Exam Practice Questions And Correct

Missouri 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 a wastewater treatment plant?
• To produce drinking water
• To remove pollutants from wastewater before discharge
• To store wastewater temporarily
• To increase the wastewater flow

Answer: B. To remove pollutants from wastewater before discharge

Rationale: The main goal of a wastewater treatment plant is to remove

pollutants and contaminants from sewage or industrial wastewater before it is discharged into the environment, protecting public health and the environment. 1 / 4

• Which of the following is a characteristic of primary treatment?
• Biological decomposition of organic matter
• Removal of settleable solids by sedimentation
• Disinfection of treated water
• Nutrient removal

Answer: B. Removal of settleable solids by sedimentation

Rationale: Primary treatment primarily focuses on the physical removal of

large solids through screening and sedimentation before biological processes.

• What does BOD stand for?
• Biological Oxygen Demand
• Biochemical Oxidation Density
• Basic Organic Decomposition
• Biological Oxidation Depth

Answer: A. Biological Oxygen Demand

Rationale: BOD measures the amount of oxygen required by microorganisms

to decompose organic matter in water, indicating the strength of wastewater.

• / 4

4. A sudden increase in BOD in the influent may cause:

• Increased sludge production
• Oxygen depletion in aeration tanks
• Improved effluent quality
• Reduced microbial activity

Answer: B. Oxygen depletion in aeration tanks

Rationale: High BOD levels demand more oxygen, which can lead to oxygen

depletion if aeration is insufficient.

• What is the main function of aeration in activated sludge systems?
• Remove grit
• Provide oxygen to microorganisms
• Separate solids from liquids
• Add chlorine to effluent

Answer: B. Provide oxygen to microorganisms

Rationale: Aeration supplies oxygen necessary for aerobic microorganisms to

break down organic matter in wastewater.

• Which sludge process reduces volume and stabilizes solids?
• Screening
• Primary settling 3 / 4

• Digestion
• Filtration

Answer: C. Digestion

Rationale: Sludge digestion, either aerobic or anaerobic, stabilizes organic

matter and reduces sludge volume.

• What is the purpose of disinfection in wastewater treatment?
• Remove suspended solids
• Eliminate pathogens
• Reduce BOD
• Remove nutrients

Answer: B. Eliminate pathogens

Rationale: Disinfection, typically using chlorine or UV, reduces disease-

causing microorganisms before effluent discharge.

• Which of the following best describes nitrification?
• Conversion of ammonia to nitrate
• Conversion of organic matter to methane
• Removal of phosphorus
• Sedimentation of solids
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