Grade IV Practice Exam Questions And

North Carolina Wastewater 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 primary function of the activated sludge

process?

• Sedimentation
• Treatment of wastewater using microorganisms to remove organic

matter

• Chlorination
• Sludge dewatering

Rationale: The activated sludge process relies on microorganisms to

biologically oxidize organic matter, reducing BOD in wastewater. 1 / 4

• What is the typical range of Mixed Liquor Suspended Solids (MLSS) in

an activated sludge system?

• 50–100 mg/L
• 100–200 mg/L
• 2000–4000 mg/L
• 5000–7000 mg/L

Rationale: MLSS in conventional activated sludge systems usually ranges

from 2000 to 4000 mg/L to maintain adequate microbial population for treatment.

• Which pathogen is of greatest concern in wastewater due to its high

resistance to disinfection?

• E. coli
• Salmonella
• Cryptosporidium
• Streptococcus

Rationale: Cryptosporidium oocysts are highly resistant to chlorine and UV,

making them a critical pathogen to monitor.

• What is the primary purpose of a grit chamber?
• Reduce BOD
• Remove sand, gravel, and heavy solids
• Clarify wastewater
• Treat nutrients 2 / 4

Rationale: Grit chambers remove dense inorganic particles that could

damage downstream equipment or settle in treatment tanks.

• What is the standard method to measure Biochemical Oxygen

Demand (BOD) of a wastewater sample?

• Chemical titration
• Colorimetry
• Incubation for 5 days at 20°C
• Filtration

Rationale: BOD5 test involves incubating a diluted sample for 5 days at

20°C to measure oxygen consumed by microorganisms.

• Which of the following processes is primarily responsible for nitrogen

removal in wastewater?

• Filtration
• Chlorination
• Nitrification and denitrification
• Flocculation

Rationale: Nitrification converts ammonia to nitrate, and denitrification

converts nitrate to nitrogen gas, removing nitrogen from wastewater.

• What is the typical detention time in a primary clarifier?
• 5–10 minutes
• 15–30 minutes 3 / 4

• 1.5–2.5 hours
• 6–12 hours

Rationale: Primary clarifiers are designed with detention times long

enough for heavy solids to settle but short enough to prevent significant decomposition.

• Which chemical is commonly used for phosphorus removal in

wastewater?

• Sodium hypochlorite
• Alum (Aluminum sulfate)
• Ferric cyanide
• Calcium chloride

Rationale: Alum precipitates phosphate as aluminum phosphate,

effectively removing phosphorus from wastewater.

• Which sludge type is typically more difficult to dewater?
• Waste activated sludge
• Primary sludge
• Grit
• Screenings

Rationale: Waste activated sludge has high water content and small floc

particles, making it harder to dewater than primary sludge.

• What is the primary cause of bulking in activated sludge

systems?

• / 4