Question

Secondary treatment of the sewage is also called biological treatment. Justify this statement and explain the process. [3]

Answer 1

Secondary treatment of sewage is called biological treatment because it involves living organisms such as aerobic or anaerobic microbes to digest the organic waste. [1]

In this process, the primary effluent is first passed into an aeration tank where vigorous growth of aerobic microbes (flocs) takes place. As a result of this, BOD gets significantly reduced. The effluent is then passed to a settling tank where flocs sediment to produce activated sludge. This sludge is pumped to an anaerobic sludge digester to digest the bacteria and fungi in the sludge. [2]