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Ontario Wastewater Operator Certificate of Qualification Class I Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf
- What is the primary purpose of a wastewater treatment plant?
- Produce drinking water
- Remove harmful contaminants from wastewater
- Generate electricity
- Increase water temperature
- Remove harmful contaminants from wastewater
Rationale: The main goal of a wastewater treatment plant is to
remove pollutants and protect public health and the environment.
- Which of the following is a physical method of wastewater treatment?
- Sedimentation
- Biological digestion 1 / 4
- Chemical precipitation
- Chlorination
- Sedimentation
Rationale: Sedimentation is a physical process that removes
suspended solids by allowing them to settle.
- What type of wastewater contains household and commercial waste?
- Industrial wastewater
- Stormwater
- Sanitary wastewater
- Agricultural runoff
- Sanitary wastewater
Rationale: Sanitary wastewater is generated from domestic and
commercial activities.
- What does BOD stand for?
- Biological Oxidation Demand
- Biochemical Oxygen Demand
- Basic Oxidation Density
- Biological Oxygen Diffusion
- Biochemical Oxygen Demand
Rationale: BOD measures the amount of oxygen required by
microorganisms to decompose organic matter in water.
- Which stage of treatment primarily removes settleable solids?
- Primary treatment 2 / 4
- Secondary treatment
- Tertiary treatment
- Disinfection
- Primary treatment
Rationale: Primary treatment uses sedimentation to remove large
settleable solids from wastewater.
- Which microorganism is most commonly used in activated sludge
- Protozoa
- Bacteria
- Algae
- Fungi
- Bacteria
processes?
Rationale: Bacteria break down organic matter in the activated
sludge process.
- What is the typical retention time in a primary sedimentation tank?
- 10–30 minutes
- 1–2 hours
- 4–6 hours
- 24 hours
- 4–6 hours
Rationale: Primary clarifiers are designed for several hours of
retention to allow solids to settle. 3 / 4
- What is the main purpose of chlorination in wastewater treatment?
- Remove solids
- Reduce nutrients
- Disinfect wastewater
- Improve taste
- Disinfect wastewater
Rationale: Chlorination kills pathogens to protect public health.
9. Nitrification converts:
- Ammonia to nitrate
- Nitrate to ammonia
- Nitrogen gas to nitrate
- Nitrate to nitrogen gas
- Ammonia to nitrate
Rationale: Nitrifying bacteria convert ammonia to nitrite and then to
nitrate.
10. Denitrification is the process by which:
- Nitrate is converted to nitrogen gas
- Ammonia is converted to nitrate
- Organic matter is oxidized
- Solids are removed
- Nitrate is converted to nitrogen gas
Rationale: Denitrification removes nitrogen from wastewater as
nitrogen gas.
- / 4
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