In sewage treatment, the "flocs" formed in aeration tanks are

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Accepted Answer

C. {'text': 'Masses of activated sludge with fungal filaments and bacteria', 'label': 'C'}

1. During secondary treatment, aerated tanks let aerobic microbes multiply.
2. NCERT describes flocs as masses of bacteria associated with fungal filaments forming mesh-like structures.
3. Flocs consume organic matter in the effluent, reducing BOD.
4. After BOD drops, flocs settle in a settling tank as "activated sludge".
_Source: NCERT Class 12 Biology, Ch 8 "Microbes in Human Welfare", §8.3_

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{'text': 'Colonies of methanogens that produce methane anaerobically', 'label': 'A'}

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{'text': 'Fine sediments of settled soil and small grit particles', 'label': 'B'}

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{'text': 'Insoluble layers of surface oil and greasy hydrocarbon films', 'label': 'D'}