Operator Grade 2 Practice Exam Questions

Rhode Island Wastewater Treatment Operator Grade 2 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following best describes the purpose of primary

treatment in a wastewater treatment plant?

• Remove dissolved nutrients
• Remove settleable solids and floatable materials
• Remove pathogens
• Reduce odor

Rationale: Primary treatment focuses on the physical removal of large

particles through sedimentation and skimming.

• What is the main function of an aeration tank in secondary treatment?
• Settle sludge 1 / 4

• Promote biological decomposition of organic matter
• Remove nutrients
• Disinfect effluent

Rationale: Aeration tanks provide oxygen to bacteria that break down

organic pollutants.

• Which microorganism is primarily responsible for breaking down

organic matter in an activated sludge system?

• Algae
• Protozoa
• Fungi
• Bacteria

Rationale: Bacteria metabolize organic compounds and convert them into

carbon dioxide, water, and biomass.

4. The purpose of sludge thickening is to:

• Remove pathogens
• Increase solids concentration before digestion
• Aerate sludge
• Reduce odors

Rationale: Thickening reduces the water content of sludge, making

digestion more efficient.

5. Chlorination is commonly used in wastewater treatment for:

• Nutrient removal 2 / 4

• Disinfection
• Sludge digestion
• Sedimentation

Rationale: Chlorine is applied to inactivate pathogens in treated

wastewater.

• What is the typical range of dissolved oxygen (DO) in an aeration tank

for effective secondary treatment?

• 0–1 mg/L
• 1–2 mg/L
• 2–4 mg/L
• 5–10 mg/L

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

for microbial activity without excessive energy use.

• Which type of sludge digestion occurs at temperatures between 95°F

and 105°F?

• Mesophilic
• Thermophilic
• Psychrophilic
• Anaerobic

Rationale: Mesophilic digestion occurs at moderate temperatures and is

common in wastewater treatment plants. 3 / 4

8. A high sludge volume index (SVI) indicates:

• Good settling characteristics
• Low solids concentration
• Bulking sludge
• Adequate aeration

Rationale: High SVI suggests the sludge is fluffy and settles poorly, often

due to filamentous bacteria.

9. Nitrification is the biological conversion of:

• Ammonia to nitrogen gas
• Ammonia to nitrate
• Nitrite to ammonia
• Nitrate to ammonia

Rationale: Nitrifying bacteria oxidize ammonia to nitrite and then to

nitrate.

10. Denitrification is important in wastewater treatment because it:

• Produces oxygen
• Removes nitrogen from wastewater
• Increases sludge volume
• Reduces phosphorus

Rationale: Denitrifying bacteria convert nitrate into nitrogen gas,

preventing eutrophication in receiving waters.

• / 4