North Carolina Water Treatment
Operator Examination — Class II
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of coagulation in water treatment?
A. To disinfect water
B. To remove dissolved gases
C. To destabilize suspended particles
D. To soften water
Coagulation adds chemicals to water to destabilize fine suspended
particles, allowing them to clump together for removal in subsequent
processes.
, 2. Which coagulant is most commonly used in municipal water
treatment?
A. Sodium hydroxide
B. Aluminum sulfate (alum)
C. Chlorine
D. Calcium carbonate
Alum is widely used because it effectively neutralizes particle charges and
forms flocs that settle easily.
3. Flocculation follows coagulation in water treatment to:
A. Remove dissolved minerals
B. Promote aggregation of destabilized particles
C. Increase water temperature
D. Filter the water
Flocculation gently mixes water to allow small destabilized particles to
collide and form larger, settleable flocs.
4. Sedimentation in water treatment is primarily used to:
A. Remove dissolved salts
B. Remove flocculated particles by gravity
C. Disinfect water
D. Adjust pH
,Sedimentation basins allow flocs formed in coagulation and flocculation to
settle, reducing turbidity.
5. What is the primary purpose of rapid sand filtration?
A. Disinfect water
B. Remove remaining suspended particles
C. Neutralize acidity
D. Add chlorine
Rapid sand filters remove particles too small to settle in sedimentation
basins, improving water clarity.
6. The rate of filtration in a rapid sand filter is usually expressed in:
A. mg/L
B. gallons per minute per square foot (gpm/ft²)
C. parts per million
D. liters per second
Filter loading rates are standardized as flow per unit area to ensure
optimal particle removal without clogging.
7. What is the primary advantage of granular activated carbon (GAC) in
water treatment?
A. Removes all bacteria
, B. Removes taste, odor, and organic chemicals
C. Softens water
D. Adjusts pH
GAC adsorbs dissolved organics, including compounds that cause taste and
odor, but is not a primary disinfectant.
8. Chlorine is commonly used in water treatment to:
A. Remove suspended solids
B. Disinfect water
C. Lower pH
D. Coagulate particles
Chlorine kills or inactivates pathogenic microorganisms, ensuring safe
drinking water.
9. What is the recommended free chlorine residual in a distribution
system?
A. 0 mg/L
B. 0.1–0.2 mg/L
C. 0.5–1.0 mg/L
D. 0.2–0.5 mg/L
Maintaining 0.2–0.5 mg/L ensures continued disinfection throughout the
distribution system without excessive chemical taste.
Operator Examination — Class II
Practice Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. What is the primary purpose of coagulation in water treatment?
A. To disinfect water
B. To remove dissolved gases
C. To destabilize suspended particles
D. To soften water
Coagulation adds chemicals to water to destabilize fine suspended
particles, allowing them to clump together for removal in subsequent
processes.
, 2. Which coagulant is most commonly used in municipal water
treatment?
A. Sodium hydroxide
B. Aluminum sulfate (alum)
C. Chlorine
D. Calcium carbonate
Alum is widely used because it effectively neutralizes particle charges and
forms flocs that settle easily.
3. Flocculation follows coagulation in water treatment to:
A. Remove dissolved minerals
B. Promote aggregation of destabilized particles
C. Increase water temperature
D. Filter the water
Flocculation gently mixes water to allow small destabilized particles to
collide and form larger, settleable flocs.
4. Sedimentation in water treatment is primarily used to:
A. Remove dissolved salts
B. Remove flocculated particles by gravity
C. Disinfect water
D. Adjust pH
,Sedimentation basins allow flocs formed in coagulation and flocculation to
settle, reducing turbidity.
5. What is the primary purpose of rapid sand filtration?
A. Disinfect water
B. Remove remaining suspended particles
C. Neutralize acidity
D. Add chlorine
Rapid sand filters remove particles too small to settle in sedimentation
basins, improving water clarity.
6. The rate of filtration in a rapid sand filter is usually expressed in:
A. mg/L
B. gallons per minute per square foot (gpm/ft²)
C. parts per million
D. liters per second
Filter loading rates are standardized as flow per unit area to ensure
optimal particle removal without clogging.
7. What is the primary advantage of granular activated carbon (GAC) in
water treatment?
A. Removes all bacteria
, B. Removes taste, odor, and organic chemicals
C. Softens water
D. Adjusts pH
GAC adsorbs dissolved organics, including compounds that cause taste and
odor, but is not a primary disinfectant.
8. Chlorine is commonly used in water treatment to:
A. Remove suspended solids
B. Disinfect water
C. Lower pH
D. Coagulate particles
Chlorine kills or inactivates pathogenic microorganisms, ensuring safe
drinking water.
9. What is the recommended free chlorine residual in a distribution
system?
A. 0 mg/L
B. 0.1–0.2 mg/L
C. 0.5–1.0 mg/L
D. 0.2–0.5 mg/L
Maintaining 0.2–0.5 mg/L ensures continued disinfection throughout the
distribution system without excessive chemical taste.
