Practice Exam 100 Questions And

Wastewater Facilities Operator Class III Practice Exam 100 Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of preliminary treatment in a wastewater

facility?

• Remove dissolved solids
• Reduce nitrogen levels
• Remove large debris and grit
• Disinfect wastewater

Rationale: Preliminary treatment focuses on removing large materials and

grit to protect downstream equipment.

2. The main function of a comminutor is to:

• Remove grit
• Shred solids into smaller particles 1 / 4

• Add oxygen
• Reduce BOD

Rationale: Comminutors grind coarse solids to prevent clogging.

3. Grit chambers are designed to remove:

• Organics
• Heavy inorganic solids
• Pathogens
• Oil and grease

Rationale: Grit chambers remove sand, gravel, and inorganic particles that

cause abrasion.

4. The primary purpose of primary clarifiers is to:

• Nitrify ammonia
• Settle suspended solids
• Remove pathogens
• Aerate wastewater

Rationale: Primary clarifiers settle solids by gravity before biological

treatment.

5. A typical detention time in a primary clarifier is:

• 5–10 minutes
• 1–5 minutes
• 1–2 hours
• 10 hours 2 / 4

Rationale: Primary clarifiers generally operate with 1–2 hours detention

for settling.

6. BOD stands for:

• Biodegradable Organic Demand
• Biochemical Oxygen Demand
• Biological Oxidation Data
• Biological Organic Decomposition

Rationale: BOD is the oxygen required by microorganisms to degrade

organics.

• The process that uses microorganisms in the presence of oxygen is

known as:

• Anaerobic digestion
• Aerobic treatment
• Denitrification
• Sedimentation

Rationale: Aerobic treatment involves oxygen-dependent microorganisms.

8. The activated sludge process relies on:

• Anaerobic bacteria
• Aerobic bacteria
• Chemical oxidation
• Physical filtration

Rationale: Activated sludge uses aerobic organisms to reduce organics. 3 / 4

9. Return activated sludge (RAS) is returned from:

• Primary clarifier
• Secondary clarifier
• Aeration tank
• Digester

Rationale: RAS is sludge settled in the secondary clarifier that is returned

to maintain biomass.

10. Sludge bulking is most commonly caused by:

• High alkalinity
• Filamentous bacteria
• Excess chlorine
• High DO

Rationale: Filamentous bacteria interfere with settling, causing bulking.

11. The purpose of waste activated sludge (WAS) is to:

• Increase DO levels
• Reduce aeration basin volume
• Control biomass level
• Remove grit

Rationale: WAS controls the amount of microorganisms in the system.

• Aeration basin DO concentration should typically be maintained at:
• / 4