Operator Class B Exam Practice Questions

South Carolina Biological Wastewater Operator Class B Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of a primary clarifier in a wastewater

treatment plant?

• Increase dissolved oxygen levels
• Remove settleable solids from wastewater
• Neutralize pH
• Kill pathogens

Rationale: The primary clarifier allows suspended solids to settle,

removing them before biological treatment.

• Which microorganism is primarily responsible for nitrification in a

biological treatment process?

• Escherichia coli 1 / 4

• Nitrosomonas
• Bacillus subtilis
• Clostridium

Rationale: Nitrosomonas oxidizes ammonia to nitrite, a key step in

nitrification.

• What is the typical range for mixed liquor suspended solids (MLSS) in

an activated sludge process for a Class B plant?

• 50–100 mg/L
• 100–200 mg/L
• 200–500 mg/L
• 2000–4000 mg/L

Rationale: Class B plants generally operate with MLSS in the 2000–

4000 mg/L range to maintain proper biological activity.

• Which parameter is most critical for maintaining a healthy activated

sludge process?

• Temperature
• Dissolved oxygen
• pH
• Conductivity

Rationale: Adequate dissolved oxygen is essential for aerobic

microorganisms to metabolize organic matter.

5. Chlorination is primarily used in wastewater treatment to:

• Reduce BOD 2 / 4

• Disinfect the effluent
• Reduce TSS
• Adjust pH

Rationale: Chlorination kills or inactivates pathogens, ensuring

effluent meets public health standards.

6. The main purpose of aeration in secondary treatment is to:

• Remove heavy metals
• Provide oxygen for microorganisms
• Settle solids
• Filter wastewater

Rationale: Aeration supplies oxygen to support the metabolism of

aerobic bacteria in the activated sludge process.

• Which of the following is a sign of sludge bulking in an activated sludge

system?

• Clear effluent
• Rapid settling
• Fluffy, non-settling sludge
• Decreased MLSS

Rationale: Bulking occurs when filamentous bacteria dominate,

resulting in poor settling sludge.

• What does BOD5 measure?
• Total suspended solids
• Oxygen demand after 24 hours 3 / 4

• Oxygen demand after 5 days
• Effluent nitrogen

Rationale: BOD5 measures the oxygen required by microorganisms

to decompose organic matter over 5 days.

9. The first step in the nitrogen cycle in wastewater treatment is:

• Denitrification
• Ammonification
• Nitrification
• Assimilation

Rationale: Ammonification converts organic nitrogen into ammonia,

which can then be nitrified.

• What is the typical detention time in a primary clarifier?
• 10–20 minutes
• 30–60 minutes
• 1–3 hours
• 6–8 hours

Rationale: A 1–3 hour detention allows settleable solids to

adequately separate from the liquid.

11. In an aerobic digester, the main purpose of aeration is to:

• Remove heavy metals
• Stabilize sludge by biological oxidation
• Sediment solids
• Adjust pH
• / 4