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

WW lab: practice questions

Our Water/Wastewater Operator bank has 15 questions on this topic. Here are 5 of them with answers; the full mock exam draws from every topic, like the real one.

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Question 1 · Wastewater Treatment Class I

How does COD differ from BOD?

  1. COD uses a strong chemical oxidant and takes hours, not days
  2. COD is always lower than BOD
  3. COD measures bacteria and is always lower than BOD
  4. COD measures bacteria directly and is always lower than BOD for the same sample
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A. COD uses a strong chemical oxidant and takes hours, not days — COD is usually higher than BOD.

Question 2 · Wastewater Treatment Class I

What does an Imhoff cone measure?

  1. pH
  2. Settleable solids in mL/L
  3. Ammonia
  4. Dissolved oxygen in the effluent
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B. Settleable solids in mL/L — Settle for 60 minutes.

Question 3 · Wastewater Treatment Class I

What does CBOD measure?

  1. Carbonaceous BOD, with nitrification inhibited
  2. Coliform BOD after chlorination
  3. Chlorine BOD, measured after the effluent is chlorinated and dechlorinated
  4. Combined BOD and COD
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A. Carbonaceous BOD, with nitrification inhibited — Many permits use CBOD.

Question 4 · Wastewater Treatment Class I

What does the total suspended solids (TSS) test measure?

  1. Dissolved salts left after evaporating a filtered sample at high temperature
  2. Solids caught on a filter, dried at 103–105°C and weighed
  3. Volatile acids in sludge
  4. Settled volume in a cone
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B. Solids caught on a filter, dried at 103–105°C and weighed — TSS is a permit parameter.

Question 5 · Wastewater Treatment Class I

Influent BOD is 200 mg/L and effluent BOD is 10 mg/L. What is the removal efficiency?

  1. 5%
  2. 90%
  3. 95%
  4. 98%
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C. 95% — (200 − 10) ÷ 200 × 100.

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