Practice Exam Questions And Correct

Maine Wastewater Operator Grade V 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 secondary treatment in

a wastewater treatment plant?

• Remove large solids
• Remove nutrients
• Reduce organic matter (BOD) biologically
• Disinfect effluent

Rationale:

Secondary treatment uses biological processes (like activated sludge or trickling filters) to reduce biochemical oxygen demand (BOD) and remove dissolved and suspended organic matter. 1 / 4

• What is the typical design detention time for an activated sludge

aeration basin?

• 0.5–1 hour
• 2–4 hours
• 4–8 hours
• 12–24 hours

Rationale:

Detention time in aeration basins is designed to provide sufficient contact between microorganisms and wastewater to achieve BOD removal, typically 4–8 hours depending on plant design.

• Which of the following parameters is most commonly used to measure

organic strength of wastewater?

• Total suspended solids
• pH
• Biochemical oxygen demand (BOD)
• Chlorine residual

Rationale:

BOD measures the amount of oxygen required by microorganisms to decompose organic matter in wastewater and is the standard indicator of organic strength. 2 / 4

• In a sequencing batch reactor (SBR), which phase follows the fill phase?
• Decant
• Idle
• React (aeration)
• Settle

Rationale:

After filling, the react phase aerates the wastewater to promote biological treatment before settling and decanting.

• What is the primary purpose of chlorination in wastewater treatment?
• Reduce BOD
• Disinfect effluent
• Remove suspended solids
• Reduce nitrogen

Rationale:

Chlorination is used to kill pathogens in the treated effluent, ensuring it meets public health and environmental discharge standards.

6. Nitrification is a biological process that converts:

• Nitrogen gas to ammonia
• Nitrites to nitrogen gas 3 / 4

• Ammonia to nitrate
• Organic nitrogen to ammonia

Rationale:

Nitrification involves the oxidation of ammonia (NH₃) to nitrite (NO₂⁻) and then to nitrate (NO₃⁻) by specialized bacteria.

• What is the typical pH range for effective biological treatment in

activated sludge systems?

A. 4.0–5.0

B. 6.5–8.5

C. 8.5–10.0

D. 5.0–6.0

Rationale:

Most microorganisms in activated sludge systems function optimally in a neutral to slightly alkaline pH range of 6.5–8.5.

• Which type of sludge digestion is commonly used for Class A biosolids

production?

• Aerobic digestion
• Pond stabilization
• Anaerobic digestion
• Lime stabilization
• / 4