Licensing Exam Practice Test Questions

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

• What is the primary purpose of secondary treatment in wastewater

facilities?

• Removal of grit
• Reduction of heavy metals
• Reduction of BOD and suspended solids
• Disinfection

Rationale: Secondary treatment uses biological processes to reduce BOD

and suspended solids significantly.

2. In an activated sludge system, the F/M ratio represents:

• Flow per million gallons
• Food-to-microorganism ratio 1 / 3

• Filtration-to-mixing ratio
• Flow-to-mass ratio

Rationale: F/M measures the balance of organic load (food) relative to

microorganisms.

3. Nitrification is the biological conversion of:

• Organic nitrogen to methane
• Nitrate to ammonia
• Ammonia to nitrate
• Oxygen to nitrogen gas

Rationale: Nitrifying bacteria convert ammonia → nitrite → nitrate.

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

• Chlorine demand
• Settling characteristics of activated sludge
• Disinfection efficiency
• Grit removal efficiency

Rationale: SVI indicates how well sludge settles in the clarifier.

5. A typical return activated sludge (RAS) rate is:

• 5–10% of inflow
• 25–100% of inflow
• 150–200% of inflow
• Greater than 300% 2 / 3

Rationale: Most plants operate RAS between 25–100% of influent flow

depending on sludge needs.

• Which microorganisms start to dominate in a low DO activated sludge

environment?

• Nitrifiers
• Filamentous bacteria
• Protozoa
• Rotifers

Rationale: Low DO encourages filamentous organisms that cause bulking.

7. The purpose of a grit chamber is to remove:

A. BOD

• Sand, gravel, and heavy inorganic materials
• Pathogens
• Fats and oils

Rationale: Grit chambers protect downstream equipment by removing

abrasive materials.

8. High chlorine demand indicates:

• High pH
• Low solids concentration
• High organic/inorganic contaminants
• Low temperature
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