Nevada Wastewater Treatment Plant
Operator Grade II Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of primary sedimentation in wastewater
treatment?
A. Remove dissolved nutrients
B. Remove fine colloidal particles
C. Remove settleable solids
D. Disinfect the wastewater
Rationale: Primary sedimentation removes settleable solids through gravity
settling, reducing the load on subsequent treatment processes.
2. Which microorganism is primarily responsible for nitrification?
A. Escherichia coli
, B. Nitrosomonas
C. Clostridium
D. Pseudomonas
Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite, which is the
first step of nitrification.
3. BOD stands for:
A. Biochemical Oxidation Demand
B. Biological Oxygen Depletion
C. Biochemical Oxygen Demand
D. Bacterial Oxidation Degree
Rationale: BOD measures the amount of oxygen microorganisms consume
while decomposing organic matter.
4. The most common method of sludge stabilization in a wastewater
plant is:
A. Filtration
B. Aerobic digestion
C. Coagulation
D. Chlorination
Rationale: Aerobic digestion reduces the organic content of sludge and
stabilizes it before disposal.
5. What is the main purpose of chlorination in wastewater treatment?
A. Remove suspended solids
, B. Reduce BOD
C. Disinfect the effluent
D. Improve settling
Rationale: Chlorination kills pathogenic organisms, ensuring the treated
wastewater is safe for discharge.
6. Which process is used to remove nitrogen from wastewater?
A. Filtration
B. Biological nitrification and denitrification
C. Sedimentation
D. Coagulation
Rationale: Nitrogen is removed biologically by converting ammonia to
nitrate (nitrification) and then to nitrogen gas (denitrification).
7. The primary purpose of an aeration tank is to:
A. Settle solids
B. Remove nutrients
C. Provide oxygen for microbial growth
D. Chlorinate effluent
Rationale: Aeration tanks supply oxygen to aerobic bacteria to biologically
degrade organic matter.
8. Which unit process removes grit from wastewater?
A. Primary clarifier
B. Secondary clarifier
, C. Trickling filter
D. Grit chamber
Rationale: Grit chambers remove heavy inorganic particles like sand, gravel,
and cinders to prevent damage to downstream equipment.
9. The term “sludge age” refers to:
A. Time sludge spends in storage
B. Age of the oldest microorganism
C. Average time solids remain in the aeration tank
D. Time for chlorine to act on sludge
Rationale: Sludge age or solids retention time helps maintain the proper
microbial population in biological treatment.
10. Which is a primary cause of foaming in activated sludge?
A. Excess chlorine
B. High nitrate levels
C. Filamentous bacteria
D. Low temperature
Rationale: Filamentous bacteria can form foam on aeration tanks, reducing
treatment efficiency.
11. The chemical formula for chlorine gas is:
A. ClO2
B. ClO
Operator Grade II Exam Practice
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of primary sedimentation in wastewater
treatment?
A. Remove dissolved nutrients
B. Remove fine colloidal particles
C. Remove settleable solids
D. Disinfect the wastewater
Rationale: Primary sedimentation removes settleable solids through gravity
settling, reducing the load on subsequent treatment processes.
2. Which microorganism is primarily responsible for nitrification?
A. Escherichia coli
, B. Nitrosomonas
C. Clostridium
D. Pseudomonas
Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite, which is the
first step of nitrification.
3. BOD stands for:
A. Biochemical Oxidation Demand
B. Biological Oxygen Depletion
C. Biochemical Oxygen Demand
D. Bacterial Oxidation Degree
Rationale: BOD measures the amount of oxygen microorganisms consume
while decomposing organic matter.
4. The most common method of sludge stabilization in a wastewater
plant is:
A. Filtration
B. Aerobic digestion
C. Coagulation
D. Chlorination
Rationale: Aerobic digestion reduces the organic content of sludge and
stabilizes it before disposal.
5. What is the main purpose of chlorination in wastewater treatment?
A. Remove suspended solids
, B. Reduce BOD
C. Disinfect the effluent
D. Improve settling
Rationale: Chlorination kills pathogenic organisms, ensuring the treated
wastewater is safe for discharge.
6. Which process is used to remove nitrogen from wastewater?
A. Filtration
B. Biological nitrification and denitrification
C. Sedimentation
D. Coagulation
Rationale: Nitrogen is removed biologically by converting ammonia to
nitrate (nitrification) and then to nitrogen gas (denitrification).
7. The primary purpose of an aeration tank is to:
A. Settle solids
B. Remove nutrients
C. Provide oxygen for microbial growth
D. Chlorinate effluent
Rationale: Aeration tanks supply oxygen to aerobic bacteria to biologically
degrade organic matter.
8. Which unit process removes grit from wastewater?
A. Primary clarifier
B. Secondary clarifier
, C. Trickling filter
D. Grit chamber
Rationale: Grit chambers remove heavy inorganic particles like sand, gravel,
and cinders to prevent damage to downstream equipment.
9. The term “sludge age” refers to:
A. Time sludge spends in storage
B. Age of the oldest microorganism
C. Average time solids remain in the aeration tank
D. Time for chlorine to act on sludge
Rationale: Sludge age or solids retention time helps maintain the proper
microbial population in biological treatment.
10. Which is a primary cause of foaming in activated sludge?
A. Excess chlorine
B. High nitrate levels
C. Filamentous bacteria
D. Low temperature
Rationale: Filamentous bacteria can form foam on aeration tanks, reducing
treatment efficiency.
11. The chemical formula for chlorine gas is:
A. ClO2
B. ClO
