Class 2 Practice Exam Questions And

Québec Wastewater Treatment Operator Class 2 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the main purpose of preliminary treatment in a wastewater

treatment plant?

• Remove dissolved nutrients
• Remove large solids and grit
• Disinfect water
• Reduce BOD

Rationale: Preliminary treatment is designed to remove large debris

and grit to prevent damage to downstream equipment.

• Which unit process primarily removes organic matter from

wastewater?

• Filtration 1 / 4

• Sedimentation
• Activated sludge
• Chlorination

Rationale: Activated sludge is a biological process that removes

organic matter through microbial activity.

• What is the typical range of dissolved oxygen (DO) required in an

aeration tank for proper biological treatment?

• 0.1–0.5 mg/L
• 1–2 mg/L
• 2–4 mg/L
• 8–10 mg/L

Rationale: Maintaining DO between 2–4 mg/L supports aerobic

microorganisms while preventing oxygen depletion.

• Which of the following is a primary method of sludge stabilization?
• Chlorination
• Anaerobic digestion
• Filtration
• Sedimentation

Rationale: Anaerobic digestion reduces volatile solids and stabilizes

sludge before disposal.

• What is the purpose of a grit chamber?
• Remove fats and oils
• Remove sand, gravel, and grit 2 / 4

• Remove organic solids
• Remove pathogens

Rationale: Grit chambers slow flow to allow heavier particles like

sand and gravel to settle.

• Which of the following is a commonly measured indicator of organic

pollution in wastewater?

• pH
• Biochemical Oxygen Demand (BOD)
• Turbidity
• Conductivity

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter.

7. Nitrification in a wastewater treatment plant converts:

• Nitrogen gas to ammonia
• Ammonia to nitrate
• Nitrate to ammonia
• Ammonia to nitrate

Rationale: Nitrification is the biological oxidation of ammonia to

nitrate by autotrophic bacteria.

• Which chemical is commonly used for disinfection in wastewater

treatment?

• Sodium hydroxide
• Chlorine 3 / 4

• Ferric chloride
• Lime

Rationale: Chlorine is widely used to inactivate pathogens before

effluent discharge.

• What is the primary function of a secondary clarifier?
• Remove grit
• Settle biological solids
• Remove large debris
• Adjust pH

Rationale: Secondary clarifiers separate biological flocs from treated

water after biological treatment.

• What type of microorganisms are mainly responsible for

breaking down organic matter in activated sludge?

• Algae
• Bacteria
• Protozoa
• Viruses

Rationale: Bacteria are the primary decomposers of organic matter

in activated sludge systems.

• What is the main cause of sludge bulking in a wastewater plant?
• High temperature
• Excess filamentous bacteria
• Low BOD
• / 4