Sludge is made up of matter. On decomposition, it produces .

Q. Sludge is made up of matter. On decomposition, it produces .

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. The solid matter produced during sewage treatment is

(a) slurry
(b) fertiliser
(c) sludge
(d) humus

Q. A sewage containing 100 mg/I of suspended solids undergoes sewage treatment units. The sludge obtained contains 30% inorganic solids while rest organic solids. If 0.6 $m^3$ of gas is produced per kg of volatile matter reduced, the total gas produced in the digestion of sludge from 1.2 MLD of sewage is: (90% of solids are removed in the treatment process and efficiency of volatile matter reduction is 1).

Q. Matter is made up of: