Operator Grade III Practice Exam

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

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

treatment plant?

• Reduce biochemical oxygen demand (BOD)
• Remove large solids and grit
• Disinfect the wastewater
• Nutrient removal

Rationale: Preliminary treatment focuses on removing large solids,

debris, and grit to protect downstream equipment.

• Which type of clarifier is typically used for secondary treatment?
• Primary clarifier 1 / 4

• Secondary clarifier
• Grit chamber
• Equalization tank

Rationale: Secondary clarifiers settle suspended biological solids

after biological treatment processes like activated sludge or trickling filters.

• What does BOD measure in wastewater?
• Total solids concentration
• The amount of oxygen required by microorganisms to decompose

organic matter

• Pathogen levels
• Chemical contaminants

Rationale: BOD (Biochemical Oxygen Demand) indicates the organic

load that microorganisms will consume.

• Which microorganism is commonly responsible for nitrification?
• Escherichia coli
• Nitrosomonas and Nitrobacter
• Staphylococcus aureus
• Pseudomonas

Rationale: Nitrifying bacteria like Nitrosomonas oxidize ammonia to

nitrite and Nitrobacter oxidize nitrite to nitrate.

• In an activated sludge process, what is the purpose of returning

settled sludge to the aeration tank? 2 / 4

• Increase effluent BOD
• Reduce aeration efficiency
• Maintain high concentration of microorganisms for

biodegradation

• Neutralize pH

Rationale: Returning activated sludge ensures sufficient

microorganisms remain to treat incoming wastewater effectively.

• Which type of sludge is produced during primary treatment?
• Primary sludge
• Secondary sludge
• Tertiary sludge
• Digested sludge

Rationale: Primary sludge consists mainly of settleable solids

removed from raw wastewater in primary clarifiers.

• What is the primary chemical used for phosphorus removal in

wastewater?

• Sodium hydroxide
• Chlorine
• Aluminum sulfate (alum) or ferric chloride
• Sodium hypochlorite

Rationale: Alum and ferric chloride react with phosphate to form

insoluble precipitates for removal. 3 / 4

• Which process converts ammonia to nitrate?
• Denitrification
• Sedimentation
• Nitrification
• Chlorination

Rationale: Nitrification is a two-step aerobic process converting

ammonia first to nitrite, then to nitrate.

• What is the purpose of anoxic zones in nitrogen removal systems?
• Promote nitrification
• Promote denitrification
• Settle solids
• Chlorinate effluent

Rationale: Anoxic zones provide conditions for bacteria to convert

nitrate to nitrogen gas.

• What is the main function of a grit chamber?
• Remove pathogens
• Reduce BOD
• Remove sand, gravel, and heavy particles
• Disinfect wastewater

Rationale: Grit chambers prevent abrasion and accumulation of

heavy solids in pumps and pipes.

• What is the typical detention time for primary sedimentation?
• 5–10 minutes
• / 4