Grade I Exam Practice Questions And

North Carolina Wastewater Operator Grade I Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following is the primary purpose of a wastewater

treatment plant?

• Increase water temperature
• Reduce pollutants to protect public health
• Add chlorine to water
• Pump water uphill

Rationale: The main purpose of a wastewater treatment plant is to

remove pollutants and protect public health and the environment.

• What is the typical range for pH in most wastewater treatment

processes? 1 / 4

A. 2–4

B. 9–12

C. 6–9

D. 6.5–8.5

Rationale: Most biological treatment processes operate best in the

neutral to slightly alkaline range of 6.5–8.5.

• Which process primarily removes suspended solids from wastewater?
• Chlorination
• Sedimentation
• Aeration
• Filtration

Rationale: Sedimentation allows suspended solids to settle out by

gravity before further treatment.

4. BOD stands for:

• Biological Oxidation Demand
• Basic Organic Dissolution
• Biochemical Oxygen Demand
• Bacterial Oxygen Depletion

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter in water.

• What is the primary function of an aeration tank in secondary

treatment?

• Remove heavy metals 2 / 4

• Provide oxygen for bacteria to degrade organic matter
• Filter out solids
• Adjust pH

Rationale: Aeration tanks supply oxygen to support microbial activity

for organic matter breakdown.

• Which microorganism is commonly used in activated sludge systems

to degrade organic waste?

• Viruses
• Bacteria
• Protozoa
• Fungi

Rationale: Bacteria are the primary decomposers in activated sludge

systems.

• What is the typical detention time in a primary clarifier?
• 5–10 minutes
• 1–2 hours
• 2–4 hours
• 12–24 hours

Rationale: Primary clarifiers are designed to allow 2–4 hours for

solids to settle.

8. Sludge thickening is performed to:

• Reduce pH
• Remove chlorine 3 / 4

• Reduce water content before digestion or disposal
• Aerate wastewater

Rationale: Thickening concentrates solids, reducing volume for

digestion or disposal.

• What type of meter is commonly used to measure flow in wastewater

collection systems?

• Thermometer
• Pressure gauge
• Parshall flume
• TDS meter

Rationale: Parshall flumes provide accurate flow measurement in

open channel systems.

• What is the typical percentage of solids removed in primary

sedimentation?

A. 10–20%

B. 30–50%

C. 60–80%

D. 90–95%

Rationale: Primary sedimentation removes roughly 30–50% of

suspended solids and some BOD.

• Which of the following is a characteristic of trickling filters?
• High sludge production
• Fixed-bed media for microbial growth
• / 4