Operator Grade II Exam Practice

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

• What is the primary purpose of primary sedimentation in wastewater

treatment?

• Remove dissolved nutrients
• Remove fine colloidal particles
• Remove settleable solids
• Disinfect the wastewater

Rationale: Primary sedimentation removes settleable solids through gravity

settling, reducing the load on subsequent treatment processes.

• Which microorganism is primarily responsible for nitrification?
• Escherichia coli 1 / 4

• Nitrosomonas
• Clostridium
• Pseudomonas

Rationale: Nitrosomonas bacteria oxidize ammonia to nitrite, which is the

first step of nitrification.

3. BOD stands for:

• Biochemical Oxidation Demand
• Biological Oxygen Depletion
• Biochemical Oxygen Demand
• Bacterial Oxidation Degree

Rationale: BOD measures the amount of oxygen microorganisms consume

while decomposing organic matter.

• The most common method of sludge stabilization in a wastewater

plant is:

• Filtration
• Aerobic digestion
• Coagulation
• Chlorination

Rationale: Aerobic digestion reduces the organic content of sludge and

stabilizes it before disposal.

• What is the main purpose of chlorination in wastewater treatment?
• Remove suspended solids 2 / 4

• Reduce BOD
• Disinfect the effluent
• Improve settling

Rationale: Chlorination kills pathogenic organisms, ensuring the treated

wastewater is safe for discharge.

• Which process is used to remove nitrogen from wastewater?
• Filtration
• Biological nitrification and denitrification
• Sedimentation
• Coagulation

Rationale: Nitrogen is removed biologically by converting ammonia to

nitrate (nitrification) and then to nitrogen gas (denitrification).

7. The primary purpose of an aeration tank is to:

• Settle solids
• Remove nutrients
• Provide oxygen for microbial growth
• Chlorinate effluent

Rationale: Aeration tanks supply oxygen to aerobic bacteria to biologically

degrade organic matter.

• Which unit process removes grit from wastewater?
• Primary clarifier
• Secondary clarifier 3 / 4

• Trickling filter
• Grit chamber

Rationale: Grit chambers remove heavy inorganic particles like sand, gravel,

and cinders to prevent damage to downstream equipment.

9. The term “sludge age” refers to:

• Time sludge spends in storage
• Age of the oldest microorganism
• Average time solids remain in the aeration tank
• Time for chlorine to act on sludge

Rationale: Sludge age or solids retention time helps maintain the proper

microbial population in biological treatment.

• Which is a primary cause of foaming in activated sludge?
• Excess chlorine
• High nitrate levels
• Filamentous bacteria
• Low temperature

Rationale: Filamentous bacteria can form foam on aeration tanks, reducing

treatment efficiency.

11. The chemical formula for chlorine gas is:

• ClO2
• ClO
• / 4