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Biology · 2024 · 2 marks
CBSE 2024 · Region 5 · Set 3 · Q20
List the events that reduce the Biochemical Oxygen Demand (BOD) of a primary effluent during sewage treatment.
List the events that reduce the Biochemical Oxygen Demand (BOD) of a primary effluent during sewage treatment.
Marking-scheme solution
₋ The primary effluent is passed into (large) aeration tank,
₋ Constantly agitated mechanically and air is pumped into it,
₋ Vigorous growth of useful aerobic microbes (fungi and bacteria) into flocs,
₋ Which consume major part of the organic matter in effluent thus
BOD of effluent is reduced.
₋
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CBSE Class 12 Biology past-paper question from the 2024 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.