Grade 6 Exam Practice Questions And

Massachusetts Wastewater Operator Grade 6 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?
• Generate electricity
• Produce drinking water
• Remove pollutants from wastewater before discharge
• Reduce air pollution

Rationale: The primary function of a wastewater treatment plant is

to remove physical, chemical, and biological pollutants from wastewater to protect public health and the environment.

• Which microorganism is commonly used in activated sludge processes

for organic matter removal? 1 / 4

• Algae
• Protozoa
• Bacteria
• Fungi

Rationale: Bacteria are the main microorganisms that metabolize

organic matter in the activated sludge process.

• What does BOD stand for?
• Biological Oxidation Demand
• Biochemical Oxygen Demand
• Base Oxidation Depth
• Biological Oxygen Depth

Rationale: BOD measures the amount of oxygen required by

microorganisms to decompose organic matter in water.

4. In wastewater treatment, nitrification refers to:

• The removal of phosphorus
• Conversion of ammonia to nitrogen gas
• Conversion of ammonia to nitrate
• Sedimentation of solids

Rationale: Nitrification is the biological oxidation of ammonia to

nitrate by nitrifying bacteria.

• What is the primary function of a clarifier in wastewater treatment?
• Aerate the water
• Settle suspended solids 2 / 4

• Remove pathogens
• Neutralize pH

Rationale: Clarifiers are used to settle and remove suspended solids

from wastewater.

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

A) 3–5

B) 9–11

C) 6.5–8.5

D) 10–12

Rationale: Most bacteria involved in wastewater treatment thrive in

a near-neutral pH range of 6.5–8.5.

• What is the function of a grit chamber?
• Remove oils
• Treat bacteria
• Remove sand and heavy inorganic solids
• Increase BOD

Rationale: Grit chambers remove heavy inorganic solids like sand

and gravel that can damage equipment.

• Which of the following best describes sludge digestion?
• Filtration of solids
• Chemical oxidation
• Biological decomposition of organic solids
• Aeration of effluent 3 / 4

Rationale: Sludge digestion reduces the volume of solids and

stabilizes organic material through microbial activity.

• Which method is commonly used for disinfection of treated

wastewater?

• Filtration
• Chloride removal
• Chlorination
• Nitrification

Rationale: Chlorination is a common method for disinfecting treated

wastewater to reduce pathogens.

• What is the primary environmental concern associated with high

levels of nitrogen in effluent?

• Air pollution
• Eutrophication of water bodies
• Soil acidification
• Increased BOD

Rationale: Excess nitrogen can lead to algal blooms and oxygen

depletion in receiving waters, a process called eutrophication.

• Which of the following is a common indicator of fecal

contamination in wastewater?

• Nitrate
• Escherichia coli (E. coli)
• Chloride
• / 4