Exam Practice Questions And Correct

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

• What is the primary purpose of a wastewater treatment plant?

a) Produce drinking water

b) Generate electricity

c) Remove pollutants from wastewater

d) Irrigate farmland

Rationale: The main goal of a wastewater treatment plant is to

remove physical, chemical, and biological pollutants to protect public health and the environment.

• What is BOD?

a) Biological oxygen deficiency 1 / 4

b) Biochemical oxygen demand

c) Basic oxygen dilution

d) Biochemical oxidation difference

Rationale: BOD measures the amount of oxygen microorganisms

need to decompose organic matter in water, indicating pollution levels.

• Which microorganism group is primarily responsible for nitrification?

a) Protozoa

b) Chemolithotrophic bacteria

c) Algae

d) Fungi

Rationale: Chemolithotrophic bacteria, such as Nitrosomonas and

Nitrobacter, oxidize ammonia to nitrate during nitrification.

• What is the ideal pH range for activated sludge processes?
• 4.5 – 5.5
• 6.5 – 8.5
• 8.5 – 10.5
• 5.0 – 6.0

Rationale: A pH of 6.5–8.5 supports microbial activity and maintains

efficient biological treatment.

• Which unit process primarily removes suspended solids?

a) Disinfection

b) Aeration 2 / 4

c) Sedimentation

d) Nitrification

Rationale: Sedimentation allows solids to settle out from

wastewater, reducing TSS before biological treatment.

• What is the main function of a clarifier?

a) Increase BOD

b) Separate solids from liquids

c) Reduce pH

d) Add nutrients

Rationale: Clarifiers are used to separate suspended solids from

treated water to improve effluent quality.

7. Sludge thickening is performed to:

a) Increase water content

b) Reduce organic matter

c) Reduce sludge volume

d) Remove nitrogen

Rationale: Thickening increases sludge solids concentration, reducing

storage and handling costs.

• What is the approximate detention time in a primary clarifier?
• 1-5 minutes
• 10-15 minutes
• 1-2 hours
• 24 hours 3 / 4

Rationale: Primary clarifiers typically retain wastewater 1–2 hours to

allow solids to settle.

9. The purpose of aeration in activated sludge is to:

a) Cool the water

b) Provide oxygen for microorganisms

c) Remove nitrogen chemically

d) Settle solids

Rationale: Aeration supplies oxygen needed by bacteria to

biologically degrade organic matter.

• What is sludge digestion?

a) Removing water from sludge

b) Stabilizing organic matter biologically

c) Chemically treating water

d) Settling solids

Rationale: Digestion reduces sludge odor, volume, and pathogens by

biological decomposition.

• Which gas is commonly produced during anaerobic digestion?

a) Oxygen

b) Nitrogen

c) Methane

d) Carbon monoxide

Rationale: Anaerobic digestion produces methane as a byproduct of

bacterial decomposition of organic matter in the absence of oxygen.

• / 4