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Question
After the secondary treatment of sewage, the effluent produced is released into the ______.
After the secondary treatment of sewage, the effluent produced is released into the ______.
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Solution
The correct option is D water bodies
Sewage (waste water generated in towns and cities) is rich in organic wastes and microbes. Hence, it is treated in sewage treatment plants to remove the wastes and impurities.
Sewage is first subjected to primary treatment in which physical removal of particles (floating debris, stones, pebbles, etc) occurs by the process of filtration and sedimentation. Filtration units are used during primary treatment to remove floating debris. This is followed by sedimentation. The sewage is kept undisturbed for quite a long time and all the solids settle down. The sediment containing the heavy insoluble particles is separated out as primary sludge. The effluent obtained from the primary treatment is taken for secondary treatment.
In secondary treatment, the primary effluent is poured into huge aeration tanks where it is continuously agitated (disturbed) by stirring and pumping it with air. This leads to rapid growth of heterotrophic aerobic microbial flocs (masses of bacteria and filamentous fungi) that feed on the organic wastes present in the sewage and degrade it. This reduces the BOD (biochemical oxygen demand) of sewage. BOD refers to the amount of oxygen that would be consumed if all the organic matter in 1 litre of water was to be oxidised by the microbes present in it. Lesser the organic matter in water, less will be the BOD.
Secondary treatment is continued until the BOD of the waste water is significantly reduced. This waste water is then passed through a settling tank where the microbial floc settles down to form activated sludge. The supernatant (water above the sediment) forms the final effluent from secondary treatment which is poured into water bodies.
Activated sludge is fed into an anaerobic sludge digester tank where anaerobic microbes digest the bacteria and fungi present in it in the absence of oxygen.
Sewage (waste water generated in towns and cities) is rich in organic wastes and microbes. Hence, it is treated in sewage treatment plants to remove the wastes and impurities.
Sewage is first subjected to primary treatment in which physical removal of particles (floating debris, stones, pebbles, etc) occurs by the process of filtration and sedimentation. Filtration units are used during primary treatment to remove floating debris. This is followed by sedimentation. The sewage is kept undisturbed for quite a long time and all the solids settle down. The sediment containing the heavy insoluble particles is separated out as primary sludge. The effluent obtained from the primary treatment is taken for secondary treatment.
In secondary treatment, the primary effluent is poured into huge aeration tanks where it is continuously agitated (disturbed) by stirring and pumping it with air. This leads to rapid growth of heterotrophic aerobic microbial flocs (masses of bacteria and filamentous fungi) that feed on the organic wastes present in the sewage and degrade it. This reduces the BOD (biochemical oxygen demand) of sewage. BOD refers to the amount of oxygen that would be consumed if all the organic matter in 1 litre of water was to be oxidised by the microbes present in it. Lesser the organic matter in water, less will be the BOD.
Secondary treatment is continued until the BOD of the waste water is significantly reduced. This waste water is then passed through a settling tank where the microbial floc settles down to form activated sludge. The supernatant (water above the sediment) forms the final effluent from secondary treatment which is poured into water bodies.
Activated sludge is fed into an anaerobic sludge digester tank where anaerobic microbes digest the bacteria and fungi present in it in the absence of oxygen.
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