GATE 2021 AR – Question 53

Infrastructure, Services and Utilities · Waste water treatment · 2 marks · Multiple select

Which statements describe the activated-sludge process?

It is aerobic.
All settled sludge is returned to the aeration tank.
All final-settling-tank effluent is returned to the aeration tank.
Sewage is aerated and agitated in aeration tanks for a few hours.

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Show answer and explanation

Correct answer: (A) It is aerobic.; (D) Sewage is aerated and agitated in aeration tanks for a few hours.

Explanation

Aeration supports aerobic microbial treatment and mixing, A, D. A controlled portion of settled activated sludge is returned, while excess sludge is wasted, so B is false. Treated final effluent is not all recycled into the aeration tank, making C false.

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