of Qualification Class II Exam Practice

Ontario Wastewater Operator Certificate of Qualification Class II Exam 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 grit chamber in a

wastewater treatment plant?

• Reduce BOD
• Remove oils and grease
• Settle heavy inorganic solids
• Disinfect effluent
• Settle heavy inorganic solids

Grit chambers are designed to remove sand, gravel, and other heavy inorganic solids that can cause wear on pumps and equipment. 1 / 4

• What is the typical retention time in a primary clarifier?
• 30 minutes to 1 hour
• 1 to 3 hours
• 4 to 6 hours
• 8 to 12 hours
• 1 to 3 hours

Primary clarifiers are designed to allow suspended solids to settle, which generally requires 1–3 hours of retention time.

3. The term BOD stands for:

• Biological Oxygen Demand
• Biochemical Oxidation Dose
• Bacterial Oxidation Demand
• Basic Oxygen Dissolution
• Biological Oxygen Demand

BOD measures the amount of oxygen required by microorganisms to decompose organic matter in water.

• What is the function of aeration in an activated sludge process?
• Remove grit
• Supply oxygen to microorganisms
• Settle solids
• Add chlorine 2 / 4

• Supply oxygen to microorganisms

Aeration provides dissolved oxygen needed by aerobic microorganisms to break down organic pollutants.

5. The main purpose of chlorination in wastewater treatment is to:

• Remove suspended solids
• Reduce nutrients
• Kill pathogens
• Improve BOD removal
• Kill pathogens

Chlorination is primarily used to disinfect treated wastewater by killing harmful microorganisms.

• Which microorganism is primarily responsible for nitrification in

wastewater?

• Bacillus
• Nitrosomonas
• E. coli
• Pseudomonas
• Nitrosomonas

Nitrosomonas bacteria oxidize ammonia to nitrite, the first step in nitrification.

7. Sludge digestion is primarily used to:

• Remove solids 3 / 4

• Reduce pathogens and stabilize sludge
• Increase BOD
• Reduce nutrient content
• Reduce pathogens and stabilize sludge

Anaerobic or aerobic digestion reduces the organic content and pathogens in sludge, making it safer for disposal.

• What is the purpose of a flow equalization basin?
• To remove grit
• To even out variations in wastewater flow
• To disinfect effluent
• To remove nutrients
• To even out variations in wastewater flow

Flow equalization reduces the impact of fluctuating influent flows on downstream treatment processes.

• The primary unit operation for removing suspended solids from

wastewater is:

• Aeration
• Screening
• Sedimentation
• Filtration
• / 4