Class II Practice Examination Questions

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

• The main purpose of primary treatment in an industrial wastewater plant

is to:

• Remove dissolved solids
• Remove settleable and floatable solids
• Oxidize organic matter
• Nitrify ammonia

Rationale: Primary treatment uses sedimentation and skimming to remove

solids before biological treatment._

2. A clarifier operates best when:

• Hydraulic loading is excessive
• Flow is evenly distributed 1 / 4

• Solids are continually resuspended
• Inlet velocities are high

Rationale: Uniform flow distribution prevents short-circuiting and

improves settling efficiency._

3. The main purpose of secondary treatment is to:

• Remove grit
• Biologically degrade organic matter
• Filter out sand
• Neutralize pH

Rationale: Secondary treatment uses microorganisms to reduce BOD

through oxidation of organics._

• Which test measures organic strength of wastewater?

A. TSS

B. VSS

C. BOD

• Conductivity

Rationale: Biochemical Oxygen Demand quantifies biodegradable organic

matter._

• / 4

5. The primary source of phosphorus in industrial wastewater is:

• Detergents and cleaning compounds
• Heavy metals
• Cooling water
• Chlorine residual

Rationale: Phosphate-based cleaners and additives contribute most

phosphorus._

6. Activated sludge returns from:

• Primary clarifier
• Secondary clarifier
• Grit chamber
• Sludge thickener

Rationale: Return activated sludge (RAS) is recycled from the secondary

clarifier to the aeration tank._

7. High mixed liquor suspended solids (MLSS) typically result in:

• Lower oxygen uptake
• Higher oxygen demand
• Improved settling always
• Reduced sludge age

Rationale: More biomass requires more oxygen for respiration._ 3 / 4

8. The food-to-microorganism (F/M) ratio is used to:

• Estimate influent flow
• Balance organic load to microbial mass
• Measure sludge volume
• Calculate sludge age

Rationale: F/M ensures optimal biological treatment efficiency._

9. Sludge bulking is often caused by:

• High pH
• Filamentous bacteria overgrowth
• Low DO only
• Excess alkalinity

Rationale: Filamentous bacteria create poor settling floc and sludge

bulking._

10. A typical DO level in an aeration basin should be:

• <0.5 mg/L
• 2.0 mg/L or higher
• 6.0 mg/L
• 0.1 mg/L

Rationale: DO above 2 mg/L supports aerobic biological activity._

• / 4