TCEQ Class II Wastewater Operator Exam Prep |questions &
answers & rationale | 2025/2026 | Latest Update| Instant download!!
1. Which of the following best describes the purpose of secondary treatment in a Class II plant?
A. Only removes solids
B. Only disinfects
C. Biologically reduces BOD and suspended solids (correct answer)
D. Only adjusts pH
Rationale: Secondary treatment uses microorganisms to degrade organics and remove suspended solids.
2. A Class II plant has 2 MGD flow with BOD of 250 mg/L. Pounds per day BOD load?
A. 2500 lbs/day
B. 4000 lbs/day
C. 4170 lbs/day (correct answer)
D. 3500 lbs/day
Rationale: Load = Flow × BOD × 8.34 = 2 × 250 × 8.34 ≈ 4170 lbs/day.
3. Which of the following is true regarding nitrification in Class II plants?
A. Only removes solids
B. Ammonia is converted to nitrate via aerobic bacteria (correct answer)
C. Only chlorine
D. Only pH
Rationale: Nitrification reduces ammonia concentration to meet permit limits.
4. Which of the following is a primary advantage of extended aeration systems?
,A. Only solids removal
B. Stable operation with reduced sludge production (correct answer)
C. Only chlorine
D. Only pH adjustment
Rationale: Extended aeration reduces sludge volume and stabilizes BOD removal.
5. A plant operates an activated sludge system with MLSS of 2500 mg/L in 2 MGD flow. Pounds of
MLSS in the aeration basin?
A. 4170 lbs
B. 41,700 lbs
C. 41,700 lbs (correct answer)
D. 417 lbs
Rationale: Pounds = Flow × MLSS × 8.34 = 2 × 2500 × 8.34 ≈ 41,700 lbs.
6. Which of the following is true regarding sludge age (SRT) in Class II plants?
A. Only pH
B. Longer SRT improves nitrification (correct answer)
C. Only solids removal
D. Only chlorine
Rationale: SRT controls biomass growth and process stability.
7. Which of the following is true regarding clarifier hydraulic loading?
A. Only solids matter
B. Excessive flow reduces settling efficiency (correct answer)
C. Only pH
D. Only chlorine
Rationale: Hydraulic overload can cause solids washout.
, 8. A plant has a flow of 3 MGD, TSS 150 mg/L. Pounds/day?
A. 2500 lbs/day
B. 3000 lbs/day
C. 3753 lbs/day (correct answer)
D. 4000 lbs/day
Rationale: Load = 3 × 150 × 8.34 ≈ 3753 lbs/day.
9. Which of the following best describes denitrification?
A. Ammonia to nitrate
B. Only chlorine
C. Nitrate is converted to nitrogen gas anaerobically (correct answer)
D. Only solids removal
Rationale: Denitrification removes nitrate to prevent eutrophication.
10. A Class II plant has BOD influent 300 mg/L, effluent 20 mg/L, flow 2 MGD. Percent BOD
removal?
A. 85%
B. 93.3% (correct answer)
C. 90%
D. 80%
Rationale: % Removal = [(300–20)/300] ×100 ≈ 93.3%.
11. Which of the following is true regarding chemical phosphorus removal?
A. Only solids removal
B. Alum or ferric salts bind phosphorus (correct answer)
C. Only chlorine
D. Only pH
Rationale: Chemicals form insoluble compounds for removal in clarifiers.
answers & rationale | 2025/2026 | Latest Update| Instant download!!
1. Which of the following best describes the purpose of secondary treatment in a Class II plant?
A. Only removes solids
B. Only disinfects
C. Biologically reduces BOD and suspended solids (correct answer)
D. Only adjusts pH
Rationale: Secondary treatment uses microorganisms to degrade organics and remove suspended solids.
2. A Class II plant has 2 MGD flow with BOD of 250 mg/L. Pounds per day BOD load?
A. 2500 lbs/day
B. 4000 lbs/day
C. 4170 lbs/day (correct answer)
D. 3500 lbs/day
Rationale: Load = Flow × BOD × 8.34 = 2 × 250 × 8.34 ≈ 4170 lbs/day.
3. Which of the following is true regarding nitrification in Class II plants?
A. Only removes solids
B. Ammonia is converted to nitrate via aerobic bacteria (correct answer)
C. Only chlorine
D. Only pH
Rationale: Nitrification reduces ammonia concentration to meet permit limits.
4. Which of the following is a primary advantage of extended aeration systems?
,A. Only solids removal
B. Stable operation with reduced sludge production (correct answer)
C. Only chlorine
D. Only pH adjustment
Rationale: Extended aeration reduces sludge volume and stabilizes BOD removal.
5. A plant operates an activated sludge system with MLSS of 2500 mg/L in 2 MGD flow. Pounds of
MLSS in the aeration basin?
A. 4170 lbs
B. 41,700 lbs
C. 41,700 lbs (correct answer)
D. 417 lbs
Rationale: Pounds = Flow × MLSS × 8.34 = 2 × 2500 × 8.34 ≈ 41,700 lbs.
6. Which of the following is true regarding sludge age (SRT) in Class II plants?
A. Only pH
B. Longer SRT improves nitrification (correct answer)
C. Only solids removal
D. Only chlorine
Rationale: SRT controls biomass growth and process stability.
7. Which of the following is true regarding clarifier hydraulic loading?
A. Only solids matter
B. Excessive flow reduces settling efficiency (correct answer)
C. Only pH
D. Only chlorine
Rationale: Hydraulic overload can cause solids washout.
, 8. A plant has a flow of 3 MGD, TSS 150 mg/L. Pounds/day?
A. 2500 lbs/day
B. 3000 lbs/day
C. 3753 lbs/day (correct answer)
D. 4000 lbs/day
Rationale: Load = 3 × 150 × 8.34 ≈ 3753 lbs/day.
9. Which of the following best describes denitrification?
A. Ammonia to nitrate
B. Only chlorine
C. Nitrate is converted to nitrogen gas anaerobically (correct answer)
D. Only solids removal
Rationale: Denitrification removes nitrate to prevent eutrophication.
10. A Class II plant has BOD influent 300 mg/L, effluent 20 mg/L, flow 2 MGD. Percent BOD
removal?
A. 85%
B. 93.3% (correct answer)
C. 90%
D. 80%
Rationale: % Removal = [(300–20)/300] ×100 ≈ 93.3%.
11. Which of the following is true regarding chemical phosphorus removal?
A. Only solids removal
B. Alum or ferric salts bind phosphorus (correct answer)
C. Only chlorine
D. Only pH
Rationale: Chemicals form insoluble compounds for removal in clarifiers.
