Question

A sewage treatment process in which a portion of the decomposer bacteria present in the waste is recycled in the beginning of the process is called

• A. Cyclic treatment
• B. Primary treatment
• C. Activated sludge treatment
• D. Tertiary treatment

Answer 1

The correct option is C Activated sludge treatment

Municipal sewage treatment is carried out in the following two stages:- primary treatment and secondary treatment. During secondary treatment, activated sludge treatment is used. During this process, the air is allowed to pass through agitating mixture to make it aerobic. This helps several aerobic microbes to grow and oxidize the organic matter present in sewage. The aerobic microbes consist of micro algae (Chlorella pyrenoidosa), micro-fungi, bacteria and protozoa. These aerobes grow in 'flocs'' and consume a major part of organic matter so that the BOD of sewage is reduced. Now the effluent is passed through a sedimentation tank where microbial 'flocks' are allowed to settle down. The settled material is called 'activated sludge'.