Class III Practice Examination Questions

Idaho Wastewater Treatment Operator Class III Practice Examination Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• The primary purpose of preliminary treatment in a wastewater plant is

to:

• Remove settleable solids
• Reduce biochemical oxygen demand
• Protect downstream equipment
• Remove nutrients
• Protect downstream equipment

Preliminary treatment removes large debris and grit that could damage pumps and mechanical units.

2. Grit chambers are designed to remove: 1 / 4

• Floating debris
• Heavy inorganic materials
• Dissolved solids
• Organic colloids
• Heavy inorganic materials

Grit consists mainly of sand, gravel, and eggshells that settle rapidly and must be removed early.

3. Typical detention time for primary clarifiers is:

• 5–10 minutes
• 15–30 minutes
• 1–2 hours
• 4–6 hours
• 1–2 hours

Primary clarification requires enough time for settleable solids to sink and scum to rise.

4. The main purpose of secondary treatment is:

• Sand removal
• Pathogen disinfection
• Organic matter reduction
• Phosphorus removal
• Organic matter reduction

Secondary biological processes target BOD and suspended organic solids using microorganisms. 2 / 4

5. High MLSS in an activated sludge system usually causes:

• Lower oxygen demand
• Improved clarifier performance
• Poor settling
• Reduced sludge age
• Poor settling

Excess solids increase blanket depth and promote bulking.

6. A typical MCRT for a conventional activated sludge plant is:

• 1–2 days
• 3–15 days
• 20–40 days
• 60+ days
• 3–15 days

Conventional systems operate with moderate sludge ages to balance growth and wasting needs.

7. The purpose of RAS (return activated sludge) is to:

• Remove pathogens
• Reduce nutrients
• Maintain MLSS in the aeration basin
• Thicken sludge
• Maintain MLSS in the aeration basin

RAS returns settled biomass to maintain proper biological activity levels. 3 / 4

8. Too low a DO concentration in the aeration basin can cause:

• Nitrification
• Sludge bulking
• Decreased denitrification
• Improved settling
• Sludge bulking

Low DO favors filamentous organisms, leading to poor settling.

9. Nitrification is the conversion of ammonia to:

• Nitrogen gas
• Organic nitrogen
• Nitrite and nitrate
• Carbon dioxide
• Nitrite and nitrate

Autotrophic bacteria oxidize ammonia first to nitrite, then nitrate.

10. Denitrification requires:

• Aerobic conditions
• Anoxic conditions
• Anaerobic conditions only
• High chlorine residues
• Anoxic conditions

Nitrate serves as the electron acceptor in the absence of dissolved oxygen.

• Chlorine used for disinfection works primarily by:
• / 4