2025 Texas Wastewater Class A Exam
Full Versions A & B with Certified
Solutions Already Graded A
Introduction
This study guide is tailored for the 2025 Texas Wastewater Class A Exam, covering Versions
A and B. It includes 100 carefully selected questions with detailed, verified answers to en-
sure comprehensive preparation. The content aligns with Texas Commission on Environmental
Quality (TCEQ) standards, focusing on wastewater treatment processes, equipment, safety,
regulations, and calculations. Unnecessary jargon is minimized to enhance clarity and study
efficiency. This 60-page document is designed to provide all necessary knowledge for success.
1 Questions and Answers
1. When is seeding of BOD samples necessary?
• Answer: Seeding is required for samples with chlorine residual, previously chlo-
rinated samples, those subjected to high temperatures, or containing high/low pH
industrial wastes. Seeding introduces microorganisms to ensure accurate biochem-
ical oxygen demand (BOD) measurements, as these conditions may inhibit natural
microbial activity. The process involves adding a known volume of microbial cul-
ture to the sample.
2. When is blue-green algae most dominant in a pond treatment system?
• Answer: Blue-green algae dominate in summer due to warmer temperatures (above
20řC) and increased sunlight, which promote photosynthesis and growth. In wastew-
ater stabilization ponds, this can lead to oxygen production during the day but may
cause odors if algae die off.
3. A 30-inch diameter wastewater interceptor is flowing half-full at 2 fps. What is the
approximate volume of wastewater flow?
• Answer: Approximately 2,200 gallons per minute (gpm). Calculation: For a half-
full pipe, the cross-sectional area is 0.5 × π × (1.25)2 = 2.45 ft2 . Flow rate: 2.45 ×
2 = 4.9 cfs. Convert to gpm: 4.9 × 449 = 2, 200 gpm.
4. A one-cylinder reciprocating sludge pump with a 10-inch bore and a 5-inch stroke
pumps at 50 cycles per minute. How long to pump 5,000 gallons of sludge?
1
, • Answer: Approximately 60 minutes. Calculation: Cylinder volume = π×(5/12)2 ×
(5/12) = 0.227 ft3 . At 50 cycles/min, flow rate = 0.227 × 50 × 7.48 = 84.5 gpm.
Time = 5, 000 ÷ 84.5 ≈ 59.2 min, rounded to 60.
5. If a centrifugal pump motor is replaced with one 25% faster, by what factor does
horsepower increase?
• Answer: 1.95 times. Horsepower varies with the cube of speed: (1.25)3 = 1.953.
This reflects the increased energy required for higher rotational speed.
6. When must TCEQ be notified about treatment facility expansions?
• Answer: Before construction begins. Per 30 TAC Chapter 305, TCEQ requires
submission of detailed engineering plans for approval to ensure compliance with
environmental regulations.
7. What is the typical gas composition in an anaerobic digester?
• Answer: Approximately 6570% methane, 2530% carbon dioxide, with trace amounts
of hydrogen sulfide and other gases. This composition supports energy recovery
and requires careful monitoring for safety.
8. What is the minimum temperature for an anaerobic digester?
• Answer: 95řF (35řC). This ensures optimal mesophilic bacterial activity for effi-
cient digestion of organic matter.
9. What wastewater treatment process operates in the endogenous bacteria growth
phase?
• Answer: Extended aeration. Low organic loading forces bacteria to metabolize
their own cell mass, reducing sludge production.
10. Why is recirculation needed in a trickling filter?
• Answer: Recirculation keeps the media wet, further reduces BOD, controls pond-
ing, and minimizes filter flies. It ensures consistent microbial activity and prevents
drying of the biofilm.
11. What type of fire extinguisher is used for a de-energized electrical control panel?
• Answer: Class A or Class C. Class A extinguishers handle ordinary combustibles,
while Class C is safe for electrical equipment when de-energized, preventing re-
ignition risks.
12. At what pH is chlorine disinfection most effective?
• Answer: pH 6.07.0. At this range, chlorine exists primarily as hypochlorous acid
(HOCl), which is highly effective at killing pathogens.
13. What is the appearance of biomass on a normally functioning RBC?
• Answer: Grey to brown, 0.050.1 inch thick. This indicates a healthy, active micro-
bial film degrading organic matter efficiently.
14. What percent solids should sludge from a primary clarifier contain?
2
Full Versions A & B with Certified
Solutions Already Graded A
Introduction
This study guide is tailored for the 2025 Texas Wastewater Class A Exam, covering Versions
A and B. It includes 100 carefully selected questions with detailed, verified answers to en-
sure comprehensive preparation. The content aligns with Texas Commission on Environmental
Quality (TCEQ) standards, focusing on wastewater treatment processes, equipment, safety,
regulations, and calculations. Unnecessary jargon is minimized to enhance clarity and study
efficiency. This 60-page document is designed to provide all necessary knowledge for success.
1 Questions and Answers
1. When is seeding of BOD samples necessary?
• Answer: Seeding is required for samples with chlorine residual, previously chlo-
rinated samples, those subjected to high temperatures, or containing high/low pH
industrial wastes. Seeding introduces microorganisms to ensure accurate biochem-
ical oxygen demand (BOD) measurements, as these conditions may inhibit natural
microbial activity. The process involves adding a known volume of microbial cul-
ture to the sample.
2. When is blue-green algae most dominant in a pond treatment system?
• Answer: Blue-green algae dominate in summer due to warmer temperatures (above
20řC) and increased sunlight, which promote photosynthesis and growth. In wastew-
ater stabilization ponds, this can lead to oxygen production during the day but may
cause odors if algae die off.
3. A 30-inch diameter wastewater interceptor is flowing half-full at 2 fps. What is the
approximate volume of wastewater flow?
• Answer: Approximately 2,200 gallons per minute (gpm). Calculation: For a half-
full pipe, the cross-sectional area is 0.5 × π × (1.25)2 = 2.45 ft2 . Flow rate: 2.45 ×
2 = 4.9 cfs. Convert to gpm: 4.9 × 449 = 2, 200 gpm.
4. A one-cylinder reciprocating sludge pump with a 10-inch bore and a 5-inch stroke
pumps at 50 cycles per minute. How long to pump 5,000 gallons of sludge?
1
, • Answer: Approximately 60 minutes. Calculation: Cylinder volume = π×(5/12)2 ×
(5/12) = 0.227 ft3 . At 50 cycles/min, flow rate = 0.227 × 50 × 7.48 = 84.5 gpm.
Time = 5, 000 ÷ 84.5 ≈ 59.2 min, rounded to 60.
5. If a centrifugal pump motor is replaced with one 25% faster, by what factor does
horsepower increase?
• Answer: 1.95 times. Horsepower varies with the cube of speed: (1.25)3 = 1.953.
This reflects the increased energy required for higher rotational speed.
6. When must TCEQ be notified about treatment facility expansions?
• Answer: Before construction begins. Per 30 TAC Chapter 305, TCEQ requires
submission of detailed engineering plans for approval to ensure compliance with
environmental regulations.
7. What is the typical gas composition in an anaerobic digester?
• Answer: Approximately 6570% methane, 2530% carbon dioxide, with trace amounts
of hydrogen sulfide and other gases. This composition supports energy recovery
and requires careful monitoring for safety.
8. What is the minimum temperature for an anaerobic digester?
• Answer: 95řF (35řC). This ensures optimal mesophilic bacterial activity for effi-
cient digestion of organic matter.
9. What wastewater treatment process operates in the endogenous bacteria growth
phase?
• Answer: Extended aeration. Low organic loading forces bacteria to metabolize
their own cell mass, reducing sludge production.
10. Why is recirculation needed in a trickling filter?
• Answer: Recirculation keeps the media wet, further reduces BOD, controls pond-
ing, and minimizes filter flies. It ensures consistent microbial activity and prevents
drying of the biofilm.
11. What type of fire extinguisher is used for a de-energized electrical control panel?
• Answer: Class A or Class C. Class A extinguishers handle ordinary combustibles,
while Class C is safe for electrical equipment when de-energized, preventing re-
ignition risks.
12. At what pH is chlorine disinfection most effective?
• Answer: pH 6.07.0. At this range, chlorine exists primarily as hypochlorous acid
(HOCl), which is highly effective at killing pathogens.
13. What is the appearance of biomass on a normally functioning RBC?
• Answer: Grey to brown, 0.050.1 inch thick. This indicates a healthy, active micro-
bial film degrading organic matter efficiently.
14. What percent solids should sludge from a primary clarifier contain?
2
