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Question #47698
The Question
An industrial effluent rich in heavy metals (such as Hg and Pb) is accidentally mixed with domestic sewage entering the aeration tank of a Sewage Treatment Plant (STP). Which of the following best explains the subsequent failure of the secondary clarifier (settling tank) to produce a clear effluent?
Options
- A.
Heavy metals competitively inhibit the respiratory enzymes of aerobic microbes, causing an immediate increase in the Biochemical Oxygen Demand (BOD) of the primary effluent.
- B.
Heavy metals denature the bacterial enzymes responsible for synthesizing extracellular polymeric substances, preventing flocculation and leading to high suspended solids in the effluent.
- C.
Heavy metals selectively eradicate fungal filaments, causing the remaining bacterial masses to undergo rapid, uncontrolled sedimentation that clogs the settling tank.
- D.
Heavy metals induce premature methanogenesis in the aeration tank, generating biogas bubbles that physically prevent the activated sludge from settling.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Activated_Sludge|Fungal_Filaments|Aerobic_Bacteria
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'flocs reduce BOD' but fail to understand the structural biochemistry of flocs (the EPS matrix) and how sedimentation mechanically depends on this matrix.
The trap in option D exploits the functional confusion between the aerobic aeration tank and the anaerobic sludge digester, testing the student's spatial awareness of STP processes.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Microbes in Human Welfare - Class 12 |
| Concept | Flocs Formation |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |