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

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Presentation on theme: "Ultraviolet (UV) Disinfection in Water Treatment Hans van Leeuwen. Department of Civil, Construction and Environmental Engineering Iowa State University."— Presentation transcript:

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

2 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 20 th century History of UV Disinfection Limited field application: Low cost and maturity of Cl 2 disinfection technology coupled with operation problems associated with early UV systems

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

4 Chlorinated disinfection byproducts (DBPs): THM, HAA etc. Potential to inactivate protozoan: Cryptosporidium - resistant to Cl 2 Increasing Popularity of UV Disinfection UV Radiation UV light: 100 to 400 nm UV spectrum – 4 regions o Vacuum UV:100–200 nm o UV – C : 200 – 280 nm o UV – B : 280 – 315 nm o UV – A : 315 – 400 nm RadioIR Visible Light UVX-Rays UV-AUV-BUV-C Vacuum UV 400nm100nm Germicidal Range 200nm300nm

5 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

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

7 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

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

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10 Mercury vapor Lamp Comparison

11 UV Lamp and UV Absorbance of DNA

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

13 ULTRAVIOLET WAVELENGTHS

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

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

16 UV dose required for a 4log inactivation of selected waterborne pathogens Pathogens UV dose mJ/cm 2 4log inactivation (99.99) Cryptosporidium parvum oocysts<10 Giardia lamblia cysts<10 Vibrio cholerae2.9 Salmonella typhi8.2 Shigella sonnei8.2 Hepatitis A virus30 Poliovirus Type 130 Rotavirus SA1136

17 Components of UV Disinfection System Components of UV 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 Open-Channel System Closed-Channel System Closed-Channel System

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

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

20 Lamp Array

21 Point Source Summation a. Intensity Attenuation Dissipation: Absorption (Bears 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: b. Calculation Protocol

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

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

24 Characteristics of Microorganisms Characteristics of Microorganisms - Inactivation governed by the DNA/RNA content Pathogens UV dose mJ/cm 2 4log inactivation (99.99) Cryptosporidium parvum oocysts<10 Giardia lamblia cysts<10 Vibrio cholerae2.9 Salmonella typhi8.2 Shigella sonnei8.2 Hepatitis A virus30 Poliovirus Type 130 Rotavirus SA1136

25 Effect of Water constituents on UV Disinfection


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