Level 3 Exam Practice Questions And

Yukon Wastewater Treatment Operator Level 3 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?
• Generate electricity
• Remove solids and contaminants from water
• Supply drinking water
• Increase water temperature
• Remove solids and contaminants from water

Rationale: The main goal of wastewater treatment is to remove physical,

chemical, and biological contaminants to protect public health and the environment. 1 / 4

• Which of the following best describes BOD (Biochemical Oxygen

Demand)?

• The total oxygen present in water
• The amount of oxygen microorganisms consume to decompose

organic matter

• The oxygen used for chemical disinfection
• The dissolved oxygen produced by photosynthesis
• The amount of oxygen microorganisms consume to decompose organic

matter

Rationale: BOD measures the oxygen demand of microorganisms during

decomposition of organic matter, indicating pollution levels.

• What is the primary function of a primary clarifier?
• Reduce nutrient levels
• Remove large suspended solids
• Kill pathogenic organisms
• Aerate the wastewater
• Remove large suspended solids

Rationale: Primary clarifiers settle out large solids and reduce the load on

secondary treatment processes.

• Activated sludge treatment relies on which process?
• Sedimentation
• Biological oxidation 2 / 4

• Filtration
• Chemical precipitation
• Biological oxidation

Rationale: Activated sludge uses microorganisms to biologically oxidize

organic pollutants.

• Which parameter is most critical for controlling nitrification in

wastewater?

• pH
• Temperature
• Dissolved oxygen
• Color
• Dissolved oxygen

Rationale: Nitrifying bacteria require sufficient dissolved oxygen to convert

ammonia to nitrate efficiently.

• What type of microorganism primarily performs denitrification?
• Aerobic bacteria
• Anaerobic bacteria
• Fungi
• Algae
• Anaerobic bacteria

Rationale: Denitrification occurs in the absence of oxygen, where bacteria

convert nitrate to nitrogen gas. 3 / 4

7. The purpose of chlorination in wastewater treatment is to:

• Remove nutrients
• Disinfect pathogens
• Neutralize pH
• Increase BOD
• Disinfect pathogens

Rationale: Chlorination kills pathogenic microorganisms, reducing health

risks before discharge or reuse.

• What is the typical retention time in a secondary clarifier?
• 10–20 minutes
• 1–3 hours
• 4–6 hours
• 12–24 hours
• 1–3 hours

Rationale: Secondary clarifiers are designed for sufficient settling time to

separate biomass from treated water.

9. Sludge digestion primarily reduces:

• Water clarity
• Volume and odor of solids
• Nitrogen content
• Heavy metals
• / 4