Practice Exam Questions And Correct

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

• What is the primary purpose of a grit chamber in a wastewater facility?
• Remove dissolved solids
• Reduce BOD
• Remove heavy inorganic materials
• Remove pathogens

Answer: C

Rationale: Grit chambers remove heavy inorganic materials like sand and

gravel to protect downstream equipment.

• What is the typical detention time in a primary clarifier? 1 / 4

• 5–10 hours
• 30–60 seconds
• 1.5–2.5 hours
• 8–12 hours

Answer: C

Rationale: Primary clarifiers generally operate with a 1.5–2.5 hour

detention time for proper settling.

• Which process is used to biologically remove BOD?
• Screening
• Grit removal
• Activated sludge
• Disinfection

Answer: C

Rationale: Activated sludge introduces microorganisms that consume

organic matter, reducing BOD.

4. In activated sludge, the term F/M ratio refers to:

• Flow/Mixing
• Food/Microorganism
• Filtration/Movement
• Fat/Microbe 2 / 4

Answer: B

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

(microorganisms), controlling process stability.

5. A low DO level in an aeration tank typically causes:

• Reduced sludge age
• Increased nitrification
• Filamentous bulking
• Lower MLSS

Answer: C

Rationale: Filamentous organisms thrive under low DO, causing bulking.

6. Chlorine is most effective as a disinfectant when pH is:

• Above 9
• Neutral
• Below 7
• Between 10–12

Answer: C

Rationale: Lower pH favors hypochlorous acid formation, the most

effective disinfectant form.

• What is the purpose of a trickling filter distributor arm? 3 / 4

• Remove solids
• Evenly spread wastewater over media
• Remove pathogens
• Store sludge

Answer: B

Rationale: Distributor arms ensure uniform distribution for effective

biological treatment.

8. The sludge blanket in a secondary clarifier should be:

• Touching the underflow
• In the scum trough
• Low and stable
• Floating

Answer: C

Rationale: A stable, low sludge blanket prevents solids overflow and

ensures proper separation.

• What is the typical DO concentration in an activated sludge aeration

tank?

• 0.5 mg/L
• 2 mg/L
• 6 mg/L
• / 4