TEXAS WASTEWATER OPERATOR
LICENSING LEVEL III QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS)
PLUS RATIONALES 2026 Q&A | INSTANT
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1. What is the primary purpose of secondary treatment in wastewater
processing?
A. Remove grit
B. Remove pathogens
C. Stabilize organic matter
D. Remove heavy metals
Answer: C
Secondary treatment focuses on biological stabilization of organic
material.
2. What is the typical dissolved oxygen (DO) range for a conventional
activated sludge aeration basin?
A. 0.5–1.0 mg/L
B. 1.5–2.0 mg/L
C. 2.0–4.0 mg/L
D. 4.0–7.0 mg/L
Answer: C
Maintaining 2–4 mg/L DO ensures proper microbial activity.
,3. What does F/M ratio represent in an activated sludge system?
A. Flow to mass
B. Food to microorganism ratio
C. Final to mixed liquor
D. Filtration to membrane
Answer: B
F/M measures the amount of organic food relative to microbial mass.
4. A high sludge volume index (SVI) usually indicates:
A. Good settling
B. Bulking sludge
C. Strong influent
D. Excess aeration
Answer: B
High SVI indicates filamentous bulking and poor settling.
5. What organism type usually dominates extended aeration plants?
A. Filamentous bacteria
B. Free-swimming ciliates
C. Amoebas
D. Rotifers
Answer: D
Rotifers thrive in older, stable sludge conditions.
6. Chlorine reacts with ammonia to form:
A. Free chlorine
B. Chloramines
,C. Hypochlorous acid
D. Chloride
Answer: B
Chlorine + ammonia → chloramines, used in disinfection.
7. The primary purpose of grit removal is:
A. Odor reduction
B. Equipment protection
C. Pathogen removal
D. Solids stabilization
Answer: B
Grit removal protects pumps and mechanical equipment from abrasion.
8. Sludge bulking is often caused by:
A. Low F/M ratio
B. High chlorine feed
C. High DO
D. Excessive wasting
Answer: A
Low F/M favors filamentous growth leading to bulking.
9. Which parameter most affects settling in the secondary clarifier?
A. Temperature
B. BOD concentration
C. SVI
D. pH
, Answer: C
SVI indicates how well sludge settles.
10. A sludge age that is too low will usually result in:
A. High DO
B. High MLSS
C. Poor settling
D. Thick sludge blanket
Answer: C
Young sludge settles poorly due to excess dispersed organisms.
11. The purpose of tertiary filtration is to remove:
A. Dissolved solids
B. Nutrients
C. Suspended solids
D. Grit
Answer: C
Tertiary filters polish effluent by removing suspended solids.
12. The primary byproduct of anaerobic digestion is:
A. Methane
B. Carbon monoxide
C. Nitrogen
D. Ozone
Answer: A
Methane is the main gas produced in anaerobic digestion.
LICENSING LEVEL III QUESTIONS AND
CORRECT ANSWERS (VERIFIED ANSWERS)
PLUS RATIONALES 2026 Q&A | INSTANT
DOWNLOAD PDF
1. What is the primary purpose of secondary treatment in wastewater
processing?
A. Remove grit
B. Remove pathogens
C. Stabilize organic matter
D. Remove heavy metals
Answer: C
Secondary treatment focuses on biological stabilization of organic
material.
2. What is the typical dissolved oxygen (DO) range for a conventional
activated sludge aeration basin?
A. 0.5–1.0 mg/L
B. 1.5–2.0 mg/L
C. 2.0–4.0 mg/L
D. 4.0–7.0 mg/L
Answer: C
Maintaining 2–4 mg/L DO ensures proper microbial activity.
,3. What does F/M ratio represent in an activated sludge system?
A. Flow to mass
B. Food to microorganism ratio
C. Final to mixed liquor
D. Filtration to membrane
Answer: B
F/M measures the amount of organic food relative to microbial mass.
4. A high sludge volume index (SVI) usually indicates:
A. Good settling
B. Bulking sludge
C. Strong influent
D. Excess aeration
Answer: B
High SVI indicates filamentous bulking and poor settling.
5. What organism type usually dominates extended aeration plants?
A. Filamentous bacteria
B. Free-swimming ciliates
C. Amoebas
D. Rotifers
Answer: D
Rotifers thrive in older, stable sludge conditions.
6. Chlorine reacts with ammonia to form:
A. Free chlorine
B. Chloramines
,C. Hypochlorous acid
D. Chloride
Answer: B
Chlorine + ammonia → chloramines, used in disinfection.
7. The primary purpose of grit removal is:
A. Odor reduction
B. Equipment protection
C. Pathogen removal
D. Solids stabilization
Answer: B
Grit removal protects pumps and mechanical equipment from abrasion.
8. Sludge bulking is often caused by:
A. Low F/M ratio
B. High chlorine feed
C. High DO
D. Excessive wasting
Answer: A
Low F/M favors filamentous growth leading to bulking.
9. Which parameter most affects settling in the secondary clarifier?
A. Temperature
B. BOD concentration
C. SVI
D. pH
, Answer: C
SVI indicates how well sludge settles.
10. A sludge age that is too low will usually result in:
A. High DO
B. High MLSS
C. Poor settling
D. Thick sludge blanket
Answer: C
Young sludge settles poorly due to excess dispersed organisms.
11. The purpose of tertiary filtration is to remove:
A. Dissolved solids
B. Nutrients
C. Suspended solids
D. Grit
Answer: C
Tertiary filters polish effluent by removing suspended solids.
12. The primary byproduct of anaerobic digestion is:
A. Methane
B. Carbon monoxide
C. Nitrogen
D. Ozone
Answer: A
Methane is the main gas produced in anaerobic digestion.
