Sewage Treatment Operator Class I
Licensing Exam Practice Test Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
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1. What is the primary purpose of preliminary treatment in a sewage
treatment plant?
A. Remove dissolved solids
B. Remove pathogens
C. Remove large debris and grit
D. Remove nutrients
Rationale: Preliminary treatment focuses on screening and grit removal to
protect downstream equipment.
2. What is the typical pH range for biological wastewater treatment?
,A. 4–5
B. 5–6
C. 6.5–8.5
D. 8.5–10
Rationale: Most microorganisms in activated sludge processes thrive in a
neutral to slightly alkaline pH.
3. In primary clarification, most of the solids removed are:
A. Colloidal solids
B. Settleable solids
C. Dissolved solids
D. Nutrient solids
Rationale: Primary clarifiers mainly remove solids that can settle by
gravity.
4. The activated sludge process relies primarily on which biological group?
A. Viruses
B. Algae
C. Bacteria
D. Protozoa
Rationale: Bacteria perform the majority of organic matter breakdown in
activated sludge.
,5. Sludge age is defined as:
A. The time sludge spends in the digester
B. The average time microorganisms remain in the system
C. The age of solids removed daily
D. The time between wasting events
Rationale: Sludge age (SRT) measures how long biomass stays in the
system, controlling treatment efficiency.
6. What does BOD measure?
A. Nitrogen concentration
B. Organic strength of wastewater
C. Suspended solids
D. Pathogen concentration
Rationale: BOD indicates how much oxygen microorganisms need to break
down organics.
7. A high F/M ratio typically causes:
A. Bulking sludge
B. Low DO
C. Young sludge with rapid bacterial growth
D. Old sludge with nitrification
, Rationale: High food-to-microorganism ratio results in fast-growing, young
biomass.
8. What is the purpose of an aeration basin?
A. Reduce pH
B. Remove grit
C. Provide oxygen for biological treatment
D. Remove heavy metals
Rationale: Aeration supplies oxygen needed to support aerobic
microorganisms.
9. Chlorination is primarily used to:
A. Remove BOD
B. Remove solids
C. Disinfect treated water
D. Reduce nutrients
Rationale: Chlorine disinfects effluent by killing pathogens.
10. A sludge that settles too slowly in the secondary clarifier is called:
A. Flocculent sludge
B. Bulking sludge
Licensing Exam Practice Test Questions
And Correct Answers (Verified Answers)
Plus Rationales 2026 Q&A | Instant
Download Pdf
1. What is the primary purpose of preliminary treatment in a sewage
treatment plant?
A. Remove dissolved solids
B. Remove pathogens
C. Remove large debris and grit
D. Remove nutrients
Rationale: Preliminary treatment focuses on screening and grit removal to
protect downstream equipment.
2. What is the typical pH range for biological wastewater treatment?
,A. 4–5
B. 5–6
C. 6.5–8.5
D. 8.5–10
Rationale: Most microorganisms in activated sludge processes thrive in a
neutral to slightly alkaline pH.
3. In primary clarification, most of the solids removed are:
A. Colloidal solids
B. Settleable solids
C. Dissolved solids
D. Nutrient solids
Rationale: Primary clarifiers mainly remove solids that can settle by
gravity.
4. The activated sludge process relies primarily on which biological group?
A. Viruses
B. Algae
C. Bacteria
D. Protozoa
Rationale: Bacteria perform the majority of organic matter breakdown in
activated sludge.
,5. Sludge age is defined as:
A. The time sludge spends in the digester
B. The average time microorganisms remain in the system
C. The age of solids removed daily
D. The time between wasting events
Rationale: Sludge age (SRT) measures how long biomass stays in the
system, controlling treatment efficiency.
6. What does BOD measure?
A. Nitrogen concentration
B. Organic strength of wastewater
C. Suspended solids
D. Pathogen concentration
Rationale: BOD indicates how much oxygen microorganisms need to break
down organics.
7. A high F/M ratio typically causes:
A. Bulking sludge
B. Low DO
C. Young sludge with rapid bacterial growth
D. Old sludge with nitrification
, Rationale: High food-to-microorganism ratio results in fast-growing, young
biomass.
8. What is the purpose of an aeration basin?
A. Reduce pH
B. Remove grit
C. Provide oxygen for biological treatment
D. Remove heavy metals
Rationale: Aeration supplies oxygen needed to support aerobic
microorganisms.
9. Chlorination is primarily used to:
A. Remove BOD
B. Remove solids
C. Disinfect treated water
D. Reduce nutrients
Rationale: Chlorine disinfects effluent by killing pathogens.
10. A sludge that settles too slowly in the secondary clarifier is called:
A. Flocculent sludge
B. Bulking sludge
