Exam Practice Questions And Correct

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

• What is the primary purpose of a wastewater treatment plant?
• Produce drinking water
• Reduce solid waste only
• Protect public health and the environment by treating wastewater
• Generate electricity

Rationale: The main goal of wastewater treatment is to remove

contaminants to prevent environmental pollution and protect public health.

2. BOD stands for:

• Biological Oxidation Demand 1 / 4

• Biochemical Oxygen Demand
• Basic Oxygen Distribution
• Biochemical Oxidation Detergent

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter in water.

• What is the typical range for BOD in municipal wastewater influent?
• 50–100 mg/L
• 100–200 mg/L
• 200–300 mg/L
• 500–700 mg/L

Rationale: Municipal wastewater typically contains 200–300 mg/L of BOD

before treatment.

4. Suspended solids in wastewater are primarily removed by:

• Chlorination
• Sedimentation
• Aeration
• Filtration

Rationale: Sedimentation allows heavier solids to settle out of the water.

• What is the main function of a primary clarifier?
• Reduce BOD
• Settle out suspended solids 2 / 4

• Remove nutrients
• Disinfect wastewater

Rationale: Primary clarifiers are designed to remove settleable solids

before biological treatment.

• Which microorganism is commonly used in activated sludge

treatment?

• Viruses
• Algae
• Bacteria
• Protozoa

Rationale: Bacteria metabolize organic matter during activated sludge

treatment.

• What is nitrification in wastewater treatment?
• Conversion of ammonia to nitrogen gas
• Conversion of ammonia to nitrite and then nitrate
• Conversion of nitrate to ammonia
• Removal of phosphorus

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

to nitrite and then nitrate.

8. Denitrification is a process that:

• Converts nitrate to ammonia
• Converts nitrate to nitrogen gas under anoxic conditions 3 / 4

• Converts ammonia to nitrate
• Removes solids from wastewater

Rationale: Denitrification occurs under anoxic conditions and reduces

nitrate to nitrogen gas, completing the nitrogen removal cycle.

• Which of the following is a common method for phosphorus removal?
• Filtration
• Chemical precipitation using alum or ferric salts
• Aeration
• Nitrification

Rationale: Chemical precipitation removes phosphorus by forming

insoluble compounds that can be settled out.

10. The purpose of disinfection in wastewater treatment is to:

• Remove solids
• Reduce BOD
• Kill or inactivate pathogenic microorganisms
• Remove phosphorus

Rationale: Disinfection targets pathogens to protect public health before

discharge or reuse.

11. Chlorine is most effective for disinfection when:

• Water is very turbid
• Water is clear and pH is around 7
• / 4