Licensing Exam 100 Practice Questions

State Water Treatment Operator Class C Licensing Exam 100 Practice Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

• What is the primary purpose of coagulation in water treatment?
• Reduce taste and odor
• Remove dissolved minerals
• Destabilize suspended particles
• Produce chlorine residual

Coagulation adds chemicals that neutralize particle charges, allowing them to clump together for removal.

2. Alum is most commonly used as a:

• Disinfectant
• Coagulant
• Corrosion inhibitor 1 / 3

• pH booster

Alum (aluminum sulfate) is the most widely used coagulant in drinking water treatment.

3. The most effective pH range for alum coagulation is typically:

A. 3.0–4.0

B. 5.0–6.0

C. 6.0–7.5

D. 8.5–10.0

Alum works best in slightly acidic to neutral conditions.

4. The main purpose of flocculation is to:

• Add chlorine
• Remove hardness
• Promote particle collisions
• Disinfect water

Gentle mixing promotes formation of larger, heavier floc particles.

5. Sedimentation removes particles primarily by:

• Filtration
• Gravity settling
• Chemical oxidation
• Air flotation

Sedimentation relies on gravity to settle floc particles.

6. Turbidity is measured in: 2 / 3

• ppm
• mg/L

C. NTU

• mL/min

Turbidity is expressed in nephelometric turbidity units.

7. A normal turbidity level entering filters should be:

• >10 NTU
• <1–5 NTU

C. 20–30 NTU

D. 50 NTU

Low turbidity improves filter performance and disinfectant effectiveness.

8. The most common filtration media used in rapid sand filters is:

• Gravel only
• Activated carbon only
• Sand and anthracite
• Clay

Dual-media filtration increases efficiency and capacity.

9. Backwashing filters is necessary to:

• Add chlorine
• Remove accumulated solids
• Increase alkalinity
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