Grade 3 Practice Exam 100 Questions

Massachusetts Wastewater Operator Grade 3 Practice Exam 100 Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

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

facility?

• Removal of grit
• Sedimentation of heavy solids
• Biological treatment to remove dissolved organics
• Screening of large debris

Rationale: Secondary treatment relies on microorganisms to break down

dissolved and colloidal organic matter.

• The activated sludge process is designed to remove what major

pollutant? 1 / 4

• Oil and grease
• Biodegradable organic matter
• Pathogens
• Heavy metals

Rationale: Activated sludge targets BOD and organic pollutants through

microbial oxidation.

3. A clarifier with short-circuiting will typically show:

• Higher sludge blanket
• Higher effluent TSS
• Lower turbidity
• Increased oxygen levels

Rationale: Short-circuiting decreases settling time, increasing suspended

solids in the effluent.

• What is the typical DO range for an aeration tank?
• 0.5–1.0 mg/L
• 6–8 mg/L
• 2.0–4.0 mg/L
• 8–10 mg/L

Rationale: Most activated sludge systems operate efficiently at 2–4 mg/L

DO.

• Sludge bulking in activated sludge is most commonly caused by: 2 / 4

• Excess chlorine
• Filamentous bacteria overgrowth
• High alkalinity
• Low F/M ratio

Rationale: Filamentous organisms cause poor settling and fluffy sludge.

6. The term F/M ratio refers to:

• Food to methane
• Flow to mass
• Food to microorganism ratio
• Flux to membrane

Rationale: F/M compares organic loading to available biomass.

7. High F/M in aeration usually results in:

• Old sludge
• Young sludge
• High SRT
• Compact floc

Rationale: High F/M promotes rapid microbial growth and young sludge

characteristics.

• Which device measures suspended solids in a sample?
• Chlorine analyzer
• Turbidimeter
• Imhoff cone 3 / 4

• Colorimeter

Rationale: Imhoff cones measure settleable solids, part of suspended solids

assessment.

9. The purpose of a digester gas safety flame trap is to:

• Increase gas pressure
• Remove water vapor
• Prevent flame from entering digester
• Reduce methane content

Rationale: Flame traps protect digesters from fire and explosion hazards.

10. A weir overflow rate is used to evaluate:

• Pump efficiency
• Final clarifier performance
• Head loss in pipes
• Flow pacing

Rationale: W.O.R. helps assess even flow distribution in clarifiers.

11. Nitrification converts ammonia to:

• Nitrogen gas
• Organic nitrogen
• Nitrate
• Chloramine

Rationale: Nitrifiers oxidize ammonia → nitrite → nitrate.

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