Practice Exam 100 Questions And

Maine Wastewater Operator Grade II Practice Exam 100 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 nutrients
• Remove pathogens
• Remove large debris and grit
• Remove dissolved solids

Rationale: Preliminary treatment removes large solids and grit to protect

downstream equipment.

• Which device is commonly used to measure flow in an open channel? 1 / 4

• Turbine meter
• Parshall flume
• Centrifugal meter
• Compound meter

Rationale: Parshall flumes are standard for open-channel flow

measurement.

• What is the typical pH range for effective biological treatment?

A. 2–4

B. 4–5

C. 6.5–8.5

D. 9–11

Rationale: Microorganisms thrive in a near-neutral pH range.

• In activated sludge, what does MLSS stand for?
• Mixed Liquor Solids Suspended
• Main Liquid Suspended Solids
• Mixed Liquor Suspended Solids
• Microbial Liquid Solids System

Rationale: MLSS refers to suspended solids in the aeration tank.

5. A pump that increases pressure by imparting velocity is called:

• Diaphragm pump
• Centrifugal pump
• Peristaltic pump 2 / 4

• Piston pump

Rationale: Centrifugal pumps impart velocity to increase pressure.

6. The main purpose of secondary treatment is:

• Odor control
• BOD removal
• Disinfection
• Sludge thickening

Rationale: Secondary treatment uses biology to remove BOD.

7. Chlorine residual is typically measured using:

• Nephelometer
• Spectrophotometer
• DPD method
• DO meter

Rationale: The DPD colorimetric method is the standard for chlorine

residual.

8. A manhole entry requires testing for:

• Temperature
• CO₂ only
• Oxygen, combustibles, toxic gases
• Vacuum pressure

Rationale: Confined space safety requires testing O₂ and hazardous gases.

• What does F/M ratio refer to? 3 / 4

• Flow/mixing
• Food-to-microorganism ratio
• Fuel/mass
• Flow-to-mass

Rationale: F/M compares organic load to biomass in activated sludge.

• Which process stabilizes sludge?
• Screening
• Filtration
• Digestion
• Disinfection

Rationale: Digestion stabilizes sludge by reducing volatile solids.

11. The main cause of filamentous bulking is:

• Low DO
• High DO
• Excess chlorine
• Low F/M or septicity

Rationale: Filaments thrive under low F/M and septic conditions.

12. A composite sample is:

• Grab sample collected once
• Sample collected over time proportionate to flow
• Filtered sample
• / 4