Question

Select the correct sequence of events in secondary treatment of sewage.

• A. Floc formation $ \rightarrow $ aerobic digestion $ \rightarrow $ settling $ \rightarrow $ anaerobic digestion
• B. Aerobic digestion $ \rightarrow $ floc formation $ \rightarrow $ settling $ \rightarrow $ anaerobic digestion
• C. Floc formation $ \rightarrow $ aerobic digestion $ \rightarrow $ anaerobic digestion $ \rightarrow $ settling
• D. Anaerobic digestion $ \rightarrow $ floc formation $ \rightarrow $ aerobic digestion $ \rightarrow $ settling

Answer 1

Answer: (A)

The effluent from primary treatment comes into the aeration tanks where the water is constantly agitated and aerobic bacteria are allowed to grow along with fungal filaments (floc formation). These flocs then aerobically digest the organic matter present in sewage. Then the flocs are allowed to settle in the settling tank. The sludge is pumped into anaerobic sludge digestors where the bacteria and fungi are digested by anaerobic bacteria and produce Biogas.