Ultraviolet (UV) Disinfection in Water Treatment Hans van Leeuwen. Department of Civil, Construction and Environmental Engineering Iowa State University April 15, 2011

History of UV Disinfection Ancient Hindu source written at least 4000 years ago - raw water be boiled, exposed to sunlight, filtered, and then cooled in an earthen vessel. Germicidal properties of sunlight: 1887 Artificial UV light (Mercury lamp) developed: 1901 First application in drinking water: Marseilles, France in 1910 Substantial research on UV in the first half of 20th century Limited field application: Low cost and maturity of Cl2 disinfection technology coupled with operation problems associated with early UV systems

Advantage and Disadvantage of UV Disinfection 9. Fouling of UV lamps

Increasing Popularity of UV Disinfection Chlorinated disinfection byproducts (DBPs): THM, HAA etc. Potential to inactivate protozoan: Cryptosporidium - resistant to Cl2 UV Radiation Radio IR Visible Light UV X-Rays UV-A UV-B UV-C Vacuum 400nm 100nm Germicidal Range 200nm 300nm l UV light: 100 to 400 nm UV spectrum – 4 regions Vacuum UV:100–200 nm UV – C : 200 – 280 nm UV – B : 280 – 315 nm UV – A : 315 – 400 nm

Germicidal Range of UV Light Vacuum UV- most effective – attenuates rapidly in short distance – not practical UV-A : less effective – long exposure time – also not practical UV disinfection – germicidal action mainly from UV- C and partly from UV - B

ULTRAVIOLET RADIATION Physical Process Damages Nucleic Acids in Organisms Stops Reproduction of Organisms by Breaking Apart the DNA Bonds Wavelengths Between 100-400 nm

Mechanisms of UV Disinfection Disinfection by UV radiation- physical process- electromagnetic waves are transferred from a UV source to an organisms cellular materials (especially genetic materials) UV light does not necessarily kill the microbial cell UV light inactivates microorganisms by damaging nucleic acids (DNA or RNA) thereby interfering with replication of the microorganisms and therefore incapable of infecting a host Different microorganisms have different degree of susceptibility to UV radiation depending on DNA content Viruses are the most resistant Microbial repair: regain of infectivity

UV Lamps UV light can be produced by the following lamps: Low-pressure (LP) mercury vapor lamps Low-pressure high-output (LPHO) mercury vapor lamps Medium-pressure (MP) mercury vapor lamps Electrode-less mercury vapor lamps Metal halide lamps Xenon lamps (pulsed UV) Eximer lamps UV lasers Full-scale drinking water applications : LP, LPHO, or MP lamps

Mercury vapor Lamp Comparison

UV Lamp and UV Absorbance of DNA

LOW AND MEDIUM PRESSURE MERCURY LAMPS LOW PRESSURE 20-25 Seconds 30% power efficiency 0.3 kW $2500 per lamp 85% at 253.7 nm MEDIUM PRESSURE 2-5 Seconds 20% power efficiency 3.0 kW $25,000 per lamp Equals 7-10 low pressure lamps Wide range wavelength

ULTRAVIOLET WAVELENGTHS

UV Dose The effectiveness of UV disinfection is based on the UV dose to which the microorganisms are exposed UV dose is analogous to Cl2 dose Cl2 dose = Cl2 conc. x contact time (t) or Cx t UV dose (D) = I x t or if intensity not constant Where, D = UV dose, mW.s/cm2 or mJ/cm2 I = UV intensity, mW/cm2 t = exposure time, s UV dose can be varied by varying either the intensity or the contact time

UV Disinfection Kinetics – Similar to Cl2 Disinfection dN/dt = Rate of change in the concentration of organisms with time k = inactivation rate constant, cm2/mW.s I = average intensity of UV light in bulk solution, mW/cm2 N = number of microorganisms at time t t = exposure time, s Residual microorganisms protected in particles

UV dose required for a 4log inactivation of selected waterborne pathogens Pathogens UV dose mJ/cm2 4log inactivation (99.99) Cryptosporidium parvum oocysts <10 Giardia lamblia cysts Vibrio cholerae 2.9 Salmonella typhi 8.2 Shigella sonnei Hepatitis A virus 30 Poliovirus Type 1 Rotavirus SA11 36 http://www.trojanuvmax.com/institutions/disinfection_article2.html

Components of UV Disinfection System Components of UV system 1. UV lamps 2. Quartz sleeves: to house and protect lamp 3. supporting structures for lamps and sleeves 4. Ballasts to supply regulated power to UV lamps 5. Power supply 6. Sleeve wiper – to clean the deposit from sleeves UV Reactors Open-Channel System Closed-Channel System

Open-Channel Disinfection System Lamp placement: horizontal and parallel to flow (a) : vertical and perpendicular to flow (b) Flows equally divided into number of channels Each channel - two or more banks of UV lamps in series Each bank - number of modules (racks of UV lamps) Each module: number of UV lamps (2, 4, 8, 12 or 16)

Closed-Channel Disinfection System Mostly flow perpendicular to UV lamp Mechanical wiping: clean quartz sleeves Drinking Water installation, Busselton, Australia

Lamp Array

Absorption (Bear’s law): Point Source Summation a. Intensity Attenuation Dissipation: b. Calculation Protocol Absorption (Bear’s law): Divide lamp into N sections Power output of each section Intensity at a given distance from a single point source of energy: Add all point-source contributions:

Factors Affecting UV Disinfection Reactor Hydraulics: reduced activation due to poor reactor hydraulics resulting short-circuiting density current – incoming water moving top/bottom of UV lamp inappropriate entry and exit conditions : uneven velocity profiles dead zones within reactor Short circuiting/dead zone reduces the contact time Remedial measures for open-channel system Submerged perforated diffuser Corner fillets in rectangular channel with horizontal lamps Flow deflectors with vertical lamps Ideally plug-flow reactor

closed-channel system Remedial measures for closed-channel system perforated plate diffuser Plumb correctly Presence of Particles: - reduce the intensity of UV dose acts as shield to protect the particle-bound pathogens

Characteristics of Microorganisms - Inactivation governed by the DNA/RNA content Pathogens UV dose mJ/cm2 4log inactivation (99.99) Cryptosporidium parvum oocysts <10 Giardia lamblia cysts Vibrio cholerae 2.9 Salmonella typhi 8.2 Shigella sonnei Hepatitis A virus 30 Poliovirus Type 1 Rotavirus SA11 36 http://www.trojanuvmax.com/institutions/disinfection_article2.html

Effect of Water constituents on UV Disinfection