Texas Wastewater Operator Certification Exam Review | Versions A & B
| 2026/2027
TCEQ Professional Licensing — 100 Practice Questions with Verified Answers and Evidence-
Based Rationales
,Appendix: Quick Reference Tables
Table 1: Wastewater Parameter Ranges
Parameter Typical Raw Wastewater Range Typical Effluent Target
BOD 100–350 mg/L <30 mg/L
TSS 100–350 mg/L <30 mg/L
pH 6.0–8.0 6.5–8.5
Ammonia-N 15–50 mg/L varies
Total Phosphorus 4–12 mg/L varies
DO 0–2 mg/L >1 mg/L (or per permit)
Table 2: Activated Sludge Parameter Quick Reference
Parameter Typical Range Purpose
MLSS 1500–4000 mg/L aerator biomass
F/M Ratio 0.2–0.5 lb BOD/lb MLSS/day process loading
SVI <150 mL/g sludge settleability; >200 = bulking
MCRT/SRT 5–15 days solids retention, varies by process
RAS Rate 25–100% of influent return microorganisms
Dissolved Oxygen 1.5–3.0 mg/L aerator
Table 3: Chlorination CT Values Reference
Organism Required CT (mg·min/L) at 10°C pH 7
E. coli 0.4
Giardia lamblia 21
Viruses 3
Table 4: 40 CFR Part 503 Biosolids Classification
Feature Class A Class B
Pathogen reduction PSRP/Equivalent PFRP/Equivalent
Vector attraction Required Required
Land application Unrestricted Site restrictions (buffer zones, crop
limits, access restrictions)
Metal limits Lower (Table 3) Higher (Table 1 ceiling)
Bagging/sale Permitted Not permitted
Table 5: TCEQ License Classes Quick Reference
Class Minimum Experience Typical Plant Size
Class D Entry-level training Small package plants
Class C 1 year experience Small plants <1 MGD
Class B 2 years at Class C OR 4 years direct Medium plants 1–5 MGD
Class A 3 years at Class B OR 6 years direct Large/complex plants >5 MGD
Table 6: Safety Quick Reference
, Hazard Standard/Limit Key Action
H₂S IDLH 100 ppm SCBA required >10 ppm
Confined Space O₂ >19.5% and <23.5% Ventilate, monitor, permit
Chlorine emergency NCl₃ detection kit Downwind evacuation
LEL <10% before entry Gas monitoring required
Section 1: Wastewater Characteristics & Physical/Chemical Parameters
1. Domestic (sanitary) wastewater typically accounts for what percentage of total flow in a municipal wastewater
collection system?
A. 20–40% B. 40–60% C. 60–80% D. 80–95%
Correct Answer: C. 60–80%
Rationale: Domestic or sanitary wastewater constitutes approximately 60–80% of the total flow in a typical municipal
collection system. The remainder comes from industrial sources, infiltration, and inflow (I&I). Reference: Metcalf &
Eddy, Wastewater Engineering.
2. A wastewater sample has a BOD₅ of 220 mg/L and a COD of 480 mg/L. What is the approximate COD-to-
BOD ratio, and what does it indicate about the wastewater?
A. 1.2 — highly biodegradable B. 2.2 — moderate biodegradability with some non-
biodegradable organics
C. 3.5 — mostly non-biodegradable D. 0.46 — extremely biodegradable
Correct Answer: B. 2.2 — moderate biodegradability with some non-biodegradable organics
Rationale: The COD/BOD ratio is 480/220 = 2.18, approximately 2.2. A ratio between 1.5–2.5 indicates moderate
biodegradability with some non-biodegradable organic matter present. Ratios above 3.0 suggest predominantly non-
biodegradable waste. Reference: TCEQ Wastewater Operator Manual.
3. In a standard BOD₅ test, the sample is incubated at what temperature and for how many days?
A. 25°C for 3 days B. 20°C for 5 days in the C. 20°C for 7 days D. 35°C for 5 days
dark
Correct Answer: B. 20°C for 5 days in the dark
Rationale: The standard BOD₅ test protocol requires incubation at 20°C (±1°C) for 5 days in complete darkness to
prevent photosynthetic oxygen production by algae. This measures the oxygen consumed by microorganisms
decomposing biodegradable organic matter. Reference: Standard Methods for the Examination of Water and
Wastewater.
4. Strong domestic wastewater typically has which approximate BOD₅ concentration?
A. 50–100 mg/L B. 110–200 mg/L C. 200–350 mg/L D. 400–600 mg/L
Correct Answer: C. 200–350 mg/L
Rationale: Strong domestic wastewater has a BOD₅ in the range of 200–350 mg/L. Weak wastewater is 50–150 mg/L,
and medium strength is 110–300 mg/L. Strong wastewater typically originates from areas with low per capita water
usage or high organic loading. Reference: Metcalf & Eddy.
| 2026/2027
TCEQ Professional Licensing — 100 Practice Questions with Verified Answers and Evidence-
Based Rationales
,Appendix: Quick Reference Tables
Table 1: Wastewater Parameter Ranges
Parameter Typical Raw Wastewater Range Typical Effluent Target
BOD 100–350 mg/L <30 mg/L
TSS 100–350 mg/L <30 mg/L
pH 6.0–8.0 6.5–8.5
Ammonia-N 15–50 mg/L varies
Total Phosphorus 4–12 mg/L varies
DO 0–2 mg/L >1 mg/L (or per permit)
Table 2: Activated Sludge Parameter Quick Reference
Parameter Typical Range Purpose
MLSS 1500–4000 mg/L aerator biomass
F/M Ratio 0.2–0.5 lb BOD/lb MLSS/day process loading
SVI <150 mL/g sludge settleability; >200 = bulking
MCRT/SRT 5–15 days solids retention, varies by process
RAS Rate 25–100% of influent return microorganisms
Dissolved Oxygen 1.5–3.0 mg/L aerator
Table 3: Chlorination CT Values Reference
Organism Required CT (mg·min/L) at 10°C pH 7
E. coli 0.4
Giardia lamblia 21
Viruses 3
Table 4: 40 CFR Part 503 Biosolids Classification
Feature Class A Class B
Pathogen reduction PSRP/Equivalent PFRP/Equivalent
Vector attraction Required Required
Land application Unrestricted Site restrictions (buffer zones, crop
limits, access restrictions)
Metal limits Lower (Table 3) Higher (Table 1 ceiling)
Bagging/sale Permitted Not permitted
Table 5: TCEQ License Classes Quick Reference
Class Minimum Experience Typical Plant Size
Class D Entry-level training Small package plants
Class C 1 year experience Small plants <1 MGD
Class B 2 years at Class C OR 4 years direct Medium plants 1–5 MGD
Class A 3 years at Class B OR 6 years direct Large/complex plants >5 MGD
Table 6: Safety Quick Reference
, Hazard Standard/Limit Key Action
H₂S IDLH 100 ppm SCBA required >10 ppm
Confined Space O₂ >19.5% and <23.5% Ventilate, monitor, permit
Chlorine emergency NCl₃ detection kit Downwind evacuation
LEL <10% before entry Gas monitoring required
Section 1: Wastewater Characteristics & Physical/Chemical Parameters
1. Domestic (sanitary) wastewater typically accounts for what percentage of total flow in a municipal wastewater
collection system?
A. 20–40% B. 40–60% C. 60–80% D. 80–95%
Correct Answer: C. 60–80%
Rationale: Domestic or sanitary wastewater constitutes approximately 60–80% of the total flow in a typical municipal
collection system. The remainder comes from industrial sources, infiltration, and inflow (I&I). Reference: Metcalf &
Eddy, Wastewater Engineering.
2. A wastewater sample has a BOD₅ of 220 mg/L and a COD of 480 mg/L. What is the approximate COD-to-
BOD ratio, and what does it indicate about the wastewater?
A. 1.2 — highly biodegradable B. 2.2 — moderate biodegradability with some non-
biodegradable organics
C. 3.5 — mostly non-biodegradable D. 0.46 — extremely biodegradable
Correct Answer: B. 2.2 — moderate biodegradability with some non-biodegradable organics
Rationale: The COD/BOD ratio is 480/220 = 2.18, approximately 2.2. A ratio between 1.5–2.5 indicates moderate
biodegradability with some non-biodegradable organic matter present. Ratios above 3.0 suggest predominantly non-
biodegradable waste. Reference: TCEQ Wastewater Operator Manual.
3. In a standard BOD₅ test, the sample is incubated at what temperature and for how many days?
A. 25°C for 3 days B. 20°C for 5 days in the C. 20°C for 7 days D. 35°C for 5 days
dark
Correct Answer: B. 20°C for 5 days in the dark
Rationale: The standard BOD₅ test protocol requires incubation at 20°C (±1°C) for 5 days in complete darkness to
prevent photosynthetic oxygen production by algae. This measures the oxygen consumed by microorganisms
decomposing biodegradable organic matter. Reference: Standard Methods for the Examination of Water and
Wastewater.
4. Strong domestic wastewater typically has which approximate BOD₅ concentration?
A. 50–100 mg/L B. 110–200 mg/L C. 200–350 mg/L D. 400–600 mg/L
Correct Answer: C. 200–350 mg/L
Rationale: Strong domestic wastewater has a BOD₅ in the range of 200–350 mg/L. Weak wastewater is 50–150 mg/L,
and medium strength is 110–300 mg/L. Strong wastewater typically originates from areas with low per capita water
usage or high organic loading. Reference: Metcalf & Eddy.
