C Exam Practice Questions And Correct

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

• What is the primary purpose of preliminary treatment in a wastewater

treatment plant?

• Remove nutrients
• Remove fine solids
• Remove large solids and debris
• Remove dissolved organics

Rationale: Preliminary treatment is designed to protect downstream

equipment by removing large solids and debris, such as sticks, rags, and plastics. 1 / 4

• Which type of grit is most commonly removed during grit chambers?
• Organic matter
• Sludge
• Sand and small stones
• Fats, oils, and grease

Rationale: Grit chambers allow heavier inorganic particles like sand and

small stones to settle out before biological treatment.

• What is the main function of a primary clarifier?
• Remove dissolved organics
• Remove settleable solids
• Disinfect effluent
• Remove nutrients

Rationale: Primary clarifiers remove settleable solids by gravity settling,

reducing the load on secondary treatment processes.

• Which type of biological treatment uses microorganisms attached to

media?

• Activated sludge
• Trickling filter
• Membrane bioreactor
• Lagoon

Rationale: Trickling filters provide a surface for microorganisms to attach

and metabolize organic matter as wastewater flows over the media. 2 / 4

• In activated sludge systems, what does "MLSS" stand for?
• Maximum liquid suspended solids
• Mixed liquor suspended solids
• Minimum level solids standard
• Microbial life suspended solids

Rationale: MLSS represents the concentration of suspended

microorganisms in the aeration tank of an activated sludge system.

• What is the typical purpose of aeration in activated sludge systems?
• Remove grit
• Remove nutrients
• Supply oxygen for microbial activity
• Disinfect wastewater

Rationale: Aeration provides oxygen necessary for aerobic microorganisms

to break down organic matter.

• Which factor has the greatest influence on sludge settling in a secondary

clarifier?

• pH
• Temperature
• MLSS concentration and flocculation
• Dissolved oxygen

Rationale: Proper floc formation and MLSS concentration are key for

effective settling in secondary clarifiers. 3 / 4

• What is the typical range of BOD5 removal in a conventional activated

sludge process?

• 20–30%
• 40–50%
• 85–95%
• 100%

Rationale: Conventional activated sludge processes typically remove 85–

95% of BOD5 under normal operating conditions.

• Which disinfectant is commonly used in municipal wastewater

treatment?

• Ammonia
• Ozone
• Chlorine
• Hydrogen peroxide

Rationale: Chlorine is widely used for disinfection due to its effectiveness

and ease of application.

• Which of the following is a common method for sludge stabilization?
• Screening
• Anaerobic digestion
• Grit removal
• Aeration
• / 4