Practice Exam Questions And Correct

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

• Which of the following is the primary purpose of preliminary

treatment in a wastewater treatment plant?

• Remove nutrients
• Remove large solids and debris
• Reduce biochemical oxygen demand (BOD)
• Disinfect effluent

Rationale: Preliminary treatment removes large solids, rags, and grit

to prevent damage to downstream equipment.

• What is the main function of primary clarifiers?
• Remove dissolved oxygen 1 / 4

• Settle suspended solids
• Remove nitrogen
• Add chemicals for disinfection

Rationale: Primary clarifiers allow suspended solids to settle out by

gravity, reducing the load on secondary treatment.

3. Activated sludge treatment is designed primarily to:

• Remove heavy metals
• Biologically remove organic matter
• Remove grit
• Increase alkalinity

Rationale: Activated sludge uses microorganisms to biologically oxidize

organic matter in wastewater.

• Which of the following parameters indicates the organic strength of

wastewater?

• Total suspended solids
• pH
• Biochemical oxygen demand (BOD)
• Temperature

Rationale: BOD measures the amount of oxygen microorganisms will

consume to decompose organic matter.

• What is the main purpose of chlorination in wastewater treatment?
• Remove solids
• Disinfect the effluent 2 / 4

• Increase pH
• Remove nutrients

Rationale: Chlorination is used to kill pathogens and reduce microbial

contamination in effluent.

6. In a trickling filter, the primary mechanism for organic removal is:

• Settling
• Biological oxidation on media surfaces
• Filtration
• Chemical precipitation

Rationale: Microorganisms grow on filter media and consume organic

matter as wastewater passes over.

• Which of the following best describes sludge digestion?
• Chemical precipitation of solids
• Biological breakdown of organic solids
• Filtration of solids
• Screening of large debris

Rationale: Sludge digestion uses anaerobic or aerobic bacteria to

reduce sludge volume and odor.

• Which type of bacteria is primarily responsible for nitrification?
• Anaerobic bacteria
• Coliform bacteria
• Autotrophic bacteria
• Heterotrophic bacteria 3 / 4

Rationale: Autotrophic bacteria convert ammonia to nitrite and then

to nitrate in the nitrification process.

• What is the typical pH range for effective nitrification?

A. 4.0–5.5

B. 5.5–6.5

C. 6.5–8.0

D. 8.5–9.5

Rationale: Nitrifying bacteria function best in slightly alkaline

conditions.

• In wastewater treatment, what is meant by “solids retention

time” (SRT)?

• The time effluent stays in the clarifier
• The average time solids remain in the biological process
• The time sludge is pumped to land application
• The detention time in preliminary treatment

Rationale: SRT represents the average time microorganisms remain in

the system, affecting treatment efficiency.

• Which of the following processes is used to remove phosphorus

chemically?

• Aeration
• Addition of alum or ferric chloride
• Filtration
• Sedimentation
• / 4