New York Wastewater Operator Certification
Exam Practice | Questions and answers 2026 |
Latest Update
1. The primary purpose of wastewater treatment is to:
A. Produce drinking water
B. Eliminate all bacteria
C. Remove contaminants to protect public health and the environment (Correct Answer)
D. Increase nutrient levels in rivers
Rationale: Wastewater treatment facilities remove pollutants such as organic matter, solids,
nutrients, and pathogens before water is discharged to receiving waters. This protects ecosystems
and public health.
2. Preliminary treatment in a wastewater plant primarily removes:
A. Dissolved solids
B. Nutrients
C. Large debris and grit (Correct Answer)
D. Pathogens
Rationale: Preliminary treatment uses screens and grit chambers to remove large materials like
rags, plastics, sand, and gravel that could damage pumps and equipment.
3. The process designed to remove sand, gravel, and other heavy inorganic
materials is:
A. Primary clarification
B. Aeration
C. Grit removal (Correct Answer)
D. Filtration
Rationale: Grit chambers slow wastewater flow so heavier inorganic particles settle out before
entering downstream treatment processes.
,4. The activated sludge process primarily removes:
A. Heavy metals
B. Grit
C. Biodegradable organic matter (Correct Answer)
D. Dissolved oxygen
Rationale: In activated sludge systems, microorganisms consume organic pollutants, reducing
BOD and stabilizing wastewater before final clarification.
5. BOD stands for:
A. Bacterial Oxygen Demand
B. Biochemical Oxygen Demand (Correct Answer)
C. Biological Oxidation Density
D. Bio-organic Dissolution
Rationale: BOD measures the amount of oxygen microorganisms require to decompose organic
material in water, indicating the strength of wastewater.
6. High BOD levels in wastewater indicate:
A. Low organic content
B. Low microbial activity
C. High concentration of biodegradable organic material (Correct Answer)
D. Excess oxygen
Rationale: Higher BOD means more organic material is present, requiring more oxygen for
microbial decomposition.
7. Primary clarifiers typically remove approximately:
A. 10% of suspended solids
B. 50–70% of suspended solids (Correct Answer)
C. 100% of solids
D. 20% of BOD only
,Rationale: Sedimentation in primary clarifiers removes settleable solids and reduces BOD
before biological treatment.
8. Dissolved oxygen in an aeration tank should typically be maintained near:
A. 0 mg/L
B. 2 mg/L (Correct Answer)
C. 10 mg/L
D. 15 mg/L
Rationale: Maintaining about 2 mg/L ensures sufficient oxygen for microorganisms without
wasting energy through excessive aeration.
9. The purpose of return activated sludge (RAS) is to:
A. Waste excess sludge
B. Maintain adequate microorganisms in the aeration tank (Correct Answer)
C. Increase oxygen concentration
D. Remove grit
Rationale: RAS recycles settled microorganisms from the secondary clarifier back to the
aeration tank to maintain biomass concentration.
10. Waste activated sludge (WAS) is removed from the system to:
A. Increase BOD
B. Control sludge age and solids concentration (Correct Answer)
C. Increase MLSS indefinitely
D. Increase aeration efficiency
Rationale: Removing excess sludge keeps the biological system balanced and prevents
excessive solids buildup.
11. MLSS refers to:
A. Maximum Liquid Suspended Solids
B. Mixed Liquor Suspended Solids (Correct Answer)
, C. Microbial Loading Sludge System
D. Maximum Loading Solids System
Rationale: MLSS represents the concentration of microorganisms and suspended solids in the
aeration tank mixture.
12. A high sludge volume index (SVI) usually indicates:
A. Excellent sludge settling
B. Poor sludge settling or bulking sludge (Correct Answer)
C. Low microbial population
D. Low BOD loading
Rationale: High SVI values indicate that sludge is fluffy and settles poorly, often due to
filamentous bacteria growth.
13. The final step before treated wastewater is discharged is usually:
A. Aeration
B. Sedimentation
C. Disinfection (Correct Answer)
D. Sludge digestion
Rationale: Disinfection destroys pathogens before treated wastewater is released into natural
water bodies.
14. The most commonly used disinfectant in wastewater plants is:
A. Ozone
B. Hydrogen peroxide
C. Chlorine (Correct Answer)
D. Bromine
Rationale: Chlorine is widely used because it is effective, reliable, and relatively inexpensive for
pathogen control.
15. Dechlorination is necessary to:
Exam Practice | Questions and answers 2026 |
Latest Update
1. The primary purpose of wastewater treatment is to:
A. Produce drinking water
B. Eliminate all bacteria
C. Remove contaminants to protect public health and the environment (Correct Answer)
D. Increase nutrient levels in rivers
Rationale: Wastewater treatment facilities remove pollutants such as organic matter, solids,
nutrients, and pathogens before water is discharged to receiving waters. This protects ecosystems
and public health.
2. Preliminary treatment in a wastewater plant primarily removes:
A. Dissolved solids
B. Nutrients
C. Large debris and grit (Correct Answer)
D. Pathogens
Rationale: Preliminary treatment uses screens and grit chambers to remove large materials like
rags, plastics, sand, and gravel that could damage pumps and equipment.
3. The process designed to remove sand, gravel, and other heavy inorganic
materials is:
A. Primary clarification
B. Aeration
C. Grit removal (Correct Answer)
D. Filtration
Rationale: Grit chambers slow wastewater flow so heavier inorganic particles settle out before
entering downstream treatment processes.
,4. The activated sludge process primarily removes:
A. Heavy metals
B. Grit
C. Biodegradable organic matter (Correct Answer)
D. Dissolved oxygen
Rationale: In activated sludge systems, microorganisms consume organic pollutants, reducing
BOD and stabilizing wastewater before final clarification.
5. BOD stands for:
A. Bacterial Oxygen Demand
B. Biochemical Oxygen Demand (Correct Answer)
C. Biological Oxidation Density
D. Bio-organic Dissolution
Rationale: BOD measures the amount of oxygen microorganisms require to decompose organic
material in water, indicating the strength of wastewater.
6. High BOD levels in wastewater indicate:
A. Low organic content
B. Low microbial activity
C. High concentration of biodegradable organic material (Correct Answer)
D. Excess oxygen
Rationale: Higher BOD means more organic material is present, requiring more oxygen for
microbial decomposition.
7. Primary clarifiers typically remove approximately:
A. 10% of suspended solids
B. 50–70% of suspended solids (Correct Answer)
C. 100% of solids
D. 20% of BOD only
,Rationale: Sedimentation in primary clarifiers removes settleable solids and reduces BOD
before biological treatment.
8. Dissolved oxygen in an aeration tank should typically be maintained near:
A. 0 mg/L
B. 2 mg/L (Correct Answer)
C. 10 mg/L
D. 15 mg/L
Rationale: Maintaining about 2 mg/L ensures sufficient oxygen for microorganisms without
wasting energy through excessive aeration.
9. The purpose of return activated sludge (RAS) is to:
A. Waste excess sludge
B. Maintain adequate microorganisms in the aeration tank (Correct Answer)
C. Increase oxygen concentration
D. Remove grit
Rationale: RAS recycles settled microorganisms from the secondary clarifier back to the
aeration tank to maintain biomass concentration.
10. Waste activated sludge (WAS) is removed from the system to:
A. Increase BOD
B. Control sludge age and solids concentration (Correct Answer)
C. Increase MLSS indefinitely
D. Increase aeration efficiency
Rationale: Removing excess sludge keeps the biological system balanced and prevents
excessive solids buildup.
11. MLSS refers to:
A. Maximum Liquid Suspended Solids
B. Mixed Liquor Suspended Solids (Correct Answer)
, C. Microbial Loading Sludge System
D. Maximum Loading Solids System
Rationale: MLSS represents the concentration of microorganisms and suspended solids in the
aeration tank mixture.
12. A high sludge volume index (SVI) usually indicates:
A. Excellent sludge settling
B. Poor sludge settling or bulking sludge (Correct Answer)
C. Low microbial population
D. Low BOD loading
Rationale: High SVI values indicate that sludge is fluffy and settles poorly, often due to
filamentous bacteria growth.
13. The final step before treated wastewater is discharged is usually:
A. Aeration
B. Sedimentation
C. Disinfection (Correct Answer)
D. Sludge digestion
Rationale: Disinfection destroys pathogens before treated wastewater is released into natural
water bodies.
14. The most commonly used disinfectant in wastewater plants is:
A. Ozone
B. Hydrogen peroxide
C. Chlorine (Correct Answer)
D. Bromine
Rationale: Chlorine is widely used because it is effective, reliable, and relatively inexpensive for
pathogen control.
15. Dechlorination is necessary to:
