Operator Grade IV Practice Exam

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

• Which of the following is the most common method for measuring

biochemical oxygen demand (BOD) in wastewater?

• Chemical titration
• Membrane filtration
• 5-day incubation method
• Spectrophotometry

Rationale: The 5-day BOD test (BOD₅) is standard for assessing the

oxygen demand of wastewater by microorganisms over five days at

20°C. 1 / 4

• The primary purpose of preliminary treatment in a wastewater plant is

to:

• Remove nutrients
• Remove large solids and debris
• Reduce BOD
• Disinfect wastewater

Rationale: Preliminary treatment, such as screening and grit

removal, prevents large solids from damaging downstream equipment.

• In activated sludge processes, the mixed liquor suspended solids

(MLSS) concentration typically ranges between:

• 50–200 mg/L
• 200–500 mg/L
• 1,500–3,000 mg/L
• 4,000–6,000 mg/L

Rationale: MLSS is maintained at levels that provide adequate

microbial population for effective treatment.

• Which type of bacteria is primarily responsible for nitrification in

wastewater treatment?

• Denitrifying bacteria
• Nitrosomonas and Nitrobacter
• Coliform bacteria
• Sulfate-reducing bacteria 2 / 4

Rationale: Nitrosomonas oxidizes ammonia to nitrite, and

Nitrobacter oxidizes nitrite to nitrate.

• What is the minimum dissolved oxygen (DO) concentration typically

required for effective nitrification?

• 0.5 mg/L
• 1 mg/L
• 2 mg/L
• 5 mg/L

Rationale: Nitrifying bacteria require sufficient oxygen to oxidize

ammonia efficiently, generally at least 2 mg/L DO.

• Which sludge treatment process reduces pathogens and odor while

stabilizing the sludge?

• Sedimentation
• Thickening
• Anaerobic digestion
• Screening

Rationale: Anaerobic digestion breaks down organic matter,

reducing pathogens and odor in sludge.

7. In wastewater treatment, chlorine is primarily used for:

• Coagulation
• Filtration
• Disinfection
• Aeration 3 / 4

Rationale: Chlorine is a strong oxidizing agent used to kill pathogenic

microorganisms in effluent.

• What is the typical range for effluent pH in a municipal wastewater

treatment plant?

• 3–5
• 5–6
• 6.5–8.5
• 9–11

Rationale: Effluent pH is maintained within 6.5–8.5 to prevent

corrosion, protect aquatic life, and comply with regulations.

• In a sequencing batch reactor (SBR), which phase comes immediately

after aeration?

• Fill
• Aeration
• Settling
• Decanting

Rationale: After aeration, the mixed liquor is allowed to settle to

separate treated water from sludge.

10. The purpose of a weir in a clarifier is to:

• Increase aeration
• Control effluent flow and maintain uniform water level
• Filter solids
• Add chemicals
• / 4