Operator Grade 4 Practice Examination

Vermont Wastewater Treatment Facility Operator Grade 4 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 dissolved solids
• Reduce BOD
• Protect downstream equipment
• Remove nutrients

Rationale: Preliminary treatment removes large debris and grit to prevent

equipment damage.

2. Grit chambers are designed mainly to remove:

• Fats, oils, and grease
• Dissolved organics 1 / 4

• Heavy inorganic particles
• Ammonia

Rationale: Grit consists of sand, gravel, and other heavy inorganics.

3. In primary clarification, the key mechanism for solids removal is:

• Adsorption
• Filtration
• Sedimentation
• Oxidation

Rationale: Primary clarifiers rely on gravity settling.

4. The primary purpose of trickling filters is:

• Solids thickening
• Biological BOD reduction
• Nutrient precipitation
• Odor control

Rationale: Trickling filters support attached-growth organisms to remove

organic matter.

5. The optimal DO level in an activated sludge aeration basin is typically:

• <0.5 mg/L
• 1.0 mg/L
• 2.0 mg/L or higher
• 10 mg/L 2 / 4

Rationale: Operators maintain ≥2 mg/L DO for stable aerobic biological

activity.

6. F/M ratio refers to:

• Flow to mass
• Food to microorganism ratio
• Fermentation mass
• Filter media loading

Rationale: F/M measures organic load relative to biomass in activated

sludge.

7. Sludge bulking is commonly caused by:

• High DO
• Excess filamentous bacteria
• Low SRT
• Proper sludge settling

Rationale: Filamentous overgrowth impairs sludge settling.

8. A high SVI generally indicates:

• Good settling
• Bulking sludge
• High DO
• Low MCRT

Rationale: Elevated SVI signals poor settleability.

9. Nitrification converts: 3 / 4

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

Rationale: Nitrifying bacteria oxidize ammonia → nitrite → nitrate.

10. Denitrification requires:

• Aerobic conditions
• High DO
• Anoxic conditions
• Chlorine

Rationale: Denitrification takes place without DO but with nitrate present.

11. Chlorine disinfection is less effective when:

• pH is low
• pH is high
• Contact time is long
• Temperature is high

Rationale: High pH reduces HOCl formation, lowering disinfection strength.

12. The primary purpose of sludge digestion is to:

• Increase sludge volume
• Increase odors
• Stabilize organic solids
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