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W.J. Kowalski1, W.P. Bahnfleth1, and T.S. Whittam2
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| A secondary application is the sterilization of surfaces or medical equipment with airborne concentrations of ozone. The use of UVGI and autoclaving typically require at least 20 minutes of exposure for complete sterilization of equipment. The use of ozone to sterilize equipment has the special advantage of both rapid inactivation and lower overall energy consumption. Applications also could include the sterilization of surfaces of contaminated rooms, biosafety cabinets, or entire buildings. Elimination of bacteria and viruses through ozonation should prove as effective in air as it does in water on a mass fraction basis, normalized to the mass of the fluid. Ozone does not react significantly with water or air in the absence of UV radiation over the short periods required for pathogen inactivation. These fluids merely provide the medium in which concentrations of ozone diffuse and react with organic molecules. Under ultraviolet irradiation, however, ozone reacts with water and decomposes into various short-lived radicals, such as the highly reactive hydroxyl radical. Theoretical and empirical evidence suggests that most of the sterilization effect results from the radicals produced, and not the ozone itself (Rice, 1997; Beltran, 1995). The decomposition reaction can be enhanced in air by the use of ultraviolet irradiation and through controlled humidity (NIST, 1992). Theoretically, therefore, the effects of ozone in air, under controlled conditions, should parallel the effects of ozone in water, and the effectiveness of ozone for eliminating airborne pathogens in either medium may be comparable. The purpose of the experiments described below was to determine the kinetics of disinfection for various concentrations of ozone in air. Two model bacteria organisms, E. coli and S. amreus, were used to assay a wide range of ozone concentrations and exposure times on killing rates. The results demonstrate that airborne ozone levels can effectively kill bacteria cells and sterilize surfaces. The results presented here demonstrate that high degrees of bacterial sterilization can be achieved with airborne ozone. The characteristics of the inactivation curves suggest strong parallels with ozonation of water-borne bacteria. The kill rates and exposure times in this experiment compare well with the best results obtained in numerous studies on the ozonation of pathogens in water. The results suggest that efficient sterilization of airstreams could be accomplished in a matter of seconds by the use of ozone. The complete form of the quation describing the inactivation curve for ozonated pathogens has been developed from basic chemical theory. This equation provides an accurate fit of the data over the entire length of the sufvival curve, including the tail. This equation also provides a mathematical means of separating this behavior of clumped bacteria from solitary bacteria, and thus allows the prediction of the effects of sonication. The use of sonication may enhance the ffect of ozonation in air as it does in water. The theoretical effect of sonication combined with ozonation in air has beed predicted, conservatively, to yield 99.9% inactivation within at least 40-60 seconds of exposure. |
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