Inactivating and eliminating bacteria from ultra pure water (UPW) systems is always a significant problem for semiconductor and pharmaceutical industries. To alleviate the problem, ultraviolet (UV) radiation—both monochromatic UV254 light and high pressure UV185 light—is traditionally used for bacterial sterilization and in the case of the later, breakdown of trace organic molecules. The focus of this work is to understand the factors that influence the effectiveness of these UV treatments on Xanthomonas sp. bacteria typically found in UPW systems. In particular, the factors associated with the reactor condition, such as the light source and environment were investigated. It is shown that inactivation follows first order kinetics, and that the rates are comparable to others found in the literature for gram negative bacteria. Also, growth phase and harvesting conditions are shown to influence inactivation rate. Furthermore, it was determined that UV185 radiation, although limited by water absorption, significantly enhances the inactivation rate of bacteria if given suitable transmission distance. Rates of inactivation were enhanced by 40% when UV185 light is used in addition to UV254 light.

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