Licensing Exam Practice Test 100

Sewage Treatment Operator Class II Licensing Exam Practice Test 100 Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of a primary clarifier in a sewage treatment

process?

• Nitrification
• Sludge digestion
• Reduction of BOD by biological oxidation
• Removal of settleable and floatable solids

Rationale: Primary clarification removes suspended solids by gravity,

decreasing solids loading to downstream processes.

• Which parameter is most commonly used to measure organic strength

of wastewater? 1 / 4

A. TSS

B. BOD

• pH
• Alkalinity

Rationale: BOD reflects biodegradable organic material, indicating

wastewater strength.

• In activated sludge, what does F/M ratio represent?
• Flow divided by mixed liquor
• Food per mass of oxygen
• Food-to-microorganism ratio
• Floc-to-microbe ratio

Rationale: F/M expresses the organic load relative to biomass for process

control.

• What is the ideal dissolved oxygen range in an aeration tank?
• 0.1–0.5 mg/L
• 0.5–1.0 mg/L
• 2.0–4.0 mg/L
• 6.0–8.0 mg/L

Rationale: DO of 2–4 mg/L supports aerobic biological activity for stable

treatment.

5. A higher SVI indicates: 2 / 4

• Good settling
• Bulking sludge
• High oxygen transfer
• Low MLSS concentration

Rationale: A high SVI (>150 mL/g) means sludge settles poorly, often due

to filamentous bacteria.

• What device measures wastewater flow in an open channel?
• Magnetic meter
• Parshall flume
• Orifice plate
• Venturi meter

Rationale: Parshall flumes accurately measure open-channel flow using

hydraulic principles.

• What is the main purpose of grit removal?
• Remove organic solids
• Reduce pathogens
• Protect equipment from abrasion
• Reduce BOD

Rationale: Grit (sand, gravel) is removed early to prevent wear and

clogging.

8. The term “sludge age” refers to: 3 / 4

• Time sludge stays in clarifier
• Average time microorganisms remain in the system
• Time before dewatering
• Time until digestion

Rationale: Sludge age = mean cell residence time (MCRT) in activated

sludge.

• What does the Weir Overflow Rate describe?
• DO loading across tanks
• Rate of solids underflow
• Flow per linear foot of weir
• Sludge settling rate

Rationale: Weir Overflow Rate ensures even effluent withdrawal and

prevents washout.

10. Nitrification converts:

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

Rationale: Nitrification is the aerobic oxidation of ammonia to nitrate by

bacteria.

• Which bacteria group performs nitrification?
• / 4