Exam 100 Practice Questions And

Maine Wastewater Operator Grade III Exam 100 Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of secondary treatment in wastewater

treatment?

• Remove grit
• Remove floatable materials
• Reduce BOD and suspended solids
• Remove nitrogen

Rationale: Secondary treatment focuses on biological processes to reduce

BOD and TSS.

• What group of microorganisms is primarily responsible for nitrification? 1 / 4

• Protozoa
• Nitrifying bacteria
• Fungi
• Algae

Rationale: Nitrification is performed by autotrophic nitrifying bacteria such

as Nitrosomonas and Nitrobacter.

3. Sludge volume index (SVI) is used to evaluate:

• pH
• Flow rate
• Settling characteristics of activated sludge
• Chlorine demand

Rationale: SVI assesses how well sludge settles in the secondary clarifier.

• What is the typical pH range for effective nitrification?

A. 4–5

B. 5–6

C. 7–8.5

D. 9–10

Rationale: Nitrifiers function best in a neutral-to-slightly-alkaline pH range.

• What is the main purpose of an aeration basin?
• Remove grit
• Settle solids
• Supply oxygen to microorganisms 2 / 4

• Remove phosphorus

Rationale: Aeration provides oxygen needed for aerobic biological

treatment.

• Which test best indicates the amount of oxygen used by microorganisms

to degrade organic matter?

A. TSS

• pH

C. BOD

• Alkalinity

Rationale: BOD measures the oxygen consumed in biodegrading organic

material.

• What does a rising sludge in a secondary clarifier indicate?
• High DO
• Denitrification in the clarifier
• Excess grease
• High chlorine

Rationale: Rising sludge is caused by nitrogen gas produced during

denitrification lifting solids.

8. Chlorine used for disinfection is most effective at:

• High pH
• Low pH
• Neutral pH 3 / 4

• Zero alkalinity

Rationale: Hypochlorous acid, the more effective disinfectant form,

dominates at lower pH.

• What type of pump is commonly used for sludge pumping?
• Centrifugal
• Positive displacement
• Jet pump
• Submersible turbine

Rationale: Thick sludges require positive displacement pumps for

consistent flow.

10. The F/M ratio in activated sludge refers to:

• Flow/Mixing
• Food/Microorganisms
• Filtration/Membrane
• Flow/Mass

Rationale: F/M describes the amount of organic load relative to biomass.

• What is the main function of a grit chamber?
• Remove organics
• Remove heavy inorganic particles
• Remove nutrients
• / 4