Grade 4 Practice Exam 100 Questions

Massachusetts Wastewater Operator Grade 4 Practice Exam 100 Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of secondary treatment in wastewater

treatment?

• Remove grit
• Remove pathogens
• Remove dissolved and colloidal organics
• Remove heavy metals

Rationale: Secondary treatment relies on biological processes to reduce

BOD by removing dissolved and colloidal organic matter.

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• What is the typical range of MCRT (Mean Cell Residence Time) for an

activated sludge conventional system?

• 1–3 days
• 3–5 days
• 5–15 days
• 20–30 days

Rationale: Conventional activated sludge commonly operates with an

MCRT of 5–15 days to maintain a stable biomass.

• In nitrification, ammonia is converted into which final product?
• Nitrogen gas
• Organic nitrogen
• Nitrate
• Nitrite

Rationale: Nitrification is a two-step aerobic process that ends with

ammonia oxidized to nitrate.

• What is the main purpose of a primary clarifier?
• Remove dissolved organics
• Realize nutrient removal
• Remove settleable and floatable solids
• Remove odor compounds 2 / 4

Rationale: Primary clarifiers settle out solids and floatables prior to

biological treatment.

• Which organism primarily carries out denitrification?
• Nitrifying bacteria
• Facultative bacteria
• Protozoa
• Aerobic fungi

Rationale: Denitrification requires facultative bacteria under anoxic

conditions using nitrate as an oxygen source.

6. A high F/M ratio in activated sludge usually results in:

• Old sludge
• Low oxygen demand
• Young sludge with dispersed growth
• Better settling sludge

Rationale: High F/M promotes rapid bacterial growth, producing lighter

non-settling floc.

• What does SVI measure? 3 / 4

• BOD removal efficiency
• Settling characteristics of sludge
• Oxygen uptake rate
• Filament density

Rationale: Sludge Volume Index indicates how well sludge settles in the

secondary clarifier.

8. Filamentous bulking in activated sludge is commonly caused by:

• High DO
• High F/M
• Low DO
• Low MLSS

Rationale: Low dissolved oxygen encourages filamentous bacteria to

proliferate, causing bulking.

9. In wastewater process control, alkalinity is most important for:

• Primary clarification
• Nitrification
• Disinfection
• Sludge digestion

Rationale: Nitrification consumes alkalinity; insufficient alkalinity can

inhibit nitrifying bacteria.

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