Operator Class II Practice Exam

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

• What is the primary purpose of primary clarification in wastewater

treatment?

• To remove dissolved nutrients
• To disinfect the wastewater
• To remove settleable solids
• To aerate the wastewater

Answer: C. To remove settleable solids

Rationale: Primary clarification is designed to remove settleable solids from

wastewater through sedimentation, reducing the load on secondary treatment processes. 1 / 4

• Which microorganism is primarily responsible for nitrification in

activated sludge systems?

• Escherichia coli
• Nitrosomonas and Nitrobacter
• Clostridium
• Pseudomonas

Answer: B. Nitrosomonas and Nitrobacter

Rationale: Nitrosomonas oxidizes ammonia to nitrite, and Nitrobacter

oxidizes nitrite to nitrate, completing the nitrification process.

• What is the typical pH range for optimal biological wastewater

treatment?

A. 3.0–5.0

B. 6.5–8.5

C. 9.0–11.0

D. 12.0–14.0

Answer: B. 6.5–8.5

Rationale: Most bacteria used in wastewater treatment thrive in near-

neutral conditions. Extremes in pH can inhibit microbial activity.

• / 4

• Which type of sludge has the highest water content?
• Digested sludge
• Dewatered sludge
• Primary sludge
• Lime-stabilized sludge

Answer: C. Primary sludge

Rationale: Primary sludge is rich in water because it has not undergone

thickening or digestion, making it more fluid.

• What is the main goal of disinfection in wastewater treatment?
• Remove heavy metals
• Eliminate pathogenic microorganisms
• Reduce total suspended solids
• Improve color

Answer: B. Eliminate pathogenic microorganisms

Rationale: Disinfection targets pathogens to protect public health before

effluent is discharged to the environment.

• Which parameter is used to measure the organic strength of

wastewater?

• Total dissolved solids (TDS)
• Biochemical oxygen demand (BOD) 3 / 4

• pH
• Turbidity

Answer: B. Biochemical oxygen demand (BOD)

Rationale: BOD measures the amount of oxygen required by microorganisms

to degrade organic matter, indicating wastewater strength.

• What is the purpose of aeration in activated sludge processes?
• To increase temperature
• To supply oxygen to microorganisms
• To remove nutrients chemically
• To settle solids

Answer: B. To supply oxygen to microorganisms

Rationale: Aeration provides dissolved oxygen needed for aerobic bacteria to

break down organic pollutants.

• In wastewater treatment, what does TSS stand for?
• Total soluble solids
• Total suspended solids
• Total sedimentary solids
• Total stable solids
• / 4