Nevada Wastewater Treatment Plant
Operator Grade III Practice Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of a secondary clarifier
in a wastewater treatment plant?
A. Remove large solids from influent
B. Neutralize pH
C. Remove suspended solids after biological treatment
D. Disinfect effluent
Rationale: The secondary clarifier allows activated sludge to settle,
separating biomass from treated water.
2. The main function of a bar screen in preliminary treatment is to:
A. Remove grit
, B. Remove large debris
C. Decrease BOD
D. Reduce nutrient levels
Rationale: Bar screens physically remove large objects such as sticks,
rags, and trash before wastewater enters downstream processes.
3. Which microorganism is most commonly responsible for nitrification
in wastewater treatment?
A. Escherichia coli
B. Nitrosomonas
C. Pseudomonas
D. Bacillus
Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite during
nitrification.
4. What is the typical pH range for activated sludge processes?
A. 4.5–5.5
B. 6.0–6.5
C. 6.5–8.5
D. 8.5–9.5
Rationale: Activated sludge performs optimally in a slightly acidic to
slightly alkaline environment, typically 6.5–8.5.
5. Which unit process is designed specifically to remove grit from
wastewater?
A. Bar screen
, B. Sedimentation tank
C. Grit chamber
D. Trickling filter
Rationale: Grit chambers settle heavy inorganic particles such as
sand and gravel while allowing organic matter to pass.
6. The term "BOD" stands for:
A. Basic Oxidation Demand
B. Biological Oxidation Determinant
C. Biochemical Oxygen Demand
D. Biological Organic Decomposition
Rationale: BOD measures the amount of dissolved oxygen required
by microorganisms to break down organic matter in water.
7. The primary objective of chlorination in wastewater treatment is to:
A. Remove suspended solids
B. Increase alkalinity
C. Disinfect effluent
D. Remove nitrogen
Rationale: Chlorine is used to kill or inactivate pathogenic
microorganisms before discharge.
8. Sludge volume index (SVI) is used to determine:
A. Settling characteristics of activated sludge
B. Total solids in sludge
C. pH of mixed liquor
, D. Alkalinity
Rationale: SVI indicates the volume occupied by settled sludge
relative to its concentration, providing insight into settleability.
9. What is the first step in the wastewater treatment process?
A. Secondary treatment
B. Disinfection
C. Preliminary treatment
D. Tertiary treatment
Rationale: Preliminary treatment removes large debris and grit to
protect downstream equipment.
10. In an aeration tank, oxygen transfer efficiency is primarily
affected by:
A. Temperature and diffuser type
B. pH only
C. Influent BOD only
D. Chlorine residual
Rationale: Oxygen transfer depends on water temperature, diffuser
design, and mixing intensity.
11. Which of the following is a primary advantage of using a rotating
biological contactor (RBC)?
A. High nutrient removal
B. Low energy consumption
C. High sludge production
Operator Grade III Practice Exam
Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. Which of the following is the primary purpose of a secondary clarifier
in a wastewater treatment plant?
A. Remove large solids from influent
B. Neutralize pH
C. Remove suspended solids after biological treatment
D. Disinfect effluent
Rationale: The secondary clarifier allows activated sludge to settle,
separating biomass from treated water.
2. The main function of a bar screen in preliminary treatment is to:
A. Remove grit
, B. Remove large debris
C. Decrease BOD
D. Reduce nutrient levels
Rationale: Bar screens physically remove large objects such as sticks,
rags, and trash before wastewater enters downstream processes.
3. Which microorganism is most commonly responsible for nitrification
in wastewater treatment?
A. Escherichia coli
B. Nitrosomonas
C. Pseudomonas
D. Bacillus
Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite during
nitrification.
4. What is the typical pH range for activated sludge processes?
A. 4.5–5.5
B. 6.0–6.5
C. 6.5–8.5
D. 8.5–9.5
Rationale: Activated sludge performs optimally in a slightly acidic to
slightly alkaline environment, typically 6.5–8.5.
5. Which unit process is designed specifically to remove grit from
wastewater?
A. Bar screen
, B. Sedimentation tank
C. Grit chamber
D. Trickling filter
Rationale: Grit chambers settle heavy inorganic particles such as
sand and gravel while allowing organic matter to pass.
6. The term "BOD" stands for:
A. Basic Oxidation Demand
B. Biological Oxidation Determinant
C. Biochemical Oxygen Demand
D. Biological Organic Decomposition
Rationale: BOD measures the amount of dissolved oxygen required
by microorganisms to break down organic matter in water.
7. The primary objective of chlorination in wastewater treatment is to:
A. Remove suspended solids
B. Increase alkalinity
C. Disinfect effluent
D. Remove nitrogen
Rationale: Chlorine is used to kill or inactivate pathogenic
microorganisms before discharge.
8. Sludge volume index (SVI) is used to determine:
A. Settling characteristics of activated sludge
B. Total solids in sludge
C. pH of mixed liquor
, D. Alkalinity
Rationale: SVI indicates the volume occupied by settled sludge
relative to its concentration, providing insight into settleability.
9. What is the first step in the wastewater treatment process?
A. Secondary treatment
B. Disinfection
C. Preliminary treatment
D. Tertiary treatment
Rationale: Preliminary treatment removes large debris and grit to
protect downstream equipment.
10. In an aeration tank, oxygen transfer efficiency is primarily
affected by:
A. Temperature and diffuser type
B. pH only
C. Influent BOD only
D. Chlorine residual
Rationale: Oxygen transfer depends on water temperature, diffuser
design, and mixing intensity.
11. Which of the following is a primary advantage of using a rotating
biological contactor (RBC)?
A. High nutrient removal
B. Low energy consumption
C. High sludge production
