Grade 5 Practice Exam Questions And

Massachusetts Wastewater Operator Grade 5 Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. The primary purpose of a wastewater treatment plant is to:

• Produce drinking water
• Generate electricity
• Protect public health and the environment by treating wastewater
• Irrigate crops

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

pollutants from sewage to prevent disease and environmental contamination.

• What is the main function of a primary clarifier?
• Remove dissolved nutrients 1 / 4

• Settle out suspended solids
• Kill pathogens
• Oxidize organic matter

Rationale: Primary clarifiers are designed to allow solids to settle out by

gravity, removing a significant portion of suspended solids.

• Which microorganism is primarily responsible for nitrification in a

biological treatment process?

• E. coli
• Nitrosomonas and Nitrobacter
• Clostridium
• Streptococcus

Rationale: Nitrifying bacteria such as Nitrosomonas convert ammonia to

nitrite and Nitrobacter convert nitrite to nitrate.

• What is the purpose of an aeration tank in activated sludge processes?
• Remove grit
• Provide oxygen for microorganisms to degrade organic matter
• Settle sludge
• Filter solids

Rationale: Aeration tanks supply oxygen to bacteria that consume organic

pollutants in wastewater.

• Which of the following is a key indicator of organic pollution in

wastewater? 2 / 4

• pH
• BOD (Biochemical Oxygen Demand)
• Temperature
• Conductivity

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter and is a primary indicator of organic pollution.

• The sludge age or mean cell residence time (MCRT) in activated sludge

processes affects:

• Water temperature
• Microbial population and process stability
• Flow rate
• pH

Rationale: MCRT determines the average time microorganisms remain in

the system, influencing biological treatment efficiency.

• What is the primary method for removing phosphorus in wastewater

treatment?

• Biological filtration
• Chemical precipitation using alum or ferric salts
• Chlorination
• Aerobic digestion 3 / 4

Rationale: Chemical precipitation with metals forms insoluble compounds

that settle out in the treatment process.

• Which disinfection method is most commonly used in Massachusetts

wastewater plants?

• Ozone
• UV
• Chlorination
• Filtration

Rationale: Chlorination is widely used for its effectiveness in inactivating

pathogens in treated effluent.

9. The term "combined sewer overflow" (CSO) refers to:

• A stormwater treatment device
• A discharge from a combined sewer during heavy rain, containing

untreated wastewater

• A type of sludge digester
• A secondary clarifier

Rationale: CSOs occur in older sewer systems where stormwater and

sewage are combined; heavy rain can cause untreated discharge.

10. pH is a measure of:

• Temperature
• Acidity or alkalinity of a solution
• / 4