Exam Practice Questions And Correct

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

• Which of the following is the primary purpose of a wastewater

treatment plant?

• Generate electricity
• Produce drinking water
• Remove pollutants from wastewater
• Store wastewater for irrigation

Rationale: Wastewater treatment plants are designed to remove

contaminants from sewage and industrial wastewater to protect public health and the environment. 1 / 4

• What is the typical range of pH for properly treated wastewater

discharged into a stream?

A. 2.0–4.0

B. 6.0–9.0

C. 10.0–12.0

D. 4.0–5.5

Rationale: Most regulatory agencies require treated effluent to have a

pH between 6 and 9 to prevent harm to aquatic life and infrastructure.

• What is the main function of a bar screen in a wastewater treatment

plant?

• Remove dissolved nutrients
• Remove biological contaminants
• Remove large solids and debris
• Remove dissolved oxygen

Rationale: Bar screens are mechanical devices that remove large

objects such as sticks, rags, and plastics before the wastewater enters primary treatment.

• Which unit process is primarily responsible for removing settleable

solids from wastewater?

• Aeration tank
• Trickling filter
• Primary clarifier
• Disinfection 2 / 4

Rationale: Primary clarifiers allow solids to settle out by gravity,

reducing the load on secondary treatment processes.

• Which of the following is a common method for disinfecting

wastewater effluent?

• Coagulation
• Flocculation
• Chlorination
• Sedimentation

Rationale: Chlorination is widely used to kill pathogenic

microorganisms in treated wastewater before discharge.

• What is the main purpose of an aeration tank in secondary treatment?
• Settle solids
• Promote microbial digestion of organic matter
• Remove heavy metals
• Screen debris

Rationale: Aeration tanks provide oxygen to microorganisms, which

digest organic pollutants in the wastewater.

• Which of the following describes BOD (Biochemical Oxygen Demand)?
• Total suspended solids in water
• The amount of nitrogen in water
• The amount of oxygen required by microorganisms to decompose

organic matter

• The concentration of chlorine in water 3 / 4

Rationale: BOD measures the oxygen demand of microorganisms as

they break down organic material, indicating the strength of wastewater.

• What does TSS stand for in wastewater treatment?
• Total soluble salts
• Typical sewage solids
• Total suspended solids
• Total standard solution

Rationale: TSS measures the concentration of solid particles suspended

in water, which is important for treatment and regulatory compliance.

• Which of the following is the main purpose of sludge digestion?
• Increase BOD
• Remove chlorine
• Reduce sludge volume and stabilize organic matter
• Remove nitrogen

Rationale: Sludge digestion reduces the volume of solids and stabilizes

organic content, making it safer for disposal or land application.

• Which type of bacteria is primarily responsible for nitrification in

wastewater treatment?

• Anaerobic bacteria
• Autotrophic bacteria
• Heterotrophic bacteria
• Facultative bacteria
• / 4