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In the conventional wastewater treatment process, the step in which microbial contaminants are removed by biological degradation in the presence of air is:
APre-screening
BSludge removal
CDisinfection
DAeration
Answer & Solution
Correct answer: D. Aeration
1. Sewage treatment proceeds through pre-screening, aeration, sedimentation, sludge removal and disinfection.
2. In the aeration step, screened wastewater is pumped to a tank where microbial contaminants are removed by biological degradation in the presence of air.
3. Pre-screening removes solids, sludge removal disposes settled solids, and disinfection kills microbes with chlorine or UV, so A, B and C are traps.
4. Hence the answer is D.
_Source: Samacheer Kalvi (TN SCERT) Class 10 Science, Unit "Environmental Management", p.331_
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