Primary sludge contains:

Q. Differentiable between primary sludge and activated sludge.

Q. Study the given differences between primary sludge and activated sludge and select the incorrect ones.

	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.

Q. Activated sludge is obtained by passing air through the sludge obtained from primary treatment.

Q. Match column A with column B and choose the correct option.

Column A	Column B
I. Primary sludge	A. Production of biogas
II. Activated sludge	B. Solids like grit
III. Anaerobic sludge digesters	C. Contains aerobic heterotrophic bacteria

Q. Assertion: A major part of the activated sludge is pumped into large tanks called anaerobic sludge digesters.
Reason: During anaerobic digestion, the anaerobic bacteria digest the organisms present in the primary sludge.