Practice Exam Questions And Correct

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

• What is the primary purpose of screening in wastewater treatment?
• To remove dissolved organic matter
• To remove large solids and debris
• To reduce nutrients
• To disinfect wastewater

Rationale: Screening removes large debris like rags, sticks, and plastics

that could damage equipment or hinder treatment processes.

• Which process is primarily used to remove suspended solids in

secondary treatment?

• Screening 1 / 4

• Disinfection
• Sedimentation
• Filtration

Rationale: Sedimentation allows suspended solids to settle out by gravity,

which is a key part of secondary treatment.

3. The most common method for disinfecting treated wastewater is:

• Filtration
• Ozonation
• Chlorination
• UV absorption

Rationale: Chlorination is widely used because it is effective, relatively

inexpensive, and provides residual disinfection.

• What is the function of an aeration basin in activated sludge treatment?
• To settle sludge
• To provide oxygen for microorganisms to degrade organic matter
• To remove heavy metals
• To screen large debris

Rationale: Aeration introduces oxygen to support aerobic bacteria that

break down organic matter.

• Which type of sludge digestion is most commonly used in municipal

plants?

• Thermal drying 2 / 4

• Chemical digestion
• Anaerobic digestion
• Filtration

Rationale: Anaerobic digestion stabilizes sludge, reduces volume, and

produces biogas.

• What does BOD measure?
• Nutrient concentration
• Suspended solids
• The amount of oxygen required by microorganisms to decompose

organic matter

• pH level

Rationale: Biochemical Oxygen Demand (BOD) indicates organic pollution

and the oxygen demand required for decomposition.

• Which is a typical BOD5 concentration for municipal raw wastewater?
• 10–20 mg/L
• 200–300 mg/L
• 800–1,000 mg/L
• 1,500–2,000 mg/L

Rationale: Raw municipal wastewater usually has BOD5 values in the 200–

300 mg/L range.

8. Nitrification in wastewater treatment converts:

• Nitrogen gas to ammonia 3 / 4

• Nitrate to ammonia
• Ammonia to nitrate
• Organic nitrogen to phosphorus

Rationale: Nitrification is a two-step aerobic process where ammonia is

first converted to nitrite and then to nitrate.

• Which factor most affects the efficiency of trickling filters?
• Chlorine residual
• Organic loading rate
• pH of effluent
• Sludge digestion

Rationale: The organic loading rate determines whether the microbial

biofilm can effectively process wastewater in a trickling filter.

• What is the typical dissolved oxygen (DO) range in an activated sludge

aeration basin?

• 0.1–0.5 mg/L
• 5–10 mg/L
• 2–4 mg/L
• 10–15 mg/L

Rationale: Maintaining 2–4 mg/L DO ensures sufficient oxygen for

microbial activity without causing excessive energy use.

• Which pH range is most suitable for activated sludge microorganisms?
• 3.0–5.0
• / 4