Operator Grade III Practice Exam

Nevada Wastewater Treatment Plant Operator Grade III Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the primary purpose of a secondary clarifier

in a wastewater treatment plant?

• Remove large solids from influent
• Neutralize pH
• Remove suspended solids after biological treatment
• Disinfect effluent

Rationale: The secondary clarifier allows activated sludge to settle,

separating biomass from treated water.

2. The main function of a bar screen in preliminary treatment is to:

• Remove grit 1 / 4

• Remove large debris
• Decrease BOD
• Reduce nutrient levels

Rationale: Bar screens physically remove large objects such as sticks,

rags, and trash before wastewater enters downstream processes.

• Which microorganism is most commonly responsible for nitrification

in wastewater treatment?

• Escherichia coli
• Nitrosomonas
• Pseudomonas
• Bacillus

Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite during

nitrification.

• What is the typical pH range for activated sludge processes?

A. 4.5–5.5

B. 6.0–6.5

C. 6.5–8.5

D. 8.5–9.5

Rationale: Activated sludge performs optimally in a slightly acidic to

slightly alkaline environment, typically 6.5–8.5.

• Which unit process is designed specifically to remove grit from

wastewater?

• Bar screen 2 / 4

• Sedimentation tank
• Grit chamber
• Trickling filter

Rationale: Grit chambers settle heavy inorganic particles such as

sand and gravel while allowing organic matter to pass.

6. The term "BOD" stands for:

• Basic Oxidation Demand
• Biological Oxidation Determinant
• Biochemical Oxygen Demand
• Biological Organic Decomposition

Rationale: BOD measures the amount of dissolved oxygen required

by microorganisms to break down organic matter in water.

7. The primary objective of chlorination in wastewater treatment is to:

• Remove suspended solids
• Increase alkalinity
• Disinfect effluent
• Remove nitrogen

Rationale: Chlorine is used to kill or inactivate pathogenic

microorganisms before discharge.

8. Sludge volume index (SVI) is used to determine:

• Settling characteristics of activated sludge
• Total solids in sludge
• pH of mixed liquor 3 / 4

• Alkalinity

Rationale: SVI indicates the volume occupied by settled sludge

relative to its concentration, providing insight into settleability.

• What is the first step in the wastewater treatment process?
• Secondary treatment
• Disinfection
• Preliminary treatment
• Tertiary treatment

Rationale: Preliminary treatment removes large debris and grit to

protect downstream equipment.

• In an aeration tank, oxygen transfer efficiency is primarily

affected by:

• Temperature and diffuser type
• pH only
• Influent BOD only
• Chlorine residual

Rationale: Oxygen transfer depends on water temperature, diffuser

design, and mixing intensity.

• Which of the following is a primary advantage of using a rotating

biological contactor (RBC)?

• High nutrient removal
• Low energy consumption
• High sludge production
• / 4