Operator Grade 3 Practice Examination

Vermont Wastewater Treatment Facility Operator Grade 3 Practice Examination Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

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

wastewater plant?

• Remove grit
• Settle heavy inorganic solids
• Reduce organic matter through biological processes
• Disinfect effluent

Rationale: Secondary treatment relies on microorganisms to remove BOD

and suspended biological solids.

• What does BOD primarily measure?
• Chemical corrosion potential
• Oxygen demand from biodegradable organics 1 / 4

• Toxicity of effluent
• Chlorine residual

Rationale: BOD reflects the oxygen required by microbes to break down

organic material.

• Typical DO concentration maintained in an activated sludge aeration

tank is:

• 0.5 mg/L
• 2.0 mg/L
• 6.0 mg/L
• 10 mg/L

Rationale: Around 2 mg/L supports aerobic microbial activity efficiently.

• What microorganism is most important in nitrification?
• Protozoa
• Fungi
• Nitrifying bacteria
• Viruses

Rationale: Nitrifiers (e.g., Nitrosomonas, Nitrobacter) oxidize ammonia to

nitrate.

5. Sludge bulking is commonly caused by:

• Excess alkalinity
• Overgrowth of filamentous organisms
• Improper chlorination 2 / 4

• Low influent flow

Rationale: Filaments interfere with settling, creating fluffy sludge.

• What does F/M ratio compare?
• Food to modulus
• Filaments to microorganisms
• Organics applied to biomass present
• Flow to membrane

Rationale: F/M = influent organics relative to biological mass in aeration.

• What is the optimal pH for nitrification?

A. 4.0–5.0

B. 5.5–6.5

C. 7.5–8.5

D. 9.0–10.0

Rationale: Nitrifiers thrive in mildly alkaline conditions.

• Which test measures settleability of activated sludge?

A. BOD

B. TSS

C. SVI

D. COD

Rationale: Sludge Volume Index indicates settling characteristics.

9. The main purpose of grit removal is to: 3 / 4

• Destroy pathogens
• Protect downstream equipment
• Remove organics
• Improve sludge digestion

Rationale: Grit causes abrasion and wear.

• What is the typical chlorine contact time for disinfection?
• 1–3 minutes
• 5–8 minutes
• 15–30 minutes
• 60–120 minutes

Rationale: Adequate CT ensures pathogen inactivation.

• What does TSS measure?
• Dissolved solids
• Organic acids
• Suspended solids that can be filtered
• Chlorine demand

Rationale: TSS captures particulate solids in wastewater.

12. A clarifier with rising solids may indicate:

• Excess alkalinity
• Hydraulic overload
• Proper sludge removal
• / 4