Practice Exam Questions And Correct

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

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

treatment plant?

• Remove nutrients
• Remove pathogens
• Remove large solids and grit
• Remove dissolved organic matter

Rationale: Preliminary treatment is designed to remove large solids, grit, and

debris to protect downstream equipment and processes.

• What is the ideal pH range for biological wastewater treatment?

A. 3.0–4.0 1 / 4

B. 5.0–6.0

C. 6.5–8.5

D. 9.0–10.0

Rationale: Most biological treatment processes, such as activated sludge,

operate efficiently in a pH range of 6.5–8.5.

• Which of the following is the most common indicator organism for

fecal contamination?

• Salmonella
• Escherichia coli (E. coli)
• Staphylococcus aureus
• Clostridium

Rationale: E. coli is widely used as an indicator for fecal contamination in

water and wastewater.

4. The purpose of chlorination in wastewater treatment is primarily to:

• Remove solids
• Disinfect wastewater
• Adjust pH
• Increase dissolved oxygen

Rationale: Chlorination is used to kill or inactivate pathogens before

discharge.

• What is the typical detention time in a secondary clarifier?
• 5–10 minutes 2 / 4

• 15–30 minutes
• 2–4 hours
• 6–8 hours

Rationale: Secondary clarifiers typically have a detention time of 2–4 hours

to allow solids to settle.

• Which of the following best describes BOD5?
• The amount of oxygen consumed by microorganisms in 5 days at

20°C

• The total dissolved oxygen in wastewater
• The oxygen needed to oxidize ammonia
• The oxygen released during photosynthesis

Rationale: BOD5 is a measure of the biodegradable organic matter in

wastewater over five days.

• What is the function of a grit chamber?
• Remove floating debris
• Remove sand, gravel, and other heavy particles
• Remove dissolved nutrients
• Kill pathogens

Rationale: Grit chambers allow heavier inorganic materials to settle while

lighter organic matter flows through.

• Which process is primarily used for nitrogen removal in wastewater?
• Sedimentation 3 / 4

• Filtration
• Biological nitrification and denitrification
• Chlorination

Rationale: Nitrogen is removed biologically through nitrification (ammonia

to nitrate) and denitrification (nitrate to nitrogen gas).

• Which sludge disposal method is most common for Class B plants?
• Ocean discharge
• Land application or landfill
• Incineration only
• Direct discharge to rivers

Rationale: Stabilized sludge from Class B plants is often disposed of via land

application or landfills following regulatory guidelines.

• Which of the following best describes a trickling filter?
• A type of chemical treatment
• A fixed-bed biological treatment process
• A type of sedimentation basin
• A disinfection process

Rationale: Trickling filters use media to support microbial growth that

removes organic matter from wastewater.

• What is the main cause of foaming in activated sludge systems?
• High nitrate
• Low temperature
• / 4