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GATE 2021 CE (CE1) – Question 22

Water and Waste Water Quality and Treatment · Primary, secondary and tertiary treatment, effluent standards · 1 mark · Multiple choice

Which statement is correct?

  1. If organic degradation exceeds aeration, river dissolved oxygen is lowest exactly at the effluent discharge point.
  2. Chemoheterotrophs are the most important species degrading organic matter in the activated-sludge process.
  3. The ratio of five-day BOD at 20°C to ultimate BOD exceeds one.
  4. A young lake with low nutrients and low plant productivity is eutrophic.

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Show answer and explanation

Correct answer: (B) Chemoheterotrophs are the most important species degrading organic matter in the activated-sludge process.

Explanation

Activated sludge relies primarily on chemoheterotrophic microorganisms, which obtain energy and carbon from organic matter. The oxygen-sag minimum generally occurs downstream, five-day BOD cannot exceed ultimate BOD, and a nutrient-poor lake is oligotrophic. **Answer: B**.