UV Photodecomposition of Water-Borne Chemicals
By Uri Levy
In many water applications, the presence of dissolved chemicals is undesired. Here are some examples: ozone in bottled water, organics in water for wafer etching, free chlorine in pre-reverse-osmosis water (damaging to the membranes), and chloramines in swimming-pool water. In water lines of pharmaceutical plants, the (minute) concentrations of most of these chemicals are strictly regulated. Fortunately, for all examples mentioned above, ultraviolet (UV) light may offer a partial or a complete solution. Under UV light at the right wavelength, all of the above-mentioned water-borne chemicals will decompose. And UV light is a very ﾓcleanﾔ technology; UV systems are easily installed in-line, typically drop very little hydraulic pressure, and are relatively inexpensive. It is thus of great interest to many water-intensive industries, to possess a theory by which the kinetics of (the time-dependence of) the concentration of the water-borne chemical in question can be predicted under various operating conditions. A very basic such theory is presented in this article. And despite the applied simplifications and the used approximations, the physical essence (applied to actual field cases) is preserved, and important insights are gained.
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