Licensing Exam Practice Questions And

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

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

plant?

• Remove nitrogen
• Remove pathogens
• Reduce biological oxygen demand
• Remove large debris and grit

Rationale: Preliminary treatment protects downstream equipment by

removing large solids and grit.

• Grit chambers are designed to remove which material? 1 / 4

• Fats, oils, and grease
• Heavy inorganic particles
• Dissolved solids
• Biological sludge

Rationale: Grit chambers remove sand, gravel, coffee grounds, and other

heavy inorganic materials.

3. In an activated sludge process, the MLSS primarily represents:

• Soluble BOD
• Suspended biomass concentration
• Alkalinity level
• Total effluent solids

Rationale: MLSS measures suspended microorganisms and solids in the

aeration basin.

• What does F/M ratio represent?
• Flow to membrane ratio
• Food-to-microorganism ratio
• Filtration mass
• Flow measurement

Rationale: F/M indicates organic load relative to biomass, controlling

process stability.

• What is the typical purpose of secondary treatment? 2 / 4

• Remove grit
• Remove dissolved and colloidal organic matter
• Adjust pH
• Add disinfectant

Rationale: Secondary treatment biologically removes remaining BOD and

TSS.

• Which type of pump is most common for raw wastewater lift stations?
• Gear pump
• Centrifugal pump
• Plunger pump
• Diaphragm pump

Rationale: Centrifugal pumps handle large flows and solids common in raw

wastewater.

• A primary clarifier typically removes what percentage of suspended

solids?

A. 5–10%

B. 10–20%

C. 50–70%

D. 90–95%

Rationale: Primary clarification removes roughly half to two-thirds of

suspended solids.

• Low DO in an aeration basin usually causes: 3 / 4

• Nitrification increase
• Filamentous bulking
• Sludge densification
• High settleability

Rationale: Low DO promotes filamentous bacteria, leading to poor

settling.

• What does SVI measure?
• Sludge odor intensity
• Settling characteristics of activated sludge
• Volatile gas production
• Influent variability

Rationale: SVI indicates how well sludge settles in the clarifier.

10. An SVI above 200 mL/g usually indicates:

• Good settling
• Bulking sludge
• Thickened sludge
• High aeration

Rationale: High SVI reflects filamentous or poorly settling sludge.

11. Chlorination is commonly used for:

• Ammonia removal
• Solids thickening
• / 4