Question

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.

• A. (i) and (ii)
• B. (ii) and (iv)
• C. only (iv)
• D. (ii) and (iii)

Answer 1

Answer: (C)

only (iv)

The primar sludge is formed during primary sewage treatment, while activated sludge is a sludge during secondary sewage treatment, little decomposition occurs during primary sludge formation, while lot of decomposition occurs during activated sludge.

So, the correct option is 'only (iv)'.