Wastewater Treatment Operator
Certification Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. The primary purpose of wastewater treatment is to
A. Reuse water for drinking
B. Protect public health and the environment
C. Generate energy
D. Reduce water bills
Answer: B
Rationale: Wastewater treatment removes contaminants to protect
human health and prevent environmental pollution.
2. Which treatment process removes large debris such as rags and
sticks?
, A. Primary clarification
B. Biological treatment
C. Screening
D. Disinfection
Answer: C
Rationale: Screening is the first step and removes large solids to protect
downstream equipment.
3. Grit removal systems are designed to remove
A. Organic solids
B. Dissolved oxygen
C. Sand, gravel, and heavy inorganic particles
D. Bacteria
Answer: C
Rationale: Grit chambers remove heavy inorganic materials that can cause
abrasion and clogging.
4. Primary treatment mainly removes
A. Dissolved solids
B. Settleable and floatable solids
C. Nutrients
D. Pathogens
,Answer: B
Rationale: Primary clarification relies on gravity settling and skimming to
remove solids.
5. Biochemical Oxygen Demand (BOD) measures
A. Oxygen solubility
B. Toxicity
C. Amount of biodegradable organic matter
D. Total solids
Answer: C
Rationale: BOD indicates how much oxygen microorganisms need to break
down organic material.
6. Which unit process is considered secondary treatment?
A. Screening
B. Grit chamber
C. Activated sludge
D. Chlorination
Answer: C
Rationale: Secondary treatment uses biological processes such as activated
sludge to remove dissolved organics.
, 7. In an activated sludge system, microorganisms are kept in suspension
by
A. Sedimentation
B. Filtration
C. Aeration
D. Chlorination
Answer: C
Rationale: Aeration supplies oxygen and mixing to keep biomass
suspended.
8. Dissolved oxygen in aeration tanks is important because it
A. Controls pH
B. Supports aerobic microorganisms
C. Removes nutrients
D. Settles solids
Answer: B
Rationale: Aerobic bacteria require oxygen to metabolize organic waste.
9. What does MLSS stand for?
A. Maximum liquid system solids
B. Mixed liquor suspended solids
Certification Exam Practice Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. The primary purpose of wastewater treatment is to
A. Reuse water for drinking
B. Protect public health and the environment
C. Generate energy
D. Reduce water bills
Answer: B
Rationale: Wastewater treatment removes contaminants to protect
human health and prevent environmental pollution.
2. Which treatment process removes large debris such as rags and
sticks?
, A. Primary clarification
B. Biological treatment
C. Screening
D. Disinfection
Answer: C
Rationale: Screening is the first step and removes large solids to protect
downstream equipment.
3. Grit removal systems are designed to remove
A. Organic solids
B. Dissolved oxygen
C. Sand, gravel, and heavy inorganic particles
D. Bacteria
Answer: C
Rationale: Grit chambers remove heavy inorganic materials that can cause
abrasion and clogging.
4. Primary treatment mainly removes
A. Dissolved solids
B. Settleable and floatable solids
C. Nutrients
D. Pathogens
,Answer: B
Rationale: Primary clarification relies on gravity settling and skimming to
remove solids.
5. Biochemical Oxygen Demand (BOD) measures
A. Oxygen solubility
B. Toxicity
C. Amount of biodegradable organic matter
D. Total solids
Answer: C
Rationale: BOD indicates how much oxygen microorganisms need to break
down organic material.
6. Which unit process is considered secondary treatment?
A. Screening
B. Grit chamber
C. Activated sludge
D. Chlorination
Answer: C
Rationale: Secondary treatment uses biological processes such as activated
sludge to remove dissolved organics.
, 7. In an activated sludge system, microorganisms are kept in suspension
by
A. Sedimentation
B. Filtration
C. Aeration
D. Chlorination
Answer: C
Rationale: Aeration supplies oxygen and mixing to keep biomass
suspended.
8. Dissolved oxygen in aeration tanks is important because it
A. Controls pH
B. Supports aerobic microorganisms
C. Removes nutrients
D. Settles solids
Answer: B
Rationale: Aerobic bacteria require oxygen to metabolize organic waste.
9. What does MLSS stand for?
A. Maximum liquid system solids
B. Mixed liquor suspended solids
