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. Chlorine dioxide (ClO₂) used for disinfection must be generated on-site because:

    Answer: It is an unstable gas that cannot be safely stored or transported

    Chlorine dioxide is a highly reactive gas that decomposes rapidly and poses explosion risks, making on-site generation mandatory.

  2. What byproduct concern is unique to chlorine dioxide disinfection?

    Answer: Formation of chlorite and chlorate ions

    Chlorine dioxide produces chlorite (ClO₂⁻) and chlorate (ClO₃⁻) as byproducts, which are regulated under the DBPR.

  3. What is the purpose of a chlorine contact chamber (CCC) in a water treatment plant?

    Answer: To ensure sufficient contact time between chlorine and water for pathogen inactivation

    The CCC is designed to maximize contact time between chlorine and water, achieving the required CT for inactivation credit under surface water treatment rules.

  4. An operator notices breakpoint chlorination requires more chlorine than expected. The most likely cause is:

    Answer: Elevated ammonia or organic nitrogen in the source water

    Elevated ammonia or organic nitrogen demands more chlorine to reach breakpoint because chloramines must first be formed and then destroyed before free chlorine residual appears.

  5. Which factor does NOT affect ozone disinfection effectiveness?

    Answer: Water fluoride concentration

    Fluoride concentration does not influence ozone disinfection; temperature, pH, and organic matter (contributing to color) all affect ozone demand and CT.

  6. Under the Surface Water Treatment Rule, what is the minimum log-inactivation credit required for Giardia lamblia?

    Answer: 3-log

    The SWTR requires at least 3-log (99.9%) inactivation of Giardia lamblia through a combination of filtration removal and disinfection CT credit.

  7. What is the key difference between primary and secondary disinfection in a treatment plant?

    Answer: Primary achieves initial pathogen inactivation; secondary maintains residual through distribution

    Primary disinfection targets pathogen inactivation at the plant, while secondary disinfection (typically chlorine or chloramine) maintains a protective residual in the distribution system.