Microbial UV Fluence-Response Assessment using a Novel UV-LED Collimated Beam System – December 2010
C Bowker, J Ducoste, A Sain, and Max Shatalov Hazen and Sawyer, Department of Civil, Construction, and Environmental Engineering, North Carolina State University, Sensor Electronic Technology, Inc. SC.
A research study has been performed to determine the ultraviolet (UV) fluence-response of several target non-pathogenic microorganisms to UV light emitting diodes (UV-LEDs) by performing collimated beam tests. UV-LEDs do not contain toxic mercury, offer design flexibility due to their small size, and have a longer operational life than mercury lamps. Comsol Multiphysics was utilized to create an optimal UV-LED collimated beam design based on number and spacing of UV-LEDs and distance of the sample from the light source while minimizing the overall cost. The optimized UV-LED collimated beam apparatus and a low-pressure mercury lamp collimated beam apparatus were used to determine the UV fluence-response of three surrogate microorganisms (E. coli, MS-2, T7) to 255 nm UV-LEDs, 275 nm UV-LEDs, and 254 nm low-pressure mercury lamps. Irradiation by low-pressure mercury lamps produced greater E. coli and MS-2 inactivation than 255 nm and 275 nm UV-LEDs and similar T7 inactivation to irradiation by 275 nm UV-LEDs. The 275 nm UV-LEDs produced more efficient T7 and E. coli inactivation than 255 nm UV-LEDs while both 255 nm and 275 nm UV-LEDs produced comparable microbial inactivation for MS-2. Differences may have been caused by a departure from the time-dose reciprocity law due to microbial repair mechanisms. … 167 The incident irradiance at the surface of the liquid sample was found for the UV-168 LED experiments using a Stellarnet BLACK-Comet-100 Spectroradiometer with an attached 169 fiber optic probe to capture fine planar variations in light intensity calibrated at both 255 170
