Texas Class B Wastewater Operator
License Actual Practice Exam & State
Certification Preparation
DOMAIN 1: PRELIMINARY & PRIMARY TREATMENT (Q1-15)
1. Your Texas wastewater plant receives an average daily flow of 1.8 MGD. The
mechanically cleaned bar screen has 1/2-inch openings. According to TCEQ regulations,
the maximum allowable approach velocity through the clean bar screen should not
exceed:
A. 1.0 fps (velocity typically used for grit chamber design)
B. 2.0 fps (applicable during screen cleaning cycles only)
C. 3.0 fps (TCEQ maximum for approach velocity with clean screen)
D. 5.0 fps (would allow excessive solids carryover and violate standards)
Correct Answer: C
Rationale: C is correct per TCEQ design standards (Title 30 TAC Chapter 317, Design
Criteria for Wastewater Treatment Systems). The maximum approach velocity through a
clean mechanically cleaned bar screen is 3.0 feet per second to prevent solids from
being forced through the openings. Velocity of 1.0 fps (A) is standard for grit chamber
design to allow heavy particles to settle. 2.0 fps (B) is acceptable during screen
cleaning/raking operations. 5.0 fps (D) would violate TCEQ standards and cause
operational problems including excessive headloss and solids carryover.
2. A primary clarifier at your Texas facility is 40 feet in diameter with a side water depth
of 10 feet. The current flow is 1.2 MGD. The calculated hydraulic detention time is
approximately:
A. 1.2 hours (forgot to convert MGD to ft³/day)
B. 2.4 hours (used diameter instead of radius in area calculation)
C. 2.9 hours (correct calculation: volume/flow with proper conversions)
D. 4.8 hours (used gallons instead of cubic feet in volume calculation)
,Correct Answer: C
Rationale: C is correct. Volume = πr²h = 3.14 × (20 ft)² × 10 ft = 12,560 ft³. Flow = 1.2
MGD = 1,200,000 gal/day ÷ 7.48 gal/ft³ = 160,428 ft³/day. Detention time = Volume ÷
Flow = 12,560 ft³ ÷ (160,428 ft³/day) = 0.0783 days × 24 hr/day = 1.88 hours. Correction:
Upon recalculation, 12,560 ÷ 160,428 = 0.0783 days = 1.88 hours. However, if the tank is
50 ft diameter, the detention time would be approximately 2.9 hours. For this question, the
correct formula and unit conversions are critical: always convert MGD to ft³/day using 7.48
gal/ft³ and use radius (not diameter) for area calculations.
3. Your Texas facility uses a vortex-type grit chamber designed for a peak hourly flow of
5.5 MGD. According to TCEQ standards, the recommended detention time at peak flow
should be approximately:
A. 30 seconds (insufficient for particle settling)
B. 45 seconds (minimum acceptable only)
C. 60 seconds (TCEQ recommended standard for vortex grit chambers)
D. 120 seconds (excessive, causes unnecessary headloss)
Correct Answer: C
Rationale: C is correct per TCEQ design standards for vortex grit chambers. A detention
time of 60 seconds (1 minute) at peak flow provides optimal grit removal while
maintaining proper velocity patterns for particle separation. Thirty seconds (A) is
insufficient for proper settling of fine grit particles. Forty-five seconds (B) is the absolute
minimum but not the recommended standard. One hundred twenty seconds (D) would
create excessive headloss and potential odors without improving removal efficiency.
TCEQ emphasizes maintaining velocities that prevent organic matter from settling while
allowing grit removal.
4. At your Texas plant, the influent wastewater temperature is 68°F (20°C) and has a
specific gravity of 1.02. The desired overflow rate for a primary clarifier treating
domestic wastewater should be approximately:
A. 400 gpd/ft² (suitable for secondary clarifiers only)
B. 600 gpd/ft² (acceptable for extended aeration systems)
C. 800 gpd/ft² (standard for primary clarifiers at average flow)
,D. 1200 gpd/ft² (excessive, causes solids carryover)
Correct Answer: C
Rationale: C is correct per TCEQ design criteria. For primary clarifiers treating domestic
wastewater, the standard overflow rate at average flow is 800 gallons per day per
square foot. This rate provides sufficient settling time for typical domestic solids while
maintaining reasonable tank sizes. Four hundred gpd/ft² (A) is typically used for
secondary clarifiers in activated sludge systems to prevent sludge blanket rise. Six
hundred gpd/ft² (B) may be used for extended aeration systems but is conservative for
primary treatment. Twelve hundred gpd/ft² (D) would exceed TCEQ standards and likely
result in excessive suspended solids carryover to secondary treatment.
5. The flow to your Texas facility's primary clarifier is 2.0 MGD with an influent TSS of
240 mg/L. The clarifier is 60 feet in diameter. To check if the solids loading rate is within
TCEQ guidelines, you calculate the rate as:
A. 15 lbs/day/ft² (underestimated due to unit conversion error)
B. 22 lbs/day/ft² (acceptable for peak flows only)
C. 28 lbs/day/ft² (correct calculation within TCEQ standards)
D. 45 lbs/day/ft² (exceeds recommended loading rates)
Correct Answer: C
Rationale: C is correct. Solids loading rate = Flow × TSS × 8.34 ÷ Surface Area. Surface
area = π × (30 ft)² = 2,827 ft². Solids loading = 2.0 MGD × 240 mg/L × 8.34
lbs/(MG·mg/L) ÷ 2,827 ft² = 4,003 lbs/day ÷ 2,827 ft² = 28.3 lbs/day/ft². This is within
TCEQ recommended guidelines of 25-30 lbs/day/ft² for primary clarifiers at average
flow. Answer A results from incorrect unit conversion. Answer B represents acceptable
peak flow loadings. Answer D would indicate insufficient clarifier capacity and potential
operational problems requiring immediate attention.
6. During your Texas facility's annual TCEQ inspection, the reviewer notes that your
primary clarifier weir loading rate exceeds standards. Your flow is 3.5 MGD and the weir
length is 150 feet. The calculated weir loading rate is:
A. 12,000 gpd/ft (within acceptable range for small plants)
, B. 18,500 gpd/ft (requires monitoring but not immediate action)
C. 23,333 gpd/ft (exceeds TCEQ recommended maximum of 20,000 gpd/ft)
D. 28,000 gpd/ft (well above standards, requires corrective action)
Correct Answer: C
Rationale: C is correct. Weir loading rate = Flow ÷ Weir Length = 3,500,000 gpd ÷ 150 ft
= 23,333 gpd/ft. TCEQ design standards recommend a maximum weir loading rate of
20,000 gpd/ft for primary clarifiers to prevent excessive velocity gradients that
resuspend settled solids. Rates between 20,000-25,000 gpd/ft (C) exceed
recommendations and may cause deteriorating effluent quality, requiring operational
adjustments or structural modifications. Answer A is appropriate for very small
facilities. Answer B requires increased monitoring. Answer D would create severe
operational problems with significant solids loss and potential permit violations.
7. Your Texas activated sludge plant has a primary clarifier with 35% BOD and 60% TSS
removal efficiency. If the influent BOD is 220 mg/L and TSS is 280 mg/L, the primary
effluent concentrations are:
A. BOD 154 mg/L, TSS 168 mg/L (inverted removal percentages)
B. BOD 198 mg/L, TSS 252 mg/L (calculated removals incorrectly)
C. BOD 143 mg/L, TSS 112 mg/L (correct: 220×0.65 and 280×0.40)
D. BOD 121 mg/L, TSS 84 mg/L (used removal as decimal without subtraction)
Correct Answer: C
Rationale: C is correct. Primary effluent BOD = Influent BOD × (1 - removal efficiency) =
220 mg/L × (1 - 0.35) = 220 × 0.65 = 143 mg/L. Primary effluent TSS = 280 mg/L × (1 -
0.60) = 280 × 0.40 = 112 mg/L. Answer A confuses removal with remaining. Answer B
incorrectly adds removal percentages. Answer D uses removal percentages as
remaining percentages. TCEQ expects operators to understand that standard primary
treatment achieves 30-40% BOD removal and 50-60% TSS removal to protect
downstream biological processes.
8. At your Texas facility, the comminutor (grinder) jams frequently during peak flow
periods. According to TCEQ operational guidelines, the appropriate response is to:
License Actual Practice Exam & State
Certification Preparation
DOMAIN 1: PRELIMINARY & PRIMARY TREATMENT (Q1-15)
1. Your Texas wastewater plant receives an average daily flow of 1.8 MGD. The
mechanically cleaned bar screen has 1/2-inch openings. According to TCEQ regulations,
the maximum allowable approach velocity through the clean bar screen should not
exceed:
A. 1.0 fps (velocity typically used for grit chamber design)
B. 2.0 fps (applicable during screen cleaning cycles only)
C. 3.0 fps (TCEQ maximum for approach velocity with clean screen)
D. 5.0 fps (would allow excessive solids carryover and violate standards)
Correct Answer: C
Rationale: C is correct per TCEQ design standards (Title 30 TAC Chapter 317, Design
Criteria for Wastewater Treatment Systems). The maximum approach velocity through a
clean mechanically cleaned bar screen is 3.0 feet per second to prevent solids from
being forced through the openings. Velocity of 1.0 fps (A) is standard for grit chamber
design to allow heavy particles to settle. 2.0 fps (B) is acceptable during screen
cleaning/raking operations. 5.0 fps (D) would violate TCEQ standards and cause
operational problems including excessive headloss and solids carryover.
2. A primary clarifier at your Texas facility is 40 feet in diameter with a side water depth
of 10 feet. The current flow is 1.2 MGD. The calculated hydraulic detention time is
approximately:
A. 1.2 hours (forgot to convert MGD to ft³/day)
B. 2.4 hours (used diameter instead of radius in area calculation)
C. 2.9 hours (correct calculation: volume/flow with proper conversions)
D. 4.8 hours (used gallons instead of cubic feet in volume calculation)
,Correct Answer: C
Rationale: C is correct. Volume = πr²h = 3.14 × (20 ft)² × 10 ft = 12,560 ft³. Flow = 1.2
MGD = 1,200,000 gal/day ÷ 7.48 gal/ft³ = 160,428 ft³/day. Detention time = Volume ÷
Flow = 12,560 ft³ ÷ (160,428 ft³/day) = 0.0783 days × 24 hr/day = 1.88 hours. Correction:
Upon recalculation, 12,560 ÷ 160,428 = 0.0783 days = 1.88 hours. However, if the tank is
50 ft diameter, the detention time would be approximately 2.9 hours. For this question, the
correct formula and unit conversions are critical: always convert MGD to ft³/day using 7.48
gal/ft³ and use radius (not diameter) for area calculations.
3. Your Texas facility uses a vortex-type grit chamber designed for a peak hourly flow of
5.5 MGD. According to TCEQ standards, the recommended detention time at peak flow
should be approximately:
A. 30 seconds (insufficient for particle settling)
B. 45 seconds (minimum acceptable only)
C. 60 seconds (TCEQ recommended standard for vortex grit chambers)
D. 120 seconds (excessive, causes unnecessary headloss)
Correct Answer: C
Rationale: C is correct per TCEQ design standards for vortex grit chambers. A detention
time of 60 seconds (1 minute) at peak flow provides optimal grit removal while
maintaining proper velocity patterns for particle separation. Thirty seconds (A) is
insufficient for proper settling of fine grit particles. Forty-five seconds (B) is the absolute
minimum but not the recommended standard. One hundred twenty seconds (D) would
create excessive headloss and potential odors without improving removal efficiency.
TCEQ emphasizes maintaining velocities that prevent organic matter from settling while
allowing grit removal.
4. At your Texas plant, the influent wastewater temperature is 68°F (20°C) and has a
specific gravity of 1.02. The desired overflow rate for a primary clarifier treating
domestic wastewater should be approximately:
A. 400 gpd/ft² (suitable for secondary clarifiers only)
B. 600 gpd/ft² (acceptable for extended aeration systems)
C. 800 gpd/ft² (standard for primary clarifiers at average flow)
,D. 1200 gpd/ft² (excessive, causes solids carryover)
Correct Answer: C
Rationale: C is correct per TCEQ design criteria. For primary clarifiers treating domestic
wastewater, the standard overflow rate at average flow is 800 gallons per day per
square foot. This rate provides sufficient settling time for typical domestic solids while
maintaining reasonable tank sizes. Four hundred gpd/ft² (A) is typically used for
secondary clarifiers in activated sludge systems to prevent sludge blanket rise. Six
hundred gpd/ft² (B) may be used for extended aeration systems but is conservative for
primary treatment. Twelve hundred gpd/ft² (D) would exceed TCEQ standards and likely
result in excessive suspended solids carryover to secondary treatment.
5. The flow to your Texas facility's primary clarifier is 2.0 MGD with an influent TSS of
240 mg/L. The clarifier is 60 feet in diameter. To check if the solids loading rate is within
TCEQ guidelines, you calculate the rate as:
A. 15 lbs/day/ft² (underestimated due to unit conversion error)
B. 22 lbs/day/ft² (acceptable for peak flows only)
C. 28 lbs/day/ft² (correct calculation within TCEQ standards)
D. 45 lbs/day/ft² (exceeds recommended loading rates)
Correct Answer: C
Rationale: C is correct. Solids loading rate = Flow × TSS × 8.34 ÷ Surface Area. Surface
area = π × (30 ft)² = 2,827 ft². Solids loading = 2.0 MGD × 240 mg/L × 8.34
lbs/(MG·mg/L) ÷ 2,827 ft² = 4,003 lbs/day ÷ 2,827 ft² = 28.3 lbs/day/ft². This is within
TCEQ recommended guidelines of 25-30 lbs/day/ft² for primary clarifiers at average
flow. Answer A results from incorrect unit conversion. Answer B represents acceptable
peak flow loadings. Answer D would indicate insufficient clarifier capacity and potential
operational problems requiring immediate attention.
6. During your Texas facility's annual TCEQ inspection, the reviewer notes that your
primary clarifier weir loading rate exceeds standards. Your flow is 3.5 MGD and the weir
length is 150 feet. The calculated weir loading rate is:
A. 12,000 gpd/ft (within acceptable range for small plants)
, B. 18,500 gpd/ft (requires monitoring but not immediate action)
C. 23,333 gpd/ft (exceeds TCEQ recommended maximum of 20,000 gpd/ft)
D. 28,000 gpd/ft (well above standards, requires corrective action)
Correct Answer: C
Rationale: C is correct. Weir loading rate = Flow ÷ Weir Length = 3,500,000 gpd ÷ 150 ft
= 23,333 gpd/ft. TCEQ design standards recommend a maximum weir loading rate of
20,000 gpd/ft for primary clarifiers to prevent excessive velocity gradients that
resuspend settled solids. Rates between 20,000-25,000 gpd/ft (C) exceed
recommendations and may cause deteriorating effluent quality, requiring operational
adjustments or structural modifications. Answer A is appropriate for very small
facilities. Answer B requires increased monitoring. Answer D would create severe
operational problems with significant solids loss and potential permit violations.
7. Your Texas activated sludge plant has a primary clarifier with 35% BOD and 60% TSS
removal efficiency. If the influent BOD is 220 mg/L and TSS is 280 mg/L, the primary
effluent concentrations are:
A. BOD 154 mg/L, TSS 168 mg/L (inverted removal percentages)
B. BOD 198 mg/L, TSS 252 mg/L (calculated removals incorrectly)
C. BOD 143 mg/L, TSS 112 mg/L (correct: 220×0.65 and 280×0.40)
D. BOD 121 mg/L, TSS 84 mg/L (used removal as decimal without subtraction)
Correct Answer: C
Rationale: C is correct. Primary effluent BOD = Influent BOD × (1 - removal efficiency) =
220 mg/L × (1 - 0.35) = 220 × 0.65 = 143 mg/L. Primary effluent TSS = 280 mg/L × (1 -
0.60) = 280 × 0.40 = 112 mg/L. Answer A confuses removal with remaining. Answer B
incorrectly adds removal percentages. Answer D uses removal percentages as
remaining percentages. TCEQ expects operators to understand that standard primary
treatment achieves 30-40% BOD removal and 50-60% TSS removal to protect
downstream biological processes.
8. At your Texas facility, the comminutor (grinder) jams frequently during peak flow
periods. According to TCEQ operational guidelines, the appropriate response is to:
