Grade 7 Exam Practice Questions And

Massachusetts Wastewater Operator Grade 7 Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of a grit chamber in a wastewater

treatment plant?

a) Remove organic matter

b) Remove sand, gravel, and other heavy inorganic solids

c) Reduce biochemical oxygen demand (BOD)

d) Chlorinate wastewater

Rationale: Grit chambers are designed to remove heavy inorganic

solids like sand and gravel to protect downstream equipment from abrasion. 1 / 4

• Which of the following is a common method for controlling odors in

wastewater treatment plants?

a) Aeration only

b) Sedimentation

c) Chemical dosing and aeration

d) Sludge thickening

Rationale: Odor control is typically achieved using aeration to reduce

anaerobic conditions and chemical dosing to neutralize odorous compounds.

• What is the typical range of dissolved oxygen (DO) concentration

required in activated sludge aeration tanks?

• 0.1–0.5 mg/L
• 1–2 mg/L
• 2–4 mg/L
• 6–8 mg/L

Rationale: DO levels of 2–4 mg/L are optimal for aerobic

microorganisms in activated sludge systems.

4. The primary purpose of secondary clarification is to:

a) Remove grit

b) Remove coarse solids

c) Settle biological flocs from aeration tanks

d) Disinfect effluent 2 / 4

Rationale: Secondary clarifiers separate the biological floc formed

during activated sludge treatment from treated water.

• What is the main objective of sludge digestion?

a) Increase sludge volume

b) Stabilize organic matter and reduce pathogens

c) Remove grit

d) Remove nutrients

Rationale: Digestion stabilizes sludge by decomposing organic

matter and reducing pathogen content.

6. In wastewater treatment, BOD5 refers to:

a) Biochemical oxygen demand in 1 hour

b) Biochemical oxygen demand over 5 days

c) Total suspended solids

d) Chemical oxygen demand

Rationale: BOD5 measures the oxygen consumed by microorganisms

over five days to indicate organic pollution strength.

• Which chemical is commonly used for phosphorus removal in

wastewater treatment?

a) Sodium hypochlorite

b) Calcium carbonate

c) Alum (aluminum sulfate)

d) Sodium hydroxide 3 / 4

Rationale: Alum binds with phosphorus to form insoluble compounds

that can be removed by sedimentation.

• What is the primary function of a bar screen in a wastewater

treatment plant?

a) Aerate the influent

b) Remove large debris like rags and sticks

c) Remove fine solids

d) Reduce BOD

Rationale: Bar screens prevent large solids from entering the

treatment process, protecting equipment and preventing blockages.

9. The sludge volume index (SVI) is used to:

a) Measure DO levels

b) Evaluate the settleability of activated sludge

c) Calculate chlorine dosage

d) Determine sludge pH

Rationale: SVI indicates how well sludge settles in a secondary

clarifier, which is important for process control.

• Which pathogen indicator is most commonly used to assess

wastewater contamination?

a) Salmonella

b) Hepatitis A

c) Escherichia coli (E. coli)

d) Influenza virus

• / 4