (a process called secondary sedimentation), the treated water can undergo additional processes (tertiary treatment) such as disinfection, filtration, etc. The final effluent can be discharged or reintroduced back into a natural water body (stream, river or bay) or another environment (surface soil, subsoil, etc.).
Tertiary Treatment
Introduction
wastewater treatment or wastewater purification consists of a series of physical, chemical and biological processes that aim to eliminate contaminants present in water, effluent from human use or other uses.
The most widespread solution for controlling wastewater pollution is to treat it in plants where most of the contaminant separation process is done, thus leaving a small part that will be completed by nature in the receiving body. For this, the level of treatment required is a function of the natural self-purification capacity of the receiving body. At the same time, the natural self-purification capacity is a function, mainly, of the flow rate of the receiving body, its oxygen content, and its ability to reoxygenate.[1] Therefore, the objective of wastewater treatment is to produce a reusable effluent in the environment and a solid waste or sludge (also called biosolid or sludge) suitable for disposal or reuse.
Wastewater is generated in residences, institutions and commercial, industrial or agricultural premises. These can be treated at the site where they are generated (for example, septic tanks or other purification means) or they can be collected and taken through a network of pipes – and eventually pumps – to a municipal treatment plant. Efforts to collect and treat discharged domestic wastewater are typically subject to local, state, and federal regulations and standards (regulations and controls). Certain contaminants of industrial origin present in wastewater often require specialized treatment processes.
Wastewater treatment begins with the physical separation of large solids (garbage) from the wastewater stream, using a system of grates (meshes), although said waste can also be crushed by special equipment; Subsequently, desanding is applied (separation of small, very dense solids such as sand) followed by primary sedimentation (or similar treatment) that separates the suspended solids existing in the wastewater. To remove dissolved metals, precipitation reactions are used, which are used to remove lead and phosphorus, mainly, in addition to experimental procedures.[2] This is followed by the progressive conversion of the dissolved biological matter into a solid biological mass using suitable bacteria, generally present in these waters. Once the biological mass is separated (a process called secondary sedimentation), the treated water can undergo additional processes (tertiary treatment) such as disinfection, filtration, etc. The final effluent can be discharged or reintroduced back into a natural water body (stream, river or bay) or another environment (surface soil, subsoil, etc.).
The new European Directive 2024/3019, of the European Parliament and of the Council, establishes a stricter framework for the treatment of urban wastewater with the purpose of improving water quality, preserving water resources, protecting the environment and moving towards climate neutrality.[3].
The current trend is for stormwater networks to be separate from the sanitation networks, instead of unitary, to prevent them from overflowing and to take advantage of their water.[4].
Description
Contenido
El proceso de tratamiento suele tener tres etapas, o más:[5].
Las aguas residuales provienen de baños, regaderas o duchas, cocinas, etc; que se evacúan a las alcantarillas o cloacas. En muchas zonas, las aguas residuales también incluyen algunas aguas sucias provenientes de industrias y comercios. La división del agua domiciliaria drenada en aguas grises y aguas negras es más común en el mundo desarrollado, el agua negra es la que procede de inodoros, orinales, cocina y el agua gris, procedente de piletas y bañeras, puede ser usada en riego de plantas y reciclada en el uso de inodoros, donde se transforma en agua negra. Las aguas negras son muy turbias y contienen muchos sólidos. Constituyen una de las causas más graves de contaminación de las aguas, por su contenido de materia orgánica, microorganismos patógenos, detergentes, etc. La evacuación de estos desagües en los cursos de agua sin tratamiento previo, puede originar graves perjuicios, es especial la descomposición de la materia orgánica por acción bacteriana produce la disminución del oxígeno disuelto, pudiendo llegar inclusive a la anulación. Muchas aguas residuales también incluyen aguas superficiales procedentes de las lluvias. Estas se llaman aguas blancas. Los desagües pluviales no son suficientemente tenidos en cuenta al analizar las causas de contaminación de las aguas, no obstante que las mismas pueden ser peligrosas. Las aguas de lluvia arrastran los elementos contaminantes presentes en la atmósfera y especialmente sustancias minerales y residuos de origen animal y vegetal acumulados en los techos, azoteas, patios, veredas, calles, etc. Las aguas residuales municipales contienen descargas residenciales, comerciales e industriales, y pueden incluir el aporte de precipitaciones pluviales cuando se usa alcantarillado de uso mixto pluvial - residuales.
La práctica de construcción de sistemas de alcantarillado combinadas es actualmente menos común en los Estados Unidos y Canadá que en el pasado, y se acepta menos dentro de las regulaciones del Reino Unido y otros países europeos, así como en otros países como Argentina. Sin embargo, el agua sucia y el agua de lluvia se recolectan y transportan en sistemas de alcantarillas separativos, llamados alcantarillas sanitarias y alcantarillas de tormenta de los Estados Unidos, y “alcantarillas fétidas” y “alcantarillas de agua superficial” en Reino Unido, o alcantarillados separativos en otros países europeos.
El agua de lluvia puede arrastrar, desde los tejados o la superficie de la tierra, varios contaminantes incluyendo partículas del suelo, metales pesados, compuestos orgánicos, basura animal, aceites y grasa. Algunas jurisdicciones requieren que el agua de lluvia reciba algunos niveles de tratamiento antes de ser descargada al ambiente.
Ejemplos de procesos de tratamientos para el agua de lluvia incluyen depósitos de sedimentación, humedales y separadores de vórtice (para remover sólidos gruesos).
El sitio donde se realizan los procesos se llama Estación depuradora de aguas residuales. El diagrama de flujo de una planta de tratamiento de aguas residuales es generalmente el mismo en todos los países:.
Physical treatment
The addition of ferric chloride "Iron (III) Chloride") largely helps to precipitate phosphorus removal and helps precipitate biosolids or sludge.
chemical treatment
This step is usually combined with solids removal procedures such as filtration. The combination of both techniques is referred to in the United States as a chemical treatment.
Methods for removing excess iron generally include transformation of chlorinated water into a generally basic solution using slaked lime; oxidation of iron by it and precipitation of ferric hydroxide from the basic solution "Base (chemistry)"). While all this is happening the OCl ion destroys pathogens from excess iron in the water.
To transform water into steam in thermal power plants, "Boiler (machine)" boilers are used at high temperatures. Since oxygen is an oxidizing agent, a reducing agent such as hydrogen is needed to remove it.
Domestic wastewater treatment includes the removal of phosphates. A very simple method is to precipitate the phosphates with slaked lime (calcium hydroxide). Phosphates can be present in many different forms such as the hydrogen phosphate ion.
It is based on two combined processes of nitrification and denitrification that lead to the production of sludge in the form of easily pourable biomass.
Stages of wastewater treatment
Primary treatment
The primary treatment is to reduce oils, greases, sands and coarse solids. This step is entirely done with machinery, hence it is also known as mechanical treatment.
Removal of solids is usually done by screening. The solids that are removed are large, for example, bottles, sticks, bags, balls, tires, etc. This prevents problems in the water treatment plant, since if these solids are not removed they can clog pipes or damage some equipment, and hinder the operation of the treatment plant.
This stage (also known as scanning or maceration) typically includes a sand flume where the velocity of the wastewater is carefully controlled to allow the sand and stones in it to take up particles. This equipment is called a sand collector. Sand and stones need to be removed early in the process to prevent damage to pumps and other equipment in the remaining stages of the treatment. Sometimes there are sand baths (sand classifier) followed by a conveyor that transports the sand to a container for deposition. The contents of the sand collector could be fed into the incinerator in a sludge plant processing, but in many cases the sand is sent to an embankment.
The abrasive-free liquid is passed through rotating screens to remove floating material and large matter such as rags; and small particles such as peas and corn. The waste is collected and may be returned to the sludge treatment plant or may be disposed of outside to fields or incineration. In maceration, the solids are cut into small particles through the use of rotating knives mounted on a rotating cylinder, used in plants that can process this waste into particles. Macerators are, however, more expensive to maintain and less reliable than physical screens.
Many plants have a settling stage where wastewater is passed through large circular or rectangular tanks. These tanks are commonly called primary clarifiers or primary settling tanks. The tanks are large enough that fecal solids can settle and floating material such as grease and plastics can rise to the surface and be skimmed. The main purpose of the primary stage is to produce a homogeneous liquid capable of being biologically treated and sludge or sludge that can be treated separately.
Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of wastewater, which derives organic waste from human waste, food waste, soaps and detergents. Most municipal plants use aerobic biological processes for this purpose.
Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen and promote the growth of biological organisms that substantially remove organic matter. It can also trap particles of material.
In older plants and plants receiving variable loads, drip filter beds are used, in which wastewater is sprayed on the surface of a deep bed composed of coke (coal), limestone or specially manufactured plastic media. Such media must have high surface areas to support the biofilms that form. The substance is distributed through rotating perforated arms that radiate from a central pivot. This distributed water drips into the bed and is collected in drains at the base. These drains also provide a source of air that infiltrates up the bed, maintaining an aerobic environment. Biological films of bacteria, protozoans and fungi form on the surface of the medium and eat or reduce the organic contents. This biofilm is often fed by insects and worms.
In some small plants, slow-revolving plates or spirals are used that are partially submerged in the water. A biotic floc is created that provides the required substrate.
The moving bed biological reactor (MBBR) assumes the addition of inert media into existing activated sludge vessels to provide active sites for biomass to gather. This conversion results in a growth system. The advantages of attached growing systems are:.
Biological aerated (or anoxic) filters (BAF) combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with filter media. The media is in suspension or supported by a layer at the bottom of the filter. The dual purpose of this media is to highly support the active biomass that binds to it and the suspended solids in the filter. The oxidation of carbon and the conversion of ammonia occurs in an aerobic medium and is sometimes achieved in a single reactor while the conversion of nitrate occurs in an aerobic manner. BAF is also operated in high flow or low flow depending on the design specified by the manufacturer.
MBR is a system with a semipermeable membrane barrier or in conjunction with a sludge process. This technology guarantees the removal of all suspended contaminants and dissolved solids. The limitation of MBR systems is directly proportional to the effective nutrient reduction of the activated sludge process. The construction and operation cost of MBR is usually higher than that of conventional wastewater treatment of this class of filters.
The final step of the secondary treatment stage is to remove biological flocs from the filter material, and produce treated water with low levels of organic matter and suspended matter. In a rural treatment plant, it is done in the secondary sedimentation tank.
Tertiary treatment
Tertiary treatment provides a final stage to increase the quality of the effluent to the required standard before it is discharged to the receiving environment (sea, river, lake, field, etc.) More than one tertiary treatment process may be used in a treatment plant. If disinfection is always practiced in the final process, it is always called polishing the effluent.
Sand filtration retains much of the suspended matter residue. The activated carbon left over from filtration retains residual toxins.
Lagoon treatment provides sedimentation and additional biological improvement by storage in puddles or artificial lagoons.[6] This is an imitation of the self-purification processes that a river or lake undergoes wastewater naturally. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, often occurs. Small filter feeding invertebrates such as Daphnia and Rotifera species effectively assist treatment by retaining fine particles.
The lagoon system is cheap and easy to maintain but has the drawbacks of requiring a large amount of space and being poorly capable of purifying the water of large nuclei.
Constructed wetlands include reed beds or a number of similar methods that provide a high degree of aerobic biological enhancement and can often be used in place of secondary treatment for small populations, including for phytoremediation. Aquatic macrophytes such as Eichhornia crassipes are a clear example of the installation of wastewater treatment systems due to their high efficiency in the oxidation of organic matter.[7][8].
An example is a small bed of reeds (or reed beds) used to clean drainage from the elephant enclosure at Chester Zoo in England.
Wastewater can also contain high levels of the nutrients nitrogen and phosphorus. It in certain forms can be toxic to fish and invertebrates at very low concentrations (e.g. ammonia) or can create unhealthy conditions in the receiving environment (e.g. weeds or algae growth). Algae can produce toxins, and their death and consumption by bacteria (decay) can deplete oxygen in the water and suffocate fish and other aquatic life. When discharged from rivers to lakes or low seas, the added nutrients can cause severe entropic losses, losing many pollution-sensitive fish in the water. Removal of nitrogen or phosphorus from wastewater can be achieved through chemical or biological precipitation.
Nitrogen removal is carried out with the biological oxidation of nitrogen from ammonia to nitrate (nitrification which involves nitrifying bacteria such as Nitrobacter and Nitrosomonus), and then through reduction, the nitrate is converted to nitrogen gas (denitrification), which is sent to the atmosphere. These conversions require carefully controlled conditions to allow proper formation of biological communities. Sand filters, lagoons, and sheet beds can be used to reduce nitrogen. Sometimes, the conversion of toxic ammonia to nitrate is only done as a tertiary treatment.
Sludge treatment
Los sólidos primarios gruesos y los biosólidos secundarios acumulados en un proceso del tratamiento de aguas residuales se debe tratar y disponer de una manera segura y eficaz. Este material a menudo se contamina inadvertidamente con los compuestos orgánicos e inorgánicos tóxicos (por ejemplo: metales pesados). El propósito de la digestión es reducir la cantidad de materia orgánica y el número de los microorganismos presentes en los sólidos que causan enfermedades. Las opciones más comunes del tratamiento incluyen la digestión anaerobia, la digestión aerobia, y el abonamiento.
Anaerobic digestion
Anaerobic digestion is a bacterial process that takes place in the absence of oxygen. The process can be thermophilic digestion in which the sludge is fermented in tanks at a temperature of 55 °C or mesophilic, at a temperature around 36 °C. However allowing shorter retention time, thus in the small tanks, thermophilic digestion is more expansive in terms of energy consumption to heat the sludge.
Anaerobic digestion generates biogas with a high proportion of methane that can be used to run tank and engines or micro turbines for other on-site processes. In large treatment plants, more electrical energy can be generated than the machines require. Methane generation is a key benefit of the anaerobic process. Its dominant disadvantage is the long time required for the process (up to 30 days) and the high cost of capital.
Advantages[10].
The Goldbar wastewater treatment plant in Edmonton, Alberta, Canada currently uses the process. Under laboratory conditions it is possible to directly generate useful amounts of electricity from organic sludge using naturally occurring electrochemically active bacteria. Potentially, this technique could lead to an environmentally friendly way of generating energy, but to be effective, a microbial fuel cell must maximize the contact area between the effluent and the bacteria-coated surface of the anode, which could seriously decrease the performance of the process.
aerobic digestion
Aerobic digestion is a bacterial process that occurs in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it to carbon dioxide. Once there is a lack of organic matter, the bacteria die and are used as food by other bacteria. This stage of the process is known as endogenous respiration. The reduction of solids occurs in this phase. Because aerobic digestion occurs much more rapidly, the capital costs of aerobic digestion are lower. However, operating costs are typically much higher for aerobic digestion due to the energy costs for the aeration needed to add oxygen to the process.
Compost or fertilizer
Composting is also an aerobic process that involves mixing wastewater solids with carbon sources such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digest solids from the wastewater and the added carbon source and, in doing so, produce a large amount of heat. Anaerobic and aerobic digestion processes can result in the destruction of disease-causing microorganisms and parasites to a sufficient level to allow the resulting digested solids to be safely applied to soil used as soil amendment material (with similar benefits to peat) or used for agriculture as fertilizer provided that the levels of toxic components are sufficiently low.
Thermal depolymerization
Thermal depolymerization uses aqueous pyrolysis to convert the reduced complex organisms to oil. The hydrogen in water inserts itself between chemical bonds in natural polymers such as fats, proteins and cellulose. The oxygen in water combines with carbon, hydrogen and metals. The result is oil, light fuel gases such as methane, propane and butane, water with soluble salts, carbon dioxide, and a small residue of inert insoluble material that resembles pulverized rock and coal. All organisms and many organic toxins are destroyed. Inorganic salts such as nitrates and phosphates remain in the water after treatment at high enough levels that additional treatment is required.
The energy from decompressing the material is recovered, and the process heat and pressure is usually powered from the light fuel gases. The oil is usually further treated to make a refined useful light grade of oil, such as some diesel and heating oils, and then sold.
The choice of a solid wastewater treatment method depends on the amount of solids generated and other site-specific conditions. However, generally composting is most often applied to small scale uses followed by aerobic digestion and then anaerobic digestion for large scales such as in municipalities.
sludge deposition
When a liquid sludge is produced, additional treatment may be required to make it suitable for final disposal. Typically, sludge is thickened (dewatered) to reduce the volumes transported for disposal. Processes to reduce water content include lagooning drying beds to produce a cake that can be applied to soil or incinerated; pressing, where mud is mechanically filtered, through cloth screens to often produce a firm cake; and centrifugation where the sludge is thickened centrifugally separating the solid and the liquid.[11] The sludge can be disposed of by liquid injection to land or by disposal in an embankment. There are concerns about sludge incineration due to air pollutants in emissions, along with the high cost of supplemental fuel, making this a less attractive and less commonly constructed means of sludge treatment and disposal.
There is no process that completely eliminates the requirements for biosolids disposal. In South Australia, after centrifugation, the sludge is completely dried by sunlight. The nutrient-rich biosolids are then provided to farmers to use as a natural fertilizer. This method has reduced the amount of landfill generated by the process each year.
Wastewater photobiopurification
Photobiopurification of wastewater is a process that involves the presence of sunlight and photosynthetic organisms for the purification process. Generally, photobiopurification is carried out by photosynthetic microorganisms, such as microalgae and cyanobacteria, in photobioreactors, reactors specifically designed to take advantage of sunlight and promote the growth of these microorganisms.[1].
Treatment in the reception environment
The introduction of wastewater that the plant treats influences the processes of many small rivers. In a wastewater treatment plant, the natural treatment processes that occur in the environment are designed, whether that environment is a natural body of water or land. If it has not been overloaded, bacteria in the environment will consume the organic contaminants, although this will reduce the oxygen levels in the water and can significantly change the overall ecology of the receiving water. Native bacterial populations feed on organic contaminants, and the numbers of disease-causing microorganisms are reduced by natural environmental conditions such as predation, exposure to ultraviolet radiation, etc. Therefore in case the receiving environment provides a high level of dilution, a high degree of wastewater treatment may not be required. However, recent evidence has shown that very low levels of certain contaminants in wastewater, including hormones (from animal agriculture and the residue of human birth control pills) and synthetic materials such as phthalates, can have an unpredictable adverse impact on the natural environment and potentially on humans if the water is reused for drinking water. In the US, uncontrolled discharges of wastewater into the environment are not permitted under law, and strict water quality requirements must be known. A significant threat in the coming decades will be the increasing uncontrolled discharges of wastewater within rapidly developing countries.
Global treatment gap
Seen from a global perspective, there is inadequate wastewater treatment capacity, especially in underdeveloped countries. This circumstance has existed since at least the 1970s and is due to overpopulation, the water crisis, and the cost of building wastewater treatment systems. The result of inadequate wastewater treatment is a significant increase in mortality from (mostly) preventable diseases; Furthermore, this impact of mortality is particularly high among infants and other children in underdeveloped countries, particularly in the continents of Africa and Asia. Particularly, in the year 2000, the United Nations has established that 2.64 billion people had inadequate wastewater treatment or disposal. This value represented 44 percent of the global population, but in Africa and Asia approximately half of the population had no access whatsoever to wastewater treatment services.
Environmental impact
Los contaminantes de las aguas servidas municipales, o aguas servidas domésticas, son los sólidos suspendidos y disueltos que consisten en: materias orgánicas e inorgánicas, nutrientes, aceites y grasas, sustancias tóxicas, y microorganismos patógenos. Los desechos humanos sin un tratamiento apropiado, eliminados en su punto de origen o recolectados y transportados, presentan un peligro de infección parasitaria (mediante el contacto directo con la materia fecal), hepatitis y varias enfermedades gastrointestinales, incluyendo el cólera y tifoidea (mediante la contaminación de la fuente de agua y la comida). Cabe mencionar que el agua de lluvia urbana puede contener los mismos contaminantes, a veces en concentraciones sorprendentemente altas.
Cuando las aguas servidas son recolectadas pero no tratadas correctamente antes de su eliminación o reutilización, existen los mismos peligros para la salud pública en las proximidades del punto de descarga. Si dicha descarga es en aguas receptoras, se presentarán peligrosos efectos adicionales (p.ej. el hábitat para la vida acuática y marina es afectada por la acumulación de los sólidos; el oxígeno es disminuido por la descomposición de la materia orgánica; y los organismos acuáticos y marinos pueden ser perjudicados aún más por las sustancias tóxicas, que pueden extenderse hasta los organismos superiores por la bio-acumulación en las cadenas alimenticias). Si la descarga entra en aguas confinadas, como un lago o una bahía, su contenido de nutrientes puede ocasionar la eutrofización, con molesta vegetación que puede afectar a las pesquerías y áreas recreativas. Los desechos sólidos generados en el tratamiento de las aguas servidas (grava, y fangos primarios y secundarios) pueden contaminar el suelo y las aguas si no son manejados correctamente.[12].
Los proyectos de aguas servidas son ejecutados a fin de evitar o aliviar los efectos de los contaminantes descritos anteriormente en cuanto al ambiente humano y natural. Cuando son ejecutados correctamente, su impacto total sobre el ambiente es positivo.
Los impactos directos incluyen la disminución de molestias y peligros para la salud pública en el área de servicio, mejoramientos en la calidad de las aguas receptoras, y aumentos en los usos beneficiosos de las aguas receptoras. Adicionalmente, la instalación de un sistema de recolección y tratamiento de las aguas servidas posibilita un control más efectivo de las aguas servidas industriales mediante su tratamiento previo y conexión con el alcantarillado público, y ofrece el potencial para la reutilización beneficiosa del efluente tratado y de los fangos.
Los impactos indirectos del tratamiento de las aguas residuales incluyen la provisión de sitios de servicio para el desarrollo, mayor productividad y rentas de las pesquerías, mayores actividades y rentas turísticas y recreativas, mayor productividad agrícola y forestal o menores requerimientos para los fertilizantes químicos, en caso de ser reutilizado el efluente y los fangos, y menores demandas sobre otras fuentes de agua como resultado de la reutilización del efluente.
De éstos, varios potenciales impactos positivos se prestan para la medición, por lo que pueden ser incorporados cuantitativamente en el análisis de los costos y beneficios de varias alternativas al planificar proyectos para las aguas servidas. Los beneficios para la salud humana pueden ser medidos, por ejemplo, mediante el cálculo de los costos evitados, en forma de los gastos médicos y días de trabajo perdidos que resultan de un saneamiento defectuoso. Los menores costos del tratamiento de agua potable e industrial y mayores rentas de la pesca, el turismo y la recreación, pueden servir como mediciones parciales de los beneficios obtenidos del mejoramiento de la calidad de las aguas receptoras. En una región donde es grande la demanda de viviendas, los beneficios provenientes de proporcionar lotes con servicios pueden ser reflejados en parte por la diferencia en costos entre la instalación de la infraestructura por adelantado o la adecuación posterior de comunidades no planificadas.
A menos que sean correctamente planificados, ubicados, diseñados, construidos, operados y mantenidos, es probable que los proyectos de aguas servidas tengan un impacto total negativo y no produzcan todos los beneficios para los cuales se hizo la inversión, afectando además en forma negativa a otros aspectos del medio ambiente.
Sociocultural problems
Treatment facilities require land; its location may result in involuntary repopulation. Furthermore, treatment and disposal works may create nuisance in the immediate vicinity, at least occasionally. Often, the lands and neighborhoods chosen correspond to "vulnerable groups" who are the least able to face the costs of relocation and whose living environment is already altered. Care should be taken to locate treatment and disposal facilities where odors or noise will not disturb residents or other users of the area, handle relocation sensitively, and include in the project abatement plan provisions to mitigate or offset adverse impacts on the human environment. Failure to include these considerations in project planning presents substantial risk.
Appropriate technology
The concept of appropriate technology in wastewater systems encompasses technical, institutional, social and economic dimensions. From a technical and institutional point of view, the selection of inappropriate technologies has been identified as one of the main causes of system failures. The wastewater environment is hostile to electronic, electrical and mechanical equipment. Its maintenance is an endless process, and requires support (spare parts, laboratories, trained technicians, specialized technical assistance, and adequate budgets). Even in developed countries, it is the simplest systems, chosen and designed with a view to maintenance, that provide the most reliable service. In developing countries, where some ingredients for a successful maintenance program may be missing, this should be the first consideration when choosing technologies for treatment plants and pumping stations.
In small communities and rural environments, technical options are often simpler, but institutional considerations combine with social ones and remain extremely important. Local institutions must be able to manage sanitation programs or systems; Community participation can be a key element in your success. The usual social and practical preferences are important; some can be modified through educational programs, but others may be rooted in cultural values and not subject to change.
Economics is part of the decision in two ways. Not surprisingly, the simplest technologies, selected for their ease of operation and maintenance, are often the least expensive to build and operate. However, even when they are not, as may be the case when large amounts of land must be acquired for stabilization ponds, a less expensive system that fails would ultimately be more expensive than a more expensive one that operates reliably.[13].
References
[1] ↑ a b Romero Rojas, Jairo A. Lagunas de estabilización de aguas residuales. Editorial Escuela Colombiana de Ingeniería. 1994 ISBN 958 8060 50 8.
[2] ↑ García Zare, Elmis Jonatan; Mejía Pardo, Patricia Isabel; Soto Abanto, Segundo Eloy; Rodriguez Paredes, Noelia Patricia; Cerna Vasquez, Marco Antonio (11 de agosto de 2023). Hydrochloric acid concentration and time to maximize lead and cadmium removal in laboratory wastewater (en inglés). doi:10.18687/laccei2023.1.1.573. Consultado el 9 de julio de 2024.: https://laccei.org/LACCEI2023-BuenosAires/meta/FP573.html
[4] ↑ Ministerio para la Transición Ecológica y el Reto Demográfico (22 de septiembre de 2022), Real Decreto 730/2022, de 6 de septiembre, por el que se regula la concesión directa de subvenciones para el desarrollo de las actuaciones complementarias de saneamiento y depuración del Marco de Actuaciones Prioritarias para Recuperar el Mar Menor y en el marco del Plan de Recuperación, Transformación y Resiliencia (Real Decreto 730/2022), pp. 130096-130112, consultado el 15 de abril de 2025 .: https://www.boe.es/diario_boe/txt.php?id=BOE-A-2022-15419
[5] ↑ Henze, M.; van Loosdrecht, M. C. M.; Ekama, G.A.; Brdjanovic, D. (2008). Biological Wastewater Treatment: Principles, Modelling and Design (en inglés). IWA Publishing (Spanish and Arabic versions are available online for free). ISBN 978-1-78040-186-7. doi:10.2166/9781780401867.: http://iwaponline.com/ebooks/book/59/Biological-Wastewater-Treatment-Principles
[6] ↑ De acuerdo a su respuesta frente al O2 las bacterias se clasifican como:
[7] ↑ Sayago, Carreño; Fernando, Uriel (2021-01). «Design, Scaling, and Development of Biofilters with E crassipes for Treatment of Water Contaminated with Cr (VI)». Water (en inglés) 13 (9): 1317. doi:10.3390/w13091317. Consultado el 19 de agosto de 2021.: https://www.mdpi.com/2073-4441/13/9/1317
[8] ↑ Sayago, Uriel Fernando Carreño (29 de abril de 2021). «Design and development of a biotreatment of E. crassipes for the decontamination of water with Chromium (VI)». Scientific Reports (en inglés) 11 (1): 9326. ISSN 2045-2322. doi:10.1038/s41598-021-88261-0. Consultado el 19 de agosto de 2021.: https://www.nature.com/articles/s41598-021-88261-0
[9] ↑ Romero Rojas, Jairo A. Lagunas de estabilización de aguas residuales. Editorial Escuela Colombiana de Ingeniería. 1994 ISBN 958 8060 50 8 Cap 4. pág. 99.
[12] ↑ Entrevista con el Msc. Ing. Nobel Francisco Rovirosa Morell sobre los aspectos técnicos-económicos-ambientales en el tratamiento de las aguas residuales urbanas Conversaciones sobre el agua, Capítulo IV.: http://www.sonia-bueno.net/41563.html
[13] ↑ «Tratamiento de aguas residuales (Estudios y practicas profesionales)». Tecnología y tratamiento de aguas residuales. 12 de junio de 2019.: https://awtsa.com/
The new European Directive 2024/3019, of the European Parliament and of the Council, establishes a stricter framework for the treatment of urban wastewater with the purpose of improving water quality, preserving water resources, protecting the environment and moving towards climate neutrality.[3].
The current trend is for stormwater networks to be separate from the sanitation networks, instead of unitary, to prevent them from overflowing and to take advantage of their water.[4].
Description
Contenido
El proceso de tratamiento suele tener tres etapas, o más:[5].
Las aguas residuales provienen de baños, regaderas o duchas, cocinas, etc; que se evacúan a las alcantarillas o cloacas. En muchas zonas, las aguas residuales también incluyen algunas aguas sucias provenientes de industrias y comercios. La división del agua domiciliaria drenada en aguas grises y aguas negras es más común en el mundo desarrollado, el agua negra es la que procede de inodoros, orinales, cocina y el agua gris, procedente de piletas y bañeras, puede ser usada en riego de plantas y reciclada en el uso de inodoros, donde se transforma en agua negra. Las aguas negras son muy turbias y contienen muchos sólidos. Constituyen una de las causas más graves de contaminación de las aguas, por su contenido de materia orgánica, microorganismos patógenos, detergentes, etc. La evacuación de estos desagües en los cursos de agua sin tratamiento previo, puede originar graves perjuicios, es especial la descomposición de la materia orgánica por acción bacteriana produce la disminución del oxígeno disuelto, pudiendo llegar inclusive a la anulación. Muchas aguas residuales también incluyen aguas superficiales procedentes de las lluvias. Estas se llaman aguas blancas. Los desagües pluviales no son suficientemente tenidos en cuenta al analizar las causas de contaminación de las aguas, no obstante que las mismas pueden ser peligrosas. Las aguas de lluvia arrastran los elementos contaminantes presentes en la atmósfera y especialmente sustancias minerales y residuos de origen animal y vegetal acumulados en los techos, azoteas, patios, veredas, calles, etc. Las aguas residuales municipales contienen descargas residenciales, comerciales e industriales, y pueden incluir el aporte de precipitaciones pluviales cuando se usa alcantarillado de uso mixto pluvial - residuales.
La práctica de construcción de sistemas de alcantarillado combinadas es actualmente menos común en los Estados Unidos y Canadá que en el pasado, y se acepta menos dentro de las regulaciones del Reino Unido y otros países europeos, así como en otros países como Argentina. Sin embargo, el agua sucia y el agua de lluvia se recolectan y transportan en sistemas de alcantarillas separativos, llamados alcantarillas sanitarias y alcantarillas de tormenta de los Estados Unidos, y “alcantarillas fétidas” y “alcantarillas de agua superficial” en Reino Unido, o alcantarillados separativos en otros países europeos.
El agua de lluvia puede arrastrar, desde los tejados o la superficie de la tierra, varios contaminantes incluyendo partículas del suelo, metales pesados, compuestos orgánicos, basura animal, aceites y grasa. Algunas jurisdicciones requieren que el agua de lluvia reciba algunos niveles de tratamiento antes de ser descargada al ambiente.
Ejemplos de procesos de tratamientos para el agua de lluvia incluyen depósitos de sedimentación, humedales y separadores de vórtice (para remover sólidos gruesos).
El sitio donde se realizan los procesos se llama Estación depuradora de aguas residuales. El diagrama de flujo de una planta de tratamiento de aguas residuales es generalmente el mismo en todos los países:.
Physical treatment
The addition of ferric chloride "Iron (III) Chloride") largely helps to precipitate phosphorus removal and helps precipitate biosolids or sludge.
chemical treatment
This step is usually combined with solids removal procedures such as filtration. The combination of both techniques is referred to in the United States as a chemical treatment.
Methods for removing excess iron generally include transformation of chlorinated water into a generally basic solution using slaked lime; oxidation of iron by it and precipitation of ferric hydroxide from the basic solution "Base (chemistry)"). While all this is happening the OCl ion destroys pathogens from excess iron in the water.
To transform water into steam in thermal power plants, "Boiler (machine)" boilers are used at high temperatures. Since oxygen is an oxidizing agent, a reducing agent such as hydrogen is needed to remove it.
Domestic wastewater treatment includes the removal of phosphates. A very simple method is to precipitate the phosphates with slaked lime (calcium hydroxide). Phosphates can be present in many different forms such as the hydrogen phosphate ion.
It is based on two combined processes of nitrification and denitrification that lead to the production of sludge in the form of easily pourable biomass.
Stages of wastewater treatment
Primary treatment
The primary treatment is to reduce oils, greases, sands and coarse solids. This step is entirely done with machinery, hence it is also known as mechanical treatment.
Removal of solids is usually done by screening. The solids that are removed are large, for example, bottles, sticks, bags, balls, tires, etc. This prevents problems in the water treatment plant, since if these solids are not removed they can clog pipes or damage some equipment, and hinder the operation of the treatment plant.
This stage (also known as scanning or maceration) typically includes a sand flume where the velocity of the wastewater is carefully controlled to allow the sand and stones in it to take up particles. This equipment is called a sand collector. Sand and stones need to be removed early in the process to prevent damage to pumps and other equipment in the remaining stages of the treatment. Sometimes there are sand baths (sand classifier) followed by a conveyor that transports the sand to a container for deposition. The contents of the sand collector could be fed into the incinerator in a sludge plant processing, but in many cases the sand is sent to an embankment.
The abrasive-free liquid is passed through rotating screens to remove floating material and large matter such as rags; and small particles such as peas and corn. The waste is collected and may be returned to the sludge treatment plant or may be disposed of outside to fields or incineration. In maceration, the solids are cut into small particles through the use of rotating knives mounted on a rotating cylinder, used in plants that can process this waste into particles. Macerators are, however, more expensive to maintain and less reliable than physical screens.
Many plants have a settling stage where wastewater is passed through large circular or rectangular tanks. These tanks are commonly called primary clarifiers or primary settling tanks. The tanks are large enough that fecal solids can settle and floating material such as grease and plastics can rise to the surface and be skimmed. The main purpose of the primary stage is to produce a homogeneous liquid capable of being biologically treated and sludge or sludge that can be treated separately.
Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of wastewater, which derives organic waste from human waste, food waste, soaps and detergents. Most municipal plants use aerobic biological processes for this purpose.
Activated sludge plants use a variety of mechanisms and processes to use dissolved oxygen and promote the growth of biological organisms that substantially remove organic matter. It can also trap particles of material.
In older plants and plants receiving variable loads, drip filter beds are used, in which wastewater is sprayed on the surface of a deep bed composed of coke (coal), limestone or specially manufactured plastic media. Such media must have high surface areas to support the biofilms that form. The substance is distributed through rotating perforated arms that radiate from a central pivot. This distributed water drips into the bed and is collected in drains at the base. These drains also provide a source of air that infiltrates up the bed, maintaining an aerobic environment. Biological films of bacteria, protozoans and fungi form on the surface of the medium and eat or reduce the organic contents. This biofilm is often fed by insects and worms.
In some small plants, slow-revolving plates or spirals are used that are partially submerged in the water. A biotic floc is created that provides the required substrate.
The moving bed biological reactor (MBBR) assumes the addition of inert media into existing activated sludge vessels to provide active sites for biomass to gather. This conversion results in a growth system. The advantages of attached growing systems are:.
Biological aerated (or anoxic) filters (BAF) combine filtration with biological carbon reduction, nitrification or denitrification. BAF usually includes a reactor filled with filter media. The media is in suspension or supported by a layer at the bottom of the filter. The dual purpose of this media is to highly support the active biomass that binds to it and the suspended solids in the filter. The oxidation of carbon and the conversion of ammonia occurs in an aerobic medium and is sometimes achieved in a single reactor while the conversion of nitrate occurs in an aerobic manner. BAF is also operated in high flow or low flow depending on the design specified by the manufacturer.
MBR is a system with a semipermeable membrane barrier or in conjunction with a sludge process. This technology guarantees the removal of all suspended contaminants and dissolved solids. The limitation of MBR systems is directly proportional to the effective nutrient reduction of the activated sludge process. The construction and operation cost of MBR is usually higher than that of conventional wastewater treatment of this class of filters.
The final step of the secondary treatment stage is to remove biological flocs from the filter material, and produce treated water with low levels of organic matter and suspended matter. In a rural treatment plant, it is done in the secondary sedimentation tank.
Tertiary treatment
Tertiary treatment provides a final stage to increase the quality of the effluent to the required standard before it is discharged to the receiving environment (sea, river, lake, field, etc.) More than one tertiary treatment process may be used in a treatment plant. If disinfection is always practiced in the final process, it is always called polishing the effluent.
Sand filtration retains much of the suspended matter residue. The activated carbon left over from filtration retains residual toxins.
Lagoon treatment provides sedimentation and additional biological improvement by storage in puddles or artificial lagoons.[6] This is an imitation of the self-purification processes that a river or lake undergoes wastewater naturally. These lagoons are highly aerobic and colonization by native macrophytes, especially reeds, often occurs. Small filter feeding invertebrates such as Daphnia and Rotifera species effectively assist treatment by retaining fine particles.
The lagoon system is cheap and easy to maintain but has the drawbacks of requiring a large amount of space and being poorly capable of purifying the water of large nuclei.
Constructed wetlands include reed beds or a number of similar methods that provide a high degree of aerobic biological enhancement and can often be used in place of secondary treatment for small populations, including for phytoremediation. Aquatic macrophytes such as Eichhornia crassipes are a clear example of the installation of wastewater treatment systems due to their high efficiency in the oxidation of organic matter.[7][8].
An example is a small bed of reeds (or reed beds) used to clean drainage from the elephant enclosure at Chester Zoo in England.
Wastewater can also contain high levels of the nutrients nitrogen and phosphorus. It in certain forms can be toxic to fish and invertebrates at very low concentrations (e.g. ammonia) or can create unhealthy conditions in the receiving environment (e.g. weeds or algae growth). Algae can produce toxins, and their death and consumption by bacteria (decay) can deplete oxygen in the water and suffocate fish and other aquatic life. When discharged from rivers to lakes or low seas, the added nutrients can cause severe entropic losses, losing many pollution-sensitive fish in the water. Removal of nitrogen or phosphorus from wastewater can be achieved through chemical or biological precipitation.
Nitrogen removal is carried out with the biological oxidation of nitrogen from ammonia to nitrate (nitrification which involves nitrifying bacteria such as Nitrobacter and Nitrosomonus), and then through reduction, the nitrate is converted to nitrogen gas (denitrification), which is sent to the atmosphere. These conversions require carefully controlled conditions to allow proper formation of biological communities. Sand filters, lagoons, and sheet beds can be used to reduce nitrogen. Sometimes, the conversion of toxic ammonia to nitrate is only done as a tertiary treatment.
Sludge treatment
Los sólidos primarios gruesos y los biosólidos secundarios acumulados en un proceso del tratamiento de aguas residuales se debe tratar y disponer de una manera segura y eficaz. Este material a menudo se contamina inadvertidamente con los compuestos orgánicos e inorgánicos tóxicos (por ejemplo: metales pesados). El propósito de la digestión es reducir la cantidad de materia orgánica y el número de los microorganismos presentes en los sólidos que causan enfermedades. Las opciones más comunes del tratamiento incluyen la digestión anaerobia, la digestión aerobia, y el abonamiento.
Anaerobic digestion
Anaerobic digestion is a bacterial process that takes place in the absence of oxygen. The process can be thermophilic digestion in which the sludge is fermented in tanks at a temperature of 55 °C or mesophilic, at a temperature around 36 °C. However allowing shorter retention time, thus in the small tanks, thermophilic digestion is more expansive in terms of energy consumption to heat the sludge.
Anaerobic digestion generates biogas with a high proportion of methane that can be used to run tank and engines or micro turbines for other on-site processes. In large treatment plants, more electrical energy can be generated than the machines require. Methane generation is a key benefit of the anaerobic process. Its dominant disadvantage is the long time required for the process (up to 30 days) and the high cost of capital.
Advantages[10].
The Goldbar wastewater treatment plant in Edmonton, Alberta, Canada currently uses the process. Under laboratory conditions it is possible to directly generate useful amounts of electricity from organic sludge using naturally occurring electrochemically active bacteria. Potentially, this technique could lead to an environmentally friendly way of generating energy, but to be effective, a microbial fuel cell must maximize the contact area between the effluent and the bacteria-coated surface of the anode, which could seriously decrease the performance of the process.
aerobic digestion
Aerobic digestion is a bacterial process that occurs in the presence of oxygen. Under aerobic conditions, bacteria rapidly consume organic matter and convert it to carbon dioxide. Once there is a lack of organic matter, the bacteria die and are used as food by other bacteria. This stage of the process is known as endogenous respiration. The reduction of solids occurs in this phase. Because aerobic digestion occurs much more rapidly, the capital costs of aerobic digestion are lower. However, operating costs are typically much higher for aerobic digestion due to the energy costs for the aeration needed to add oxygen to the process.
Compost or fertilizer
Composting is also an aerobic process that involves mixing wastewater solids with carbon sources such as sawdust, straw or wood chips. In the presence of oxygen, bacteria digest solids from the wastewater and the added carbon source and, in doing so, produce a large amount of heat. Anaerobic and aerobic digestion processes can result in the destruction of disease-causing microorganisms and parasites to a sufficient level to allow the resulting digested solids to be safely applied to soil used as soil amendment material (with similar benefits to peat) or used for agriculture as fertilizer provided that the levels of toxic components are sufficiently low.
Thermal depolymerization
Thermal depolymerization uses aqueous pyrolysis to convert the reduced complex organisms to oil. The hydrogen in water inserts itself between chemical bonds in natural polymers such as fats, proteins and cellulose. The oxygen in water combines with carbon, hydrogen and metals. The result is oil, light fuel gases such as methane, propane and butane, water with soluble salts, carbon dioxide, and a small residue of inert insoluble material that resembles pulverized rock and coal. All organisms and many organic toxins are destroyed. Inorganic salts such as nitrates and phosphates remain in the water after treatment at high enough levels that additional treatment is required.
The energy from decompressing the material is recovered, and the process heat and pressure is usually powered from the light fuel gases. The oil is usually further treated to make a refined useful light grade of oil, such as some diesel and heating oils, and then sold.
The choice of a solid wastewater treatment method depends on the amount of solids generated and other site-specific conditions. However, generally composting is most often applied to small scale uses followed by aerobic digestion and then anaerobic digestion for large scales such as in municipalities.
sludge deposition
When a liquid sludge is produced, additional treatment may be required to make it suitable for final disposal. Typically, sludge is thickened (dewatered) to reduce the volumes transported for disposal. Processes to reduce water content include lagooning drying beds to produce a cake that can be applied to soil or incinerated; pressing, where mud is mechanically filtered, through cloth screens to often produce a firm cake; and centrifugation where the sludge is thickened centrifugally separating the solid and the liquid.[11] The sludge can be disposed of by liquid injection to land or by disposal in an embankment. There are concerns about sludge incineration due to air pollutants in emissions, along with the high cost of supplemental fuel, making this a less attractive and less commonly constructed means of sludge treatment and disposal.
There is no process that completely eliminates the requirements for biosolids disposal. In South Australia, after centrifugation, the sludge is completely dried by sunlight. The nutrient-rich biosolids are then provided to farmers to use as a natural fertilizer. This method has reduced the amount of landfill generated by the process each year.
Wastewater photobiopurification
Photobiopurification of wastewater is a process that involves the presence of sunlight and photosynthetic organisms for the purification process. Generally, photobiopurification is carried out by photosynthetic microorganisms, such as microalgae and cyanobacteria, in photobioreactors, reactors specifically designed to take advantage of sunlight and promote the growth of these microorganisms.[1].
Treatment in the reception environment
The introduction of wastewater that the plant treats influences the processes of many small rivers. In a wastewater treatment plant, the natural treatment processes that occur in the environment are designed, whether that environment is a natural body of water or land. If it has not been overloaded, bacteria in the environment will consume the organic contaminants, although this will reduce the oxygen levels in the water and can significantly change the overall ecology of the receiving water. Native bacterial populations feed on organic contaminants, and the numbers of disease-causing microorganisms are reduced by natural environmental conditions such as predation, exposure to ultraviolet radiation, etc. Therefore in case the receiving environment provides a high level of dilution, a high degree of wastewater treatment may not be required. However, recent evidence has shown that very low levels of certain contaminants in wastewater, including hormones (from animal agriculture and the residue of human birth control pills) and synthetic materials such as phthalates, can have an unpredictable adverse impact on the natural environment and potentially on humans if the water is reused for drinking water. In the US, uncontrolled discharges of wastewater into the environment are not permitted under law, and strict water quality requirements must be known. A significant threat in the coming decades will be the increasing uncontrolled discharges of wastewater within rapidly developing countries.
Global treatment gap
Seen from a global perspective, there is inadequate wastewater treatment capacity, especially in underdeveloped countries. This circumstance has existed since at least the 1970s and is due to overpopulation, the water crisis, and the cost of building wastewater treatment systems. The result of inadequate wastewater treatment is a significant increase in mortality from (mostly) preventable diseases; Furthermore, this impact of mortality is particularly high among infants and other children in underdeveloped countries, particularly in the continents of Africa and Asia. Particularly, in the year 2000, the United Nations has established that 2.64 billion people had inadequate wastewater treatment or disposal. This value represented 44 percent of the global population, but in Africa and Asia approximately half of the population had no access whatsoever to wastewater treatment services.
Environmental impact
Los contaminantes de las aguas servidas municipales, o aguas servidas domésticas, son los sólidos suspendidos y disueltos que consisten en: materias orgánicas e inorgánicas, nutrientes, aceites y grasas, sustancias tóxicas, y microorganismos patógenos. Los desechos humanos sin un tratamiento apropiado, eliminados en su punto de origen o recolectados y transportados, presentan un peligro de infección parasitaria (mediante el contacto directo con la materia fecal), hepatitis y varias enfermedades gastrointestinales, incluyendo el cólera y tifoidea (mediante la contaminación de la fuente de agua y la comida). Cabe mencionar que el agua de lluvia urbana puede contener los mismos contaminantes, a veces en concentraciones sorprendentemente altas.
Cuando las aguas servidas son recolectadas pero no tratadas correctamente antes de su eliminación o reutilización, existen los mismos peligros para la salud pública en las proximidades del punto de descarga. Si dicha descarga es en aguas receptoras, se presentarán peligrosos efectos adicionales (p.ej. el hábitat para la vida acuática y marina es afectada por la acumulación de los sólidos; el oxígeno es disminuido por la descomposición de la materia orgánica; y los organismos acuáticos y marinos pueden ser perjudicados aún más por las sustancias tóxicas, que pueden extenderse hasta los organismos superiores por la bio-acumulación en las cadenas alimenticias). Si la descarga entra en aguas confinadas, como un lago o una bahía, su contenido de nutrientes puede ocasionar la eutrofización, con molesta vegetación que puede afectar a las pesquerías y áreas recreativas. Los desechos sólidos generados en el tratamiento de las aguas servidas (grava, y fangos primarios y secundarios) pueden contaminar el suelo y las aguas si no son manejados correctamente.[12].
Los proyectos de aguas servidas son ejecutados a fin de evitar o aliviar los efectos de los contaminantes descritos anteriormente en cuanto al ambiente humano y natural. Cuando son ejecutados correctamente, su impacto total sobre el ambiente es positivo.
Los impactos directos incluyen la disminución de molestias y peligros para la salud pública en el área de servicio, mejoramientos en la calidad de las aguas receptoras, y aumentos en los usos beneficiosos de las aguas receptoras. Adicionalmente, la instalación de un sistema de recolección y tratamiento de las aguas servidas posibilita un control más efectivo de las aguas servidas industriales mediante su tratamiento previo y conexión con el alcantarillado público, y ofrece el potencial para la reutilización beneficiosa del efluente tratado y de los fangos.
Los impactos indirectos del tratamiento de las aguas residuales incluyen la provisión de sitios de servicio para el desarrollo, mayor productividad y rentas de las pesquerías, mayores actividades y rentas turísticas y recreativas, mayor productividad agrícola y forestal o menores requerimientos para los fertilizantes químicos, en caso de ser reutilizado el efluente y los fangos, y menores demandas sobre otras fuentes de agua como resultado de la reutilización del efluente.
De éstos, varios potenciales impactos positivos se prestan para la medición, por lo que pueden ser incorporados cuantitativamente en el análisis de los costos y beneficios de varias alternativas al planificar proyectos para las aguas servidas. Los beneficios para la salud humana pueden ser medidos, por ejemplo, mediante el cálculo de los costos evitados, en forma de los gastos médicos y días de trabajo perdidos que resultan de un saneamiento defectuoso. Los menores costos del tratamiento de agua potable e industrial y mayores rentas de la pesca, el turismo y la recreación, pueden servir como mediciones parciales de los beneficios obtenidos del mejoramiento de la calidad de las aguas receptoras. En una región donde es grande la demanda de viviendas, los beneficios provenientes de proporcionar lotes con servicios pueden ser reflejados en parte por la diferencia en costos entre la instalación de la infraestructura por adelantado o la adecuación posterior de comunidades no planificadas.
A menos que sean correctamente planificados, ubicados, diseñados, construidos, operados y mantenidos, es probable que los proyectos de aguas servidas tengan un impacto total negativo y no produzcan todos los beneficios para los cuales se hizo la inversión, afectando además en forma negativa a otros aspectos del medio ambiente.
Sociocultural problems
Treatment facilities require land; its location may result in involuntary repopulation. Furthermore, treatment and disposal works may create nuisance in the immediate vicinity, at least occasionally. Often, the lands and neighborhoods chosen correspond to "vulnerable groups" who are the least able to face the costs of relocation and whose living environment is already altered. Care should be taken to locate treatment and disposal facilities where odors or noise will not disturb residents or other users of the area, handle relocation sensitively, and include in the project abatement plan provisions to mitigate or offset adverse impacts on the human environment. Failure to include these considerations in project planning presents substantial risk.
Appropriate technology
The concept of appropriate technology in wastewater systems encompasses technical, institutional, social and economic dimensions. From a technical and institutional point of view, the selection of inappropriate technologies has been identified as one of the main causes of system failures. The wastewater environment is hostile to electronic, electrical and mechanical equipment. Its maintenance is an endless process, and requires support (spare parts, laboratories, trained technicians, specialized technical assistance, and adequate budgets). Even in developed countries, it is the simplest systems, chosen and designed with a view to maintenance, that provide the most reliable service. In developing countries, where some ingredients for a successful maintenance program may be missing, this should be the first consideration when choosing technologies for treatment plants and pumping stations.
In small communities and rural environments, technical options are often simpler, but institutional considerations combine with social ones and remain extremely important. Local institutions must be able to manage sanitation programs or systems; Community participation can be a key element in your success. The usual social and practical preferences are important; some can be modified through educational programs, but others may be rooted in cultural values and not subject to change.
Economics is part of the decision in two ways. Not surprisingly, the simplest technologies, selected for their ease of operation and maintenance, are often the least expensive to build and operate. However, even when they are not, as may be the case when large amounts of land must be acquired for stabilization ponds, a less expensive system that fails would ultimately be more expensive than a more expensive one that operates reliably.[13].
References
[1] ↑ a b Romero Rojas, Jairo A. Lagunas de estabilización de aguas residuales. Editorial Escuela Colombiana de Ingeniería. 1994 ISBN 958 8060 50 8.
[2] ↑ García Zare, Elmis Jonatan; Mejía Pardo, Patricia Isabel; Soto Abanto, Segundo Eloy; Rodriguez Paredes, Noelia Patricia; Cerna Vasquez, Marco Antonio (11 de agosto de 2023). Hydrochloric acid concentration and time to maximize lead and cadmium removal in laboratory wastewater (en inglés). doi:10.18687/laccei2023.1.1.573. Consultado el 9 de julio de 2024.: https://laccei.org/LACCEI2023-BuenosAires/meta/FP573.html
[4] ↑ Ministerio para la Transición Ecológica y el Reto Demográfico (22 de septiembre de 2022), Real Decreto 730/2022, de 6 de septiembre, por el que se regula la concesión directa de subvenciones para el desarrollo de las actuaciones complementarias de saneamiento y depuración del Marco de Actuaciones Prioritarias para Recuperar el Mar Menor y en el marco del Plan de Recuperación, Transformación y Resiliencia (Real Decreto 730/2022), pp. 130096-130112, consultado el 15 de abril de 2025 .: https://www.boe.es/diario_boe/txt.php?id=BOE-A-2022-15419
[5] ↑ Henze, M.; van Loosdrecht, M. C. M.; Ekama, G.A.; Brdjanovic, D. (2008). Biological Wastewater Treatment: Principles, Modelling and Design (en inglés). IWA Publishing (Spanish and Arabic versions are available online for free). ISBN 978-1-78040-186-7. doi:10.2166/9781780401867.: http://iwaponline.com/ebooks/book/59/Biological-Wastewater-Treatment-Principles
[6] ↑ De acuerdo a su respuesta frente al O2 las bacterias se clasifican como:
[7] ↑ Sayago, Carreño; Fernando, Uriel (2021-01). «Design, Scaling, and Development of Biofilters with E crassipes for Treatment of Water Contaminated with Cr (VI)». Water (en inglés) 13 (9): 1317. doi:10.3390/w13091317. Consultado el 19 de agosto de 2021.: https://www.mdpi.com/2073-4441/13/9/1317
[8] ↑ Sayago, Uriel Fernando Carreño (29 de abril de 2021). «Design and development of a biotreatment of E. crassipes for the decontamination of water with Chromium (VI)». Scientific Reports (en inglés) 11 (1): 9326. ISSN 2045-2322. doi:10.1038/s41598-021-88261-0. Consultado el 19 de agosto de 2021.: https://www.nature.com/articles/s41598-021-88261-0
[9] ↑ Romero Rojas, Jairo A. Lagunas de estabilización de aguas residuales. Editorial Escuela Colombiana de Ingeniería. 1994 ISBN 958 8060 50 8 Cap 4. pág. 99.
[12] ↑ Entrevista con el Msc. Ing. Nobel Francisco Rovirosa Morell sobre los aspectos técnicos-económicos-ambientales en el tratamiento de las aguas residuales urbanas Conversaciones sobre el agua, Capítulo IV.: http://www.sonia-bueno.net/41563.html
[13] ↑ «Tratamiento de aguas residuales (Estudios y practicas profesionales)». Tecnología y tratamiento de aguas residuales. 12 de junio de 2019.: https://awtsa.com/
Anaerobic oxidation is defined as that in which the decomposition takes place in the absence of dissolved oxygen and the oxygen of organic compounds, nitrates and nitrites, sulfates and CO, is used as an electron acceptor. In the process known as denitrification, nitrates and nitrites are used by facultative bacteria, under anoxic conditions, intermediate conditions, with the formation of CO, water and gaseous nitrogen as final products.[9].
Phosphorus removal can be effected biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria called polyphosphate-accumulating organisms enrich and selectively accumulate large amounts of phosphorus within their cells. When the biomass enriched in these bacteria is separated from the treated water, the bacterial biosolids have a high fertilizer value. Phosphorus removal can also be achieved, generally by chemical precipitation with iron (for example: ferric chloride) or aluminum (for example: alum) salts. The resulting chemical sludge, however, is difficult to operate, and the use of chemicals in the treatment process is expensive. Although this makes the operation difficult and often dirty, chemical phosphorus removal requires a significantly smaller equipment footprint than biological removal and is easier to operate.
The purpose of disinfection in wastewater treatment is to substantially reduce the number of living organisms in the water that will be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water that is treated (for example: turbidity, pH, etc.), the type of disinfection that is used, the dose of disinfectant (concentration and time), and other environmental variables. Cloudy water will be treated with less success since the solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high fluxes work against effective disinfection. Common disinfection methods include ozone, chlorine, or UV light. Chloramine, which is used for drinking water, is not used in wastewater treatment due to its persistence.
Chlorine disinfection remains the most common form of wastewater disinfection in North America due to its low cost history and long-term effectiveness. A disadvantage is that chlorine disinfection of residual organic material can generate organically chlorinated compounds that may be carcinogenic or harmful to the environment. Residual chlorine or "chloramines" may also be able to organically chlorine the material in the natural aquatic environment. Additionally, because residual chlorine is toxic to aquatic species, the treated effluent must be chemically dechlorinated, adding complexity and cost to the treatment.
Ultraviolet (UV) light is becoming the most common means of disinfection in the UK due to concerns about the impacts of chlorine on wastewater treatment and on organic chlorination in receiving waters. UV radiation is used to damage the genetic structure of bacteria, viruses, and other pathogens, rendering them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that target microorganisms are not shielded from UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from UV light).
Ozone (O) is generated by passing oxygen (O) through a high voltage potential, which adds a third oxygen atom and forms O. Ozone is very unstable and reactive and oxidizes most of the organic material it comes into contact with, thereby destroying many disease-causing microorganisms. Ozone is considered safer than chlorine because, while chlorine has to be stored on site (highly poisonous in case of accidental release), ozone is placed as needed. Ozonation also produces fewer byproducts than chlorine disinfection. A disadvantage of ozone disinfection is the high cost of ozone generating equipment, and that the qualification of operators must be high.
Anaerobic oxidation is defined as that in which the decomposition takes place in the absence of dissolved oxygen and the oxygen of organic compounds, nitrates and nitrites, sulfates and CO, is used as an electron acceptor. In the process known as denitrification, nitrates and nitrites are used by facultative bacteria, under anoxic conditions, intermediate conditions, with the formation of CO, water and gaseous nitrogen as final products.[9].
Phosphorus removal can be effected biologically in a process called enhanced biological phosphorus removal. In this process, specific bacteria called polyphosphate-accumulating organisms enrich and selectively accumulate large amounts of phosphorus within their cells. When the biomass enriched in these bacteria is separated from the treated water, the bacterial biosolids have a high fertilizer value. Phosphorus removal can also be achieved, generally by chemical precipitation with iron (for example: ferric chloride) or aluminum (for example: alum) salts. The resulting chemical sludge, however, is difficult to operate, and the use of chemicals in the treatment process is expensive. Although this makes the operation difficult and often dirty, chemical phosphorus removal requires a significantly smaller equipment footprint than biological removal and is easier to operate.
The purpose of disinfection in wastewater treatment is to substantially reduce the number of living organisms in the water that will be discharged back into the environment. The effectiveness of disinfection depends on the quality of the water that is treated (for example: turbidity, pH, etc.), the type of disinfection that is used, the dose of disinfectant (concentration and time), and other environmental variables. Cloudy water will be treated with less success since the solid matter can shield organisms, especially from ultraviolet light or if contact times are low. Generally, short contact times, low doses and high fluxes work against effective disinfection. Common disinfection methods include ozone, chlorine, or UV light. Chloramine, which is used for drinking water, is not used in wastewater treatment due to its persistence.
Chlorine disinfection remains the most common form of wastewater disinfection in North America due to its low cost history and long-term effectiveness. A disadvantage is that chlorine disinfection of residual organic material can generate organically chlorinated compounds that may be carcinogenic or harmful to the environment. Residual chlorine or "chloramines" may also be able to organically chlorine the material in the natural aquatic environment. Additionally, because residual chlorine is toxic to aquatic species, the treated effluent must be chemically dechlorinated, adding complexity and cost to the treatment.
Ultraviolet (UV) light is becoming the most common means of disinfection in the UK due to concerns about the impacts of chlorine on wastewater treatment and on organic chlorination in receiving waters. UV radiation is used to damage the genetic structure of bacteria, viruses, and other pathogens, rendering them incapable of reproduction. The key disadvantages of UV disinfection are the need for frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure that target microorganisms are not shielded from UV radiation (i.e., any solids present in the treated effluent may protect microorganisms from UV light).
Ozone (O) is generated by passing oxygen (O) through a high voltage potential, which adds a third oxygen atom and forms O. Ozone is very unstable and reactive and oxidizes most of the organic material it comes into contact with, thereby destroying many disease-causing microorganisms. Ozone is considered safer than chlorine because, while chlorine has to be stored on site (highly poisonous in case of accidental release), ozone is placed as needed. Ozonation also produces fewer byproducts than chlorine disinfection. A disadvantage of ozone disinfection is the high cost of ozone generating equipment, and that the qualification of operators must be high.