WASTEWATER OPERATOR CLASS II
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
treatment plant?
A. Remove dissolved organic matter
B. Remove grit and large debris
C. Reduce pathogens
D. Adjust pH
Correct Answer: B
Rationale: Preliminary treatment protects downstream equipment by
removing large solids and grit that could cause abrasion or clogging.
2. Which unit process is mainly responsible for settling of suspended solids?
A. Aeration basin
B. Primary clarifier
C. Trickling filter
D. Disinfection basin
Correct Answer: B
Rationale: Primary clarifiers use gravity to settle suspended solids and
remove floatable materials.
3. Biochemical Oxygen Demand (BOD) measures:
A. Total suspended solids
B. Oxygen needed to oxidize inorganic matter
C. Oxygen required by microorganisms to decompose organic matter
D. Dissolved oxygen in water
, Correct Answer: C
Rationale: BOD indicates the amount of biodegradable organic matter
present in wastewater.
4. Which microorganism is most responsible for organic matter removal in
activated sludge?
A. Algae
B. Protozoa
C. Bacteria
D. Viruses
Correct Answer: C
Rationale: Bacteria metabolize organic pollutants and are the primary
organisms in activated sludge.
5. Dissolved oxygen in an aeration tank should generally be maintained above:
A. 0.1 mg/L
B. 0.5 mg/L
C. 2.0 mg/L
D. 10 mg/L
Correct Answer: C
Rationale: Maintaining DO above 2.0 mg/L supports aerobic biological
activity and prevents odors.
6. The main purpose of return activated sludge (RAS) is to:
A. Waste excess solids
B. Maintain microorganisms in the aeration tank
C. Increase effluent flow
D. Improve disinfection
Correct Answer: B
Rationale: RAS returns settled biomass to maintain adequate microbial
population for treatment.
7. Sludge age is also known as:
A. Food-to-microorganism ratio
B. Mean cell residence time
C. Hydraulic retention time
D. Sludge volume index
, Correct Answer: B
Rationale: Sludge age describes the average time microorganisms remain
in the system.
8. What does a high sludge volume index (SVI) indicate?
A. Dense, fast-settling sludge
B. Poor settling sludge
C. High dissolved oxygen
D. Low organic loading
Correct Answer: B
Rationale: High SVI values indicate bulking sludge that settles poorly.
9. Trickling filters primarily rely on:
A. Chemical oxidation
B. Anaerobic digestion
C. Biological growth on media
D. Physical filtration only
Correct Answer: C
Rationale: Microorganisms grow on the media surface and degrade
organic matter as wastewater passes over them.
10.Which factor most affects nitrification?
A. Temperature
B. Color
C. Turbidity
D. Odor
Correct Answer: A
Rationale: Nitrifying bacteria are highly sensitive to temperature changes.
11.Ammonia is converted to nitrate through:
A. Denitrification
B. Nitrification
C. Digestion
D. Chlorination
Correct Answer: B
Rationale: Nitrification is the aerobic biological oxidation of ammonia to
nitrate.
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
treatment plant?
A. Remove dissolved organic matter
B. Remove grit and large debris
C. Reduce pathogens
D. Adjust pH
Correct Answer: B
Rationale: Preliminary treatment protects downstream equipment by
removing large solids and grit that could cause abrasion or clogging.
2. Which unit process is mainly responsible for settling of suspended solids?
A. Aeration basin
B. Primary clarifier
C. Trickling filter
D. Disinfection basin
Correct Answer: B
Rationale: Primary clarifiers use gravity to settle suspended solids and
remove floatable materials.
3. Biochemical Oxygen Demand (BOD) measures:
A. Total suspended solids
B. Oxygen needed to oxidize inorganic matter
C. Oxygen required by microorganisms to decompose organic matter
D. Dissolved oxygen in water
, Correct Answer: C
Rationale: BOD indicates the amount of biodegradable organic matter
present in wastewater.
4. Which microorganism is most responsible for organic matter removal in
activated sludge?
A. Algae
B. Protozoa
C. Bacteria
D. Viruses
Correct Answer: C
Rationale: Bacteria metabolize organic pollutants and are the primary
organisms in activated sludge.
5. Dissolved oxygen in an aeration tank should generally be maintained above:
A. 0.1 mg/L
B. 0.5 mg/L
C. 2.0 mg/L
D. 10 mg/L
Correct Answer: C
Rationale: Maintaining DO above 2.0 mg/L supports aerobic biological
activity and prevents odors.
6. The main purpose of return activated sludge (RAS) is to:
A. Waste excess solids
B. Maintain microorganisms in the aeration tank
C. Increase effluent flow
D. Improve disinfection
Correct Answer: B
Rationale: RAS returns settled biomass to maintain adequate microbial
population for treatment.
7. Sludge age is also known as:
A. Food-to-microorganism ratio
B. Mean cell residence time
C. Hydraulic retention time
D. Sludge volume index
, Correct Answer: B
Rationale: Sludge age describes the average time microorganisms remain
in the system.
8. What does a high sludge volume index (SVI) indicate?
A. Dense, fast-settling sludge
B. Poor settling sludge
C. High dissolved oxygen
D. Low organic loading
Correct Answer: B
Rationale: High SVI values indicate bulking sludge that settles poorly.
9. Trickling filters primarily rely on:
A. Chemical oxidation
B. Anaerobic digestion
C. Biological growth on media
D. Physical filtration only
Correct Answer: C
Rationale: Microorganisms grow on the media surface and degrade
organic matter as wastewater passes over them.
10.Which factor most affects nitrification?
A. Temperature
B. Color
C. Turbidity
D. Odor
Correct Answer: A
Rationale: Nitrifying bacteria are highly sensitive to temperature changes.
11.Ammonia is converted to nitrate through:
A. Denitrification
B. Nitrification
C. Digestion
D. Chlorination
Correct Answer: B
Rationale: Nitrification is the aerobic biological oxidation of ammonia to
nitrate.
