1
TEXAS WASTEWATER CLASS D 2026/2027
ACTUAL EXAM Complete Certification Exam |
Questions & Verified Answers | TCEQ
Wastewater License Prep
Section 1: Wastewater Treatment Processes
Q1: The primary purpose of primary treatment in a wastewater plant is to:
A. Remove dissolved organic matter using bacteria.
B. Remove settleable solids and floating materials.
C. Disinfect the effluent with chlorine or UV.
D. Remove nutrients like nitrogen and phosphorus.
Answer: B
Verified Rationale: Primary treatment relies on physical processes such as sedimentation and
skimming to remove settleable solids and floatables before biological treatment begins.
Q2: In the activated sludge process, the mixed liquor suspended solids (MLSS) are primarily:
A. Inert inorganic particles
B. A mixture of microorganisms and organic matter actively treating wastewater
C. Chemical coagulants added for phosphorus removal
D. Grit and sand from preliminary treatment
Answer: B
Verified Rationale: MLSS is the concentration of active microorganisms and organic material in
the aeration tank that metabolizes pollutants.
Q3: Which secondary treatment technology uses a rotating biological contactor (RBC)?
A. Trickling filter
B. Activated sludge
C. Fixed-film reactor
D. Oxidation ditch
Answer: C
Verified Rationale: An RBC is a fixed-film process where biofilm on rotating disks treats
wastewater as it turns.
,2
Q4: Tertiary treatment is primarily implemented to:
A. Reduce biochemical oxygen demand to zero
B. Remove residual suspended solids and nutrients
C. Eliminate the need for disinfection
D. Replace secondary clarifiers
Answer: B
Verified Rationale: Tertiary steps such as filtration and chemical precipitation polish effluent by
removing nutrients and remaining solids.
Q5: A lagoon system achieves treatment mainly through:
A. High-rate anaerobic digestion
B. Natural biological and physical processes over long detention times
C. Chemical coagulation and flocculation
D. Membrane bioreactor filtration
Answer: B
Verified Rationale: Lagoons use extended detention and natural microbial activity to stabilize
wastewater without intensive mechanical equipment.
Q6: Which parameter best indicates the organic strength of incoming raw wastewater?
A. pH
B. Total suspended solids
C. BOD5
D. Chlorine residual
Answer: C
Verified Rationale: Five-day biochemical oxygen demand (BOD5) quantifies the biodegradable
organic load entering the plant.
Q7: In a trickling filter, the microbial growth that attaches to the media is called:
A. Zoogloea
B. Biofilm
C. Floc
D. Sludge blanket
Answer: B
Verified Rationale: Microorganisms form a biofilm on the filter media that degrades pollutants as
wastewater flows past.
Q8: The main purpose of recirculation in a trickling filter is to:
A. Increase chlorine demand
B. Distribute flow and maintain moist media
, 3
C. Reduce primary clarifier loading
D. Eliminate sludge production
Answer: B
Verified Rationale: Recirculation wets the biofilm, dilutes incoming BOD, and improves oxygen
transfer.
Q9: Which process upgrade would most effectively enhance nitrogen removal?
A. Add alum feed
B. Implement nitrification/denitrification zones
C. Increase chlorine dose
D. Install a gravity thickener
Answer: B
Verified Rationale: Separate aerobic and anoxic zones promote nitrification followed by
denitrification that converts nitrate to nitrogen gas.
Q10: A high sludge volume index (SVI) above 200 mL/g typically signals:
A. Excellent settling sludge
B. Potential bulking or poor settleability
C. Low organic loading
D. Complete nitrification
Answer: B
Verified Rationale: Elevated SVI indicates bulky or filamentous sludge that settles poorly and
can carry over the weir.
Section 2: Safety Procedures
Q11: Before entering a permit-required confined space, the operator must first:
A. Ventilate for 5 min only
B. Complete atmospheric testing and secure an entry permit
C. Spray deodorizing chemicals
D. Notify the fire department
Answer: B
Verified Rationale: OSHA 1910.146 mandates pre-entry atmospheric monitoring and a signed
permit for worker safety.
Q12: Hydrogen sulfide (H2S) at 100 ppm is considered:
A. Immediately dangerous to life and health (IDLH)
B. Below the OSHA 8-hr TWA
C. A mild odor nuisance
D. Safe for short exposure without PPE
TEXAS WASTEWATER CLASS D 2026/2027
ACTUAL EXAM Complete Certification Exam |
Questions & Verified Answers | TCEQ
Wastewater License Prep
Section 1: Wastewater Treatment Processes
Q1: The primary purpose of primary treatment in a wastewater plant is to:
A. Remove dissolved organic matter using bacteria.
B. Remove settleable solids and floating materials.
C. Disinfect the effluent with chlorine or UV.
D. Remove nutrients like nitrogen and phosphorus.
Answer: B
Verified Rationale: Primary treatment relies on physical processes such as sedimentation and
skimming to remove settleable solids and floatables before biological treatment begins.
Q2: In the activated sludge process, the mixed liquor suspended solids (MLSS) are primarily:
A. Inert inorganic particles
B. A mixture of microorganisms and organic matter actively treating wastewater
C. Chemical coagulants added for phosphorus removal
D. Grit and sand from preliminary treatment
Answer: B
Verified Rationale: MLSS is the concentration of active microorganisms and organic material in
the aeration tank that metabolizes pollutants.
Q3: Which secondary treatment technology uses a rotating biological contactor (RBC)?
A. Trickling filter
B. Activated sludge
C. Fixed-film reactor
D. Oxidation ditch
Answer: C
Verified Rationale: An RBC is a fixed-film process where biofilm on rotating disks treats
wastewater as it turns.
,2
Q4: Tertiary treatment is primarily implemented to:
A. Reduce biochemical oxygen demand to zero
B. Remove residual suspended solids and nutrients
C. Eliminate the need for disinfection
D. Replace secondary clarifiers
Answer: B
Verified Rationale: Tertiary steps such as filtration and chemical precipitation polish effluent by
removing nutrients and remaining solids.
Q5: A lagoon system achieves treatment mainly through:
A. High-rate anaerobic digestion
B. Natural biological and physical processes over long detention times
C. Chemical coagulation and flocculation
D. Membrane bioreactor filtration
Answer: B
Verified Rationale: Lagoons use extended detention and natural microbial activity to stabilize
wastewater without intensive mechanical equipment.
Q6: Which parameter best indicates the organic strength of incoming raw wastewater?
A. pH
B. Total suspended solids
C. BOD5
D. Chlorine residual
Answer: C
Verified Rationale: Five-day biochemical oxygen demand (BOD5) quantifies the biodegradable
organic load entering the plant.
Q7: In a trickling filter, the microbial growth that attaches to the media is called:
A. Zoogloea
B. Biofilm
C. Floc
D. Sludge blanket
Answer: B
Verified Rationale: Microorganisms form a biofilm on the filter media that degrades pollutants as
wastewater flows past.
Q8: The main purpose of recirculation in a trickling filter is to:
A. Increase chlorine demand
B. Distribute flow and maintain moist media
, 3
C. Reduce primary clarifier loading
D. Eliminate sludge production
Answer: B
Verified Rationale: Recirculation wets the biofilm, dilutes incoming BOD, and improves oxygen
transfer.
Q9: Which process upgrade would most effectively enhance nitrogen removal?
A. Add alum feed
B. Implement nitrification/denitrification zones
C. Increase chlorine dose
D. Install a gravity thickener
Answer: B
Verified Rationale: Separate aerobic and anoxic zones promote nitrification followed by
denitrification that converts nitrate to nitrogen gas.
Q10: A high sludge volume index (SVI) above 200 mL/g typically signals:
A. Excellent settling sludge
B. Potential bulking or poor settleability
C. Low organic loading
D. Complete nitrification
Answer: B
Verified Rationale: Elevated SVI indicates bulky or filamentous sludge that settles poorly and
can carry over the weir.
Section 2: Safety Procedures
Q11: Before entering a permit-required confined space, the operator must first:
A. Ventilate for 5 min only
B. Complete atmospheric testing and secure an entry permit
C. Spray deodorizing chemicals
D. Notify the fire department
Answer: B
Verified Rationale: OSHA 1910.146 mandates pre-entry atmospheric monitoring and a signed
permit for worker safety.
Q12: Hydrogen sulfide (H2S) at 100 ppm is considered:
A. Immediately dangerous to life and health (IDLH)
B. Below the OSHA 8-hr TWA
C. A mild odor nuisance
D. Safe for short exposure without PPE
