Texas Wastewater Class A Exam Versions A
and B Official Practice Exam Actual Exam
2026/2027 with Detailed Rationales |
Complete Exam-Style Questions | Pass
Guaranteed – A+ Graded
══════════════════════════════════════
SECTION 1: TREATMENT PROCESSES & PROCESS CONTROL Q1 – Q10
══════════════════════════════════════
Question 1 of 50
A 1.2-MGD extended aeration activated sludge plant has been operating with an MLSS
concentration of 1800 mg/L. The operator notices pin floc in the clarifier and rising sludge
during the last two evening shifts. The plant is designed for nitrification and operates at a
20-day SRT.
A. Increase the MLSS to 2800 mg/L to improve settling
B. Maintain the MLSS between 2500 and 3500 mg/L for extended aeration nitrification ✓
CORRECT
C. Decrease the MLSS to 1200 mg/L to reduce clarifier loading
D. Add ferric chloride to the aeration basin to improve floc density
Correct Answer: B
Rationale: Extended aeration systems are designed to operate at MLSS concentrations
between 2500 and 3500 mg/L to achieve complete nitrification and produce a stable,
well-digested sludge, and the low concentration of 1800 mg/L explains the pin floc and rising
sludge caused by insufficient biomass and premature denitrification in the clarifier. Option A
identifies a value within the correct range but presents it as an arbitrary increase rather than
the established operational target, which could lead an operator to overshoot the upper
design limit. Always verify your plant's approved design basis before making significant
process changes.
Question 2 of 50
,A 0.8-MGD oxidation ditch facility is required to achieve biological nitrogen removal. The
operator has been maintaining a dissolved oxygen concentration of 2.5 mg/L throughout the
entire ditch and is unable to meet the total nitrogen effluent limit of 5 mg/L.
A. Increase the DO setpoint to 4.0 mg/L throughout the ditch to enhance nitrification
B. Add an external carbon source to the ditch to improve denitrification
C. Reduce the SRT to 5 days to promote faster nitrogen uptake
D. Create an anoxic zone by reducing DO to less than 0.5 mg/L in select rotor-off sections ✓
CORRECT
Correct Answer: D
Rationale: Biological nitrogen removal requires both aerobic conditions for nitrification and
anoxic conditions for denitrification, and oxidation ditches achieve this by alternating rotor
operation to create zones with DO below 0.5 mg/L where denitrification can occur. Option A
is incorrect because maintaining high DO throughout the entire ditch prevents denitrification
from occurring, which is why the total nitrogen limit cannot be met. In practice, oxidation
ditch operators typically use timers or variable-speed rotors to establish predictable anoxic
zones without sacrificing nitrification capacity.
Question 3 of 50
A trickling filter treating 0.1 MGD of municipal wastewater has a media depth of 6 feet and a
diameter of 60 feet. The plant superintendent asks the operator to evaluate whether the filter
is operating within TCEQ design guidelines for a high-rate application.
A. The hydraulic loading is approximately 1.6 MGD per acre and the unit is underloaded for
high-rate operation ✓ CORRECT
B. The hydraulic loading is approximately 3.2 MGD per acre and the unit meets high-rate
design criteria
C. The hydraulic loading is approximately 0.8 MGD per acre and the unit is overloaded for
standard-rate operation
D. The hydraulic loading is approximately 4.5 MGD per acre and recirculation should be
increased
Correct Answer: A
Rationale: The filter surface area is 2,827 square feet or 0.065 acres, yielding a hydraulic
loading of approximately 1.6 MGD per acre, which falls well below the 10 to 30 MGD per acre
typically required for high-rate trickling filter operation under TCEQ design standards. Option
B nearly doubles the actual loading calculation and would incorrectly classify this
standard-rate unit as a high-rate filter. Always verify your total applied flow including
recirculation when classifying trickling filter hydraulic loading rates.
Question 4 of 50
, A rotating biological contactor installation consists of four stages in series treating 0.4 MGD
of domestic wastewater with an influent BOD5 of 220 mg/L. The first stage shafts are
covered with a heavy gray slime and the operator reports a strong rotten-egg odor near the
covers.
A. Increase the rotational speed to 3 rpm to shear off excess biomass
B. Add sodium hydroxide to the first stage to raise the pH above 8.5
C. Reduce the organic loading to the first stage by adding a baffle or increasing the number of
shafts ✓ CORRECT
D. Decrease the influent BOD5 by routing raw wastewater around the RBC units
Correct Answer: C
Rationale: RBC first stages are typically designed for an organic loading of 25 to 30 pounds of
BOD5 per 1000 square feet per day, and excessive loading causes heavy biomass growth, gray
slime, and anaerobic conditions that produce hydrogen sulfide odors. Option A would strip
biomass but does not address the root cause of organic overloading, and increasing speed
beyond manufacturer specifications can damage shafts and bearings. In practice, RBC
installations should be designed with sufficient first-stage surface area or staging to keep
organic loading within manufacturer and TCEQ guidelines.
Question 5 of 50
An anaerobic digester at a 2.5-MGD conventional activated sludge plant has been
experiencing foaming and elevated gas production. The laboratory reports volatile acids of
1200 mg/L and total alkalinity of 3500 mg/L as CaCO3.
A. The VA/Alk ratio of 0.20 indicates the digester is operating normally and no action is
needed
B. The VA/Alk ratio of 0.34 indicates potential process instability and pH buffering capacity
should be monitored closely ✓ CORRECT
C. The VA/Alk ratio of 0.50 indicates imminent digester failure and lime must be added
immediately
D. The VA/Alk ratio of 0.15 indicates the digester is underloaded and more primary sludge
should be added
Correct Answer: B
Rationale: The volatile acids to alkalinity ratio is calculated by dividing 1200 mg/L by 3500
mg/L to yield 0.34, and TCEQ operational guidelines indicate that ratios above 0.3 signal
potential process instability even when pH remains near neutral due to adequate buffering.
Option A uses an incorrect calculation and would lead an operator to ignore a developing
imbalance that could progress to souring if organic loading increases or temperature drops.
Experienced operators monitor this ratio weekly because it provides an early warning of
digester stress before pH begins to fall.
and B Official Practice Exam Actual Exam
2026/2027 with Detailed Rationales |
Complete Exam-Style Questions | Pass
Guaranteed – A+ Graded
══════════════════════════════════════
SECTION 1: TREATMENT PROCESSES & PROCESS CONTROL Q1 – Q10
══════════════════════════════════════
Question 1 of 50
A 1.2-MGD extended aeration activated sludge plant has been operating with an MLSS
concentration of 1800 mg/L. The operator notices pin floc in the clarifier and rising sludge
during the last two evening shifts. The plant is designed for nitrification and operates at a
20-day SRT.
A. Increase the MLSS to 2800 mg/L to improve settling
B. Maintain the MLSS between 2500 and 3500 mg/L for extended aeration nitrification ✓
CORRECT
C. Decrease the MLSS to 1200 mg/L to reduce clarifier loading
D. Add ferric chloride to the aeration basin to improve floc density
Correct Answer: B
Rationale: Extended aeration systems are designed to operate at MLSS concentrations
between 2500 and 3500 mg/L to achieve complete nitrification and produce a stable,
well-digested sludge, and the low concentration of 1800 mg/L explains the pin floc and rising
sludge caused by insufficient biomass and premature denitrification in the clarifier. Option A
identifies a value within the correct range but presents it as an arbitrary increase rather than
the established operational target, which could lead an operator to overshoot the upper
design limit. Always verify your plant's approved design basis before making significant
process changes.
Question 2 of 50
,A 0.8-MGD oxidation ditch facility is required to achieve biological nitrogen removal. The
operator has been maintaining a dissolved oxygen concentration of 2.5 mg/L throughout the
entire ditch and is unable to meet the total nitrogen effluent limit of 5 mg/L.
A. Increase the DO setpoint to 4.0 mg/L throughout the ditch to enhance nitrification
B. Add an external carbon source to the ditch to improve denitrification
C. Reduce the SRT to 5 days to promote faster nitrogen uptake
D. Create an anoxic zone by reducing DO to less than 0.5 mg/L in select rotor-off sections ✓
CORRECT
Correct Answer: D
Rationale: Biological nitrogen removal requires both aerobic conditions for nitrification and
anoxic conditions for denitrification, and oxidation ditches achieve this by alternating rotor
operation to create zones with DO below 0.5 mg/L where denitrification can occur. Option A
is incorrect because maintaining high DO throughout the entire ditch prevents denitrification
from occurring, which is why the total nitrogen limit cannot be met. In practice, oxidation
ditch operators typically use timers or variable-speed rotors to establish predictable anoxic
zones without sacrificing nitrification capacity.
Question 3 of 50
A trickling filter treating 0.1 MGD of municipal wastewater has a media depth of 6 feet and a
diameter of 60 feet. The plant superintendent asks the operator to evaluate whether the filter
is operating within TCEQ design guidelines for a high-rate application.
A. The hydraulic loading is approximately 1.6 MGD per acre and the unit is underloaded for
high-rate operation ✓ CORRECT
B. The hydraulic loading is approximately 3.2 MGD per acre and the unit meets high-rate
design criteria
C. The hydraulic loading is approximately 0.8 MGD per acre and the unit is overloaded for
standard-rate operation
D. The hydraulic loading is approximately 4.5 MGD per acre and recirculation should be
increased
Correct Answer: A
Rationale: The filter surface area is 2,827 square feet or 0.065 acres, yielding a hydraulic
loading of approximately 1.6 MGD per acre, which falls well below the 10 to 30 MGD per acre
typically required for high-rate trickling filter operation under TCEQ design standards. Option
B nearly doubles the actual loading calculation and would incorrectly classify this
standard-rate unit as a high-rate filter. Always verify your total applied flow including
recirculation when classifying trickling filter hydraulic loading rates.
Question 4 of 50
, A rotating biological contactor installation consists of four stages in series treating 0.4 MGD
of domestic wastewater with an influent BOD5 of 220 mg/L. The first stage shafts are
covered with a heavy gray slime and the operator reports a strong rotten-egg odor near the
covers.
A. Increase the rotational speed to 3 rpm to shear off excess biomass
B. Add sodium hydroxide to the first stage to raise the pH above 8.5
C. Reduce the organic loading to the first stage by adding a baffle or increasing the number of
shafts ✓ CORRECT
D. Decrease the influent BOD5 by routing raw wastewater around the RBC units
Correct Answer: C
Rationale: RBC first stages are typically designed for an organic loading of 25 to 30 pounds of
BOD5 per 1000 square feet per day, and excessive loading causes heavy biomass growth, gray
slime, and anaerobic conditions that produce hydrogen sulfide odors. Option A would strip
biomass but does not address the root cause of organic overloading, and increasing speed
beyond manufacturer specifications can damage shafts and bearings. In practice, RBC
installations should be designed with sufficient first-stage surface area or staging to keep
organic loading within manufacturer and TCEQ guidelines.
Question 5 of 50
An anaerobic digester at a 2.5-MGD conventional activated sludge plant has been
experiencing foaming and elevated gas production. The laboratory reports volatile acids of
1200 mg/L and total alkalinity of 3500 mg/L as CaCO3.
A. The VA/Alk ratio of 0.20 indicates the digester is operating normally and no action is
needed
B. The VA/Alk ratio of 0.34 indicates potential process instability and pH buffering capacity
should be monitored closely ✓ CORRECT
C. The VA/Alk ratio of 0.50 indicates imminent digester failure and lime must be added
immediately
D. The VA/Alk ratio of 0.15 indicates the digester is underloaded and more primary sludge
should be added
Correct Answer: B
Rationale: The volatile acids to alkalinity ratio is calculated by dividing 1200 mg/L by 3500
mg/L to yield 0.34, and TCEQ operational guidelines indicate that ratios above 0.3 signal
potential process instability even when pH remains near neutral due to adequate buffering.
Option A uses an incorrect calculation and would lead an operator to ignore a developing
imbalance that could progress to souring if organic loading increases or temperature drops.
Experienced operators monitor this ratio weekly because it provides an early warning of
digester stress before pH begins to fall.
