Operator Class A Practice Exam Questions

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

• Which microorganism is primarily responsible for nitrification in

wastewater treatment?

• Escherichia coli
• Pseudomonas
• Nitrosomonas
• Clostridium

Rationale: Nitrosomonas oxidizes ammonia to nitrite, which is the first step

in nitrification.

• What is the main purpose of secondary treatment in a wastewater

treatment plant? 1 / 4

• Remove large solids
• Disinfect wastewater
• Remove dissolved and suspended organic matter biologically
• Remove nutrients

Rationale: Secondary treatment uses microorganisms to degrade organic

matter and reduce BOD.

• Which parameter is most commonly used to measure the strength of

wastewater?

• pH
• Temperature
• BOD (Biochemical Oxygen Demand)
• Conductivity

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter.

• In activated sludge systems, what does SRT (Sludge Retention Time)

indicate?

• The time sludge spends in the clarifier
• The time solids settle in primary sedimentation
• The average time biomass stays in the system
• The reaction time in the aeration tank

Rationale: SRT reflects how long microorganisms are maintained to

achieve treatment efficiency. 2 / 4

• What is the main function of a clarifier in wastewater treatment?
• Remove nutrients
• Settle suspended solids
• Oxidize ammonia
• Disinfect effluent

Rationale: Clarifiers allow solids to settle by gravity, reducing TSS in the

effluent.

• What is the typical pH range for optimal biological treatment?

A. 3.0 – 5.0

B. 9.0 – 11.0

C. 6.5 – 8.5

D. 10.0 – 12.0

Rationale: Most microorganisms function best in near-neutral conditions.

7. Denitrification is the process of:

• Converting ammonia to nitrite
• Converting nitrate to nitrogen gas
• Oxidizing organic matter
• Settling solids

Rationale: Denitrification reduces nitrate to nitrogen gas, removing

nitrogen from wastewater.

• Which type of sludge is returned to maintain biomass in an activated

sludge process? 3 / 4

• Primary sludge
• Return activated sludge (RAS)
• Digested sludge
• Biosolids

Rationale: RAS keeps the microbial population in the aeration tank for

effective treatment.

• What is the primary purpose of disinfection in wastewater treatment?
• Remove suspended solids
• Destroy pathogens
• Reduce nitrogen
• Increase alkalinity

Rationale: Disinfection kills or inactivates disease-causing microorganisms

before discharge.

• Which gas is commonly produced in anaerobic digestion?
• Oxygen
• Carbon monoxide
• Methane
• Nitrogen

Rationale: Anaerobic bacteria produce methane and carbon dioxide during

the digestion of sludge.

• Which of the following is a common cause of bulking in activated

sludge?

• / 4