Hannah Saunder's MSPH Technical Report Defense
|December 07, 2005|
|Hannah Saunder’s MSPH Technical Report Defense is scheduled for December 6th at 9:00AM in 2005 Michael Hooker Research Center. Full details follow.Inactivation of Adenoviruses type 5 and 41 by Low and Medium Pressure UV Light
Abstract UV technology is a promising candidate disinfection technology for compliance with the Stage 2 Disinfectants and Disinfection Byproduct rule (DBPR) and Long Term 2 Enhanced Surface Water Treatment Rule requiring further drinking water treatment for certain pathogens and DBP reductions. Ultraviolet (UV) irradiation is an effective drinking water disinfection treatment for inactivation of many important waterborne pathogens that are resistant to chemical disinfection and it does not appreciably produce potentially harmful disinfection by-products. However, certain enteric viruses are much more resistant to UV than vegetative bacteria, parasites, and even bacterial spores. UV technology is not currently optimized due to a lack of understanding of its inactivation effectiveness. Data are lacking on the relative effectiveness of low pressure (low intensity and monochromatic) and medium pressure (high intensity and polychromatic) mercury lamps against relatively UV-resistant viruses such as adenoviruses. This study investigates the effects of low and medium pressure UV radiation on adenovirus 5 (Ad5), and adenovirus 41 (Ad 41) in model waters. In a collimated (quasi-parallel) beam UV disinfection system using low and medium pressure lamps applied to dispersed Ad5 in Dulbecco?s PBS log10 reductions at absorbance-corrected UV doses of 40, 80, and 120 mJ/cm2 were 1.8, 2.9, and 3.5 with low pressure lamps and 2.9, 3.8, and 4.7 with medium pressure lamps, respectively. With the same set-up, low and medium pressure UV applied to dispersed Ad41 in Dulbecco?s PBS gave log10 reductions at absorbance-corrected UV doses of 50, 100, and 150 mJ/cm2 were 0.35, 1.1, and 2.4 with low pressure lamps and 0.8, 1.6, and 3.4 with medium pressure lamps, respectively. In a highly colored natural water diluted to a DOC of approximately 20 mg/L and dispersed Ad5, low pressure UV log10 reductions of dispersed Ad5 were 1.3, 2.2, and 3.0 absorbance-corrected UV doses of 40, 80, and 120 mJ/cm2, respectively. In this same diluted natural water spiked with Bentonite clay to 5 NTU, low pressure log10 reductions of Ad5 were 1.6, 3.6, and 4.3 at absorbance-corrected UV doses of 40, 80, and 120 mJ/cm2, respectively. Thus, at the same UV doses the medium pressure lamps inactivated adenoviruses more effectively than did the LP lamps. Waters containing higher levels of dissolved organics, such as humic and fulvic acids, reduced the efficiency of UV inactivation of adenoviruses. Waters containing clay particles actually increased the effectiveness of UV for Ad disinfection. We hypothesize that clay particles may scatter UV light and in a collimated beam set-up, thereby increasing viral exposure to UV radiation. Data from these studies will inform the decision-making process to develop guidance for optimized pathogen inactivation in water by UV disinfection.
For further information please contact Rebecca Riggsbee Lloyd by email at Rebecca_Lloyd@unc.edu