Questions And Correct Answers

Northwest Territories Wastewater Treatment Operator Level 3 Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the primary purpose of a primary clarifier in

a wastewater treatment plant?

• Remove dissolved nutrients
• Remove settleable solids
• Reduce bacterial populations
• Adjust pH

Answer: B

Rationale: Primary clarifiers are designed to remove settleable solids and

floating material through sedimentation, reducing the load on secondary treatment processes. 1 / 4

2. The main function of aeration in an activated sludge process is to:

• Kill pathogens
• Provide oxygen for microorganisms
• Settle solids
• Neutralize pH

Answer: B

Rationale: Aeration supplies oxygen needed by aerobic microorganisms to

metabolize organic matter in wastewater.

• Which of the following microorganisms is most common in the

activated sludge process?

• Viruses
• Protozoa
• Bacteria
• Algae

Answer: C

Rationale: Bacteria are the primary microorganisms responsible for breaking

down organic matter in activated sludge systems.

• What is the ideal temperature range for mesophilic anaerobic

digestion?

A. 5–15°C

B. 20–30°C

C. 30–40°C

D. 50–60°C 2 / 4

Answer: C

Rationale: Mesophilic digestion occurs optimally in the range of 30–40°C,

providing stable microbial activity for sludge stabilization.

• Which of the following parameters is used to measure the strength of

wastewater?

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

Answer: C

Rationale: BOD measures the amount of oxygen required by microorganisms

to decompose organic matter, indicating wastewater strength.

• In a sequencing batch reactor (SBR), which phase comes immediately

after aeration?

• Fill
• Settle
• Decant
• Idle

Answer: B

Rationale: After the aeration phase in an SBR, solids are allowed to settle so

that treated water can be decanted. 3 / 4

• Nitrification in wastewater treatment is a two-step process. Which

organisms are responsible for converting ammonia to nitrite?

• Nitrobacter
• Pseudomonas
• Nitrosomonas
• Escherichia

Answer: C

Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite in the

nitrification process.

• What is the primary purpose of chlorination in wastewater treatment?
• Remove solids
• Disinfect effluent
• Remove nutrients
• Adjust pH

Answer: B

Rationale: Chlorination kills or inactivates pathogenic microorganisms in

treated wastewater before discharge.

• Which of the following is a key advantage of trickling filters over

activated sludge systems?

• Lower energy requirements
• Faster treatment
• Smaller footprint
• Higher oxygen demand
• / 4