Practice Exam Questions And Correct

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

• Which of the following is the primary purpose of a primary clarifier?
• Disinfect effluent
• Remove settleable solids
• Aerate wastewater
• Neutralize pH

Rationale: Primary clarifiers remove settleable solids through sedimentation

before secondary treatment.

2. The purpose of an aeration tank in activated sludge treatment is to:

• Remove grit
• Provide oxygen for microbial degradation of organic matter 1 / 4

• Settle sludge
• Chlorinate effluent

Rationale: Aeration tanks supply oxygen to microorganisms to break down

organic matter.

• What is the typical range for dissolved oxygen in an aeration tank?
• 0–1 mg/L
• 1–2 mg/L
• 2–4 mg/L
• 5–10 mg/L

Rationale: Maintaining 2–4 mg/L ensures aerobic microbes function

efficiently.

4. The purpose of a bar screen is to:

• Remove grit
• Remove large debris
• Dechlorinate effluent
• Reduce BOD

Rationale: Bar screens capture large objects that could damage downstream

equipment.

• Which of the following chemicals is commonly used for phosphorus

removal in wastewater?

• Sodium hypochlorite
• Alum (Aluminum sulfate) 2 / 4

• Sodium hydroxide
• Ferric chloride

Rationale: Alum precipitates phosphorus, reducing eutrophication in

receiving waters.

6. The most common method for disinfecting wastewater is:

• Ultraviolet light
• Chlorination
• Ozonation
• Filtration

Rationale: Chlorination is widely used for its effectiveness and cost

efficiency.

• What is the purpose of a grit chamber?
• Remove organics
• Remove sand, gravel, and other heavy inorganic solids
• Neutralize pH
• Settle suspended solids

Rationale: Grit chambers prevent abrasion and sedimentation problems in

pumps and pipes.

8. BOD5 is a measure of:

• Total suspended solids
• Organic matter biodegradable in 5 days 3 / 4

• Pathogens
• Nitrogen content

Rationale: BOD5 measures the amount of oxygen required by microbes to

decompose organic matter over five days.

• Which of the following is considered a primary pollutant?
• Phosphates
• Suspended solids
• Nitrites
• Nitrates

Rationale: Primary pollutants are directly discharged and typically include

suspended solids.

• What is the purpose of sludge thickening?
• Aerate sludge
• Reduce water content to decrease sludge volume
• Remove pathogens
• Disinfect effluent

Rationale: Thickening concentrates solids, reducing handling and disposal

costs.

11. The term “MLSS” stands for:

• Maximum Liquid Settling Solids
• Mixed Liquor Suspended Solids
• / 4