Operator Class I Practice Exam Questions

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

• What is the primary purpose of a wastewater treatment plant?
• Produce drinking water
• Reduce pollutants in wastewater before discharge
• Remove solids for reuse in agriculture
• Increase water temperature

Rationale: The main goal of wastewater treatment is to reduce

pollutants to protect public health and the environment.

• Which of the following is considered a biological process in

wastewater treatment?

• Filtration
• Activated sludge process 1 / 4

• Chemical coagulation
• Sedimentation

Rationale: The activated sludge process relies on microorganisms to

degrade organic matter biologically.

• What does BOD stand for?
• Biological Oxidation Demand
• Biochemical Oxygen Demand
• Basic Oxygen Demand
• Biological Oxygen Distribution

Rationale: BOD measures the amount of oxygen microorganisms

need to decompose organic matter in water.

• Which of the following is a primary treatment process?
• Trickling filter
• Sedimentation
• Activated sludge
• Chlorination

Rationale: Sedimentation removes settleable solids from wastewater

in the primary treatment stage.

5. Nitrification is a process in which:

• Ammonia is converted to nitrate
• Nitrate is converted to ammonia
• Nitrogen gas is added to water
• Nitrite is converted to ammonia 2 / 4

Rationale: Nitrification is the biological oxidation of ammonia to

nitrate by specialized bacteria.

• Which of the following is considered a secondary treatment method?
• Screening
• Grit removal
• Activated sludge
• Chlorination

Rationale: Secondary treatment uses biological processes, such as

activated sludge, to reduce dissolved and suspended organic matter.

7. The primary purpose of grit removal is to:

• Prevent damage to pumps and equipment
• Remove dissolved solids
• Reduce BOD
• Chlorinate wastewater

Rationale: Grit removal prevents sand, gravel, and other abrasive

materials from damaging equipment.

8. The term “sludge” refers to:

• Settled solids from wastewater treatment
• Effluent water
• Chemicals added to water
• Pathogens in water

Rationale: Sludge is the accumulation of solids removed during

treatment. 3 / 4

9. The most common pathogen found in untreated wastewater is:

• Influenza virus
• E. coli
• Hepatitis B
• Salmonella typhi

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

wastewater.

• What is the purpose of chlorine in wastewater treatment?
• Remove solids
• Increase oxygen content
• Disinfect wastewater
• Enhance biological activity

Rationale: Chlorine is primarily used for disinfection, killing

pathogens before discharge.

• What is the typical detention time for primary sedimentation

tanks?

• 5–10 minutes
• 30–45 minutes
• 1–2 hours
• 4–6 hours

Rationale: Primary sedimentation tanks typically have a detention

time of 1–2 hours to allow solids to settle.

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