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Biology · 2022 · 2 marks
CBSE 2022 · Region 5 · Set 2 · Q5
Study the given diagram of Sewage Treatment Plant (S.T.P.) and answer the questions that follow: S.T.P. (Sewage Treatment Plant) (A) S.T.P. (Sewage…
Study the given diagram of Sewage Treatment Plant (S.T.P.) and answer the questions that follow :
S.T.P. (Sewage Treatment Plant) (A) S.T.P. (Sewage Treatment Plant) (B)
(a)
Which one of the two 'S.T.P.' (A) or (B) will be more effective in treating the human excreta in the municipal waste?
(b)
Write the steps followed in carrying the treatment of the sewage in step (Z), once the BOD of sewage is reduced significantly till it is passed on to the "anaerobic sludge digesters".
Marking-scheme solution
(a)
S.T.P (B) / B
(b)
● The effluent is passed into the settling tanks
The bacterial 'flocs' are allowed to settle (sediment is called activated sludge)
a small part of the 'activated sludge' is pumped back into the aeration tanks as inoculum (for secondary/biological treatment)
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CBSE Class 12 Biology past-paper question from the 2022 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.