Consider the following statements regarding biological characteristics and performance evaluation:

Question

Consider the following statements regarding biological characteristics and performance evaluation:

I. Presence of coliforms in treated effluent indicates possible faecal contamination.

II. High Sludge Volume Index (SVI) indicates poor settling characteristics of secondary sludge.

III. Performance evaluation of a plant should be done only once, after construction.

Which of the statements given above is/are correct?

1. A. I and II only (Correct answer)
2. B. I and III only
3. C. II and III only
4. D. I, II and III

Correct Answer

Option A — I and II only

Detailed Solution & Explanation

The correct answer is I and II only.

Key Points

• Statement I is correct. Coliforms in treated effluent indicate possible faecal contamination, which is precisely their role as indicator organisms.
• Statement II is correct. A high Sludge Volume Index means the sludge occupies a large volume after settling — in other words, it settles poorly. Values above roughly 150 mL/g indicate bulking.
• Statement III is incorrect, and obviously so. Performance evaluation is a continuous, routine activity, not a one-off exercise after construction. A plant's performance changes constantly with load, temperature, sludge age and equipment condition.

Additional Information

• SVI is the volume in millilitres occupied by one gram of suspended solids after 30 minutes of settling in a one-litre cylinder. Good settling is around 80-120 mL/g.
• High SVI is usually caused by filamentous bulking, from low F/M ratio, nutrient deficiency, low DO or septic influent. The filaments bridge between flocs and stop them compacting.
• Routine monitoring is also a legal obligation, not merely good practice: consent conditions issued by the State Pollution Control Board require periodic sampling and reporting.
• The pattern to notice across this paper's statement questions is that the false statement is usually flagged by an absolute — "only once" here, "always" and "only" elsewhere.