Question

Activated sludge is

• A. sediment and bacterial flocs
• B. anaerobically digested flocs
• C. sedimented primary effluent
• D. fluid containing anaerobic bacteria

Answer 1

The correct option is A sediment and bacterial flocs

During the secondary treatment of the sewage the BOD of the effluent is being reduced. Once the BOD of the sewage is reduced significantly, the effulent is then allowed to pass into a settling tank in which the bacterial ‘flocs’ are allowed to sediment. This sediment is called as activated sludge. A smal part of the activated sludge is pumped back into the aeration tank to serve as the inoculum.
The remaining major part of the sludge is pumped into large tanks called anaerobic sludge digesters. Here, other kinds of bacteria, which grow anaerobically, digest the bacteria and the fungi in the sludge. The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.