Operator Level 3 Practice Exam

Prince Edward Island Wastewater Operator Level 3 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the primary purpose of secondary treatment

in wastewater treatment?

• Disinfection
• Biological removal of organic matter
• Sedimentation
• Sludge dewatering

Rationale: Secondary treatment primarily removes biodegradable

organic matter through microbial processes.

• The most common method for measuring wastewater pH in the field

is: 1 / 4

• Gravimetric analysis
• Spectrophotometry
• pH meter
• Turbidity meter

Rationale: A pH meter provides accurate, immediate measurements

of hydrogen ion concentration in wastewater.

3. Activated sludge systems rely on:

• Anaerobic bacteria
• Aerobic bacteria
• Chemical oxidation
• Physical filtration

Rationale: Activated sludge uses aerobic bacteria to digest organic

pollutants.

• What is the main goal of a primary clarifier?
• Biological treatment
• Sludge thickening
• Removal of settleable solids
• Nutrient removal

Rationale: Primary clarifiers settle out suspended solids from raw

wastewater.

5. Nitrification in wastewater treatment converts:

• Nitrite to nitrogen gas
• Ammonia to nitrate 2 / 4

• Nitrate to ammonia
• Organic nitrogen to ammonia

Rationale: Nitrification is the aerobic conversion of ammonia (NH₃) to

nitrate (NO₃⁻) via nitrite (NO₂⁻).

6. Denitrification in wastewater treatment requires:

• Aerobic conditions
• Anoxic conditions
• High chlorine levels
• Low BOD

Rationale: Denitrification occurs under anoxic conditions where

nitrate is reduced to nitrogen gas.

7. Sludge digestion in anaerobic digesters produces primarily:

• Oxygen
• Methane
• Nitrogen
• Carbon monoxide

Rationale: Anaerobic digestion breaks down organic matter,

producing methane and carbon dioxide.

• A wastewater flow rate of 10,000 m³/day with an average BOD₅ of 200

mg/L requires what mass of BOD to be removed daily?

• 2,000 kg
• 20,000 kg
• 2,000 kg 3 / 4

• 200 kg

Rationale: Mass BOD = flow × concentration. Convert mg/L to kg/m³: 10,000 × 0.2 = 2,000 kg/day.

• The term “sludge age” or “mean cell residence time (MCRT)” refers to:
• Hydraulic retention time
• Average time microorganisms remain in the system
• Age of the plant operator
• Time sludge is stored after dewatering

Rationale: MCRT indicates how long microorganisms stay in the

activated sludge system, influencing treatment efficiency.

• Which of the following is a key indicator of organic pollution in

wastewater?

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

Rationale: BOD measures the amount of oxygen required by

microorganisms to degrade organic matter.

11. The purpose of chlorination in wastewater treatment is:

• BOD removal
• Nitrate removal
• Disinfection
• Phosphorus removal
• / 4