Texas Wastewater Operator – TCEQ Class III |questions & answers
& rationale | 2025/2026 | Latest Update| Instant download!!
1. Which of the following is true regarding nutrient removal in Class III plants?
A. Only BOD removal matters
B. Only TSS removal matters
C. Only chlorine
D. Nitrogen and phosphorus are removed to meet stringent permit limits (correct answer)
Rationale: Class III plants often discharge to sensitive waters, requiring advanced nutrient removal to
prevent eutrophication.
2. A plant has a flow of 5 MGD, influent BOD 300 mg/L, effluent 20 mg/L. Pounds/day
BOD removed?
A. 5000 lbs/day
B. 6000 lbs/day
C. 6180 lbs/day (correct answer)
D. 6500 lbs/day
Rationale: Pounds removed = Flow × (BOD_in – BOD_out) × 8.34 = 5 × (300–20) × 8.34 ≈ 6180 lbs/day.
3. Which of the following is true regarding nitrification in Class III plants?
A. Optional
B. Only solids removal
C. Only chlorine
D. Converts ammonia to nitrate using aerobic bacteria (correct answer)
Rationale: Nitrification is essential for advanced nitrogen removal and regulatory compliance.
4. A Class III plant operates an extended aeration system. Which of the following is true?
A. Only solids removal
B. Provides stable operation and reduces sludge production (correct answer)
C. Only chlorine
D. Only pH
Rationale: Extended aeration stabilizes BOD removal and minimizes excess sludge.
5. Which of the following is true regarding sludge age (SRT) in Class III plants?
,A. Optional
B. Only solids
C. Only pH
D. Longer SRT improves nitrification and treatment stability (correct answer)
Rationale: SRT controls microbial populations and enhances nutrient removal.
6. Which of the following best describes the purpose of a secondary clarifier?
A. Only chlorine
B. Settles biological solids from aeration basins (correct answer)
C. Only pH
D. Only solids
Rationale: Secondary clarifiers separate activated sludge from treated wastewater.
7. A plant has 4 MGD flow, effluent TSS 25 mg/L. Pounds/day?
A. 800 lbs/day
B. 834 lbs/day
C. 8340 lbs/day (correct answer)
D. 9000 lbs/day
Rationale: Load = Flow × Concentration × 8.34 = 4 × 25 × 8.34 ≈ 8340 lbs/day. (Note: check units: MGD ×
mg/L × 8.34 = lbs/day)
8. Which of the following is true regarding chemical phosphorus removal in Class III
plants?
A. Only pH
B. Only solids removal
C. Only chlorine
D. Chemicals form insoluble compounds that settle in clarifiers (correct answer)
Rationale: Alum, ferric salts, or lime are used to remove phosphorus to meet advanced discharge limits.
9. Which of the following is true regarding denitrification in Class III plants?
A. Only solids removal
B. Only pH
C. Only chlorine
D. Nitrate is converted to nitrogen gas in anoxic conditions (correct answer)
Rationale: Denitrification removes nitrate, preventing eutrophication.
, 10. A Class III plant has 3.5 MGD, effluent nitrate 10 mg/L. Pounds/day nitrogen load?
A. 250 lbs/day
B. 290 lbs/day
C. 292 lbs/day (correct answer)
D. 300 lbs/day
Rationale: Load = Flow × Concentration × 8.34 = 3.5 × 10 × 8.34 ≈ 292 lbs/day.
11. Which of the following is true regarding aeration control?
A. Only chlorine
B. Only pH
C. Only solids
D. DO and MLSS control ensures efficient BOD and nitrification removal (correct answer)
Rationale: Proper DO levels maintain aerobic microbial activity for treatment efficiency.
12. Which of the following is true regarding sludge thickening in Class III plants?
A. Only disinfects
B. Reduces sludge volume before dewatering (correct answer)
C. Only chlorine
D. Only pH
Rationale: Thickening concentrates solids for easier and more efficient dewatering.
13. Which of the following is true regarding anaerobic digesters?
A. Only solids removal
B. Only pH
C. Only chlorine
D. Stabilizes sludge and produces methane for energy (correct answer)
Rationale: Anaerobic digestion reduces sludge volume and generates biogas.
14. A plant has 2 MGD, BOD 280 mg/L, effluent 25 mg/L. Pounds/day removed?
A. 4000 lbs/day
B. 4500 lbs/day
C. 4404 lbs/day (correct answer)
D. 4600 lbs/day
Rationale: Pounds removed = Flow × (BOD_in – BOD_out) × 8.34 = 2 × (280–25) × 8.34 ≈ 4404 lbs/day.
& rationale | 2025/2026 | Latest Update| Instant download!!
1. Which of the following is true regarding nutrient removal in Class III plants?
A. Only BOD removal matters
B. Only TSS removal matters
C. Only chlorine
D. Nitrogen and phosphorus are removed to meet stringent permit limits (correct answer)
Rationale: Class III plants often discharge to sensitive waters, requiring advanced nutrient removal to
prevent eutrophication.
2. A plant has a flow of 5 MGD, influent BOD 300 mg/L, effluent 20 mg/L. Pounds/day
BOD removed?
A. 5000 lbs/day
B. 6000 lbs/day
C. 6180 lbs/day (correct answer)
D. 6500 lbs/day
Rationale: Pounds removed = Flow × (BOD_in – BOD_out) × 8.34 = 5 × (300–20) × 8.34 ≈ 6180 lbs/day.
3. Which of the following is true regarding nitrification in Class III plants?
A. Optional
B. Only solids removal
C. Only chlorine
D. Converts ammonia to nitrate using aerobic bacteria (correct answer)
Rationale: Nitrification is essential for advanced nitrogen removal and regulatory compliance.
4. A Class III plant operates an extended aeration system. Which of the following is true?
A. Only solids removal
B. Provides stable operation and reduces sludge production (correct answer)
C. Only chlorine
D. Only pH
Rationale: Extended aeration stabilizes BOD removal and minimizes excess sludge.
5. Which of the following is true regarding sludge age (SRT) in Class III plants?
,A. Optional
B. Only solids
C. Only pH
D. Longer SRT improves nitrification and treatment stability (correct answer)
Rationale: SRT controls microbial populations and enhances nutrient removal.
6. Which of the following best describes the purpose of a secondary clarifier?
A. Only chlorine
B. Settles biological solids from aeration basins (correct answer)
C. Only pH
D. Only solids
Rationale: Secondary clarifiers separate activated sludge from treated wastewater.
7. A plant has 4 MGD flow, effluent TSS 25 mg/L. Pounds/day?
A. 800 lbs/day
B. 834 lbs/day
C. 8340 lbs/day (correct answer)
D. 9000 lbs/day
Rationale: Load = Flow × Concentration × 8.34 = 4 × 25 × 8.34 ≈ 8340 lbs/day. (Note: check units: MGD ×
mg/L × 8.34 = lbs/day)
8. Which of the following is true regarding chemical phosphorus removal in Class III
plants?
A. Only pH
B. Only solids removal
C. Only chlorine
D. Chemicals form insoluble compounds that settle in clarifiers (correct answer)
Rationale: Alum, ferric salts, or lime are used to remove phosphorus to meet advanced discharge limits.
9. Which of the following is true regarding denitrification in Class III plants?
A. Only solids removal
B. Only pH
C. Only chlorine
D. Nitrate is converted to nitrogen gas in anoxic conditions (correct answer)
Rationale: Denitrification removes nitrate, preventing eutrophication.
, 10. A Class III plant has 3.5 MGD, effluent nitrate 10 mg/L. Pounds/day nitrogen load?
A. 250 lbs/day
B. 290 lbs/day
C. 292 lbs/day (correct answer)
D. 300 lbs/day
Rationale: Load = Flow × Concentration × 8.34 = 3.5 × 10 × 8.34 ≈ 292 lbs/day.
11. Which of the following is true regarding aeration control?
A. Only chlorine
B. Only pH
C. Only solids
D. DO and MLSS control ensures efficient BOD and nitrification removal (correct answer)
Rationale: Proper DO levels maintain aerobic microbial activity for treatment efficiency.
12. Which of the following is true regarding sludge thickening in Class III plants?
A. Only disinfects
B. Reduces sludge volume before dewatering (correct answer)
C. Only chlorine
D. Only pH
Rationale: Thickening concentrates solids for easier and more efficient dewatering.
13. Which of the following is true regarding anaerobic digesters?
A. Only solids removal
B. Only pH
C. Only chlorine
D. Stabilizes sludge and produces methane for energy (correct answer)
Rationale: Anaerobic digestion reduces sludge volume and generates biogas.
14. A plant has 2 MGD, BOD 280 mg/L, effluent 25 mg/L. Pounds/day removed?
A. 4000 lbs/day
B. 4500 lbs/day
C. 4404 lbs/day (correct answer)
D. 4600 lbs/day
Rationale: Pounds removed = Flow × (BOD_in – BOD_out) × 8.34 = 2 × (280–25) × 8.34 ≈ 4404 lbs/day.
