A Licensing Exam Practice Test 100

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

• What is the primary purpose of coagulation in water treatment?
• Remove dissolved salts
• Destabilize colloidal particles
• Improve taste and odor
• Remove hardness

Coagulation neutralizes charges on colloids so they can clump and settle.

• Alum performs best at which pH range? 1 / 4

A. 3.0–4.0

B. 5.5–6.0

C. 6.0–7.5

D. 8.5–10.0

Alum requires slightly acidic to neutral pH for optimal floc formation.

• Which factor has the greatest impact on filtration efficiency?
• Water temperature
• Raw water color
• Filter age
• Filter loading rate

Lower loading rates improve particle removal and filter run length.

• What is the purpose of backwashing a filter?
• Increase turbidity
• Remove accumulated solids
• Add disinfectant
• Reduce pH

Backwashing clears trapped particles, restoring filter capacity and flow.

• The breakpoint chlorination curve’s "hump" is caused by formation of

what? 2 / 4

• THMs
• Chloramines
• Ferric hydroxides
• Peroxides

Chloramines form and temporarily consume chlorine demand before true breakpoint.

• Free chlorine is defined as a combination of…
• Chlorine + organics
• Chlorine + bromide
• Hypochlorous acid + hypochlorite ion
• Chloramines in solution

Free chlorine consists of HOCl and OCl⁻, the active disinfectant forms.

7. The most powerful disinfecting species of chlorine is:

• OCl⁻
• HOCl
• Cl₂ gas
• Chlorite

HOCl is more effective than OCl⁻ due to greater oxidizing capability.

• Which parameter indicates the strength of the floc formed? 3 / 4

• Temperature
• Conductivity
• Mixing intensity (G value)
• Color

Proper G-values ensure collisions between particles without breaking floc.

9. Excessive turbidity breakthrough in a filter normally indicates:

• Low chlorine dose
• High alkalinity
• Filter is overloaded or due for backwash
• High pH

Breakthrough means solids have saturated the filter media.

• What is the minimum CT requirement for 3-log Giardia inactivation

using free chlorine at 10°C?

• 20
• 60
• 90

D. 150

EPA CT tables show ~90 mg·min/L for 3-log Giardia at 10°C.

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