Operator Class III Exam Practice

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

• What is the primary purpose of a bar screen in a wastewater

treatment plant?

• To remove dissolved solids
• To remove large solids and debris
• To disinfect wastewater
• To remove nutrients
• To remove large solids and debris

Rationale: Bar screens prevent large objects from entering

downstream equipment, protecting pumps and treatment units.** 1 / 4

2. The main goal of primary sedimentation is to:

• Remove pathogens
• Reduce biological oxygen demand (BOD)
• Remove settleable solids
• Remove dissolved nutrients
• Remove settleable solids

Rationale: Primary sedimentation tanks allow solids to settle, reducing

the load on secondary treatment.**

• What is the typical detention time for primary clarifiers?
• 10–20 minutes
• 1–2 hours
• 2–4 hours
• 12–24 hours
• 2–4 hours

Rationale: This duration allows sufficient time for solids to settle

without over-retaining water, which could cause septic conditions.**

• Which of the following is a primary purpose of secondary treatment?
• Remove pathogens
• Remove biodegradable organic matter
• Remove large solids
• Remove oil and grease
• Remove biodegradable organic matter 2 / 4

Rationale: Secondary treatment relies on biological processes to

degrade organic matter, reducing BOD before discharge.**

• Activated sludge is an example of which type of treatment?
• Physical
• Chemical
• Biological
• Tertiary
• Biological

Rationale: Activated sludge uses microorganisms to break down

organic pollutants in wastewater.**

• What is the main function of aeration in activated sludge systems?
• Remove large debris
• Provide oxygen to microorganisms
• Reduce sludge volume
• Clarify water
• Provide oxygen to microorganisms

Rationale: Microbes in the aeration tank need oxygen for aerobic

metabolism to degrade organic matter effectively.**

7. The term “MLSS” in wastewater treatment stands for:

• Maximum Liquid Suspended Solids
• Mixed Liquor Suspended Solids
• Minimum Loading Sewage Solids
• Multi-Level Sludge System 3 / 4

• Mixed Liquor Suspended Solids

Rationale: MLSS refers to the concentration of suspended solids in the

aeration tank, including both microorganisms and wastewater solids.**

• Which factor most directly affects the settling rate of sludge?
• Temperature
• Sludge age
• Sludge volume index
• pH
• Sludge volume index

Rationale: Sludge volume index (SVI) measures the settleability of

sludge; lower SVI indicates better settling.**

• What is the primary role of secondary clarifiers?
• Aerate wastewater
• Settle activated sludge
• Remove oils and grease
• Neutralize pH
• Settle activated sludge

Rationale: Secondary clarifiers separate biomass from treated water

before it is discharged or recycled to the aeration tank.**

• What is the typical range of dissolved oxygen in an aeration

tank?

• 0–0.5 mg/L
• / 4