Level I Practice Exam Questions And

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

• Which of the following best describes the primary purpose of a

wastewater treatment plant?

• To produce drinking water
• To remove pollutants from wastewater before discharge
• To increase water hardness
• To add chemicals for industrial use

Rationale: The main goal of wastewater treatment is to remove

contaminants and pollutants to protect public health and the environment.

2. BOD stands for:

• Biological Oxidation Demand 1 / 4

• Biochemical Oxygen Demand
• Basic Oxygen Detergent
• Bacterial Oxidation Demand

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter in water.

3. The first step in most wastewater treatment plants is:

• Disinfection
• Screening and grit removal
• Biological treatment
• Sludge dewatering

Rationale: Screening removes large solids and grit removal prevents

damage to equipment.

• Which type of bacteria is primarily responsible for breaking down

organic matter in activated sludge systems?

• Nitrifying bacteria
• Heterotrophic bacteria
• Sulfate-reducing bacteria
• Methanogens

Rationale: Heterotrophic bacteria consume organic carbon, reducing

BOD.

• Sludge settling occurs in which part of the treatment process?
• Aeration basin
• Secondary clarifier 2 / 4

• Primary screen
• Disinfection chamber

Rationale: Clarifiers allow solids to settle from the liquid after

biological treatment.

• Which of the following is a common method for sludge disposal?
• Deep well injection
• Land application
• Ocean dumping
• Open burning

Rationale: Land application recycles nutrients and is an

environmentally safe method of sludge disposal.

7. The process of removing nitrogen from wastewater is called:

• Chlorination
• Nitrification-denitrification
• Sedimentation
• Flocculation

Rationale: Nitrogen is removed biologically through nitrification

followed by denitrification.

• A wastewater flow of 1 million gallons per day (MGD) is equal to how

many gallons per minute (GPM)?

A. 694

B. 694.44

C. 1,000 3 / 4

D. 1,440

Rationale: 1 MGD ÷ 1,440 minutes/day = 694.44 GPM.

• Which chemical is commonly used for disinfection of wastewater?
• Ammonia
• Chlorine
• Sulfate
• Fluoride

Rationale: Chlorine effectively kills pathogenic microorganisms in

wastewater.

• The primary purpose of aeration in an activated sludge process

is to:

• Remove solids
• Provide oxygen for microorganisms
• Adjust pH
• Disinfect water

Rationale: Oxygen supports the growth and activity of aerobic

bacteria.

• Which of the following pH levels is considered neutral?
• 0
• 7
• 7
• 14

Rationale: A pH of 7 is neutral; below 7 is acidic and above 7 is basic.

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