Level 3 Practice Exam 100 Questions And

Alberta Wastewater Treatment Operator Level 3 Practice Exam 100 Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of secondary treatment in a wastewater

plant?

• Remove grit
• Remove large solids
• Disinfect wastewater
• Biologically remove dissolved and colloidal organic matter

Rationale: Secondary treatment uses microorganisms to remove dissolved

and colloidal organics.

• / 4

• Which parameter best indicates the strength of organic pollution

entering a biological treatment system?

A. TSS

• Alkalinity

C. BOD5

• Chlorides

Rationale: BOD5 measures biodegradable organic matter and is the main

indicator of wastewater strength.

3. In an activated sludge plant, a low DO concentration typically causes:

• Increased sludge settling
• Reduced filament growth
• Poor nitrification
• Increased oxygen transfer

Rationale: Nitrifiers require high DO; low DO suppresses nitrification.

• What is the typical DO range for an aeration basin?
• 0.1–0.5 mg/L
• 0.5–1.0 mg/L
• 2.0–4.0 mg/L
• 5.0–7.0 mg/L

Rationale: Most activated sludge systems operate best with 2–4 mg/L DO. 2 / 4

5. Sludge bulking in the secondary clarifier is commonly caused by:

• Excess alkalinity
• High SVI
• Increased DO
• Filamentous bacteria overgrowth

Rationale: Filamentous bacteria prevent compact settling and cause

bulking.

6. The purpose of RAS (Return Activated Sludge) is to:

• Dispose of extra sludge
• Reduce BOD in effluent
• Backwash filters
• Return settled biomass to the aeration basin

Rationale: RAS returns microorganisms to maintain MLSS levels.

• Which process removes ammonia by converting it to nitrate?
• Denitrification
• Sedimentation
• Nitrification
• Gas stripping

Rationale: Nitrification oxidizes ammonia to nitrite and then nitrate. 3 / 4

• Denitrification requires what type of conditions?
• Aerobic
• Mixed liquor
• Anoxic
• Anaerobic

Rationale: Denitrifying bacteria require nitrate but no dissolved oxygen.

9. The sludge age (SRT) mainly controls:

• Clarifier performance
• Headloss in filters
• Chlorine dose
• Microbial population growth and system stability

Rationale: SRT dictates how long microbes stay in the system, affecting

process stability.

10. High MLSS in the aeration basin generally results in:

• Lower oxygen demand
• Higher oxygen demand
• Lower sludge age
• Increased wasting need

Rationale: More biomass requires more oxygen to stay active.

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