Page 1 of 105
Virginia Wastewater Works Operator Class 3 Practice
ACTUAL EXAM QUESTIONS AND CORRECT DETAILED
ANSWERS LATEST UPDATE THIS YEAR
Virginia Wastewater Works Operator Class 3 Practice Exam
This comprehensive practice exam is designed for the Virginia Wastewater Works Operator
Class 3 certification, based on Virginia Administrative Code requirements and ABC standardized
testing.
Exam Domains (Class 3 Level)
Based on the Virginia regulatory framework and standardized testing, the Class 3 exam covers :
1. Preliminary Treatment – Screening, grit removal, flow equalization
2. Primary Treatment – Sedimentation, clarification, scum removal
3. Secondary Treatment (Activated Sludge) – Aeration, MLSS, RAS/WAS, F/M ratio, SVI
4. Secondary Treatment (Fixed Film) – Trickling filters, RBCs
5. Tertiary Treatment & Disinfection – Filtration, chlorination, dechlorination, UV
6. Solids Handling – Thickening, digestion, dewatering, biosolids disposal
7. Laboratory & Process Control – BOD, TSS, pH, DO, settleability
8. Pumps, Motors, & Maintenance – Centrifugal pumps, positive displacement pumps,
preventive maintenance
9. Safety & Regulations – Confined space, H₂S, lockout/tagout, VPDES permits
10. Nutrient Removal – Biological nitrogen removal, chemical phosphorus removal
Practice Questions (1-100)
, Page 2 of 105
Domain 1: Preliminary & Primary Treatment (Questions 1-15)
1. What is the primary purpose of a bar screen in a wastewater treatment plant?
• A) Remove sand and grit
• B) Remove large solids and debris
• C) Remove dissolved organic matter
• D) Equalize flow
Answer: B
Rationale: Bar screens physically remove large solids (rags, sticks, plastics) to protect
downstream equipment from damage or clogging .
2. Which process follows screening in a typical wastewater treatment plant?
• A) Grit removal
• B) Chlorination
• C) Filtration
• D) Sludge digestion
Answer: A
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Rationale: Grit removal comes after screening to remove sand, gravel, and other heavy particles
that can cause equipment wear .
3. A grit channel is designed to maintain what flow velocity to settle grit while keeping
organics suspended?
• A) 0.5-0.8 ft/s
• B) 1.0-1.5 ft/s
• C) 2.0-3.0 ft/s
• D) 4.0-5.0 ft/s
Answer: B
*Rationale: Grit channels maintain a velocity of approximately 1.0-1.5 ft/s to allow heavier grit
particles to settle while keeping lighter organic solids suspended.*
4. What is the typical detention time for a primary clarifier in a municipal wastewater plant?
• A) 30-60 minutes
• B) 1-2 hours
• C) 2-4 hours
• D) 6-12 hours
Answer: B
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Rationale: Primary clarifiers typically have detention times of 1 to 2 hours, allowing sufficient
time for solids to settle by gravity .
5. What is the expected TSS removal efficiency of a well-operated primary clarifier?
• A) 20-30%
• B) 40-50%
• C) 50-70%
• D) 80-90%
Answer: C
*Rationale: Primary clarifiers typically remove 50-70% of suspended solids and 25-40% of BOD.*
6. What instrument is used to measure sludge blanket depth in a clarifier?
• A) pH meter
• B) Dissolved oxygen probe
• C) Sludge judge (core sampler)
• D) Turbidimeter
Answer: C
Virginia Wastewater Works Operator Class 3 Practice
ACTUAL EXAM QUESTIONS AND CORRECT DETAILED
ANSWERS LATEST UPDATE THIS YEAR
Virginia Wastewater Works Operator Class 3 Practice Exam
This comprehensive practice exam is designed for the Virginia Wastewater Works Operator
Class 3 certification, based on Virginia Administrative Code requirements and ABC standardized
testing.
Exam Domains (Class 3 Level)
Based on the Virginia regulatory framework and standardized testing, the Class 3 exam covers :
1. Preliminary Treatment – Screening, grit removal, flow equalization
2. Primary Treatment – Sedimentation, clarification, scum removal
3. Secondary Treatment (Activated Sludge) – Aeration, MLSS, RAS/WAS, F/M ratio, SVI
4. Secondary Treatment (Fixed Film) – Trickling filters, RBCs
5. Tertiary Treatment & Disinfection – Filtration, chlorination, dechlorination, UV
6. Solids Handling – Thickening, digestion, dewatering, biosolids disposal
7. Laboratory & Process Control – BOD, TSS, pH, DO, settleability
8. Pumps, Motors, & Maintenance – Centrifugal pumps, positive displacement pumps,
preventive maintenance
9. Safety & Regulations – Confined space, H₂S, lockout/tagout, VPDES permits
10. Nutrient Removal – Biological nitrogen removal, chemical phosphorus removal
Practice Questions (1-100)
, Page 2 of 105
Domain 1: Preliminary & Primary Treatment (Questions 1-15)
1. What is the primary purpose of a bar screen in a wastewater treatment plant?
• A) Remove sand and grit
• B) Remove large solids and debris
• C) Remove dissolved organic matter
• D) Equalize flow
Answer: B
Rationale: Bar screens physically remove large solids (rags, sticks, plastics) to protect
downstream equipment from damage or clogging .
2. Which process follows screening in a typical wastewater treatment plant?
• A) Grit removal
• B) Chlorination
• C) Filtration
• D) Sludge digestion
Answer: A
, Page 3 of 105
Rationale: Grit removal comes after screening to remove sand, gravel, and other heavy particles
that can cause equipment wear .
3. A grit channel is designed to maintain what flow velocity to settle grit while keeping
organics suspended?
• A) 0.5-0.8 ft/s
• B) 1.0-1.5 ft/s
• C) 2.0-3.0 ft/s
• D) 4.0-5.0 ft/s
Answer: B
*Rationale: Grit channels maintain a velocity of approximately 1.0-1.5 ft/s to allow heavier grit
particles to settle while keeping lighter organic solids suspended.*
4. What is the typical detention time for a primary clarifier in a municipal wastewater plant?
• A) 30-60 minutes
• B) 1-2 hours
• C) 2-4 hours
• D) 6-12 hours
Answer: B
, Page 4 of 105
Rationale: Primary clarifiers typically have detention times of 1 to 2 hours, allowing sufficient
time for solids to settle by gravity .
5. What is the expected TSS removal efficiency of a well-operated primary clarifier?
• A) 20-30%
• B) 40-50%
• C) 50-70%
• D) 80-90%
Answer: C
*Rationale: Primary clarifiers typically remove 50-70% of suspended solids and 25-40% of BOD.*
6. What instrument is used to measure sludge blanket depth in a clarifier?
• A) pH meter
• B) Dissolved oxygen probe
• C) Sludge judge (core sampler)
• D) Turbidimeter
Answer: C
