'Flocs' formed during the secondary treatment of sewage contain

Bacteria, fungi and protozoa

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Bacteria, virus and protozoa

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Bacteria, algae and protozoa

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Virus, prions and mycorhiza

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Solution

The correct option is A Bacteria, fungi and protozoa
During the secondary treatment primary effluent is passed into large aeration tank where it is constantly agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs.
The biological floc is composed of bacteria, fungi and protozoa. Bacteria involve around 95% of the total microbial population of the activated sludge and they are essential for the degradation of organic substances in wastewater treatment systems.

Suggest Corrections

	Primary Sludge	Activated sludge
(i)	It is sludge formed during primary sewage treatment.	It is sludge formed during secondary sewage treatment.
(ii)	It possesses flocs of decomposer microbes.	It does not possess flocs of decomposer microbes.
(iii)	It does not require aeration.	Formation of activated sludge requires aeration.
(iv)	A lot of decomposition occurs during formation of primary sludge.	Very little decomposition occurs during formation of activated sludge.