Texas Wastewater Class A Certification
Exam ACTUAL EXAM 2026/2027 |
Practice Test | 200+ Questions | TCEQ
Requirements | Verified Q&A | Pass
Guaranteed - A+ Graded
DOMAIN 1: WASTEWATER TREATMENT PROCESSES
Q1: Activated Sludge F/M Ratio
What does the Food-to-Microorganism (F/M) ratio indicate in the activated sludge
process?
A. The ratio of oxygen to microorganisms
B. The ratio of BOD to MLVSS in the aeration tank [CORRECT]
C. The ratio of sludge age to hydraulic retention time
D. The ratio of nitrogen to phosphorus in the influent
Rationale:
The F/M ratio is calculated as BOD (food) / MLVSS (microorganisms) and is used to control
the growth rate of microorganisms in the aeration tank. A high F/M ratio can lead to dispersed
growth, while a low F/M ratio can cause filamentous bulking.
Texas Note: TCEQ requires operators to maintain F/M ratios between 0.2–0.5 lb BOD/lb
MLVSS/day for conventional activated sludge systems.
Q2: Sludge Volume Index (SVI)
An SVI of 250 mL/g indicates:
A. Good settling sludge
B. Bulking sludge [CORRECT]
C. Pin floc
D. Over-aerated sludge
,Rationale:
SVI values >150 mL/g typically indicate bulking sludge , which settles poorly and can lead to
solids washout. Values <100 mL/g indicate good settling, while 100–150 mL/g is acceptable.
Texas Note: TCEQ considers SVI a critical control parameter for secondary clarifier
performance.
Q3: Mean Cell Residence Time (MCRT)
What is the primary purpose of controlling MCRT in activated sludge?
A. To maximize oxygen transfer
B. To control sludge age and solids inventory [CORRECT]
C. To reduce BOD loading
D. To increase hydraulic retention time
Rationale:
MCRT (calculated as total MLSS / WAS flow rate ) controls the average time solids remain
in the system, ensuring proper sludge age for nitrification and solids stabilization.
Texas Note: TCEQ requires MCRT >5 days for nitrification in cold weather.
Q4: Return Activated Sludge (RAS) Rate
If the RAS rate is too low, what will occur in the secondary clarifier?
A. Increased sludge blanket depth
B. Solids washout and poor effluent quality [CORRECT]
C. Excessive sludge thickening
D. Reduced BOD removal
Rationale:
Insufficient RAS reduces the MLSS concentration in the aeration tank, leading to poor floc
formation and solids washout in the effluent.
Texas Note: TCEQ recommends RAS rates of 25–50% of influent flow for conventional
systems.
Q5: Nitrification Process
Which bacteria are primarily responsible for nitrification in activated sludge?
A. Nitrosomonas and Nitrobacter [CORRECT]
B. E. coli and Streptococcus
,C. Bacillus and Clostridium
D. Pseudomonas and Flavobacterium
Rationale:
Nitrosomonas oxidizes ammonia (NH₃) to nitrite (NO₂⁻), and Nitrobacter oxidizes nitrite to
nitrate (NO₃⁻).
Texas Note: TCEQ requires ammonia-N < 2 mg/L in effluent for most Class A permits.
Q6: Denitrification Process
What is the primary electron donor in biological denitrification?
A. Oxygen
B. Nitrate
C. Organic carbon (BOD) [CORRECT]
D. Phosphorus
Rationale:
Denitrifying bacteria use organic carbon (BOD) as an electron donor to reduce nitrate (NO₃⁻)
to nitrogen gas (N₂).
Texas Note: TCEQ encourages BNR (Biological Nutrient Removal) for facilities discharging
to nutrient-sensitive waters.
Q7: Trickling Filter Hydraulic Loading
What is the typical hydraulic loading rate for a standard-rate trickling filter?
A. 1–4 gpm/ft² [CORRECT]
B. 5–10 gpm/ft²
C. 10–20 gpm/ft²
D. 0.1–0.5 gpm/ft²
Rationale:
Standard-rate trickling filters operate at 1–4 gpm/ft² to ensure proper wetting and biofilm
contact.
Texas Note: TCEQ requires effluent recirculation for high-strength waste or cold weather
operations.
Q8: Rotating Biological Contactors (RBCs)
, What is the primary advantage of RBCs over activated sludge?
A. Higher energy consumption
B. Lower sludge production and operational simplicity [CORRECT]
C. Faster nitrification rates
D. Better phosphorus removal
Rationale:
RBCs use rotating discs to grow biofilm, requiring less energy and producing less sludge
than activated sludge.
Texas Note: TCEQ approves RBCs for small to medium-sized plants with consistent
loading.
Q9: Moving Bed Biofilm Reactor (MBBR)
What is the key feature of an MBBR?
A. Fixed media with no moving parts
B. Suspended plastic media with biofilm [CORRECT]
C. Anaerobic digestion capability
D. Chemical phosphorus removal
Rationale:
MBBRs use suspended plastic carriers to grow biofilm, combining the benefits of activated
sludge and fixed-film systems.
Texas Note: TCEQ allows MBBRs for BOD removal and nitrification in upgrades.
Q10: Facultative Lagoon Operation
What is the primary mechanism of BOD removal in a facultative lagoon?
A. Sedimentation
B. Aerobic and anaerobic microbial action [CORRECT]
C. Chemical precipitation
D. UV disinfection
Rationale:
Facultative lagoons have an aerobic surface layer and an anaerobic bottom layer, allowing
both aerobic and anaerobic BOD removal.
Texas Note: TCEQ requires minimum 3–5 feet depth and 20–45 days detention time for
facultative lagoons.
Exam ACTUAL EXAM 2026/2027 |
Practice Test | 200+ Questions | TCEQ
Requirements | Verified Q&A | Pass
Guaranteed - A+ Graded
DOMAIN 1: WASTEWATER TREATMENT PROCESSES
Q1: Activated Sludge F/M Ratio
What does the Food-to-Microorganism (F/M) ratio indicate in the activated sludge
process?
A. The ratio of oxygen to microorganisms
B. The ratio of BOD to MLVSS in the aeration tank [CORRECT]
C. The ratio of sludge age to hydraulic retention time
D. The ratio of nitrogen to phosphorus in the influent
Rationale:
The F/M ratio is calculated as BOD (food) / MLVSS (microorganisms) and is used to control
the growth rate of microorganisms in the aeration tank. A high F/M ratio can lead to dispersed
growth, while a low F/M ratio can cause filamentous bulking.
Texas Note: TCEQ requires operators to maintain F/M ratios between 0.2–0.5 lb BOD/lb
MLVSS/day for conventional activated sludge systems.
Q2: Sludge Volume Index (SVI)
An SVI of 250 mL/g indicates:
A. Good settling sludge
B. Bulking sludge [CORRECT]
C. Pin floc
D. Over-aerated sludge
,Rationale:
SVI values >150 mL/g typically indicate bulking sludge , which settles poorly and can lead to
solids washout. Values <100 mL/g indicate good settling, while 100–150 mL/g is acceptable.
Texas Note: TCEQ considers SVI a critical control parameter for secondary clarifier
performance.
Q3: Mean Cell Residence Time (MCRT)
What is the primary purpose of controlling MCRT in activated sludge?
A. To maximize oxygen transfer
B. To control sludge age and solids inventory [CORRECT]
C. To reduce BOD loading
D. To increase hydraulic retention time
Rationale:
MCRT (calculated as total MLSS / WAS flow rate ) controls the average time solids remain
in the system, ensuring proper sludge age for nitrification and solids stabilization.
Texas Note: TCEQ requires MCRT >5 days for nitrification in cold weather.
Q4: Return Activated Sludge (RAS) Rate
If the RAS rate is too low, what will occur in the secondary clarifier?
A. Increased sludge blanket depth
B. Solids washout and poor effluent quality [CORRECT]
C. Excessive sludge thickening
D. Reduced BOD removal
Rationale:
Insufficient RAS reduces the MLSS concentration in the aeration tank, leading to poor floc
formation and solids washout in the effluent.
Texas Note: TCEQ recommends RAS rates of 25–50% of influent flow for conventional
systems.
Q5: Nitrification Process
Which bacteria are primarily responsible for nitrification in activated sludge?
A. Nitrosomonas and Nitrobacter [CORRECT]
B. E. coli and Streptococcus
,C. Bacillus and Clostridium
D. Pseudomonas and Flavobacterium
Rationale:
Nitrosomonas oxidizes ammonia (NH₃) to nitrite (NO₂⁻), and Nitrobacter oxidizes nitrite to
nitrate (NO₃⁻).
Texas Note: TCEQ requires ammonia-N < 2 mg/L in effluent for most Class A permits.
Q6: Denitrification Process
What is the primary electron donor in biological denitrification?
A. Oxygen
B. Nitrate
C. Organic carbon (BOD) [CORRECT]
D. Phosphorus
Rationale:
Denitrifying bacteria use organic carbon (BOD) as an electron donor to reduce nitrate (NO₃⁻)
to nitrogen gas (N₂).
Texas Note: TCEQ encourages BNR (Biological Nutrient Removal) for facilities discharging
to nutrient-sensitive waters.
Q7: Trickling Filter Hydraulic Loading
What is the typical hydraulic loading rate for a standard-rate trickling filter?
A. 1–4 gpm/ft² [CORRECT]
B. 5–10 gpm/ft²
C. 10–20 gpm/ft²
D. 0.1–0.5 gpm/ft²
Rationale:
Standard-rate trickling filters operate at 1–4 gpm/ft² to ensure proper wetting and biofilm
contact.
Texas Note: TCEQ requires effluent recirculation for high-strength waste or cold weather
operations.
Q8: Rotating Biological Contactors (RBCs)
, What is the primary advantage of RBCs over activated sludge?
A. Higher energy consumption
B. Lower sludge production and operational simplicity [CORRECT]
C. Faster nitrification rates
D. Better phosphorus removal
Rationale:
RBCs use rotating discs to grow biofilm, requiring less energy and producing less sludge
than activated sludge.
Texas Note: TCEQ approves RBCs for small to medium-sized plants with consistent
loading.
Q9: Moving Bed Biofilm Reactor (MBBR)
What is the key feature of an MBBR?
A. Fixed media with no moving parts
B. Suspended plastic media with biofilm [CORRECT]
C. Anaerobic digestion capability
D. Chemical phosphorus removal
Rationale:
MBBRs use suspended plastic carriers to grow biofilm, combining the benefits of activated
sludge and fixed-film systems.
Texas Note: TCEQ allows MBBRs for BOD removal and nitrification in upgrades.
Q10: Facultative Lagoon Operation
What is the primary mechanism of BOD removal in a facultative lagoon?
A. Sedimentation
B. Aerobic and anaerobic microbial action [CORRECT]
C. Chemical precipitation
D. UV disinfection
Rationale:
Facultative lagoons have an aerobic surface layer and an anaerobic bottom layer, allowing
both aerobic and anaerobic BOD removal.
Texas Note: TCEQ requires minimum 3–5 feet depth and 20–45 days detention time for
facultative lagoons.
