Practice Examination Questions And

Iowa Wastewater Operator Grade II Practice Examination Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. The primary purpose of preliminary treatment in a wastewater plant is:

• Remove nutrients
• Reduce biochemical oxygen demand
• Protect downstream equipment
• Remove pathogens

Preliminary treatment removes large debris and grit, preventing wear and clogging of pumps and downstream units.

2. Grit chambers are designed mainly to remove:

• Organic solids
• Heavy inorganic particles
• Fats, oils, and grease 1 / 4

• Colloidal material

Grit chambers remove sand, gravel, and similar inorganic particles that would settle rapidly.

3. The typical detention time for primary clarifiers is:

• 5–10 minutes
• 15–20 minutes
• 30–45 minutes
• 1.5–2.5 hours

Primary clarifiers commonly use 1.5–2.5 hours to allow primary sludge settling.

4. Sludge that has undergone anaerobic digestion will typically show:

• Increased volatile solids
• Increased pathogens
• Higher odor potential
• Reduced volatile solids

Anaerobic digestion stabilizes sludge by reducing volatile solids.

• What is the main function of secondary treatment?
• Remove grit
• Thicken sludge
• Remove biodegradable organic matter
• Disinfect wastewater

Secondary biological processes oxidize dissolved and suspended organics. 2 / 4

6. The activated sludge process relies on:

• Chlorination
• Suspended microbial growth
• Attached microbial growth
• Membrane separation

Activated sludge uses suspended microorganisms mixed with aerated wastewater.

• A typical return activated sludge (RAS) rate as a percentage of influent

flow is:

A. 5–10%

B. 10–20%

C. 25–100%

D. 150–200%

RAS normally falls within 25–100% to maintain mixed liquor concentration.

8. The purpose of waste activated sludge (WAS) withdrawal is to:

• Increase mixed liquor concentration
• Control sludge age
• Remove grit
• Increase BOD loading

WAS removal sets the system’s solids retention time.

• Filamentous bulking typically results in: 3 / 4

• High DO in the clarifier
• Rapid settling sludge
• Poor settling and sludge blanket rise
• Thick sludge blanket

Filamentous organisms cause slow, fluffy settling, leading to bulking.

10. Nitrification converts:

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

Nitrification is the aerobic oxidation of ammonia to nitrate.

11. Denitrification occurs under:

• Aerobic conditions
• Anoxic conditions
• Anaerobic conditions only
• Super-saturated DO conditions

Denitrification requires anoxic environments where nitrate replaces oxygen as the electron acceptor.

12. Chlorine disinfection effectiveness decreases when:

• pH decreases
• pH increases
• Temperature increases
• / 4