Exam Practice Questions And Correct

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

• Which of the following is the primary purpose of the activated sludge

process?

• Sedimentation
• Filtration
• Biological treatment of wastewater
• Chemical precipitation

Rationale: The activated sludge process is designed to biologically remove

organic matter from wastewater using microorganisms.

• What is the typical range for mixed liquor suspended solids (MLSS) in an

activated sludge aeration tank? 1 / 4

• 50–100 mg/L
• 100–200 mg/L
• 200–500 mg/L
• 2,000–4,000 mg/L

Rationale: Class IV operators maintain MLSS in the range of 2,000–4,000

mg/L to ensure effective biological treatment.

• Which of the following processes is used primarily for phosphorus

removal in wastewater treatment?

• Chlorination
• Chemical precipitation
• Filtration
• Aeration

Rationale: Phosphorus is typically removed using chemical precipitation

with agents like alum or ferric chloride.

• What is the main cause of sludge bulking in an activated sludge system?
• Excess aeration
• Low influent BOD
• Filamentous bacteria overgrowth
• High chlorine residual

Rationale: Sludge bulking occurs when filamentous bacteria proliferate,

causing poor settling characteristics.

• In trickling filters, what is the primary function of the microbial biofilm?
• Absorb heavy metals 2 / 4

• Filter solids
• Break down organic matter
• Neutralize pH

Rationale: Microorganisms in the biofilm metabolize organic material as

wastewater passes over the filter media.

• Which of the following is a common sign of nitrification failure in a

wastewater treatment plant?

• Low BOD removal
• Ammonia concentration increase
• High chlorine demand
• Foam formation

Rationale: Nitrification converts ammonia to nitrate; failure leads to

elevated ammonia levels in the effluent.

• Which parameter is most commonly used to assess organic strength in

wastewater?

• pH
• Turbidity
• Biochemical Oxygen Demand (BOD)
• Temperature

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter.

• What is the main purpose of chlorination in wastewater treatment?
• Increase alkalinity 3 / 4

• Reduce solids
• Disinfection
• Enhance nitrification

Rationale: Chlorination is primarily used to kill pathogenic organisms in

treated effluent.

• Which of the following is a common byproduct of anaerobic digestion of

sludge?

• Nitrate
• Oxygen
• Methane
• Hydrogen peroxide

Rationale: Anaerobic digestion breaks down organic matter and produces

methane and carbon dioxide.

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

treatment plant?

• Remove organic matter
• Remove sand, gravel, and other heavy inorganic solids
• Aerate wastewater
• Adjust pH

Rationale: Grit chambers remove heavy, inorganic solids that can damage

pumps and equipment.

• Which of the following best describes the function of a clarifier?
• Aerate wastewater
• / 4