Exam Practice Questions And Correct

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

• The main purpose of primary treatment in a wastewater treatment

plant is to:

• Remove dissolved nutrients
• Remove settleable solids
• Disinfect the wastewater
• Remove pathogens

Answer: B

Rationale: Primary treatment focuses on the physical removal of

settleable solids through sedimentation. 1 / 4

2. Activated sludge process is an example of:

• Physical treatment
• Biological treatment
• Chemical treatment
• Tertiary treatment

Answer: B

Rationale: Activated sludge uses microorganisms to biologically

degrade organic matter in wastewater.

• What is the typical range for mixed liquor suspended solids (MLSS) in

an activated sludge system?

• 50–100 mg/L
• 100–200 mg/L
• 2000–4000 mg/L
• 5000–7000 mg/L

Answer: C

Rationale: MLSS in an activated sludge system is generally maintained

between 2000–4000 mg/L to ensure proper microbial activity.

4. Nitrification in wastewater treatment converts:

• Nitrite to ammonia
• Ammonia to nitrate
• Nitrate to ammonia
• Nitrogen gas to nitrate

Answer: B 2 / 4

Rationale: Nitrification is a two-step biological process where

ammonia is first converted to nitrite and then to nitrate by nitrifying bacteria.

• Denitrification occurs under what conditions?
• Aerobic
• Anoxic
• Anaerobic
• Photosynthetic

Answer: B

Rationale: Denitrification requires an anoxic environment, where

nitrate is converted to nitrogen gas.

• The most common method for measuring biochemical oxygen demand

(BOD) is over a period of:

• 1 day
• 3 days
• 5 days
• 10 days

Answer: C

Rationale: BOD₅ (five-day BOD test) is the standard for measuring the

amount of oxygen consumed by microorganisms over 5 days at 20°C.

7. Sludge digestion is primarily used to:

• Increase odor
• Stabilize organic matter 3 / 4

• Remove nutrients
• Improve filtration

Answer: B

Rationale: Digestion stabilizes organic solids, reduces pathogens, and

minimizes odor.

• Which of the following is a primary function of the aeration tank?
• Settling solids
• Disinfection
• Provide oxygen for microorganisms
• Filtration

Answer: C

Rationale: The aeration tank supplies oxygen to bacteria for the

decomposition of organic matter.

9. The F/M ratio in wastewater treatment refers to:

• Flow per meter
• Food to microorganism ratio
• Filtration method
• Floc formation

Answer: B

Rationale: F/M ratio is the ratio of the organic load (food) to the mass

of microorganisms in the system.

10. Chlorine is added to wastewater primarily to:

• Remove solids
• / 4