Practice Exam Questions And Correct

Ohio Wastewater Operator Class C Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2025|2026 Q&A | Instant Download Pdf

• What is the primary purpose of a grit chamber in a wastewater

treatment plant?

• Remove organic solids
• Remove dissolved nutrients
• Remove sand, gravel, and heavy solids
• Reduce BOD

Rationale: Grit chambers are designed to remove heavy inorganic solids

like sand, gravel, and grit to protect downstream equipment and prevent accumulation in tanks. 1 / 4

2. The pH of typical municipal wastewater ranges between:

A. 4.0 – 5.0

B. 6.5 – 8.5

C. 8.0 – 10.0

D. 3.0 – 6.0

Rationale: Municipal wastewater usually has a near-neutral pH between

6.5 and 8.5 to maintain microbial activity and protect infrastructure.

• Which microorganism is most important in the biological treatment of

wastewater?

• Viruses
• Bacteria
• Protozoa
• Algae

Rationale: Bacteria are the primary agents for breaking down organic

matter during biological wastewater treatment.

• What is the main purpose of primary sedimentation tanks?
• Nutrient removal
• Settle suspended solids
• Aeration
• Disinfection

Rationale: Primary sedimentation tanks allow solids to settle out of

wastewater by gravity before biological treatment. 2 / 4

5. Activated sludge is primarily used to:

• Remove grit
• Remove heavy metals
• Biologically remove organic matter
• Chlorinate wastewater

Rationale: Activated sludge contains microorganisms that digest organic

pollutants in wastewater, reducing BOD and suspended solids.

• Which test measures the amount of oxygen required by bacteria to

decompose organic matter?

A. COD

B. TSS

C. BOD

• pH

Rationale: Biochemical Oxygen Demand (BOD) quantifies the oxygen

consumed by microorganisms as they decompose organic matter.

• What is the function of a clarifier in wastewater treatment?
• Chlorinate water
• Aerate water
• Allow solids to settle
• Filter water

Rationale: Clarifiers provide quiescent conditions for suspended solids to

settle, reducing TSS in effluent. 3 / 4

• Which chemical is commonly used for disinfection in wastewater

plants?

• Sodium hydroxide
• Sulfuric acid
• Chlorine
• Alum

Rationale: Chlorine is widely used for disinfection due to its effectiveness in

killing pathogens.

• What is the purpose of aeration in activated sludge systems?
• Increase TSS
• Remove grit
• Supply oxygen for microorganisms
• Remove chlorine

Rationale: Aeration provides oxygen to aerobic bacteria, enabling them to

metabolize organic matter.

• What is the primary source of nitrogen in wastewater?
• Industrial solvents
• Human waste
• Grit
• Chlorine

Rationale: Human waste contains ammonia, urea, and other nitrogen

compounds that contribute to wastewater nitrogen.

• / 4