Washington Wastewater Treatment Plant Operator Group II Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

Washington Wastewater Treatment Plant Operator Group II Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The primary purpose of preliminary treatment in a wastewater

treatment plant is to:

• Remove dissolved organic matter
• Remove large solids and grit
• Reduce nutrient levels
• Disinfect wastewater

Rationale: Preliminary treatment involves screening and grit removal to

protect downstream equipment and prevent operational issues.

• What is the typical pH range for the activated sludge process to

function efficiently? 1 / 4

A. 4.5–5.5

B. 6.0–6.5

C. 6.5–8.5

D. 9.0–10.0

Rationale: The biological processes in activated sludge require near-

neutral pH; extreme acidity or alkalinity can inhibit microbial activity.

• Which microorganism is primarily responsible for nitrification?
• Protozoa
• Nitrosomonas and Nitrobacter bacteria
• Fungi
• Algae

Rationale: Nitrosomonas oxidizes ammonia to nitrite, and Nitrobacter

oxidizes nitrite to nitrate, completing the nitrification process.

4. The main purpose of chlorination in wastewater treatment is to:

• Remove solids
• Disinfect wastewater
• Remove phosphorus
• Enhance biological treatment

Rationale: Chlorination kills or inactivates pathogenic microorganisms to

prevent waterborne disease.

5. BOD (Biochemical Oxygen Demand) is a measure of:

• Total dissolved solids 2 / 4

• The amount of oxygen required by microorganisms to decompose

organic matter

• Alkalinity
• pH

Rationale: BOD quantifies the oxygen demand of biodegradable organic

matter, indicating wastewater strength.

6. Grit chambers are designed primarily to remove:

• Organic solids
• Sand, gravel, and other heavy inert particles
• Fats and oils
• Dissolved nutrients

Rationale: Grit chambers slow water flow to allow heavy particles like

sand and gravel to settle before entering treatment units.

• Which process is used to remove nitrogen biologically from

wastewater?

• Chlorination
• Sedimentation
• Nitrification and denitrification
• Filtration

Rationale: Nitrification converts ammonia to nitrate, and denitrification

converts nitrate to nitrogen gas, removing nitrogen biologically. 3 / 4

• What is the primary function of a secondary clarifier?
• Separate treated water from biomass (sludge)
• Remove grit
• Disinfect wastewater
• Remove dissolved oxygen

Rationale: Secondary clarifiers settle out biological solids produced in the

secondary treatment process.

9. In wastewater treatment, the term “sludge age” refers to:

• The age of the plant
• The average time solids remain in the biological treatment system
• The age of operators
• The time wastewater spends in grit removal

Rationale: Sludge age or solids retention time affects microbial population

balance and treatment efficiency.

10. Anaerobic digestion of sludge primarily produces:

• Oxygen
• Methane and carbon dioxide
• Nitrogen gas
• Phosphate

Rationale: Anaerobic bacteria break down organic matter without oxygen,

generating methane and CO₂ as byproducts.

• / 4