Practice Test Geeks(WTO) Water Treatment Operator Certification Practice Test
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Disinfection Processes Flashcards

7 cards from real WTO practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A water plant uses ozone as a primary disinfectant. What secondary disinfectant must also be used?

    Answer: A residual-forming disinfectant such as chlorine or chloramine

    Ozone does not persist in the distribution system, so a secondary disinfectant (chlorine or chloramine) must be added to maintain a detectable residual as required by regulations.

  2. Which of the following best describes the concept of 'disinfectant demand'?

    Answer: The amount of disinfectant consumed by reactions with organic matter and reducing substances before a residual forms

    Disinfectant demand is the portion of applied disinfectant consumed by reactions with organic matter, metals, and other substances, preventing it from forming a residual.

  3. At what pH range is hypochlorous acid (HOCl) the predominant form of free chlorine?

    Answer: pH below 7.5

    HOCl predominates at pH below approximately 7.5; above this, the less effective hypochlorite ion (OCl⁻) becomes dominant.

  4. What is the maximum contaminant level (MCL) for total trihalomethanes (TTHMs) under the Stage 2 DBPR?

    Answer: 0.080 mg/L

    The Stage 2 DBPR sets the MCL for TTHMs at 0.080 mg/L (80 µg/L), enforced as a locational running annual average (LRAA).

  5. Which condition promotes the formation of bromate during ozone disinfection?

    Answer: High bromide concentration and high ozone dose

    Bromate forms when ozone oxidizes bromide ions; higher bromide levels and higher ozone doses increase bromate formation.

  6. An operator increases the ammonia feed rate when making chloramines. The most likely result if too much ammonia is added is:

    Answer: Excess ammonia in the distribution system promoting nitrification

    Excess ammonia beyond the chlorine-to-nitrogen ratio needed to form monochloramine leaves free ammonia that fuels nitrifying bacteria in the distribution system.

  7. What type of chlorine residual is measured after the breakpoint has been reached?

    Answer: Free chlorine residual

    After breakpoint, all combined chlorine (chloramines) has been destroyed; any additional chlorine added exists as free chlorine residual.