Exam Practice Questions And Correct

Michigan Wastewater Operator Class D Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the primary purpose of a wastewater

treatment plant?

• To produce drinking water
• To remove contaminants from wastewater
• To generate electricity
• To recycle solid waste

Rationale: The main goal of a wastewater treatment plant is to remove

pollutants from wastewater before it is discharged into the environment.

• What does BOD stand for?
• Biological Oxygen Demand 1 / 4

• Biochemical Oxygen Discharge
• Biochemical Oxygen Demand
• Bacterial Oxidation Degree

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter in water, a key parameter in wastewater treatment.

• Which process is typically the first step in wastewater treatment?
• Biological treatment
• Preliminary treatment (screening and grit removal)
• Disinfection
• Sludge digestion

Rationale: Preliminary treatment removes large solids and grit to protect

downstream equipment and processes.

4. The main function of a grit chamber is to:

• Remove oils and grease
• Remove bacteria
• Remove sand, gravel, and heavy particles
• Remove dissolved chemicals

Rationale: Grit chambers remove heavy inorganic particles that can

damage pumps and other equipment.

• Which of the following is a primary treatment method?
• Trickling filter 2 / 4

• Activated sludge process
• Sedimentation
• Chlorination

Rationale: Sedimentation allows solids to settle out of wastewater, which

is the main process in primary treatment.

6. The typical retention time in a primary clarifier is:

• 5–10 minutes
• 1–2 hours
• 6–8 hours
• 12–24 hours

Rationale: Primary clarifiers typically retain wastewater for 1–2 hours to

allow solids to settle.

• What is the function of an aeration tank in activated sludge systems?
• Remove grit
• Provide oxygen for microbial breakdown of organic matter
• Settle solids
• Filter water

Rationale: Aeration tanks supply oxygen so microorganisms can digest

organic pollutants.

• Which microorganism is commonly used in wastewater treatment to

digest organic matter?

• Algae 3 / 4

• Protozoa
• Bacteria
• Viruses

Rationale: Bacteria are the primary decomposers in biological wastewater

treatment.

• What is the typical range of BOD removal in primary treatment?

A. 10–20%

B. 30–40%

C. 25–50%

D. 60–80%

Rationale: Primary treatment removes about 25–50% of the incoming BOD.

• Which of the following is a secondary treatment method?
• Screening
• Grit removal
• Activated sludge process
• Sedimentation

Rationale: Secondary treatment focuses on removing dissolved and

suspended organic matter, typically using biological processes like activated sludge.

11. The purpose of chlorination in wastewater treatment is:

• Remove suspended solids
• Disinfect the treated effluent
• / 4