Oregon Wastewater Treatment Operator
Level I Practice Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download
Pdf
1. Which of the following best describes the primary purpose of a
wastewater treatment plant?
A. To produce drinking water
B. To remove pollutants from wastewater before discharge
C. To increase water hardness
D. 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:
A. Biological Oxidation Demand
, B. Biochemical Oxygen Demand
C. Basic Oxygen Detergent
D. 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:
A. Disinfection
B. Screening and grit removal
C. Biological treatment
D. Sludge dewatering
Rationale: Screening removes large solids and grit removal prevents
damage to equipment.
4. Which type of bacteria is primarily responsible for breaking down
organic matter in activated sludge systems?
A. Nitrifying bacteria
B. Heterotrophic bacteria
C. Sulfate-reducing bacteria
D. Methanogens
Rationale: Heterotrophic bacteria consume organic carbon, reducing
BOD.
5. Sludge settling occurs in which part of the treatment process?
A. Aeration basin
B. Secondary clarifier
, C. Primary screen
D. Disinfection chamber
Rationale: Clarifiers allow solids to settle from the liquid after
biological treatment.
6. Which of the following is a common method for sludge disposal?
A. Deep well injection
B. Land application
C. Ocean dumping
D. 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:
A. Chlorination
B. Nitrification-denitrification
C. Sedimentation
D. Flocculation
Rationale: Nitrogen is removed biologically through nitrification
followed by denitrification.
8. 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
, D. 1,440
Rationale: 1 MGD ÷ 1,440 minutes/day = 694.44 GPM.
9. Which chemical is commonly used for disinfection of wastewater?
A. Ammonia
B. Chlorine
C. Sulfate
D. Fluoride
Rationale: Chlorine effectively kills pathogenic microorganisms in
wastewater.
10. The primary purpose of aeration in an activated sludge process
is to:
A. Remove solids
B. Provide oxygen for microorganisms
C. Adjust pH
D. Disinfect water
Rationale: Oxygen supports the growth and activity of aerobic
bacteria.
11. Which of the following pH levels is considered neutral?
A. 0
B. 7
C. 7
D. 14
Rationale: A pH of 7 is neutral; below 7 is acidic and above 7 is basic.
Level I Practice Exam Questions And
Correct Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant Download
1. Which of the following best describes the primary purpose of a
wastewater treatment plant?
A. To produce drinking water
B. To remove pollutants from wastewater before discharge
C. To increase water hardness
D. 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:
A. Biological Oxidation Demand
, B. Biochemical Oxygen Demand
C. Basic Oxygen Detergent
D. 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:
A. Disinfection
B. Screening and grit removal
C. Biological treatment
D. Sludge dewatering
Rationale: Screening removes large solids and grit removal prevents
damage to equipment.
4. Which type of bacteria is primarily responsible for breaking down
organic matter in activated sludge systems?
A. Nitrifying bacteria
B. Heterotrophic bacteria
C. Sulfate-reducing bacteria
D. Methanogens
Rationale: Heterotrophic bacteria consume organic carbon, reducing
BOD.
5. Sludge settling occurs in which part of the treatment process?
A. Aeration basin
B. Secondary clarifier
, C. Primary screen
D. Disinfection chamber
Rationale: Clarifiers allow solids to settle from the liquid after
biological treatment.
6. Which of the following is a common method for sludge disposal?
A. Deep well injection
B. Land application
C. Ocean dumping
D. 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:
A. Chlorination
B. Nitrification-denitrification
C. Sedimentation
D. Flocculation
Rationale: Nitrogen is removed biologically through nitrification
followed by denitrification.
8. 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
, D. 1,440
Rationale: 1 MGD ÷ 1,440 minutes/day = 694.44 GPM.
9. Which chemical is commonly used for disinfection of wastewater?
A. Ammonia
B. Chlorine
C. Sulfate
D. Fluoride
Rationale: Chlorine effectively kills pathogenic microorganisms in
wastewater.
10. The primary purpose of aeration in an activated sludge process
is to:
A. Remove solids
B. Provide oxygen for microorganisms
C. Adjust pH
D. Disinfect water
Rationale: Oxygen supports the growth and activity of aerobic
bacteria.
11. Which of the following pH levels is considered neutral?
A. 0
B. 7
C. 7
D. 14
Rationale: A pH of 7 is neutral; below 7 is acidic and above 7 is basic.
