Operator Class 3 Practice Examination

Maryland Wastewater Treatment Operator Class 3 Practice Examination Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of secondary treatment in a wastewater

treatment process?

• Remove grit
• Settle heavy solids
• Biologically remove dissolved and colloidal organics
• Disinfect the effluent

Answer: C

Rationale: Secondary treatment relies on microorganisms to stabilize and

remove organic matter that primary treatment cannot remove.

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• Which laboratory test is most commonly used to measure organic

strength of wastewater?

A. TSS

• pH

C. BOD5

• Chlorine residual

Answer: C

Rationale: BOD5 measures biodegradable organic material and is a key

parameter in wastewater treatment evaluation.

• What does F/M ratio represent in activated sludge?
• Flow to mass
• Floc to mixed liquor
• Food to microorganism ratio
• Filtrate measurement

Answer: C

Rationale: F/M expresses the balance between incoming organic load

(food) and biomass (microorganisms).

• The primary function of a grit chamber is to: 2 / 4

• Remove oils
• Remove heavy inorganic particles
• Remove pathogens
• Aerate wastewater

Answer: B

Rationale: Grit chambers remove sand, gravel, and other heavy particles to

protect downstream equipment.

5. A clarifier experiencing rising sludge is most likely caused by:

• High chlorine dose
• Denitrification
• Low pH
• Excessive sludge wasting

Answer: B

Rationale: Denitrification creates nitrogen gas bubbles that lift sludge to

the surface.

• What is the primary purpose of a digester?
• Aerate sludge
• Stabilize sludge
• Remove grit
• Increase BOD 3 / 4

Answer: B

Rationale: Digesters break down organic solids and reduce pathogens,

stabilizing the sludge.

• What does MLVSS represent?
• Mixed liquor volatile solids
• Mixed liquor volatile suspended solids
• Milliliters of sludge solids
• Minimal volatile solids

Answer: B

Rationale: MLVSS measures living biomass in activated sludge and is used

for process control.

8. Nitrification converts ammonia into:

• Methane
• Sulfates
• Nitrites and nitrates
• Hydrogen gas

Answer: C

Rationale: Nitrifying bacteria oxidize ammonia to nitrite and nitrate in two

biological steps.

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