Ultraviolet (UV) irradiation is being used with increasing regularity for swimming pool water treatment. When properly designed and operated, UV-based systems can be effective for disinfection and for photolysis of chemical constituents. However, proper design of UV systems requires information regarding the basic physics and chemistry that govern their behavior. The focus of this presentation will be on the effects of UV systems on swimming pool chemistry, as well as the effects of swimming pool chemistry on the behavior of UV systems. Experiments were conducted to examine the effectiveness of UV irradiation as a process for photolytic degradation of inorganic chloramines. The results of these experiments allowed definition of the wavelength-dependence of these reactions, their kinetics, mechanisms, and the (stable) products of photodecay. These experiments also allowed for characterization of the effects of solution chemistry (pH and common buffers) on reaction kinetics and product formation. Water chemistry can also have a profound influence on the behavior of UV reactors. Measurements of aqueous constituents in swimming pool water samples indicated that most pool waters will transmit UV radiation at wavelengths above (ca.) 240 nm quite effectively; however, at shorter wavelengths, UV absorbance can be quite high. Although a number of compounds could contribute to this behavior, available data indicate that nitrate (NO3-) is an important contributor to UV absorbance at wavelengths below roughly 240 nm in most pools. The effects of NO3- on process performance of UV systems will be presented. This presentation will include information as to how this fundamental information should be incorporated into the design of UV systems for swimming pool water treatment. The results of these experiments also provide some information regarding the selection of a UV system for swimming pool applications. Dr. Blatchley has been a Professor in the School of Engineering at Purdue University since 1999. He earned his Masters Degree and Ph.D. in Civil Environmental Engineering from the University of California, Berkeley. He is a Professional Engineer in the State of Indiana and a Board Certified Environmental Engineer in the Specialty of Water Supply and Wastewater from the American Academy of Environmental Engineers. He has worked to receive U.S. Patents on two inventions, receiving one in 1999 while the patent is pending on the other. He is a member of the American Academy of Environmental Engineers, American Chemical Society, American Society of Civil Engineers, Association of Environmental Engineering and Science Professors, Indiana Water Environment Association, International Water Association, and the Water Environment Federation.
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