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The aeration tank of a… (Class 12 Biology SQP 2023-24, Q26)

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BiologyCBSE Class 12 · Sample paper, session 2023-24 · 3 marks · Short answer

CBSE Class 12 Biology sample paper 2023-24: question 26

From the official CBSE sample question paper for 2023-24, section C, question 26, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q26 · 3 marks · Short answerCompetency-basedBiodiversity and Conservation

The aeration tank of a sewage treatment plant is not functioning properly. Explain in detail the impact of this on the treatment of sewage and BOD of the effluent.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

Open one hint at a time and try again before the next.

Hint 1

Which stage of sewage treatment uses the aeration tank?

Hint 2

What do aerobic microbes need, and what structures do they form there?

Hint 3

Link microbial consumption of organic matter to BOD.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. Secondary (biological) treatment of sewage, which takes place in the aeration tank, will be badly affected.

    ½ mark

  2. If the aeration tank does not work, air will not be pumped into the effluent.

    ½ mark

  3. Without oxygen, useful aerobic microbes cannot grow vigorously into flocs (masses of bacteria joined with fungal filaments into mesh-like structures).

    ½ mark

  4. So the organic matter in the effluent will not be consumed by these microbes.

    ½ mark

  5. The BOD will not fall. BOD is the amount of oxygen that would be used if all the organic matter in one litre of water were oxidised by bacteria.

    ½ mark

  6. Since higher BOD means greater polluting potential, the effluent will remain highly polluted with organic matter and high BOD. It will also not form activated sludge properly and cannot be discharged safely.

    ½ mark

Answer: No aeration means no aerobic flocs, so organic matter is not degraded and BOD stays high; the effluent remains polluted.

Where the marks are

  • Secondary treatment affected (0.5 mark)
  • No air pumped in (0.5 mark)
  • Aerobic microbes fail to form flocs (0.5 mark)
  • Organic matter not consumed (0.5 mark)
  • BOD not reduced, with BOD explained (0.5 mark)
  • Effluent stays polluted/high BOD (0.5 mark)

Revise the chapter

Practise this chapterBoard-style questions from Biodiversity and Conservation, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2023-24: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.