Class 12 · Microbes in Human Welfare

Primary vs Secondary Sewage Treatment — NEET Biology

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What is the key difference between primary and secondary sewage treatment?

NCERT Biology · Class 12 · Chapter 8 · Paragraph 45
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Assertion (A): Secondary sewage treatment involves mechanical agitation to promote microbial activity. Reason (R): Primary effluent is passed into large settling tanks where it is constantly agitated mechanically.

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Correct answer: C If assertion is true but reason is false.

NCERT confirms secondary treatment uses mechanical agitation (Assertion true). However, NCERT states “Primary effluent is passed into large aeration tanks where it is constantly agitated mechanically” - the Reason incorrectly places this in settling tanks instead of aeration tanks, making it false. This tests understanding of where mechanical agitation occurs in the treatment process.

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Microbes in Human Welfare, Class 12 NCERT Biology.

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