Class 12th Biology 2017 Set1 Outside Delhi Board Paper Solution
Secondary treatment of the sewage is also called Biological treatment. Justify this statement and explain the process.
Secondary treatment or Biological treatment:
In secondary treatment primary effluent is passed into large acration tanks where iti is constantantly agitated mechanically and air is pumped to it.
Due to this useful aerobic microbes grow rapidly and form flocs. While growing, these microbes consume the major part of the organic matter in the effluent.
This significantly reduces the BOD of the effluent. BOD is a measure of the organic matter present in the water. The greater the BOD of waste water, more is its polluting potential.
When BOD of sewage or waste water is reduced, the effluent is then passed into Settling tank where the bacteria flocs allowed to sediment. This sediment is called activated sludge.
A small part of the activated sludge is pumped back into the acration tank to serve as the inoculum.The remaining part is passed into large tanks called anaerobic sludge digesters.
In the digesters, heterotrophic microbes anaerobically digest bacteria and fungi in sludge producing mixture of gases such as methane, H2S, CO2 .
These gasses forms the biogas and can be used as source of energy as it is inflammable. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.
Secondary treatment of the sewage is also called Biological treatment because in secondary treatment biological factors/organisms play a major role in the treatment. So it is called biological treatment.
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