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Standard IX
Biology
Water Recycling
Select the co...
Question

Select the correct statement regarding activated sludge formed during secondary sewage treatment.

A
A small part of it is rapidly pumped back from sedimentation to aeration tank.
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B
It absorbs pathogenic bacteria present in waste water while sinking to the bottom of the settling tank.
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C
A major part of it Is anaerobically digested.
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D
Both (a) and (c)
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Solution

The correct option is B Both (a) and (c)
A small part of activated sludge is pumped back from sedimentation to aeration tank. But it dos not absorb pathogenic bacteria.
A major part of activated sludge is anaerobically digested by methanogens.
So, the correct option is 'Both (a) and (c)'

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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.
Q. During secondary sewage treatment,
Flocs from the settling tank are sent for their digestion
Only a part of it is sent as inoculum in the aeration tank
Then the aeration tank is agitated where this inoculum multiplies for the development of flocs

I have a doubt,
Can we not transfer all the flocs from the sediment tank to the aviation tank and not just the small inoculum? Because now even if we don't agitate the aeration tank but allow the flocs in the aeration tank to break down the sewage the same process would occur in the aeration tank in a much less time and we would also be saving the energy spent in the agitation of aeration tank.
Q. Study the given differences between primary sludge and activated sludge and select the incorrect ones.
Primary SludgeActivated 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. Refer the given flowchart of sewage treatment, accordingly match Column I with Column II and select the correct answer from the codes given below:


Column IColumn IIA.The stage in which physicaltreament of sewage is done(i)Anaerobic degestion of activatedsludge and production of biogasB.The stage in which biologicaltreatment of sewage is done(ii)Activated sludgeC.Name of the sediment in primary treatment(iii)Aeration tanksD.It is carried to aeration tanks fromprimary settling(iv)Primary effluentE.Name of the sediment in secondary treatment (v)Primary sludgeFSite of flocs growth(vi)Secondary treatmentGFunction of sludge digester(vii)Primary
Q. Which of the following is pumped into anaerobic sludge digesters during the sewage treatment?
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