Exam Practice Questions And Correct

Wastewater Operator Class III Licensing Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The primary purpose of a grit chamber in a wastewater treatment

plant is to:

• Remove fine suspended solids
• Reduce organic load
• Remove heavy inorganic solids like sand and gravel
• Promote bacterial growth

Rationale: Grit chambers are designed to remove heavy inorganic

particles that could damage equipment or settle in downstream processes. 1 / 4

• Which microorganism is primarily responsible for nitrification in

activated sludge systems?

• Escherichia coli
• Nitrosomonas and Nitrobacter
• Bacillus subtilis
• Pseudomonas aeruginosa

Rationale: Nitrosomonas oxidizes ammonia to nitrite, and

Nitrobacter oxidizes nitrite to nitrate, completing the nitrification process.

3. The function of an aeration tank in an activated sludge system is to:

• Clarify the wastewater
• Supply oxygen for microbial decomposition of organic matter
• Remove grit and debris
• Neutralize pH

Rationale: Aeration tanks provide oxygen to support aerobic

microorganisms in breaking down organic pollutants.

4. Sludge volume index (SVI) is used to measure:

• Oxygen demand
• Settling characteristics of activated sludge
• BOD removal efficiency
• Nutrient concentration

Rationale: SVI helps operators assess how well sludge will settle in

the secondary clarifier, impacting plant performance. 2 / 4

• What is the primary purpose of disinfection in wastewater treatment?
• Remove solids
• Reduce odor
• Destroy pathogenic microorganisms
• Improve nutrient removal

Rationale: Disinfection, often with chlorine or UV, reduces the risk of

disease transmission from treated effluent.

• Which chemical is most commonly used for coagulation in wastewater

treatment?

• Sodium hydroxide
• Aluminum sulfate (alum)
• Sodium bicarbonate
• Calcium carbonate

Rationale: Alum causes fine suspended particles to clump together,

forming flocs that settle more easily.

7. In a trickling filter, the medium is used to:

• Aerate wastewater
• Support biofilm growth for organic matter decomposition
• Remove heavy metals
• Filter out grit

Rationale: The medium provides a surface for microorganisms to

attach and degrade organic pollutants as wastewater flows over it. 3 / 4

• What is the typical BOD removal efficiency of a conventional activated

sludge system?

A. 30–40%

B. 50–60%

C. 85–95%

D. 100%

Rationale: Properly operated conventional activated sludge systems

are highly effective at removing biodegradable organic matter.

9. The main purpose of a primary clarifier is to:

• Remove dissolved nutrients
• Settle out suspended solids
• Provide disinfection
• Reduce ammonia concentration

Rationale: Primary clarifiers allow heavy solids to settle by gravity,

reducing the load on secondary treatment.

• Which process converts ammonia to nitrate?
• Denitrification
• Nitrification
• Phosphorus removal
• Chlorination

Rationale: Nitrification is a two-step aerobic process converting

ammonia first to nitrite and then to nitrate.

• / 4