Exam Practice Questions And Correct

Montana Wastewater Operator Class 2 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 preliminary

treatment in a wastewater treatment plant?

• Remove nutrients
• Remove large solids and debris
• Reduce BOD
• Disinfect effluent

Rationale: Preliminary treatment is designed to remove large solids,

debris, and grit that could damage equipment or hinder downstream processes. 1 / 4

• What is the typical pH range for activated sludge processes?
• 4.0 – 5.5
• 5.5 – 6.5
• 6.5 – 8.5
• 8.5 – 10.0

Rationale: Activated sludge microorganisms perform optimally

within a pH range of 6.5 to 8.5.

• Which unit process is primarily used to remove settleable solids?
• Filtration
• Primary clarifier
• Aeration tank
• Disinfection

Rationale: Primary clarifiers allow solids to settle by gravity before

biological treatment.

• What is the main function of aeration in secondary treatment?
• Remove nutrients
• Provide oxygen for microorganisms to degrade organic matter
• Remove pathogens
• Reduce TSS

Rationale: Aeration supplies oxygen to microorganisms, which is

essential for biological decomposition of organic waste.

5. In a trickling filter, the medium is typically:

• Sand 2 / 4

• Activated carbon
• Rock, plastic, or other inert media
• Clay

Rationale: Trickling filters use media such as rock or plastic to

support microbial growth for wastewater treatment.

6. Sludge volume index (SVI) measures:

• Flow rate
• Settling characteristics of sludge
• BOD removal efficiency
• Nutrient concentration

Rationale: SVI indicates how well sludge settles and is important for

controlling activated sludge systems.

• Which of the following pathogens is most resistant to chlorine

disinfection?

• E. coli
• Salmonella
• Cryptosporidium
• Giardia

Rationale: Cryptosporidium oocysts are highly resistant to chlorine,

requiring alternative disinfection methods.

8. BOD5 refers to:

• Biological Oxygen Demand measured over 3 days
• Biochemical Oxygen Demand measured over 5 days 3 / 4

• Total oxygen in water
• Dissolved oxygen concentration

Rationale: BOD5 measures the amount of oxygen microorganisms

consume in 5 days while degrading organic matter.

• What is the purpose of a chlorination contact chamber?
• Remove solids
• Remove nutrients
• Allow sufficient time for chlorine to inactivate pathogens
• Enhance settling

Rationale: Contact time ensures chlorine adequately disinfects

wastewater.

10. Nitrification is the biological conversion of:

• Ammonia to nitrogen gas
• Nitrite to nitrogen gas
• Ammonia to nitrite and then nitrate
• Nitrate to ammonia

Rationale: Nitrification is a two-step aerobic process converting

ammonia to nitrite (by Nitrosomonas) and then nitrite to nitrate (by Nitrobacter).

11. Denitrification converts nitrate into:

• Nitrite
• Nitrogen gas
• Ammonia
• / 4