Question:
In sewage treatment, formation of activated sludge takes place during ___________.
In sewage treatment, formation of activated sludge takes place during ___________.
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Activated sludge is the sediment of microbial flocs from the aerated tank.
Updated On: Nov 12, 2026
- preliminary
- primary
- secondary
- tertiary
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Verified By Collegedunia
The Correct Option is C
Solution and Explanation
Step 1: Understanding the Concept
Primary treatment only removes floating and settleable solids by physical methods.
Step 2: Secondary treatment
The primary effluent is aerated in tanks so that aerobic bacteria and fungi grow as flocs and consume organic matter, lowering the BOD.
Step 3: Activated sludge
The flocs are allowed to settle. This sediment is the activated sludge, and part of it is returned to the aeration tank as inoculum.
Final Answer:
Activated sludge forms during secondary treatment. \[ \boxed{\text{(C) }\text{secondary}} \]
Primary treatment only removes floating and settleable solids by physical methods.
Step 2: Secondary treatment
The primary effluent is aerated in tanks so that aerobic bacteria and fungi grow as flocs and consume organic matter, lowering the BOD.
Step 3: Activated sludge
The flocs are allowed to settle. This sediment is the activated sludge, and part of it is returned to the aeration tank as inoculum.
Final Answer:
Activated sludge forms during secondary treatment. \[ \boxed{\text{(C) }\text{secondary}} \]
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