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Ultraviolet Disinfection Systems Flashcards

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

Read the first 7 Ultraviolet Disinfection Systems flashcards as text

  1. Under the USEPA Surface Water Treatment Rule, what minimum UV dose (mJ/cm²) achieves 3-log inactivation of Cryptosporidium?

    Answer: 40 mJ/cm²

    The USEPA LT2ESWTR specifies that 40 mJ/cm² of validated UV dose achieves 3-log (99.9%) inactivation credit for Cryptosporidium.

  2. What is the 'reduction equivalent dose' (RED) concept used in UV reactor validation?

    Answer: The equivalent collimated-beam dose that produces the same log inactivation as the reactor under challenge test conditions

    RED translates reactor performance into a collimated-beam equivalent dose, allowing comparison with bench-scale dose-response data to confirm log-inactivation credit.

  3. Which hydraulic condition inside a UV reactor reduces germicidal effectiveness by allowing some water to pass through with minimal UV exposure?

    Answer: Short-circuiting or channeling

    Short-circuiting creates preferential flow paths where portions of the water receive insufficient UV exposure time, reducing the effective dose delivered.

  4. What is the primary reason iron and manganese are problematic for UV disinfection systems?

    Answer: They deposit on the quartz sleeve, reducing UV transmission and increasing cleaning frequency

    Oxidized iron and manganese form scale on the quartz sleeve, blocking UV transmission and necessitating frequent chemical or mechanical cleaning to maintain dose delivery.

  5. What type of ballast is required for pulsed UV lamp operation in advanced disinfection systems?

    Answer: Electronic high-frequency ballast with pulsed power delivery capability

    Pulsed UV systems require electronic ballasts capable of delivering controlled, high-peak power pulses to the lamp rather than continuous sinusoidal power.

  6. When sizing a UV system, why is the 'worst-case' UVT value rather than the average UVT used for design?

    Answer: To ensure adequate dose delivery even during periods of poorest water quality

    Designing for the lowest expected UVT ensures the system delivers the required validated dose even when water quality is at its worst, maintaining regulatory compliance continuously.

  7. What distinguishes a UV-AOPs (Advanced Oxidation Process) system from a standard UV disinfection system?

    Answer: UV-AOPs combines UV with hydrogen peroxide or ozone to generate hydroxyl radicals for contaminant destruction

    UV-AOPs generates highly reactive hydroxyl radicals by photolytically decomposing H₂O₂ or O₃ with UV light, enabling destruction of trace organic contaminants like PFAS precursors and pesticides.