GATE CE 2021 Set 1 — Question 22
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Environmental Engineering → Wastewater Treatment Processes → Activated Sludge Process
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Question
Which one of the following is correct?
Correct answer
(B) The most important type of species involved in the degradation of organic matter in the case of activated sludge process based wastewater treatment is chemoheterotrophs.
Solution
Step-by-step evaluation of options:
(A) Incorrect. According to the Streeter-Phelps oxygen sag model, the dissolved oxygen (DO) reaches its minimum value at the 'critical point' downstream from the point of discharge, not at the point of discharge (P) itself.
(B) Correct. Chemoheterotrophs are organisms that obtain both energy and carbon from organic compounds. They are the primary biological agents responsible for breaking down organic matter in the activated sludge process.
(C) Incorrect. represents the oxygen consumed over 5 days, while ultimate BOD is the total oxygen required for complete stabilization. Therefore, is always less than ultimate BOD, making the ratio less than 1.
(D) Incorrect. A lake with low nutrient content and low productivity is termed an oligotrophic lake. A eutrophic lake is one that is rich in nutrients and supports high plant/algal growth.
(A) Incorrect. According to the Streeter-Phelps oxygen sag model, the dissolved oxygen (DO) reaches its minimum value at the 'critical point' downstream from the point of discharge, not at the point of discharge (P) itself.
(B) Correct. Chemoheterotrophs are organisms that obtain both energy and carbon from organic compounds. They are the primary biological agents responsible for breaking down organic matter in the activated sludge process.
(C) Incorrect. represents the oxygen consumed over 5 days, while ultimate BOD is the total oxygen required for complete stabilization. Therefore, is always less than ultimate BOD, making the ratio less than 1.
(D) Incorrect. A lake with low nutrient content and low productivity is termed an oligotrophic lake. A eutrophic lake is one that is rich in nutrients and supports high plant/algal growth.
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