Licensing Exam Practice Test Questions

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

Q1. What is the primary purpose of secondary treatment in wastewater systems?

• Remove heavy solids
• Disinfect remaining organisms
• Oxidize and stabilize organic material
• Remove grit
• Oxidize and stabilize organic material

Secondary treatment uses biological processes to break down dissolved and suspended organic matter.

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Q2. Which device is commonly used to measure wastewater flow in an open channel?

• Pressure gauge
• Venturi meter
• Electromagnetic flow meter
• Parshall flume
• Parshall flume

Parshall flumes provide accurate open-channel flow measurement using a known head-to-flow relationship.

Q3. What does BOD measure?

• Nutrients
• Solids
• Oxygen demand by microorganisms
• pH
• Oxygen demand by microorganisms

BOD indicates how much oxygen microbes need to degrade organic waste.

Q4. Which microorganisms are primarily responsible for nitrification?

• Anaerobic bacteria
• Fungi
• Nitrosomonas and Nitrobacter 2 / 4

• Protozoa
• Nitrosomonas and Nitrobacter

These bacteria oxidize ammonia to nitrite and nitrate.

Q5. The purpose of grit removal is to:

• Remove pathogens
• Reduce TSS
• Protect mechanical equipment
• Remove dissolved organics
• Protect mechanical equipment

Grit can damage pumps and reduce tank volume; grit removal protects equipment.

Q6. A settling tank designed for biological sludge thickening is called:

• Aeration tank
• Imhoff tank
• Secondary clarifier
• Digester
• Imhoff tank

Imhoff tanks allow settling and digestion in separate compartments.

Q7. Sludge with low dissolved oxygen tends to: 3 / 4

• Settle well
• Become septic
• Grow filaments
• Increase alkalinity
• Become septic

Low DO leads to anaerobic conditions that produce odors and sludge septicity.

Q8. The F/M ratio increases when:

• Flow increases and biomass decreases
• Biomass increases and flow decreases
• DO increases
• Sludge wasting decreases
• Flow increases and biomass decreases

High food relative to microorganisms increases F/M.

Q9. Chlorine demand is the difference between chlorine applied and:

• Chlorine remaining after 30 minutes
• Free ammonia

C. BOD

• Total suspended solids
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