Primary sewage treatment is characterised by
A{'text': 'Aerobic biological digestion by mesh-forming microbes', 'label': 'A'}
B{'text': 'Physical removal of particles via filtration and sedimentation', 'label': 'B'}
C{'text': 'Anaerobic digestion of settled sludge producing biogas', 'label': 'C'}
D{'text': 'Precise BOD measurement by chemical assays in the lab', 'label': 'D'}
Answer & Solution
Correct answer: B. {'text': 'Physical removal of particles via filtration and sedimentation', 'label': 'B'}
1. Primary treatment is a physical (not biological) step.
2. Sequential filtration removes floating debris.
3. Sedimentation separates grit and settleable solids into primary sludge.
4. The supernatant effluent then goes to secondary (biological) treatment.
_Source: NCERT Class 12 Biology, Ch 8 "Microbes in Human Welfare", §8.3_
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