Match List-I (Performance Indicator) with List-II (Indication) and select the correct code:

Question

Match List-I (Performance Indicator) with List-II (Indication) and select the correct code:

List-I

i. BOD removal

ii. SS removal

iii. SVI

iv. F/M ratio

List-II

a. Settling properties

b. Organic-load efficiency

c. Solids-separation

d. Substrate/Biomass balance

Choose the correct match:

1. A. i-b, ii-c, iii-a, iv-d (Correct answer)
2. B. i-c, ii-b, iii-d, iv-a
3. C. i-b, ii-a, iii-c, iv-d
4. D. i-d, ii-c, iii-b, iv-a

Correct Answer

Option A — i-b, ii-c, iii-a, iv-d

Detailed Solution & Explanation

The correct answer is i-b, ii-c, iii-a, iv-d.

Key Points

• Each indicator reports on a different aspect of plant performance:
  • i. BOD removal - b. Organic-load efficiency. How well the biological stage is stabilising organic matter.
  • ii. SS removal - c. Solids-separation. How well the clarifiers are physically separating solids.
  • iii. SVI - a. Settling properties. How readily the activated sludge compacts.
  • iv. F/M ratio - d. Substrate/biomass balance. Food supplied per unit of micro-organisms held.

Additional Information

• The F/M ratio — kg BOD applied per day per kg MLSS — is the master control variable of the activated sludge process. Conventional plants run at about 0.2-0.4; extended aeration at 0.05-0.15.
• The two ends of that range fail differently. Too low an F/M starves the organisms and encourages filamentous bulking; too high leaves organisms dispersed and unable to floc, so solids escape over the clarifier weir.
• SVI and F/M are linked, which is why an operator reads them together: a drifting F/M ratio usually shows up as a rising SVI before it shows up in the effluent.
• Sludge age (SRT) is the companion parameter, and it is what actually determines whether slow-growing nitrifiers can establish themselves in the tank.