Virginia Wastewater Works Operator Class 3 Practice
Examination 100 Questions And Correct Answers (100%
Verified Answers) Plus Rationales Q&A
1. Which measurement verifies chlorine residual?
A. pH meter
B. DO probe
C. DPD colorimetric test
D. Turbidimeter
Answer: C
Rationale: The DPD test detects free and total chlorine colorimetrically.
2. What does a high SVI (>150) usually indicate?
A. Good settling
B. Low MLSS
C. Bulking sludge
D. High DO
Answer: C
Rationale: High SVI correlates with poor sludge compaction.
3. What is the purpose of an aeration blower?
A. Pump sludge
B. Supply oxygen for biological activity
C. Remove scum
,D. Adjust alkalinity
Answer: B
Rationale: Blowers maintain aerobic conditions in activated sludge.
4. Which process converts ammonia to nitrate?
A. Denitrification
B. Precipitation
C. Nitrification
D. Flocculation
Answer: C
Rationale: Nitrification oxidizes ammonia to nitrite and nitrate.
5. What is the main purpose of secondary treatment?
A. Remove large debris
B. Remove most organics via biological processes
C. Disinfect wastewater
D. Thicken sludge
Answer: B
Rationale: Secondary treatment biologically reduces organic content.
6. Which safety device detects low oxygen in confined spaces?
A. Sludge judge
B. Oxygen meter
C. Flow meter
D. Barometer
,Answer: B
Rationale: Oxygen meters ensure safe atmospheric conditions.
7. What process occurs when bacteria convert nitrate to nitrogen gas?
A. Coagulation
B. Denitrification
C. Aeration
D. Sedimentation
Answer: B
Rationale: Denitrification reduces nitrate under anoxic conditions.
8. What is the primary function of a digester mixing system?
A. Reduce odor
B. Maintain uniform temperature and solids distribution
C. Increase flow rate
D. Remove grit
, Rationale: Proper mixing stabilizes digestion and prevents stratification.
9. Which factor most influences settling in a clarifier?
A. Alkalinity
B. Temperature
C. Sludge blanket depth
D. Chlorine dose
Answer: C
Rationale: Excessive blankets impair separation and cause carryover.
10. What is a common cause of foaming in activated sludge?
A. High alkalinity
B. Nocardia filaments
C. High chlorine
D. Low temperature
Answer: B
Rationale: Nocardia species produce stable foam.
11. What is the typical efficiency of secondary BOD removal?
A. 10–20%
B. 25–40%
C. 50–60%
D. 85–95%
Examination 100 Questions And Correct Answers (100%
Verified Answers) Plus Rationales Q&A
1. Which measurement verifies chlorine residual?
A. pH meter
B. DO probe
C. DPD colorimetric test
D. Turbidimeter
Answer: C
Rationale: The DPD test detects free and total chlorine colorimetrically.
2. What does a high SVI (>150) usually indicate?
A. Good settling
B. Low MLSS
C. Bulking sludge
D. High DO
Answer: C
Rationale: High SVI correlates with poor sludge compaction.
3. What is the purpose of an aeration blower?
A. Pump sludge
B. Supply oxygen for biological activity
C. Remove scum
,D. Adjust alkalinity
Answer: B
Rationale: Blowers maintain aerobic conditions in activated sludge.
4. Which process converts ammonia to nitrate?
A. Denitrification
B. Precipitation
C. Nitrification
D. Flocculation
Answer: C
Rationale: Nitrification oxidizes ammonia to nitrite and nitrate.
5. What is the main purpose of secondary treatment?
A. Remove large debris
B. Remove most organics via biological processes
C. Disinfect wastewater
D. Thicken sludge
Answer: B
Rationale: Secondary treatment biologically reduces organic content.
6. Which safety device detects low oxygen in confined spaces?
A. Sludge judge
B. Oxygen meter
C. Flow meter
D. Barometer
,Answer: B
Rationale: Oxygen meters ensure safe atmospheric conditions.
7. What process occurs when bacteria convert nitrate to nitrogen gas?
A. Coagulation
B. Denitrification
C. Aeration
D. Sedimentation
Answer: B
Rationale: Denitrification reduces nitrate under anoxic conditions.
8. What is the primary function of a digester mixing system?
A. Reduce odor
B. Maintain uniform temperature and solids distribution
C. Increase flow rate
D. Remove grit
, Rationale: Proper mixing stabilizes digestion and prevents stratification.
9. Which factor most influences settling in a clarifier?
A. Alkalinity
B. Temperature
C. Sludge blanket depth
D. Chlorine dose
Answer: C
Rationale: Excessive blankets impair separation and cause carryover.
10. What is a common cause of foaming in activated sludge?
A. High alkalinity
B. Nocardia filaments
C. High chlorine
D. Low temperature
Answer: B
Rationale: Nocardia species produce stable foam.
11. What is the typical efficiency of secondary BOD removal?
A. 10–20%
B. 25–40%
C. 50–60%
D. 85–95%
