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Question #46579
The Question
An operational Sewage Treatment Plant (STP) accidentally receives a massive influx of untreated industrial effluent rich in heavy metals (density > 5 g/cm³). Which of the following represents the most likely sequence of events during the biological treatment phase and its ecological consequence upon discharge into a nearby river?
Options
- A.
Heavy metals inhibit microbial enzymes in the aeration tank, arresting BOD reduction and causing the discharge of organic-rich effluent that shifts the receiving water body to anaerobic decomposition.
- B.
The heavy metals undergo biomagnification within the aerobic flocs, accelerating the oxidation of organic matter but causing severe toxicity later in the anaerobic sludge digesters.
- C.
Primary treatment efficiency decreases due to heavy metal toxicity, leading to high dissolved oxygen (DO) in the aeration tank and subsequent failure of floc formation.
- D.
Heavy metals stimulate the rapid growth of anaerobic bacteria in the aeration tank, prematurely producing biogas and preventing the formation of activated sludge.
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|Decomposition Rate Modifiers|Microbial Aerobic Respiration
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that 'secondary treatment reduces BOD' without linking the biological vulnerability of the 'flocs' to industrial pollutants.
The trap lies in confusing the physical nature of primary treatment with the biological nature of secondary treatment, and testing the inverse relationship between BOD and DO in receiving waters.
Option B acts as a 'Common Half-Truth' trap by correctly mentioning biomagnification but incorrectly applying it to accelerate oxidation.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Microbes in Human Welfare - Class 12 |
| Concept | Activated Sludge Inoculum |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |