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

WW secondary: fixed film: practice questions

Our Water/Wastewater Operator bank has 6 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

What is a trickling filter?

  1. A chemical clarifier
  2. A bed of media where wastewater trickles over a biological slime layer
  3. A sand filter used to polish the final effluent before discharge
  4. A sand filter for final effluent
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B. A bed of media where wastewater trickles over a biological slime layer — Microbes on the media consume organics.

Question 2 · Wastewater Treatment Class I

What is sloughing in a trickling filter?

  1. Flies breeding in the media
  2. Pieces of biofilm breaking off the media
  3. Media cracking
  4. Water ponding on top of the media because the distributor arm has stopped
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B. Pieces of biofilm breaking off the media — Sloughed solids settle in the secondary clarifier.

Question 3 · Wastewater Treatment Class I

How can filter flies on a trickling filter be controlled?

  1. Turn off the flow to the filter for several days
  2. Increase recirculation or flood the filter briefly
  3. Lower the temperature
  4. Turn off all flow to the filter for several days until the flies leave
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B. Increase recirculation or flood the filter briefly — Keeping media wet disrupts fly breeding.

Question 4 · Wastewater Treatment Class I

What causes ponding on a trickling filter?

  1. Excess biological growth or debris plugging the media
  2. Cold weather alone
  3. High chlorine in the influent
  4. Too little flow reaching the media, so the slime layer dries out and dies
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A. Excess biological growth or debris plugging the media — Flushing or chlorinating the influent can help.

Question 5 · Wastewater Treatment Class I

What does white or gray biomass on RBC disks suggest?

  1. Sulfur bacteria from overloading or low oxygen
  2. Normal winter growth
  3. Healthy, normal growth of nitrifying bacteria in the last stages of the unit
  4. Nitrification only
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A. Sulfur bacteria from overloading or low oxygen — Healthy biomass is brown.

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