Contenido

La estabilización de los lodos tiene el objetivo de: reducir la presencia de patógenos; eliminar los olores desagradables; y, reducir o eliminar su potencial de putrefacción.

Los medios de estabilización más eficaces para alcanzar estos objetivos son: la reducción biológica del contenido de materia volátil; la oxidación química de la materia volátil; la adición de agentes químicos para hace que el lodo no sea adecuado para la supervivencia de microorganismos; y la aplicación de calor para la desinfección o esterilización del lodo.

Las técnicas más utilizadas para la estabilización de los lodos son: la digestión aerobia; la digestión anaerobia; la estabilización con cal; el tratamiento térmico; y, el compostaje.[3]​.

Anaerobic digestion

This sludge stabilization process is based on the degradation of organic matter, in the absence of molecular oxygen. It is one of the oldest processes.

The organic matter contained in the mixture of primary and secondary sludge is converted, mainly, into methane (CH) and carbon dioxide (CO).

The process takes place in a completely closed reactor, where sludge is introduced, either continuously or intermittently, remaining inside the reactor for considerable times. The stabilized sludge extracted from the reactor has a reduced concentration of organic matter and live pathogens.

The digesters used are classified into low load reactors and high load reactors.

In low load digesters, the sludge mixture is not heated nor its contents mixed, retention times vary between 30 and 60 days.

High load digesters, on the other hand, have devices to heat and mix the sludge contained in the digester. The processes for mixing sludge can be through gas recirculation, through mechanical mixers, through pumping or mixers with suction tubes. The retention time for this type of digesters is generally less than 15 days.

The two processes can be combined in what is called a two-stage process.

The gas produced in the anaerobic digestion of domestic wastewater contains between 65 and 70% methane and between 25 and 30% carbon dioxide, in much smaller quantities nitrogen, hydrogen, hydrogen sulfide and others.

Digestion gas, which has a caloric value of approximately 22,400 kJ/m (natural gas has a caloric value of 37,300 kJ/m), can be used as fuel.

aerobic digestion

Aerobic digestion is generally used for plants with relatively low capacity. The main advantages of aerobic digestion are: lower BOD concentrations are achieved in the supernatant liquid: the initial investment is usually lower; A biologically stable final product is obtained, without odors. The disadvantages can be significant, including: a higher energy cost associated with supplying the necessary oxygen; The characteristics of the digested sludge are not the best to apply mechanical dehydration. It should also be remembered that anaerobic digestion is also very delicate in terms of operation.

La función del espesado es la de aumentar la fracción sólida de los lodos, para reducir el costo de los tratamientos posteriores, reduciendo los volúmenes a ser procesados. Las técnicas usadas para el espesamiento son: por sedimentación o por gravedad; por flotación; y por centrifugado.

Gravity thickened

Gravity thickening is carried out in a tank similar to a settler, generally constructed in a round shape. This procedure is more effective when dealing with sludge extracted from the primary treatment.

The sludge is deposited at the bottom from where it is removed and pumped to the digesters.

Thickened by flotation

Among the various processes known to thicken sludge by flotation, the most used is that of introducing a liquid solution to which dissolved air has been introduced under pressure. When the pressure of the liquid is reduced, when introduced into the flotation tank, small air bubbles are created that adhere to the sludge and make it float, where it is collected with a skimmer. This procedure is effective for the treatment of biological culture in suspension.

Thickened by centrifugation

It is used to thicken and dewater, mainly active sludge.

Con el incremento de las exigencias de carácter ambiental, la normativa de calidad de lodos para ser devueltos al ambiente se ha ido incrementando, de la misma forma se han ido incrementando las exigencias en el monitoreo de la calidad de los lodos, tanto en su estado líquido como cuando están ya secos. Como consecuencia se ha incrementado también las exigencias de desinfección de los lodos, como la última etapa del tratamiento, para eliminar los patógenos. Los medios más adecuados para desinfectar los lodos son: la pasteurización y el almacenamiento a largo plazo.

Cuando la composición química de los lodos no lo permite su reutilización en la agricultura, deberá ser dispuesto en rellenos sanitarios adecuadamente preparados para ello.

Pasteurization

Pasteurization is mainly used in countries where the regulations explicitly establish this procedure for disinfecting the sludge that is spread during the plant growth period, spring and summer. Presumably the number of countries that establish these requirements will increase in the future.

The equipment currently used for sludge pasteurization makes this procedure unfeasible in developing countries.

Long term storage

Generally, liquid sludge can be stored in lagoons excavated in the ground, waiting for favorable conditions to be applied to the soil, as long as the chemical composition allows it, or in structures designed for drying.

The sludge stored in lagoons increases its concentration if evaporation is greater than precipitation, or if it is adequately protected.

Retention times in excavated lagoons can vary from 60 days, when the average temperature is 20.C, to 120 days, when the average temperature is 4.C.

A nivel mundial el tratamiento de las aguas residuales tiene una cobertura significativamente menor que la cobertura de suministro de agua segura, y el tratamiento de los lodos tiene una cobertura aún menor. Esta situación sin embargo está cambiando, y las legislaciones de diversos países ya regulan las condiciones bajo las cuales puede darse la reutilización de los lodos derivados del tratamiento de las aguas servidas de origen domiciliar. A continuación se describen algunas situaciones particulares:[1]​.

Argentina

Waste sludge composting plants have been implemented for later application as biosolids in agriculture.

Chili

In 2009, DS N°4/2009 Minsal, “Regulation for management of sludge generated in wastewater treatment plants” was promulgated and published considering that the operation of wastewater treatment plants generates a large amount of sludge, which requires adequate management to prevent possible negative impacts on human health and the environment.

Additionally, considering that sludge, due to its high organic matter content, can contribute to improving the physical conditions of soils, that is, constitute a contribution to those that require increasing their porosity, the stability of aggregates, moisture retention, and aeration, as is the case of thin and/or degraded soils. Likewise, due to its content of heavy metals and other contaminants, it can contribute to the contamination of soil and agricultural products.

Finally, the physical properties of the sludge determine that, in its transportation and final disposal, differentiated management of household solid waste is required.

Considering all of the above, this regulation establishes the sanitary classification of sludge and the minimum sanitary requirements for its management, in addition to the restrictions, requirements and technical conditions for the application of sludge on certain soils.

Denmark

Most of the stabilized sludge is used as fertilizer on agricultural lands. The percentage of reuse of wastewater sludge is 72%, 20% is destined for incineration, and 8% is disposed of.

Spain

Waste organic materials from the collection of separated urban waste, as well as from industry, wastewater and sludge from treatment plants are intended to be used in agriculture since it is considered the most appropriate destination for this type of materials from an environmental and economic point of view. The application of residual sludge is studied to control leaks of phytosanitary products into the aquifer.

Europe, Australia, the United States and other countries

Research is currently being carried out to use specially treated sludge to stop the contamination of aquifers by phytosanitary products and their impurities. They will also serve to accelerate the decontamination of soils that are already affected. They are also applied as fertilizers on agricultural land.

Mexico

The Official Mexican Standard NOM-004- SEMARNAT-2002 for sludge and biosolids was recently approved, which establishes the maximum permissible limits of contaminants contained for their use and final disposal.

Contenido

La estabilización de los lodos tiene el objetivo de: reducir la presencia de patógenos; eliminar los olores desagradables; y, reducir o eliminar su potencial de putrefacción.

Los medios de estabilización más eficaces para alcanzar estos objetivos son: la reducción biológica del contenido de materia volátil; la oxidación química de la materia volátil; la adición de agentes químicos para hace que el lodo no sea adecuado para la supervivencia de microorganismos; y la aplicación de calor para la desinfección o esterilización del lodo.

Las técnicas más utilizadas para la estabilización de los lodos son: la digestión aerobia; la digestión anaerobia; la estabilización con cal; el tratamiento térmico; y, el compostaje.[3]​.

Anaerobic digestion

This sludge stabilization process is based on the degradation of organic matter, in the absence of molecular oxygen. It is one of the oldest processes.

The organic matter contained in the mixture of primary and secondary sludge is converted, mainly, into methane (CH) and carbon dioxide (CO).

The process takes place in a completely closed reactor, where sludge is introduced, either continuously or intermittently, remaining inside the reactor for considerable times. The stabilized sludge extracted from the reactor has a reduced concentration of organic matter and live pathogens.

The digesters used are classified into low load reactors and high load reactors.

In low load digesters, the sludge mixture is not heated nor its contents mixed, retention times vary between 30 and 60 days.

High load digesters, on the other hand, have devices to heat and mix the sludge contained in the digester. The processes for mixing sludge can be through gas recirculation, through mechanical mixers, through pumping or mixers with suction tubes. The retention time for this type of digesters is generally less than 15 days.

The two processes can be combined in what is called a two-stage process.

The gas produced in the anaerobic digestion of domestic wastewater contains between 65 and 70% methane and between 25 and 30% carbon dioxide, in much smaller quantities nitrogen, hydrogen, hydrogen sulfide and others.

Digestion gas, which has a caloric value of approximately 22,400 kJ/m (natural gas has a caloric value of 37,300 kJ/m), can be used as fuel.

aerobic digestion

Aerobic digestion is generally used for plants with relatively low capacity. The main advantages of aerobic digestion are: lower BOD concentrations are achieved in the supernatant liquid: the initial investment is usually lower; A biologically stable final product is obtained, without odors. The disadvantages can be significant, including: a higher energy cost associated with supplying the necessary oxygen; The characteristics of the digested sludge are not the best to apply mechanical dehydration. It should also be remembered that anaerobic digestion is also very delicate in terms of operation.

La función del espesado es la de aumentar la fracción sólida de los lodos, para reducir el costo de los tratamientos posteriores, reduciendo los volúmenes a ser procesados. Las técnicas usadas para el espesamiento son: por sedimentación o por gravedad; por flotación; y por centrifugado.

Gravity thickened

Gravity thickening is carried out in a tank similar to a settler, generally constructed in a round shape. This procedure is more effective when dealing with sludge extracted from the primary treatment.

The sludge is deposited at the bottom from where it is removed and pumped to the digesters.

Thickened by flotation

Among the various processes known to thicken sludge by flotation, the most used is that of introducing a liquid solution to which dissolved air has been introduced under pressure. When the pressure of the liquid is reduced, when introduced into the flotation tank, small air bubbles are created that adhere to the sludge and make it float, where it is collected with a skimmer. This procedure is effective for the treatment of biological culture in suspension.

Thickened by centrifugation

It is used to thicken and dewater, mainly active sludge.

Con el incremento de las exigencias de carácter ambiental, la normativa de calidad de lodos para ser devueltos al ambiente se ha ido incrementando, de la misma forma se han ido incrementando las exigencias en el monitoreo de la calidad de los lodos, tanto en su estado líquido como cuando están ya secos. Como consecuencia se ha incrementado también las exigencias de desinfección de los lodos, como la última etapa del tratamiento, para eliminar los patógenos. Los medios más adecuados para desinfectar los lodos son: la pasteurización y el almacenamiento a largo plazo.

Cuando la composición química de los lodos no lo permite su reutilización en la agricultura, deberá ser dispuesto en rellenos sanitarios adecuadamente preparados para ello.

Pasteurization

Pasteurization is mainly used in countries where the regulations explicitly establish this procedure for disinfecting the sludge that is spread during the plant growth period, spring and summer. Presumably the number of countries that establish these requirements will increase in the future.

The equipment currently used for sludge pasteurization makes this procedure unfeasible in developing countries.

Long term storage

Generally, liquid sludge can be stored in lagoons excavated in the ground, waiting for favorable conditions to be applied to the soil, as long as the chemical composition allows it, or in structures designed for drying.

The sludge stored in lagoons increases its concentration if evaporation is greater than precipitation, or if it is adequately protected.

Retention times in excavated lagoons can vary from 60 days, when the average temperature is 20.C, to 120 days, when the average temperature is 4.C.

A nivel mundial el tratamiento de las aguas residuales tiene una cobertura significativamente menor que la cobertura de suministro de agua segura, y el tratamiento de los lodos tiene una cobertura aún menor. Esta situación sin embargo está cambiando, y las legislaciones de diversos países ya regulan las condiciones bajo las cuales puede darse la reutilización de los lodos derivados del tratamiento de las aguas servidas de origen domiciliar. A continuación se describen algunas situaciones particulares:[1]​.

Argentina

Waste sludge composting plants have been implemented for later application as biosolids in agriculture.

Chili

In 2009, DS N°4/2009 Minsal, “Regulation for management of sludge generated in wastewater treatment plants” was promulgated and published considering that the operation of wastewater treatment plants generates a large amount of sludge, which requires adequate management to prevent possible negative impacts on human health and the environment.

Additionally, considering that sludge, due to its high organic matter content, can contribute to improving the physical conditions of soils, that is, constitute a contribution to those that require increasing their porosity, the stability of aggregates, moisture retention, and aeration, as is the case of thin and/or degraded soils. Likewise, due to its content of heavy metals and other contaminants, it can contribute to the contamination of soil and agricultural products.

Finally, the physical properties of the sludge determine that, in its transportation and final disposal, differentiated management of household solid waste is required.

Considering all of the above, this regulation establishes the sanitary classification of sludge and the minimum sanitary requirements for its management, in addition to the restrictions, requirements and technical conditions for the application of sludge on certain soils.

Denmark

Most of the stabilized sludge is used as fertilizer on agricultural lands. The percentage of reuse of wastewater sludge is 72%, 20% is destined for incineration, and 8% is disposed of.

Spain

Waste organic materials from the collection of separated urban waste, as well as from industry, wastewater and sludge from treatment plants are intended to be used in agriculture since it is considered the most appropriate destination for this type of materials from an environmental and economic point of view. The application of residual sludge is studied to control leaks of phytosanitary products into the aquifer.

Europe, Australia, the United States and other countries

Research is currently being carried out to use specially treated sludge to stop the contamination of aquifers by phytosanitary products and their impurities. They will also serve to accelerate the decontamination of soils that are already affected. They are also applied as fertilizers on agricultural land.

Mexico

The Official Mexican Standard NOM-004- SEMARNAT-2002 for sludge and biosolids was recently approved, which establishes the maximum permissible limits of contaminants contained for their use and final disposal.