Explain the different step involve in the secondry treatment of sewage

1.	Explain the different step involve in the secondry treatment of sewage
Answer» Secondary treatment/Biological treatment: Primary effluent is passed through large aeration tanks with constant mechanical agitation and air supply. Useful aerobic microbes grow rapidly and form flocs. The growing microbes consume organic matter and thereby, reduce the BOD of the effluent. After this, the effluent is passed into the settling tank. The bacterial flocs settle down and the sediment is now called activated sludge. A small part of the sludge is used as an inoculum in the aeration tank and the remaining part is passed into large tanks called anaerobic sludge digestors. In the digestors, heterotrophic microbes anaerobically digest bacteria and fungi in the sludge producing a mixture of gases such as methane, hydrogen sulphide and CO2\xa0which form biogas.

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