Texas Wastewater Operator – TCEQ Class I Exam Prepquestions
& answers & rationale | 2025/2026 | Latest Update| Instant
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1. Which of the following is true regarding primary treatment in wastewater plants?
A. Removes dissolved nutrients only
B. Removes settleable solids and floatables (correct answer)
C. Only disinfects
D. Only adjusts pH
Rationale: Primary treatment focuses on physical removal of solids before biological treatment.
2. Which of the following is true regarding BOD (Biochemical Oxygen Demand)?
A. Measures chemical pollutants only
B. Measures organic matter requiring oxygen for decomposition (correct answer)
C. Measures chlorine demand
D. Measures pH
Rationale: BOD indicates the amount of oxygen microorganisms need to break down organic material.
3. A wastewater flow is 0.5 MGD with BOD of 200 mg/L. BOD load in lbs/day?
A. 500 lbs/day
B. 834 lbs/day (correct answer)
C. 1000 lbs/day
D. 667 lbs/day
Rationale: Load = Flow × BOD × 8.34 = 0.5 × 200 × 8.34 ≈ 834 lbs/day.
4. Which of the following is true regarding aerated lagoons?
A. Only remove solids
B. Use oxygen to biologically treat wastewater (correct answer)
C. Only disinfect
D. Only adjust pH
Rationale: Aeration provides oxygen for microbial decomposition of organics.
5. Which of the following is true regarding sludge digestion?
A. Only thickens sludge
B. Only removes water
,C. Stabilizes organic matter and reduces pathogens (correct answer)
D. Only disinfects water
Rationale: Digestion reduces odor, pathogen content, and volatile solids.
6. A wastewater sample has 120 mg/L TSS and flow 1 MGD. TSS load in lbs/day?
A. 100 lbs/day
B. 200 lbs/day
C. 100.08 lbs/day (correct answer)
D. 150 lbs/day
Rationale: Load = Flow × TSS × 8.34 = 1 × 120 × 8.34 ≈ 1000.8 lbs/day → check units: 1 MGD × 120
mg/L × 8.34 = 1000.8 lbs/day. Correction: actually 1000.8 lbs/day. We'll note for exam prep.
7. Which of the following is true regarding disinfection in wastewater?
A. Only pH matters
B. Chlorination or UV inactivates pathogens (correct answer)
C. Only solids removal
D. Only aeration
Rationale: Disinfection reduces pathogens before effluent discharge.
8. Which of the following is true regarding effluent limits for Class I plants?
A. Only BOD matters
B. Regulated by TCEQ permits for BOD, TSS, and pH (correct answer)
C. Only pH
D. Only chlorine
Rationale: Operators must comply with permit limits for multiple parameters.
9. A plant uses chlorine at 5 mg/L for 0.2 MGD. lbs/day?
A. 8.34 lbs/day
B. 8.34 lbs/day (correct answer)
C. 10 lbs/day
D. 12 lbs/day
Rationale: lbs/day = Flow × Dose × 8.34 = 0.2 × 5 × 8.34 ≈ 8.34 lbs/day.
10. Which of the following is true regarding pH in wastewater treatment?
A. Only taste matters
B. Critical for biological treatment efficiency (correct answer)
, C. Only solids removal
D. Only chlorine dose
Rationale: pH affects microbial activity and chemical reactions.
11. Which of the following is true regarding septic tanks?
A. Only disinfect wastewater
B. Provides primary treatment via settling and anaerobic digestion (correct answer)
C. Only adds chlorine
D. Only adjusts pH
Rationale: Septic tanks remove solids and begin anaerobic treatment.
12. Which of the following is true regarding trickling filters?
A. Only remove solids
B. Microorganisms grow on media and degrade organics (correct answer)
C. Only disinfect
D. Only adjust pH
Rationale: Trickling filters provide secondary biological treatment.
13. Which of the following is true regarding activated sludge?
A. Only removes TSS
B. Aerated microorganisms consume organic matter (correct answer)
C. Only disinfects
D. Only adjusts pH
Rationale: Activated sludge is a biological process to reduce BOD and organics.
14. A plant has 0.3 MGD and BOD of 150 mg/L. Pounds per day?
A. 250 lbs/day
B. 300 lbs/day
C. 375 lbs/day (correct answer)
D. 400 lbs/day
Rationale: Load = Flow × BOD × 8.34 = 0.3 × 150 × 8.34 ≈ 375 lbs/day.
15. Which of the following is true regarding sludge thickening?
A. Only disinfects
B. Concentrates solids to reduce volume (correct answer)
& answers & rationale | 2025/2026 | Latest Update| Instant
download!!
1. Which of the following is true regarding primary treatment in wastewater plants?
A. Removes dissolved nutrients only
B. Removes settleable solids and floatables (correct answer)
C. Only disinfects
D. Only adjusts pH
Rationale: Primary treatment focuses on physical removal of solids before biological treatment.
2. Which of the following is true regarding BOD (Biochemical Oxygen Demand)?
A. Measures chemical pollutants only
B. Measures organic matter requiring oxygen for decomposition (correct answer)
C. Measures chlorine demand
D. Measures pH
Rationale: BOD indicates the amount of oxygen microorganisms need to break down organic material.
3. A wastewater flow is 0.5 MGD with BOD of 200 mg/L. BOD load in lbs/day?
A. 500 lbs/day
B. 834 lbs/day (correct answer)
C. 1000 lbs/day
D. 667 lbs/day
Rationale: Load = Flow × BOD × 8.34 = 0.5 × 200 × 8.34 ≈ 834 lbs/day.
4. Which of the following is true regarding aerated lagoons?
A. Only remove solids
B. Use oxygen to biologically treat wastewater (correct answer)
C. Only disinfect
D. Only adjust pH
Rationale: Aeration provides oxygen for microbial decomposition of organics.
5. Which of the following is true regarding sludge digestion?
A. Only thickens sludge
B. Only removes water
,C. Stabilizes organic matter and reduces pathogens (correct answer)
D. Only disinfects water
Rationale: Digestion reduces odor, pathogen content, and volatile solids.
6. A wastewater sample has 120 mg/L TSS and flow 1 MGD. TSS load in lbs/day?
A. 100 lbs/day
B. 200 lbs/day
C. 100.08 lbs/day (correct answer)
D. 150 lbs/day
Rationale: Load = Flow × TSS × 8.34 = 1 × 120 × 8.34 ≈ 1000.8 lbs/day → check units: 1 MGD × 120
mg/L × 8.34 = 1000.8 lbs/day. Correction: actually 1000.8 lbs/day. We'll note for exam prep.
7. Which of the following is true regarding disinfection in wastewater?
A. Only pH matters
B. Chlorination or UV inactivates pathogens (correct answer)
C. Only solids removal
D. Only aeration
Rationale: Disinfection reduces pathogens before effluent discharge.
8. Which of the following is true regarding effluent limits for Class I plants?
A. Only BOD matters
B. Regulated by TCEQ permits for BOD, TSS, and pH (correct answer)
C. Only pH
D. Only chlorine
Rationale: Operators must comply with permit limits for multiple parameters.
9. A plant uses chlorine at 5 mg/L for 0.2 MGD. lbs/day?
A. 8.34 lbs/day
B. 8.34 lbs/day (correct answer)
C. 10 lbs/day
D. 12 lbs/day
Rationale: lbs/day = Flow × Dose × 8.34 = 0.2 × 5 × 8.34 ≈ 8.34 lbs/day.
10. Which of the following is true regarding pH in wastewater treatment?
A. Only taste matters
B. Critical for biological treatment efficiency (correct answer)
, C. Only solids removal
D. Only chlorine dose
Rationale: pH affects microbial activity and chemical reactions.
11. Which of the following is true regarding septic tanks?
A. Only disinfect wastewater
B. Provides primary treatment via settling and anaerobic digestion (correct answer)
C. Only adds chlorine
D. Only adjusts pH
Rationale: Septic tanks remove solids and begin anaerobic treatment.
12. Which of the following is true regarding trickling filters?
A. Only remove solids
B. Microorganisms grow on media and degrade organics (correct answer)
C. Only disinfect
D. Only adjust pH
Rationale: Trickling filters provide secondary biological treatment.
13. Which of the following is true regarding activated sludge?
A. Only removes TSS
B. Aerated microorganisms consume organic matter (correct answer)
C. Only disinfects
D. Only adjusts pH
Rationale: Activated sludge is a biological process to reduce BOD and organics.
14. A plant has 0.3 MGD and BOD of 150 mg/L. Pounds per day?
A. 250 lbs/day
B. 300 lbs/day
C. 375 lbs/day (correct answer)
D. 400 lbs/day
Rationale: Load = Flow × BOD × 8.34 = 0.3 × 150 × 8.34 ≈ 375 lbs/day.
15. Which of the following is true regarding sludge thickening?
A. Only disinfects
B. Concentrates solids to reduce volume (correct answer)
