III Practice Exam Questions And Correct

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

• Which of the following is the primary purpose of preliminary

treatment in a wastewater treatment plant?

• Remove dissolved nutrients
• Remove large solids and debris
• Reduce biochemical oxygen demand
• Disinfect wastewater
• Remove large solids and debris

Rationale: Preliminary treatment is designed to remove large solids

and debris such as rags, sticks, and grit to protect downstream equipment. 1 / 4

• What is the main function of an aeration basin in activated sludge

treatment?

• Remove grit
• Oxidize organic matter
• Remove nitrogen
• Settle solids
• Oxidize organic matter

Rationale: Aeration basins provide oxygen to microorganisms,

allowing them to metabolize and break down organic pollutants.

• Which of the following best describes the term “sludge age” or “mean

cell residence time (MCRT)”?

• The hydraulic retention time of the plant
• The average time solids remain in the treatment system
• The age of the oldest operator on staff
• The time required for sludge dewatering
• The average time solids remain in the treatment system

Rationale: Sludge age or MCRT measures how long microorganisms

remain in the system, which affects treatment efficiency.

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

A. 4.0–5.5

B. 6.5–8.5

C. 9.0–10.5

D. 3.0–4.0 2 / 4

B. 6.5–8.5

Rationale: Most biological treatment processes function best within

a near-neutral pH range to maintain microbial activity.

• Which of the following pathogens is commonly found in untreated

wastewater?

• Escherichia coli
• Lactobacillus
• Streptomyces
• Bacillus subtilis
• Escherichia coli

Rationale: E. coli is a fecal coliform bacterium commonly present in

sewage and used as an indicator of contamination.

• What is the main purpose of chlorination in wastewater treatment?
• Remove solids
• Reduce biochemical oxygen demand
• Disinfect pathogens
• Remove nutrients
• Disinfect pathogens

Rationale: Chlorination is primarily used to kill or inactivate

pathogenic microorganisms before discharge.

• Which of the following is a secondary treatment process?
• Grit chamber
• Sedimentation 3 / 4

• Trickling filter
• Screening
• Trickling filter

Rationale: Trickling filters are biological treatment units that remove

dissolved and suspended organic matter, classifying them as secondary treatment.

• What does BOD stand for?
• Biochemical Oxygen Demand
• Biological Oxidation Density
• Base Oxygen Dosage
• Biotic Oxidation Demand
• Biochemical Oxygen Demand

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter in water.

• Which of the following best describes the purpose of a clarifier in

wastewater treatment?

• Aerate wastewater
• Remove solids through settling
• Remove nutrients
• Adjust pH
• Remove solids through settling

Rationale: Clarifiers allow suspended solids to settle out from the

wastewater by gravity.

• / 4