Arizona Wastewater Treatment
Operator Certification Exam – Grade 2
Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationale 2026 Q&A| Instant Download
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1. Which of the following is the primary purpose of preliminary
treatment in a wastewater treatment plant?
A. To disinfect wastewater
B. To remove large solids and grit
C. To reduce biochemical oxygen demand (BOD)
D. To promote nitrification
The preliminary treatment process focuses on screening and grit
removal to protect downstream equipment and processes.
2. What unit process is typically used to remove settleable solids from
raw wastewater?
A. Trickling filter
B. Chlorination
C. Primary sedimentation tank
D. Activated sludge aeration tank
, Primary sedimentation tanks allow heavier solids to settle out by
gravity before biological treatment.
3. In an activated sludge system, what is the purpose of return
activated sludge (RAS)?
A. To remove scum from the surface
B. To disinfect effluent
C. To feed chemicals to the aeration basin
D. To maintain a high concentration of microorganisms in the
aeration tank
Recycling a portion of settled biomass back to the aeration basin
sustains microbial populations essential for organic matter
degradation.
4. Which of the following values represents a typical dissolved oxygen
(DO) concentration in a properly functioning aeration basin?
A. 0.1–0.5 mg/L
B. 1.0–2.0 mg/L
C. 2.0–4.0 mg/L
D. 6.0–8.0 mg/L
Sufficient DO (usually above about 2 mg/L) is necessary to support
aerobic microorganisms in the aeration process.
5. What is the primary goal of secondary wastewater treatment?
A. To remove heavy metals
B. To biologically remove organic matter and suspended solids
C. To add nutrients to the wastewater
D. To adjust pH to neutral
Secondary treatment uses biological processes to significantly reduce
organic load and suspended solids.
6. Which microorganism group is primarily responsible for nitrification?
A. Fungi
, B. Protozoa
C. Autotrophic bacteria
D. Algae
Nitrifying autotrophic bacteria oxidize ammonia to nitrite and nitrate
in wastewater treatment.
7. What does BOD stand for?
A. Biological Oxygen Demand
B. Biodegradable Organic Discharge
C. Biochemical Oxygen Demand
D. Baseline Organic Data
BOD measures the amount of oxygen required by microorganisms to
decompose organic matter.
8. Which of the following is a consequence of high BOD in wastewater
effluent discharged to a water body?
A. Increased pH
B. Oxygen depletion in the receiving water
C. Enhanced aquatic plant growth due to oxygen increase
D. Reduced ammonia levels
High BOD leads to oxygen consumption in the receiving water, which
can harm aquatic life.
9. What is the purpose of chlorine contact tanks?
A. To settle solids
B. To aerate effluent
C. To provide sufficient time for disinfection to occur
D. To remove nutrients
Contact tanks guarantee adequate time for chlorine to inactivate
pathogens before discharge.
10. Which of the following statements about sludge thickening is
true?
Operator Certification Exam – Grade 2
Exam Practice Questions And Correct
Answers (Verified Answers) Plus
Rationale 2026 Q&A| Instant Download
1. Which of the following is the primary purpose of preliminary
treatment in a wastewater treatment plant?
A. To disinfect wastewater
B. To remove large solids and grit
C. To reduce biochemical oxygen demand (BOD)
D. To promote nitrification
The preliminary treatment process focuses on screening and grit
removal to protect downstream equipment and processes.
2. What unit process is typically used to remove settleable solids from
raw wastewater?
A. Trickling filter
B. Chlorination
C. Primary sedimentation tank
D. Activated sludge aeration tank
, Primary sedimentation tanks allow heavier solids to settle out by
gravity before biological treatment.
3. In an activated sludge system, what is the purpose of return
activated sludge (RAS)?
A. To remove scum from the surface
B. To disinfect effluent
C. To feed chemicals to the aeration basin
D. To maintain a high concentration of microorganisms in the
aeration tank
Recycling a portion of settled biomass back to the aeration basin
sustains microbial populations essential for organic matter
degradation.
4. Which of the following values represents a typical dissolved oxygen
(DO) concentration in a properly functioning aeration basin?
A. 0.1–0.5 mg/L
B. 1.0–2.0 mg/L
C. 2.0–4.0 mg/L
D. 6.0–8.0 mg/L
Sufficient DO (usually above about 2 mg/L) is necessary to support
aerobic microorganisms in the aeration process.
5. What is the primary goal of secondary wastewater treatment?
A. To remove heavy metals
B. To biologically remove organic matter and suspended solids
C. To add nutrients to the wastewater
D. To adjust pH to neutral
Secondary treatment uses biological processes to significantly reduce
organic load and suspended solids.
6. Which microorganism group is primarily responsible for nitrification?
A. Fungi
, B. Protozoa
C. Autotrophic bacteria
D. Algae
Nitrifying autotrophic bacteria oxidize ammonia to nitrite and nitrate
in wastewater treatment.
7. What does BOD stand for?
A. Biological Oxygen Demand
B. Biodegradable Organic Discharge
C. Biochemical Oxygen Demand
D. Baseline Organic Data
BOD measures the amount of oxygen required by microorganisms to
decompose organic matter.
8. Which of the following is a consequence of high BOD in wastewater
effluent discharged to a water body?
A. Increased pH
B. Oxygen depletion in the receiving water
C. Enhanced aquatic plant growth due to oxygen increase
D. Reduced ammonia levels
High BOD leads to oxygen consumption in the receiving water, which
can harm aquatic life.
9. What is the purpose of chlorine contact tanks?
A. To settle solids
B. To aerate effluent
C. To provide sufficient time for disinfection to occur
D. To remove nutrients
Contact tanks guarantee adequate time for chlorine to inactivate
pathogens before discharge.
10. Which of the following statements about sludge thickening is
true?
