Licensing Exam Practice Test Questions

Sewage Treatment Operator Class I Licensing Exam Practice Test Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of preliminary treatment in a sewage

treatment plant?

• Remove dissolved solids
• Remove pathogens
• Remove large debris and grit
• Remove nutrients

Rationale: Preliminary treatment focuses on screening and grit removal to

protect downstream equipment.

• What is the typical pH range for biological wastewater treatment? 1 / 4

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:

• Colloidal solids
• Settleable solids
• Dissolved solids
• Nutrient solids

Rationale: Primary clarifiers mainly remove solids that can settle by

gravity.

• The activated sludge process relies primarily on which biological group?
• Viruses
• Algae
• Bacteria
• Protozoa

Rationale: Bacteria perform the majority of organic matter breakdown in

activated sludge. 2 / 4

5. Sludge age is defined as:

• The time sludge spends in the digester
• The average time microorganisms remain in the system
• The age of solids removed daily
• The time between wasting events

Rationale: Sludge age (SRT) measures how long biomass stays in the

system, controlling treatment efficiency.

• What does BOD measure?
• Nitrogen concentration
• Organic strength of wastewater
• Suspended solids
• Pathogen concentration

Rationale: BOD indicates how much oxygen microorganisms need to break

down organics.

7. A high F/M ratio typically causes:

• Bulking sludge
• Low DO
• Young sludge with rapid bacterial growth
• Old sludge with nitrification 3 / 4

Rationale: High food-to-microorganism ratio results in fast-growing, young

biomass.

• What is the purpose of an aeration basin?
• Reduce pH
• Remove grit
• Provide oxygen for biological treatment
• Remove heavy metals

Rationale: Aeration supplies oxygen needed to support aerobic

microorganisms.

9. Chlorination is primarily used to:

• Remove BOD
• Remove solids
• Disinfect treated water
• Reduce nutrients

Rationale: Chlorine disinfects effluent by killing pathogens.

10. A sludge that settles too slowly in the secondary clarifier is called:

• Flocculent sludge
• Bulking sludge
• / 4