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Photocatalytic oxidation is a process in which a semiconductor upon adsorption of a photon acts as a catalyst in producing reactive radicals, mainly •OH radicals, which in turn can oxidize contaminant species. These •OH radicals completely mineralize even the dead microbial species to carbon dioxide and water, thus providing a highly efficient, non-residual disinfecting mechanism. Past research at the University of Florida has proven TiO2 photocatalysis with 350 nm ultraviolet (UVA) light as a highly effective process for complete inactivation of airborne microbes. However, the overall efficiency of the technology needs to be improved to make it commercially viable as an air disinfection process and as a defense against the threat of bio-terrorism. The present research investigates the enhancement in the photocatalytic rate of destruction of microbes with an Ag-TiO2 photocatalyst. The effectiveness of this enhanced photocatalyst has been successfully tested for bacterial spores, gram-positive bacteria, gram-negative bacteria, fungal spores and virus in a still air as well as a recirculating air experimental facility. Bacillus cereus, Staphylococcus aureus, Escherichia coli, Aspergillus niger, and MS2 Bacteriophage have been used as indexes to demonstrate the high disinfection efficiency of the Ag-TiO2/+UVA process. The results indicate complete inactivation of Bacillus cereus bacterial spores in about 10 minutes and Aspergillus niger fungal spores in 30 minutes with the enhanced photocatalytic process. The relative humidity (RH) of air is known to have an effect on the rate of photocatalysis. In this research, the effect of RH on photocatalytic disinfection has been experimentally and theoretically analyzed. An optimum RH range of 35-65% has been determined for photocatalytic destruction of Bacillus cereus spores in indoor air, and possible explanations of these results have been presented. The effect of surface roughness of photocatalytic reactor passages on the process reaction kinetics has also been studied. Two different shapes of roughness elements have been investigated, and their optimum heights and pitch ratios (along and across the flow direction) for maximum enhancement in turbulence quantities, and hence improvement in mass transport, have been determined using FLUENT. An optimum height of 0.1 mm and optimum pitch ratios in the range 8-10 were found.
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