UV FUNDAMENTALS

F Ultraviolet is… u A Type of Electromagnetic Energy u Found Between X-Rays and Visible Light u Wavelength Range: 5 nm to 400 nm Rays Rays X Rays Ultraviolet Visible Infrared RadioFrequencies Wavelength (m) The Electromagnetic Spectrum What is UV?

The Electromagnetic Spectrum nanometres 185 nm nm Rays Rays X Rays Ultraviolet Visible Infrared RadioFrequencies Wavelength (m)

Increasing Water Penetration Increasing Energy VUV Vacuum UV UVCGermicidalUVBSuntan UVA Blacklight 100 nm nm What is UV?

hc UV Energy E : λ λ h : c : λ : E = Energy carried by a light beam Plancks constant = 6.62 x joule-second Velocity of light = x 10 8 m/s Wavelength of light, nanometers (nm)

UV Dosage UV Intensity x Time UV Intensity Time Note : UV Dosage = : µW-s/cm 2 : µW/cm 2 : seconds Industry standard disinfection dose equals 30 µW-s/cm 2 Effective dosage can be improved by decreasing the flow rate decreasing the flow rate use UV lamps with greater UV intensity use UV lamps with greater UV intensity Change in water quality affects UV dose

How Is Ultraviolet Light Generated? ELECTRODE + ELECTRODE - Excitation of Hg Atom Mercury Vapor Arc Tube

UV Absorption by DNA Relative Effectiveness Germicidal Wavelength (nm)

UV Transmittance - a beam of UV light is directed through a sample of water to be tested, using a known UV light source. The amount (%) of UV which transmits through the the sample is measured and thus gives an indication of water quality. Average UV transmissivity of some different water sources: Measuring Water Quality For Proper UV System Sizing UV absorbed in fluid 40 mm wide sample cell UV Method #1: % UV Transmission % UV Transmission Distilled water ~ 98% Well water ~ 70% River water ~ 50% Waste water ~ 40% Food process ~ 20% UV sensor UV light source Spectrophotometer

UV Lamp Life Lamp Output % Hours Low Pressure SuperTOC Medium Pressure Advanced SuperTOC UV Lamp Technology 140% = Initial UV dose of new lamp 100% = Desired minimum dose at end of lamp life Standard Medium Pressure UV Output Degradation Low Pressure – 5% Loss/1000 hrs Std. Med Press – 10% Loss/1000 hrs SuperTOC – 5% Loss/1000 hrs

Aging of UV Lamps Quartz UV Quartz New Lamp Aged Lamp Solarization Solarization – Heat & high intensity UV cause build-up of impurities in quartz matrix as lamp ages which increasingly filters out lower UV wavelengths 100%60% 100%

Temperature of Low Pressure UV Lamp Surface (°C) Temperature of Water Relative UV Output NM Effect of Fluid Temperature on UV Lamp Performance UV(%) Medium Pressure Lamp UV Output Low Pressure Lamp UV Output (°C) (°F) Optimum temperature – low pressure lamp

TOC Reduction Mechanisms of UV 1.) Conversion of non-ionic organic molecules to charged species enabling ion exchange removal 2.) Production of hydroxyl radicals (OH) which oxidize amenable molecular bonds causing photochemical breakdown 3.) Emission of high energy photons which dissociate refractory molecular bonds % Contribution to TOC Reduction* 25%65%10% * - approximate value, depends on contaminant(s)

Mixed-Bed DI UV and Deionization TOC Reduction Mechanism # 1 Conversion into a charged species

TOC Reduction Mechanism The OH radical is one of the most powerful oxidizing agents known to science. H + OH H2OH2OH2OH2O UV <242nm CO H 2 O Organics + OH Hydroxyl free-radicals (OH) are mainly responsible for oxidizing the organics to carbon dioxide and water molecules. # 2 Creation of hydroxyl radicals

Oxidation Potential F 2 OH OH O O 3 H 2 O 2 Cl eV 2.80 eV 2.42 eV 2.07 eV 1.70 eV 1.36 eV * eV = electron volts Second strongest oxidant

OH Hydroxyl Radicals H 2 O Water O H H UV H H H 2 O + hv H( 2 S 1/2 ) + OH( 2 H) Primary process for photolysis: Generating the Hydroxyl Radical OH In Water With Ultraviolet Light Energy *This reaction becomes possible energetically at wavelengths less than 242nm. J. Gilbert, J. Pitts, Photochemistry, 200

Progress of the reaction Final state Energy required to overcome inter-molecular bonds Net energy change Energy Barrier Ground state OH CN OH H Energy OH CNO + H H Initial Reactant O COH + H 2 N Intermediary Photon Energy via UV Light Source Water TOC Reduction Mechanism # 3 Dissociation of molecular bonds

Bond Dissociation Energies In Organic Compounds Possibility of Dissociation with 185 nm UV Maximum Wavelength for Dissociation DissociationEnergy yesyesnoyesyesyesyesyesnoyesnonoyesyesyesnoyesyesnoyesyesyes CCCCCCCCCCCCHNNNNNNOOOCCCCCCCCCCCCHNNNNNNOOO Bond C Cl F H N O O (aldehydes) O (ketones) H N H (NH) H (NH 3 ) O O (O2) O H (water)