Licensure Exam Practice Test Questions

Certified Wastewater Operator Licensure Exam Practice Test Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. The main objective of wastewater treatment is to:

• Produce drinking water
• Remove pollutants and protect public health
• Generate electricity
• Increase nutrient levels

Rationale: The goal of wastewater treatment is to remove contaminants

from sewage to prevent environmental pollution and protect human health.

2. Primary treatment mainly removes:

• Dissolved gases 1 / 4

• Settleable and floatable solids
• Nutrients
• Pathogens

Rationale: Primary treatment focuses on removing suspended solids

through sedimentation and skimming.

3. Secondary treatment primarily targets:

• Heavy metals
• Organic matter (BOD reduction)
• Grit
• Oils and greases

Rationale: Secondary treatment uses biological processes to reduce

biochemical oxygen demand (BOD) and organic pollutants.

4. Activated sludge process relies on:

• Aerobic microorganisms
• Anaerobic bacteria
• Chemical flocculants
• Chlorination

Rationale: The activated sludge process depends on aerobic microbes that

consume organic matter in the presence of oxygen.

• / 4

5. The main purpose of aeration in activated sludge is to:

• Cool the wastewater
• Remove solids
• Supply oxygen for microorganisms
• Disinfect the water

Rationale: Aeration provides oxygen necessary for aerobic bacteria to

decompose organic pollutants.

6. In wastewater treatment, BOD stands for:

• Biological Oxidation Demand
• Biochemical Oxygen Demand
• Bio-Oxygen Distribution
• Basic Oxygen Dissolution

Rationale: BOD measures the amount of oxygen microorganisms need to

decompose organic matter.

7. The term “MLSS” refers to:

• Mixed Liquor Solids and Sludge
• Mixed Liquor Suspended Solids
• Mainline Sludge Settlers
• Mixed Lime Slurry Solution

Rationale: MLSS measures the concentration of suspended solids in the

aeration tank of an activated sludge system. 3 / 4

8. The sludge age or mean cell residence time (MCRT) is:

• The average time microorganisms remain in the system
• The time it takes for solids to settle
• The time for disinfection
• The detention time of influent

Rationale: MCRT determines how long microorganisms stay in the

activated sludge process to stabilize organic matter.

9. A clarifier’s main function is to:

• Add oxygen
• Mix chemicals
• Settle out suspended solids
• Filter effluent

Rationale: Clarifiers separate solids from liquid by gravity, producing

clarified effluent and concentrated sludge.

10. The main purpose of disinfection in wastewater treatment is to:

• Remove solids
• Control odors
• Destroy pathogenic microorganisms
• Reduce BOD
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