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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. What is 'UV fluence' (also called UV dose) and how is it expressed?

    Answer: The product of UV irradiance and exposure time, expressed in mJ/cm²

    UV fluence is the product of irradiance (mW/cm²) and contact time (seconds), yielding a dose in mJ/cm² that determines inactivation efficacy.

  2. Why is a quartz sleeve used around UV lamps in water systems rather than direct lamp-to-water contact?

    Answer: It isolates the lamp from water while transmitting UV-C, protecting the lamp and allowing safe replacement

    The quartz sleeve keeps the lamp dry and at optimal operating temperature while transmitting UV-C radiation through to the water with minimal attenuation.

  3. A UV system's 'validated dose' is established through what process?

    Answer: USEPA/DVGW-compliant bioassay challenge testing at a certified hydraulics test facility

    Validated doses must be established by third-party bioassay testing at certified facilities following USEPA UV Disinfection Guidance Manual or equivalent protocols.

  4. Which water quality parameter, if elevated, most reduces UV system effectiveness by absorbing UV light before it reaches pathogens?

    Answer: Color and dissolved organic carbon (DOC)

    Dissolved organic carbon, tannins, and color compounds absorb UV at 254 nm, lowering UVT and reducing germicidal dose delivered to microorganisms.

  5. What operational advantage do medium-pressure (MP) UV lamps have over low-pressure (LP) lamps?

    Answer: Polychromatic UV output that addresses photoreactivation more effectively and requires fewer lamps

    MP lamps emit UV across a broad spectrum (200–400 nm), which can damage multiple DNA repair pathways and reduce photoreactivation, often allowing fewer lamps per installation.

  6. In a UV reactor, what is the role of the UV intensity sensor (radiometer)?

    Answer: To continuously monitor in-situ UV irradiance and trigger alarms if dose delivery falls below setpoints

    The UV intensity sensor provides real-time irradiance data used with flow rate to calculate delivered dose, and alarms when irradiance drops below minimum validated levels.

  7. What is 'photoreactivation' in the context of UV disinfection?

    Answer: The repair of UV-induced DNA damage by microorganisms exposed to visible or near-UV light after treatment

    Photoreactivation occurs when UV-damaged microorganisms use light-dependent enzymes (photolyases) to repair thymine dimers, potentially restoring infectivity.