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Water & Wastewater Operator (WPI/ABC Class I) — Practice Exam

WT treatment: coagulation: practice questions

Our Water/Wastewater Operator bank has 5 questions on this topic. Here are 4 of them with answers; the full mock exam draws from every topic, like the real one.

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Question 1 · Water Treatment Class I

What is the purpose of coagulation in water treatment?

  1. Killing bacteria with a strong oxidant so the filters don't foul with biological growth
  2. Killing bacteria with a strong oxidant before filtration
  3. Softening water by removing calcium and magnesium
  4. Neutralizing particle charges so fine particles can clump together
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D. Neutralizing particle charges so fine particles can clump together — Coagulants such as alum or ferric chloride destabilize colloids.

Question 2 · Water Treatment Class I

How long does rapid (flash) mixing typically last?

  1. About 6 hours
  2. 2 to 4 hours
  3. About 20 to 30 minutes, with tapered mixing energy
  4. Seconds, up to about a minute
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D. Seconds, up to about a minute — Rapid mix disperses coagulant quickly and evenly.

Question 3 · Water Treatment Class I

What does alum consume when it reacts in water?

  1. Dissolved oxygen
  2. Chlorine residual
  3. Alkalinity
  4. Fluoride
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C. Alkalinity — Low-alkalinity water may need lime or soda ash added.

Question 4 · Water Treatment Class I

Which chemical is a common coagulant?

  1. Aluminum sulfate (alum)
  2. Hydrofluosilicic acid
  3. Calcium hypochlorite
  4. Sodium thiosulfate, added before the rapid mix
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A. Aluminum sulfate (alum) — Ferric chloride and polyaluminum chloride are others.

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