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 primary purpose of preliminary treatment in a wastewater plant is

to:

• Remove nutrients
• Remove large debris
• Remove dissolved solids
• Provide disinfection

Rationale: Preliminary treatment protects downstream equipment by

removing rags, sticks, grit, and trash.

2. The most common type of bacteria in activated sludge is:

• Viruses
• Aerobic bacteria 1 / 3

• Anaerobic bacteria
• Parasites

Rationale: Activated sludge relies on aerobic microorganisms to

degrade organic matter.

3. BOD stands for:

• Biological Oxygen Dispersal
• Biochemical Oxygen Demand
• Basic Oxygen Dissolution
• Biological Oxidation Discharge

Rationale: BOD measures oxygen demand for biological

decomposition of organics.

4. A clarifier is primarily designed to:

• Introduce turbulence
• Settle solids
• Aerate wastewater
• Remove grease

Rationale: Clarifiers remove suspended solids from wastewater by

gravity settling.

5. The typical pH range for biological treatment processes is:

A. 2–4

B. 4–6

C. 6.5–8.5 2 / 3

D. 9–11

Rationale: Microorganisms thrive best in a near-neutral pH range.

6. The primary purpose of wastewater aeration is to:

• Remove grit
• Neutralize pH
• Add oxygen for microorganisms
• Disinfect

Rationale: Oxygen supports aerobic bacteria that break down

organics.

7. Sludge age (SRT) refers to:

• Filter bed media lifespan
• Chemical reaction time
• Time biomass remains in the system
• Pump lifecycle

Rationale: SRT measures the average time solids stay in the activated

sludge system.

8. A typical dissolved oxygen level for aeration basins is:

• 0–0.5 mg/L
• 1–2 mg/L
• 2–4 mg/L
• 6–8 mg/L

Rationale: Aerobic treatment needs 2–4 mg/L DO for efficient

biological activity.

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