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Question #46574
The Question
A municipal sewage treatment plant (STP) receives an accidental influx of industrial wastewater rich in toxic heavy metals. Despite normal primary treatment, the effluent discharged into the nearby river causes massive fish mortality due to hypoxia. Which of the following best explains the biological failure at the STP?
Options
- A.
Heavy metals prevent the physical settling of primary sludge during primary treatment, causing a high organic load to bypass the biological treatment phase.
- B.
Heavy metals act as enzyme inhibitors for aerobic microbes in the aeration tank, causing a population collapse and a failure to reduce the Biochemical Oxygen Demand (BOD).
- C.
Heavy metals competitively inhibit the enzymes of methanogenic bacteria in the anaerobic sludge digester, preventing the breakdown of activated sludge.
- D.
Heavy metals directly increase the dissolved oxygen (DO) in the aeration tank, leading to premature oxidation of organic matter and high effluent toxicity.
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 Inoculum|Aerobic Microbes|BOD Logic
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: This question tests the integration of 'Biomolecules' (enzyme inhibition by heavy metals) with 'Microbes in Human Welfare' (STP functioning).
Students often memorize that 'Secondary treatment reduces BOD' but fail to recognize the biochemical vulnerability of the aerobic microbes.
The trap lies in distinguishing between the physical processes of primary treatment and the enzyme-dependent biological processes of secondary treatment.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Microbes in Human Welfare - Class 12 |
| Concept | BOD (Biochemical Oxygen Demand) Logic |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |