Wastewater Operator Class I Licensing
Exam Practice Questions And Correct
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Rationales 2026 Q&A | Instant
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1. What is the primary purpose of a wastewater treatment plant?
A. Generate electricity
B. Remove contaminants from wastewater
C. Increase water hardness
D. Produce drinking water
Rationale: The primary purpose of a wastewater treatment plant is to
remove physical, chemical, and biological contaminants from wastewater
before discharging it into the environment.
2. Which of the following is considered a physical treatment process?
A. Chlorination
, B. Sedimentation
C. Biological filtration
D. Aeration
Rationale: Sedimentation is a physical process that removes suspended
solids by allowing them to settle under gravity.
3. In wastewater terminology, BOD stands for:
A. Biological Oxidation Demand
B. Biochemical Oxygen Determination
C. Biochemical Oxygen Demand
D. Biological Oxidation Depth
Rationale: BOD measures the amount of dissolved oxygen needed by
microorganisms to break down organic matter in water.
4. Which unit process is primarily used to remove suspended solids?
A. Disinfection
B. Aeration
C. Filtration
D. Sedimentation
Rationale: Sedimentation removes suspended solids from wastewater by
gravity settling.
5. What is the typical range of BOD in domestic wastewater?
A. 10–50 mg/L
B. 50–100 mg/L
, C. 200–300 mg/L
D. 500–800 mg/L
Rationale: Domestic wastewater usually contains BOD levels between 200–
300 mg/L.
6. Which of the following is a characteristic of primary treatment?
A. Biological nutrient removal
B. Removal of settleable solids
C. Advanced filtration
D. Chemical coagulation
Rationale: Primary treatment focuses on removing settleable solids and
floating material.
7. Chlorination is used primarily for:
A. Disinfection
B. Sedimentation
C. Biological treatment
D. Filtration
Rationale: Chlorination kills or inactivates pathogens in wastewater to
reduce disease risk.
8. Sludge digestion is primarily intended to:
A. Remove heavy metals
B. Stabilize organic solids
, C. Reduce chlorine demand
D. Increase BOD
Rationale: Sludge digestion stabilizes organic matter in sludge, reducing
odors and pathogen content.
9. Which of the following is NOT a type of wastewater?
A. Domestic
B. Industrial
C. Stormwater
D. Groundwater
Rationale: Groundwater is naturally occurring water below the surface,
not wastewater.
10. What is the main function of an aeration basin in secondary
treatment?
A. Remove grit
B. Provide oxygen for biological processes
C. Settle solids
D. Filter water
Rationale: Aeration basins supply oxygen to microorganisms to biodegrade
organic pollutants.
11. Which microorganism is commonly used in activated sludge
systems?
A. Virus
Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of a wastewater treatment plant?
A. Generate electricity
B. Remove contaminants from wastewater
C. Increase water hardness
D. Produce drinking water
Rationale: The primary purpose of a wastewater treatment plant is to
remove physical, chemical, and biological contaminants from wastewater
before discharging it into the environment.
2. Which of the following is considered a physical treatment process?
A. Chlorination
, B. Sedimentation
C. Biological filtration
D. Aeration
Rationale: Sedimentation is a physical process that removes suspended
solids by allowing them to settle under gravity.
3. In wastewater terminology, BOD stands for:
A. Biological Oxidation Demand
B. Biochemical Oxygen Determination
C. Biochemical Oxygen Demand
D. Biological Oxidation Depth
Rationale: BOD measures the amount of dissolved oxygen needed by
microorganisms to break down organic matter in water.
4. Which unit process is primarily used to remove suspended solids?
A. Disinfection
B. Aeration
C. Filtration
D. Sedimentation
Rationale: Sedimentation removes suspended solids from wastewater by
gravity settling.
5. What is the typical range of BOD in domestic wastewater?
A. 10–50 mg/L
B. 50–100 mg/L
, C. 200–300 mg/L
D. 500–800 mg/L
Rationale: Domestic wastewater usually contains BOD levels between 200–
300 mg/L.
6. Which of the following is a characteristic of primary treatment?
A. Biological nutrient removal
B. Removal of settleable solids
C. Advanced filtration
D. Chemical coagulation
Rationale: Primary treatment focuses on removing settleable solids and
floating material.
7. Chlorination is used primarily for:
A. Disinfection
B. Sedimentation
C. Biological treatment
D. Filtration
Rationale: Chlorination kills or inactivates pathogens in wastewater to
reduce disease risk.
8. Sludge digestion is primarily intended to:
A. Remove heavy metals
B. Stabilize organic solids
, C. Reduce chlorine demand
D. Increase BOD
Rationale: Sludge digestion stabilizes organic matter in sludge, reducing
odors and pathogen content.
9. Which of the following is NOT a type of wastewater?
A. Domestic
B. Industrial
C. Stormwater
D. Groundwater
Rationale: Groundwater is naturally occurring water below the surface,
not wastewater.
10. What is the main function of an aeration basin in secondary
treatment?
A. Remove grit
B. Provide oxygen for biological processes
C. Settle solids
D. Filter water
Rationale: Aeration basins supply oxygen to microorganisms to biodegrade
organic pollutants.
11. Which microorganism is commonly used in activated sludge
systems?
A. Virus
