Wastewater Treatment Operator Level II Exam
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
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1. What is the primary purpose of a clarifier in a wastewater
treatment plant?
a. To disinfect the water
b. To remove suspended solids
c. To aerate the wastewater
d. To add nutrients
b. To remove suspended solids
Clarifiers allow solids to settle out of wastewater, reducing
turbidity and preparing water for further treatment.
2. Which of the following is the main biological process in an
activated sludge system?
a. Nitrification
b. Sedimentation
c. Filtration
d. Photosynthesis
a. Nitrification
Activated sludge relies on microorganisms to convert ammonia to
nitrate in a process called nitrification.
3. What is the typical range of dissolved oxygen (DO) in a well-
operated aeration tank?
, a. 0.5–1 mg/L
b. 2–4 mg/L
c. 4–6 mg/L
d. 8–10 mg/L
c. 4–6 mg/L
This DO range supports microbial activity without causing
excessive energy consumption.
4. Which chemical is commonly used for disinfection in wastewater
treatment?
a. Chlorine
b. Fluoride
c. Sodium hydroxide
d. Calcium carbonate
a. Chlorine
Chlorine is effective in killing pathogenic organisms before effuent
discharge.
5. What is the main function of a sludge digester?
a. Increase water flow
b. Reduce sludge volume
c. Aerate the water
d. Remove dissolved oxygen
b. Reduce sludge volume
Digesters break down organic matter, reducing volume and
producing biogas.
6. What is the meaning of BOD in wastewater treatment?
a. Biochemical oxygen demand
b. Biological oxidation degree
, c. Base oxidation demand
d. Basic organic decomposition
a. Biochemical oxygen demand
BOD measures the oxygen required by microorganisms to
decompose organic matter.
7. Which process converts ammonia to nitrate in wastewater
treatment?
a. Denitrification
b. Nitrification
c. Coagulation
d. Flocculation
b. Nitrification
Nitrification is carried out by autotrophic bacteria, converting
ammonia into nitrate.
8. What is the typical retention time for primary clarifiers?
a. 30–60 minutes
b. 1–2 hours
c. 4–6 hours
d. 12–24 hours
b. 1–2 hours
This allows sufficient time for solids to settle without excessive
detention.
9. Which of the following is an effect of low DO in an aeration tank?
a. Enhanced nitrification
b. Odor production
c. Reduced sludge production
d. Improved efluent quality
, b. Odor production
Low DO leads to anaerobic conditions, causing hydrogen sulfide
and other odorous compounds.
10. What is the main purpose of using alum in wastewater
treatment?
a. Disinfect water
b. Remove phosphorus and suspended solids
c. Increase pH
d. Reduce BOD
b. Remove phosphorus and suspended solids
Alum acts as a coagulant to bind fine particles and phosphates for
removal.
11. Which microorganism group is primarily responsible for
breaking down organic matter in an aerobic digester?
a. Protozoa
b. Anaerobic bacteria
c. Aerobic bacteria
d. Fungi
c. Aerobic bacteria
Aerobic bacteria metabolize organic compounds efficiently in
oxygen-rich conditions.
12. What is the function of a trickling filter?
a. Remove chlorine
b. Promote microbial growth on media for organic removal
c. Settle solids
d. Increase BOD
b. Promote microbial growth on media for organic removal
Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a clarifier in a wastewater
treatment plant?
a. To disinfect the water
b. To remove suspended solids
c. To aerate the wastewater
d. To add nutrients
b. To remove suspended solids
Clarifiers allow solids to settle out of wastewater, reducing
turbidity and preparing water for further treatment.
2. Which of the following is the main biological process in an
activated sludge system?
a. Nitrification
b. Sedimentation
c. Filtration
d. Photosynthesis
a. Nitrification
Activated sludge relies on microorganisms to convert ammonia to
nitrate in a process called nitrification.
3. What is the typical range of dissolved oxygen (DO) in a well-
operated aeration tank?
, a. 0.5–1 mg/L
b. 2–4 mg/L
c. 4–6 mg/L
d. 8–10 mg/L
c. 4–6 mg/L
This DO range supports microbial activity without causing
excessive energy consumption.
4. Which chemical is commonly used for disinfection in wastewater
treatment?
a. Chlorine
b. Fluoride
c. Sodium hydroxide
d. Calcium carbonate
a. Chlorine
Chlorine is effective in killing pathogenic organisms before effuent
discharge.
5. What is the main function of a sludge digester?
a. Increase water flow
b. Reduce sludge volume
c. Aerate the water
d. Remove dissolved oxygen
b. Reduce sludge volume
Digesters break down organic matter, reducing volume and
producing biogas.
6. What is the meaning of BOD in wastewater treatment?
a. Biochemical oxygen demand
b. Biological oxidation degree
, c. Base oxidation demand
d. Basic organic decomposition
a. Biochemical oxygen demand
BOD measures the oxygen required by microorganisms to
decompose organic matter.
7. Which process converts ammonia to nitrate in wastewater
treatment?
a. Denitrification
b. Nitrification
c. Coagulation
d. Flocculation
b. Nitrification
Nitrification is carried out by autotrophic bacteria, converting
ammonia into nitrate.
8. What is the typical retention time for primary clarifiers?
a. 30–60 minutes
b. 1–2 hours
c. 4–6 hours
d. 12–24 hours
b. 1–2 hours
This allows sufficient time for solids to settle without excessive
detention.
9. Which of the following is an effect of low DO in an aeration tank?
a. Enhanced nitrification
b. Odor production
c. Reduced sludge production
d. Improved efluent quality
, b. Odor production
Low DO leads to anaerobic conditions, causing hydrogen sulfide
and other odorous compounds.
10. What is the main purpose of using alum in wastewater
treatment?
a. Disinfect water
b. Remove phosphorus and suspended solids
c. Increase pH
d. Reduce BOD
b. Remove phosphorus and suspended solids
Alum acts as a coagulant to bind fine particles and phosphates for
removal.
11. Which microorganism group is primarily responsible for
breaking down organic matter in an aerobic digester?
a. Protozoa
b. Anaerobic bacteria
c. Aerobic bacteria
d. Fungi
c. Aerobic bacteria
Aerobic bacteria metabolize organic compounds efficiently in
oxygen-rich conditions.
12. What is the function of a trickling filter?
a. Remove chlorine
b. Promote microbial growth on media for organic removal
c. Settle solids
d. Increase BOD
b. Promote microbial growth on media for organic removal
