WASTEWATER OPERATOR CLASS III
LICENSING EXAM QUESTION AND
CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES 2026 Q&A
INSTANT DOWNLOAD PDF
1. What is the primary purpose of preliminary treatment in a wastewater
plant?
A. Remove dissolved organics
B. Reduce pathogens
C. Remove large debris and grit
D. Adjust pH
Answer: C
Rationale: Preliminary treatment protects downstream equipment by removing
large solids and grit.
2. Which unit process primarily removes settleable solids?
A. Aeration basin
B. Primary clarifier
C. Trickling filter
D. Disinfection basin
Answer: B
Rationale: Primary clarifiers allow gravity settling of suspended solids.
3. The main purpose of secondary treatment is to:
A. Remove grit
B. Disinfect effluent
C. Biologically remove dissolved and colloidal organics
D. Remove nutrients only
,Answer: C
Rationale: Secondary treatment relies on microorganisms to reduce BOD and
TSS.
4. Which microorganism is most responsible for BOD removal in activated
sludge?
A. Algae
B. Protozoa
C. Bacteria
D. Rotifers
Answer: C
Rationale: Heterotrophic bacteria consume organic matter, reducing BOD.
5. A high sludge volume index (SVI) indicates:
A. Good settling sludge
B. Low MLSS
C. Poor settling, bulking sludge
D. Excess DO
Answer: C
Rationale: High SVI means sludge occupies excessive volume and settles poorly.
6. Typical dissolved oxygen (DO) in an aeration basin should be:
A. 0–0.5 mg/L
B. 1.0–3.0 mg/L
C. 5–7 mg/L
D. Above saturation
Answer: B
Rationale: Adequate DO supports aerobic microorganisms without wasting
energy.
7. What causes filamentous bulking?
A. High chlorine dose
B. Low DO or nutrient imbalance
C. Excess alkalinity
D. High temperature only
, Answer: B
Rationale: Filamentous organisms thrive under low DO or nutrient-deficient
conditions.
8. The F/M ratio represents:
A. Flow divided by MLSS
B. Food (BOD) to microorganism ratio
C. Sludge age
D. Oxygen demand
Answer: B
Rationale: F/M helps control biological process performance.
9. Extended aeration systems typically operate at:
A. High F/M
B. Short sludge age
C. Low F/M and long sludge age
D. No wasting
Answer: C
Rationale: Extended aeration promotes endogenous respiration and stable
operation.
10.What is the main function of return activated sludge (RAS)?
A. Waste excess solids
B. Maintain MLSS in aeration basin
C. Increase DO
D. Remove nutrients
Answer: B
Rationale: RAS returns settled biomass to sustain biological treatment.
11.Nitrification converts ammonia to:
A. Nitrogen gas
B. Nitrate
C. Organic nitrogen
D. Nitrite only
LICENSING EXAM QUESTION AND
CORRECT ANSWERS (VERIFIED
ANSWERS) PLUS RATIONALES 2026 Q&A
INSTANT DOWNLOAD PDF
1. What is the primary purpose of preliminary treatment in a wastewater
plant?
A. Remove dissolved organics
B. Reduce pathogens
C. Remove large debris and grit
D. Adjust pH
Answer: C
Rationale: Preliminary treatment protects downstream equipment by removing
large solids and grit.
2. Which unit process primarily removes settleable solids?
A. Aeration basin
B. Primary clarifier
C. Trickling filter
D. Disinfection basin
Answer: B
Rationale: Primary clarifiers allow gravity settling of suspended solids.
3. The main purpose of secondary treatment is to:
A. Remove grit
B. Disinfect effluent
C. Biologically remove dissolved and colloidal organics
D. Remove nutrients only
,Answer: C
Rationale: Secondary treatment relies on microorganisms to reduce BOD and
TSS.
4. Which microorganism is most responsible for BOD removal in activated
sludge?
A. Algae
B. Protozoa
C. Bacteria
D. Rotifers
Answer: C
Rationale: Heterotrophic bacteria consume organic matter, reducing BOD.
5. A high sludge volume index (SVI) indicates:
A. Good settling sludge
B. Low MLSS
C. Poor settling, bulking sludge
D. Excess DO
Answer: C
Rationale: High SVI means sludge occupies excessive volume and settles poorly.
6. Typical dissolved oxygen (DO) in an aeration basin should be:
A. 0–0.5 mg/L
B. 1.0–3.0 mg/L
C. 5–7 mg/L
D. Above saturation
Answer: B
Rationale: Adequate DO supports aerobic microorganisms without wasting
energy.
7. What causes filamentous bulking?
A. High chlorine dose
B. Low DO or nutrient imbalance
C. Excess alkalinity
D. High temperature only
, Answer: B
Rationale: Filamentous organisms thrive under low DO or nutrient-deficient
conditions.
8. The F/M ratio represents:
A. Flow divided by MLSS
B. Food (BOD) to microorganism ratio
C. Sludge age
D. Oxygen demand
Answer: B
Rationale: F/M helps control biological process performance.
9. Extended aeration systems typically operate at:
A. High F/M
B. Short sludge age
C. Low F/M and long sludge age
D. No wasting
Answer: C
Rationale: Extended aeration promotes endogenous respiration and stable
operation.
10.What is the main function of return activated sludge (RAS)?
A. Waste excess solids
B. Maintain MLSS in aeration basin
C. Increase DO
D. Remove nutrients
Answer: B
Rationale: RAS returns settled biomass to sustain biological treatment.
11.Nitrification converts ammonia to:
A. Nitrogen gas
B. Nitrate
C. Organic nitrogen
D. Nitrite only
