III Certification Exam Practice Questions

Wastewater Treatment Operator Class III Certification Exam Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• Which of the following best describes BOD (Biochemical Oxygen

Demand)?

• The amount of dissolved oxygen in water
• The oxygen required by chemicals in water
• The amount of oxygen required by microorganisms to decompose

organic matter

• The total oxygen present in wastewater

Rationale:

BOD measures the oxygen microorganisms consume to break down organic material, indicating the strength of wastewater. 1 / 4

2. The primary purpose of a grit chamber is to:

• Remove organic solids
• Remove sand, gravel, and heavy solids
• Aerate wastewater
• Settle suspended solids

Rationale:

Grit chambers remove heavy inorganic materials that can damage equipment and reduce treatment efficiency.

• Which of the following is a characteristic of anaerobic digestion?
• Produces more sludge than aerobic digestion
• Produces methane and carbon dioxide as by-products
• Requires continuous aeration
• Requires high levels of dissolved oxygen

Rationale:

Anaerobic digestion occurs in the absence of oxygen and produces methane and CO₂.

4. In activated sludge processes, the F/M ratio refers to:

• Filtration to mixing ratio
• Food to microorganism ratio
• Flow to mass ratio
• Floc to mixed liquor ratio 2 / 4

Rationale:

The F/M ratio indicates the amount of organic matter available per unit of microbial mass.

• Which type of sludge is returned to maintain microbial population in

an aeration tank?

• Waste sludge
• Return activated sludge (RAS)
• Digested sludge
• Primary sludge

Rationale:

Return activated sludge is recycled to maintain a healthy population of microorganisms for treatment.

6. Chlorination of wastewater primarily targets:

• Removal of suspended solids
• Disinfection of pathogens
• Reduction of BOD
• Removal of nutrients

Rationale:

Chlorine is used to kill disease-causing organisms before discharge.

7. The main objective of secondary treatment is to:

• Remove grit and large solids
• Remove dissolved and suspended organic matter 3 / 4

• Disinfect wastewater
• Reduce nutrients

Rationale:

Secondary treatment biologically removes organic pollutants using microorganisms.

8. Nitrification in wastewater treatment converts:

• Ammonia to nitrogen gas
• Nitrite to nitrogen gas
• Ammonia to nitrate
• Organic nitrogen to ammonia

Rationale:

Nitrification is an aerobic process where ammonia is converted first to nitrite and then nitrate.

9. Denitrification in wastewater treatment converts nitrate to:

• Nitrite
• Nitrogen gas
• Ammonia
• Organic nitrogen

Rationale:

Denitrification is an anoxic process where nitrate is converted to harmless nitrogen gas.

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