California Wastewater Treatment
Operator Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2025/2026 Q&A | Instant
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1. What is the primary purpose of secondary treatment in a wastewater
plant?
A. Remove grit and large solids
B. Reduce organic material and suspended solids
C. Disinfect effluent
D. Remove heavy metals
Secondary treatment uses biological processes to reduce the amount of
biodegradable organic material and suspended solids left after primary
treatment.
2. Which process uses microorganisms to break down organic matter in
wastewater?
A. Sedimentation
B. Biological treatment
C. Filtration
D. Coagulation
Biological treatment relies on bacteria and other microorganisms to
consume organic pollutants.
,3. What is the function of a clarifier?
A. Aerate the wastewater
B. Introduce chlorine
C. Separate solids from liquid by gravity
D. Remove odors
Clarifiers allow heavier solids to settle to the bottom and lighter
materials to rise for removal.
4. Which law governs the discharge of pollutants into U.S. waters?
A. Safe Drinking Water Act
B. Clean Water Act
C. RCRA
D. Title 22
The Clean Water Act regulates discharges of pollutants and sets water
quality standards.
5. What is the term for the material settled in a primary clarifier?
A. Scum
B. Primary sludge
C. Biosolids
D. Effluent
Primary sludge is the solid material that settles during primary
treatment.
6. Which gas is commonly produced in anaerobic digesters?
A. Oxygen
B. Methane
, C. Carbon monoxide
D. Nitrogen
Methane is produced during anaerobic digestion and can be used for
energy.
7. A BOD test measures:
A. Total suspended solids
B. Biochemical oxygen demand
C. Chlorine residual
D. Ammonia concentration
BOD measures the amount of oxygen consumed by microorganisms
breaking down organic matter.
8. What is the optimal pH range for most activated sludge processes?
A. 5.0–6.0
B. 6.0–7.0
C. 6.5–8.5
D. 8.5–9.5
Activated sludge bacteria thrive in a near-neutral pH range of 6.5 to 8.5.
9. What is the purpose of wasting sludge in an activated sludge process?
A. Increase sludge age
B. Increase MLSS
C. Control biomass and maintain treatment efficiency
D. Prevent grit accumulation
Wasting sludge removes excess biomass to maintain steady treatment
conditions.
Operator Exam Questions And Correct
Answers (Verified Answers) Plus
Rationales 2025/2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of secondary treatment in a wastewater
plant?
A. Remove grit and large solids
B. Reduce organic material and suspended solids
C. Disinfect effluent
D. Remove heavy metals
Secondary treatment uses biological processes to reduce the amount of
biodegradable organic material and suspended solids left after primary
treatment.
2. Which process uses microorganisms to break down organic matter in
wastewater?
A. Sedimentation
B. Biological treatment
C. Filtration
D. Coagulation
Biological treatment relies on bacteria and other microorganisms to
consume organic pollutants.
,3. What is the function of a clarifier?
A. Aerate the wastewater
B. Introduce chlorine
C. Separate solids from liquid by gravity
D. Remove odors
Clarifiers allow heavier solids to settle to the bottom and lighter
materials to rise for removal.
4. Which law governs the discharge of pollutants into U.S. waters?
A. Safe Drinking Water Act
B. Clean Water Act
C. RCRA
D. Title 22
The Clean Water Act regulates discharges of pollutants and sets water
quality standards.
5. What is the term for the material settled in a primary clarifier?
A. Scum
B. Primary sludge
C. Biosolids
D. Effluent
Primary sludge is the solid material that settles during primary
treatment.
6. Which gas is commonly produced in anaerobic digesters?
A. Oxygen
B. Methane
, C. Carbon monoxide
D. Nitrogen
Methane is produced during anaerobic digestion and can be used for
energy.
7. A BOD test measures:
A. Total suspended solids
B. Biochemical oxygen demand
C. Chlorine residual
D. Ammonia concentration
BOD measures the amount of oxygen consumed by microorganisms
breaking down organic matter.
8. What is the optimal pH range for most activated sludge processes?
A. 5.0–6.0
B. 6.0–7.0
C. 6.5–8.5
D. 8.5–9.5
Activated sludge bacteria thrive in a near-neutral pH range of 6.5 to 8.5.
9. What is the purpose of wasting sludge in an activated sludge process?
A. Increase sludge age
B. Increase MLSS
C. Control biomass and maintain treatment efficiency
D. Prevent grit accumulation
Wasting sludge removes excess biomass to maintain steady treatment
conditions.
