Québec Wastewater Treatment Operator Class 3 Exam Questions & Answers 2026 | Instant PDF Download

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Operator Class 3 Exam Questions And v v v v v




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Rationales 2026 Q&A | Instant Downloa v v v v v




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1. The primary purpose of a grit chamber in wastewater treatment is to:
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a) Remove dissolved organic matter
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b) Settle heavy inorganic particles
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c) Reduce BOD v




d) Neutralize pH v




b) Settle heavy inorganic particles
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Rationale: Grit chambers are designed to remove sand, gravel, and other
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dense particles that can damage equipment and reduce treatment effici
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ency.

,2. Which of the following is the most common method for disinfecting tr
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eated wastewater?
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a) Filtration
b) Chlorination
c) Sedimentation
d) Aeration
b) Chlorination
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Rationale: Chlorination is widely used to kill pathogenic microorganis
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ms before discharge or reuse.
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3. What is the typical function of a primary clarifier?
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a) Reduce nutrient concentration
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b) Remove settleable solids v v




c) Aerate wastewater v




d) Add chemicals
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b) Remove settleable solids
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Rationale: Primary clarifiers allow solids to settle by gravity, reducing
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suspended solids load for secondary treatment.
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4. In activated sludge systems, the main purpose of aeration is to:
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a) Reduce pH v




b) Provide oxygen for microbial metabolism
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c) Remove grit v




d) Increase BOD v




b) Provide oxygen for microbial metabolism
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, Rationale: Oxygen is required for aerobic bacteria to metabolize orga
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nic matter in the wastewater.
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5. Which parameter measures the amount of oxygen consumed by
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microorganisms in 5 days? v v v




a) COD
b) BOD5
c) TSS
d) DO
b) BOD5
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Rationale: BOD5 (Biochemical Oxygen Demand over 5 days) is a stand
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ard measure of organic pollution in wastewater.
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6. Nitrification in wastewater treatment converts:
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a) Ammonia to nitrate v v




b) Nitrate to ammonia v v




c) Nitrogen gas to ammonia v v v




d) Nitrite to organic nitrogen
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a) Ammonia to nitrate v v




Rationale: Nitrification is a two-v v v v




step aerobic process performed by autotrophic bacteria, converting am
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monia to nitrite and then nitrate.
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7. Denitrification requires which condition to occur?v v v v v




a) Aerobic
b) Anaerobic
c) High pH v

, d) Low temperature v




b) Anaerobic
Rationale: Denitrifying bacteria reduce nitrate to nitrogen gas in the a
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bsence of oxygen. v v




8. What is the main purpose of a secondary clarifier?
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a) Remove heavy metals v v




b) Settle biological flocs v v




c) Neutralize pH v




d) Filter solids v




b) Settle biological flocs
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Rationale: Secondary clarifiers separate the biomass (activated sludg
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e) from treated water for recycling or disposal.
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9. Total Suspended Solids (TSS) in wastewater primarily measure:
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a) Dissolved nutrients v




b) Particulate matter v




c) Dissolved oxygen v




d) Pathogens
b) Particulate matter v




Rationale: TSS represents the solids that are suspended in water and can
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affect treatment processes and water quality.
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10. Which of the following is an advantage of extended aeration s
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ystems?
a) Requires less energy than trickling filters
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