Ultraviolet UV Disinfection in Water Treatment Hans van

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 q Ancient Hindu source written at least 4000 years ago - raw water be boiled, exposed to sunlight, filtered, and then cooled in an earthen vessel. q. Germicidal properties of sunlight: 1887 q Artificial UV light (Mercury lamp) developed: 1901 q First application in drinking water: Marseilles, France in 1910 q Substantial research on UV in the first half of 20 th century q Limited field application: Low cost and maturity of Cl 2 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 q Chlorinated disinfection byproducts (DBPs): THM, HAA etc. q Potential to inactivate protozoan: Cryptosporidium - resistant to Cl 2 UV Radiation 400 nm Radio IR q UV light: 100 to 400 nm Visible Light 100 nm UV X-Rays UV spectrum – 4 regions o Vacuum UV: 100– 200 nm l UV-A UV-B UV-C Vacuum UV o UV – C : 200 – 280 nm o UV – B : 280 – 315 nm 300 nm o UV – A : 315 – 400 nm 200 nm Germicidal Range

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

ULTRAVIOLET RADIATION n n 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 q Disinfection by UV radiation- physical process- electromagnetic waves are transferred from a UV source to an organisms cellular materials (especially genetic materials) q UV light does not necessarily kill the microbial cell q. 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 q Different microorganisms have different degree of susceptibility to UV radiation depending on DNA content q Viruses are the most resistant q. Microbial repair: regain of infectivity

UV Lamps q UV light can be produced by the following lamps: Ø Low-pressure (LP) mercury vapor lamps Ø Low-pressure high-output (LPHO) mercury vapor lamps Ø Medium-pressure (MP) mercury vapor lamps Ø Electrode-less mercury vapor lamps Ø Metal halide lamps Ø Xenon lamps (pulsed UV) Ø Eximer lamps Ø 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 n 20 -25 Seconds n 30% power efficiency n 0. 3 k. W n $2500 per lamp n 85% at 253. 7 nm MEDIUM PRESSURE n 2 -5 Seconds n 20% power efficiency n 3. 0 k. W n $25, 000 per lamp n Equals 7 -10 low pressure lamps n Wide range wavelength

ULTRAVIOLET WAVELENGTHS

UV Dose q The effectiveness of UV disinfection is based on the UV dose to which the microorganisms are exposed q UV dose is analogous to Cl 2 dose = Cl 2 conc. x contact time (t) or Cx t UV dose (D) = I x t or if intensity not constant Where, D = UV dose, m. W. s/cm 2 or m. J/cm 2 I = UV intensity, m. W/cm 2 t = exposure time, s q UV dose can be varied by varying either the intensity or the contact time

UV Disinfection Kinetics – Similar to Cl 2 Disinfection d. N/dt = Rate of change in the concentration of organisms with time k = inactivation rate constant, cm 2/m. W. s I = average intensity of UV light in bulk solution, m. W/cm 2 N = number of microorganisms at time t t = exposure time, s Residual microorganisms protected in particles

UV dose required for a 4 log inactivation of selected waterborne pathogens Pathogens UV dose m. J/cm 2 4 log inactivation (99. 99) Cryptosporidium parvum oocysts <10 Giardia lamblia cysts <10 Vibrio cholerae 2. 9 Salmonella typhi 8. 2 Shigella sonnei 8. 2 Hepatitis A virus 30 Poliovirus Type 1 30 Rotavirus SA 11 36 http: //www. trojanuvmax. com/institutions/disinfection_article 2. html

Components of UV Disinfection System q 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 v Open-Channel System v Closed-Channel System

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

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

Lamp Array

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 q Reactor Hydraulics: reduced activation due to poor reactor hydraulics resulting short-circuiting Ø density current – incoming water moving top/bottom of UV lamp Øinappropriate entry and exit conditions : uneven velocity profiles Ødead zones within reactor Short circuiting/dead zone reduces the contact time v 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

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

q Characteristics of Microorganisms - Inactivation governed by the DNA/RNA content Pathogens UV dose m. J/cm 2 4 log inactivation (99. 99) Cryptosporidium parvum oocysts <10 Giardia lamblia cysts <10 Vibrio cholerae 2. 9 Salmonella typhi 8. 2 Shigella sonnei 8. 2 Hepatitis A virus 30 Poliovirus Type 1 30 Rotavirus SA 11 36 http: //www. trojanuvmax. com/institutions/disinfection_article 2. html

Effect of Water constituents on UV Disinfection