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ULTRAVIOLET (UV) RADIATION DISINFECTION

ULTRAVIOLET (UV) RADIATION DISINFECTION. UV Radiation. UV Disinfection. Physical process ( inducing photobiochemical changes within microorganisms ) Two conditions must be met: Radiation of sufficent energy to alter chemical bonds must be available

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ULTRAVIOLET (UV) RADIATION DISINFECTION

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  1. ULTRAVIOLET (UV) RADIATION DISINFECTION

  2. UV Radiation

  3. UV Disinfection • Physicalprocess (inducingphotobiochemicalchangeswithinmicroorganisms) • Twoconditionsmust be met: • Radiation of sufficentenergytoalterchemicalbondsmust be available • Suchradiationmust be absorbedbythetargetmoleculeormicroorganism • Eʎ = (h*Cv*AN)/ʎ Eʎ= Radiantenergyassociatedwithgivenwl(kcal/einstein) h = Planck’sconstant, 1.583 * 10-37kcal.s Cv = Speed of electromagneticradiation in a vacuum, 3 * 1017nm/s ʎ = Wl of electromagneticradiation, nm AN = Avogadro’snumber, 6.023*1023photons/einstein

  4. Eʎ = 112.8 kcal/einstein ʎ = 253.7 nm

  5. Physicalprocess (inducingphotobiochemicalchangeswithinmicroorganisms) • Twoconditionsmust be met: • Radiation of sufficentenergytoalterchemicalbondsmust be available • Suchradiationmust be absorbedbythetargetmoleculeormicroorganism DNA and RNA arethetwomostcommonforms of nucleidacid, thatconsists of singleordoublestrandedpolymerscomprisingbuildingblockscallednucleotides. Purines: Adenine, Guanine Pyrimidines: Thymine, Cytosine (DNA), Uracil, Cytosine (RNA) Strongabsorbers of UV light.

  6. Source of UV Radiation • Low-PressureLow-intensity UV Lamps: Produceessentiallymonochromatic UV light at 253.7 nm. UV light is producedbymercury at lowvaporpressure. • Low-PressureHigh-Intensity UV Lamps: Mercury-indium amalgam is used. Allows2-4 timesgreater UV-C output. 25% greaterlamp life. • Medium-PressureHigh-Intensity UV Lamps: Mercuryvaporemission is carriedout at higherlamppressuresandtemperatures. Producepolychromatic UV light.

  7. UV ReactorConfiguration • Open – ChannelDisinfectionSystems Lampplacement can be • Horizontal • Vertical • Closed – ChannelDisinfectionSystems • Inmostdesignconfigurations, thedirection of flow is perpendiculartotheplacement of thelamps

  8. UV Intensityand UV Dose • UV Intensity is a measure of radiativepowerperunit of exposedarea. The total UV intensity at a point in space is thesum of theintensity of UV lightfromalldirections. • UV Dose is theintegral of UV intensityduringexposureperiod.

  9. UV Dose D = I x t D = UV dose, mWs / cm2 I = UV intensity, mW / cm2 t = Exposure time, s

  10. UV DisinfectionKinetics • Themeasuredconcentration of microorganismsbeforeandafterexposureprovidestheresponse, orlogreduction of microorganismsfromexposureto UV light. • LogReduction = log (N0 / N), where, • N0 is theconcentration of infectiousmicroorganismsbeforeexposureto UV light • N is theconcentration of infectiousmicroorganismsafterexposureto UV light. • UV dose – responserelationships can be expressed as eithertheproportion of microorganismsinactivated (logreduction) ortheproportion of microorganismsremaining (logsurvival) as a function of UV dose.

  11. FactorsAffecting UV Disinfection • Flow Rate • UVT • SuspendedSolids • WaterQuality • Iron • Hardness D = I x t

  12. UVT • UVT is thepercantage of lightpassingthroughmaterialover a specifieddistance.

  13. SuspendedSolids • Shadowing • Microbeswithinparticles • Potentialformicrobestopassthroughsystemwithoutseeing UV light

  14. WaterQuality • IronandHardness Deposition of minerals on thesleeve

  15. WaterQuality • Iron is a strongabsorber of UV light

  16. Advantages of UV Disinfection • Effectivedisinfectant • Moreeffectivethanchlorine in inactivatingmostviruses, spores, cysts • No chemicaladditionrequired • No formation of disinfectionbyproducts • Waterretainsitsnaturalflavourandsmell • Microorganisminactivationachievedwithinseconds • Maxoperationalsafety • Minimal operatingcosts

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