Activated sludge should have the ability to settle quickly so that it can

Options

A. be rapidly pumped back from sedimentation tank to aeration tank
B. absorbd pathogenic bacteria present in waste water while sinking to the bottom of the settling tank
C. be discarded and anaerobically digested
D. absorb colloidal organic matter

Answer

A

Explanation

In the secondary treatment of waste water, when BOD of sewage has reduced, the effluent is passed into setting tank. Here, the bacterial flocs settle and the sediment is 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 digesters. That's why activated sludge should have the ability to settle quickly.