Question

Which ONE of the following options CORRECTLY matches the processes associated with the growth condition given in the table?

Process	Growth Condition
(P) Activated sludge process	(i) Anaerobic suspended growth
(Q) Anaerobic filter	(ii) Anaerobic attached growth
(R) Trickling filter	(iii) Aerobic suspended growth
(S) Anaerobic digestion	(iv) Aerobic attached growth

• A. (P) - (ii); (Q) - (iii); (R) - (iv); (S) - (i)
• B. (P) - (iii); (Q) - (ii); (R) - (iv); (S) - (i)
• C. (P) - (iii); (Q) - (i); (R) - (iv); (S) - (ii)
• D. (P) - (iv); (Q) - (iii); (R) - (ii); (S) - (i)

Hint:

Classify each process along two axes: growth mode (suspended versus attached) and oxygen requirement (aerobic versus anaerobic).

Answer 1

The Correct Option is B

This question requires matching four wastewater treatment processes to the correct biological growth condition, based on whether the process is aerobic or anaerobic and whether the microorganisms grow suspended in the liquid or attached to a fixed medium.
Step 1: Classify the activated sludge process (P). In the activated sludge process, microorganisms form flocs that remain suspended and mixed within the aeration tank, and air or oxygen is continuously supplied. This makes it aerobic suspended growth, which is condition (iii).
Step 2: Classify the anaerobic filter (Q). An anaerobic filter is a fixed-film reactor where wastewater passes over a stationary packing medium on which anaerobic microorganisms attach and grow, in the absence of oxygen. This makes it anaerobic attached growth, condition (ii).
Step 3: Classify the trickling filter (R). In a trickling filter, wastewater trickles over a bed of stones or plastic media coated with a biofilm, and the process is aerobic since air circulates through the bed. Since the biomass grows attached to the media, this is aerobic attached growth, condition (iv).
Step 4: Classify anaerobic digestion (S). Anaerobic digestion, typically used for sludge stabilization, takes place in a mixed, sealed tank where microorganisms are suspended in the sludge slurry without oxygen. This makes it anaerobic suspended growth, condition (i).
Step 5: Match and conclude. The complete correct pairing is (P)-(iii), (Q)-(ii), (R)-(iv), (S)-(i), which is option (B).