II Licensing Exam Practice Test

Water Pollution Control 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

treatment?

• Remove grit
• Remove heavy metals
• Biologically degrade dissolved and suspended organics
• Add disinfectants

Answer: C

Rationale: Secondary treatment focuses on biological processes that

remove organic material using microorganisms.

• In activated sludge systems, F/M ratio represents the relationship

between food and what? 1 / 4

• Flow
• Microorganisms
• Metals
• Mixed liquor temperature

Answer: B

Rationale: The F/M ratio compares the mass of organic matter to the mass

of microorganisms available to consume it.

3. A clarifier experiencing sludge rising is likely due to:

• Low temperature
• Denitrification
• High DO
• Low detention time

Answer: B

Rationale: Denitrification produces nitrogen gas bubbles that lift sludge to

the surface.

4. The purpose of bar screens is to:

• Remove dissolved solids
• Remove large debris
• Reduce BOD
• Reduce ammonia

Answer: B

Rationale: Screening eliminates large objects to protect downstream

equipment. 2 / 4

5. Chlorine residual in treated effluent is used to measure:

• Flow rate
• Remaining available chlorine after demand is met
• Sludge age
• pH levels

Answer: B

Rationale: Residual chlorine indicates unused chlorine following the

disinfection demand.

• What does MLSS stand for?
• Mixed Liquid Sludge Sample
• Micro-Level System Solids
• Mixed Liquor Suspended Solids
• Multi-Layer Solids System

Answer: C

Rationale: MLSS is the suspended solids concentration in the aeration tank.

7. A high sludge age typically leads to:

• Lower F/M ratio
• Higher BOD removal
• More filamentous bacteria
• Lower DO levels

Answer: A 3 / 4

Rationale: As sludge age increases, the population of microorganisms

increases, lowering the F/M ratio.

• What causes filamentous bulking?
• High DO
• Excess chlorine
• Low F/M or septic influent
• Low sludge age

Answer: C

Rationale: Low nutrient conditions or septicity promote filamentous

organism growth.

9. An RBC (rotating biological contactor) uses:

• Chemical oxidation
• Attached biofilm
• UV radiation
• Settling velocity

Answer: B

Rationale: RBC units rely on fixed-film microorganisms rotating through

wastewater.

10. The primary gas produced during anaerobic digestion is:

• Nitrogen
• Oxygen
• Methane
• / 4