Québec Wastewater Treatment
Operator Class 3 Practice Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The primary purpose of a grit chamber in wastewater treatment is to:
a) Remove dissolved organic matter
b) Settle heavy inorganic particles
c) Reduce BOD
d) Neutralize pH
b) Settle heavy inorganic particles
Rationale: Grit chambers are designed to remove sand, gravel, and
other dense particles that can damage equipment and reduce
treatment efficiency.
,2. Which of the following is the most common method for disinfecting
treated wastewater?
a) Filtration
b) Chlorination
c) Sedimentation
d) Aeration
b) Chlorination
Rationale: Chlorination is widely used to kill pathogenic
microorganisms before discharge or reuse.
3. What is the typical function of a primary clarifier?
a) Reduce nutrient concentration
b) Remove settleable solids
c) Aerate wastewater
d) Add chemicals
b) Remove settleable solids
Rationale: Primary clarifiers allow solids to settle by gravity,
reducing suspended solids load for secondary treatment.
4. In activated sludge systems, the main purpose of aeration is to:
a) Reduce pH
b) Provide oxygen for microbial metabolism
c) Remove grit
d) Increase BOD
b) Provide oxygen for microbial metabolism
, Rationale: Oxygen is required for aerobic bacteria to metabolize
organic matter in the wastewater.
5. Which parameter measures the amount of oxygen consumed by
microorganisms in 5 days?
a) COD
b) BOD5
c) TSS
d) DO
b) BOD5
Rationale: BOD5 (Biochemical Oxygen Demand over 5 days) is a
standard measure of organic pollution in wastewater.
6. Nitrification in wastewater treatment converts:
a) Ammonia to nitrate
b) Nitrate to ammonia
c) Nitrogen gas to ammonia
d) Nitrite to organic nitrogen
a) Ammonia to nitrate
Rationale: Nitrification is a two-step aerobic process performed by
autotrophic bacteria, converting ammonia to nitrite and then nitrate.
7. Denitrification requires which condition to occur?
a) Aerobic
b) Anaerobic
c) High pH
, d) Low temperature
b) Anaerobic
Rationale: Denitrifying bacteria reduce nitrate to nitrogen gas in the
absence of oxygen.
8. What is the main purpose of a secondary clarifier?
a) Remove heavy metals
b) Settle biological flocs
c) Neutralize pH
d) Filter solids
b) Settle biological flocs
Rationale: Secondary clarifiers separate the biomass (activated
sludge) from treated water for recycling or disposal.
9. Total Suspended Solids (TSS) in wastewater primarily measure:
a) Dissolved nutrients
b) Particulate matter
c) Dissolved oxygen
d) Pathogens
b) Particulate matter
Rationale: TSS represents the solids that are suspended in water and
can affect treatment processes and water quality.
10. Which of the following is an advantage of extended aeration
systems?
a) Requires less energy than trickling filters
Operator Class 3 Practice Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. The primary purpose of a grit chamber in wastewater treatment is to:
a) Remove dissolved organic matter
b) Settle heavy inorganic particles
c) Reduce BOD
d) Neutralize pH
b) Settle heavy inorganic particles
Rationale: Grit chambers are designed to remove sand, gravel, and
other dense particles that can damage equipment and reduce
treatment efficiency.
,2. Which of the following is the most common method for disinfecting
treated wastewater?
a) Filtration
b) Chlorination
c) Sedimentation
d) Aeration
b) Chlorination
Rationale: Chlorination is widely used to kill pathogenic
microorganisms before discharge or reuse.
3. What is the typical function of a primary clarifier?
a) Reduce nutrient concentration
b) Remove settleable solids
c) Aerate wastewater
d) Add chemicals
b) Remove settleable solids
Rationale: Primary clarifiers allow solids to settle by gravity,
reducing suspended solids load for secondary treatment.
4. In activated sludge systems, the main purpose of aeration is to:
a) Reduce pH
b) Provide oxygen for microbial metabolism
c) Remove grit
d) Increase BOD
b) Provide oxygen for microbial metabolism
, Rationale: Oxygen is required for aerobic bacteria to metabolize
organic matter in the wastewater.
5. Which parameter measures the amount of oxygen consumed by
microorganisms in 5 days?
a) COD
b) BOD5
c) TSS
d) DO
b) BOD5
Rationale: BOD5 (Biochemical Oxygen Demand over 5 days) is a
standard measure of organic pollution in wastewater.
6. Nitrification in wastewater treatment converts:
a) Ammonia to nitrate
b) Nitrate to ammonia
c) Nitrogen gas to ammonia
d) Nitrite to organic nitrogen
a) Ammonia to nitrate
Rationale: Nitrification is a two-step aerobic process performed by
autotrophic bacteria, converting ammonia to nitrite and then nitrate.
7. Denitrification requires which condition to occur?
a) Aerobic
b) Anaerobic
c) High pH
, d) Low temperature
b) Anaerobic
Rationale: Denitrifying bacteria reduce nitrate to nitrogen gas in the
absence of oxygen.
8. What is the main purpose of a secondary clarifier?
a) Remove heavy metals
b) Settle biological flocs
c) Neutralize pH
d) Filter solids
b) Settle biological flocs
Rationale: Secondary clarifiers separate the biomass (activated
sludge) from treated water for recycling or disposal.
9. Total Suspended Solids (TSS) in wastewater primarily measure:
a) Dissolved nutrients
b) Particulate matter
c) Dissolved oxygen
d) Pathogens
b) Particulate matter
Rationale: TSS represents the solids that are suspended in water and
can affect treatment processes and water quality.
10. Which of the following is an advantage of extended aeration
systems?
a) Requires less energy than trickling filters
