UC San Diego

A terrorist attack involving chemical and/or biological warfare agents is a growing possibility. Since anthrax is considered as an immediate public-health threat that can be created by a warfare agent, it is imperative to investigate the potential remediation technologies effective against this threat. In this study, the effectiveness of two gaseous disinfectants, ozone and chlorine dioxide, to inactivate B.subtilis spores - as surrogate to B.anthracis that can cause the infectious anthrax disease - was investigated. The inactivation rates and mechanisms of the spores by these disinfectants were investigated in both the gaseous and aqueous phases under various experimental conditions. In the gaseous phase, chlorine dioxide was found to be at least ten times more effective than ozone for inactivation of the spores under the similar conditions. The rate of inactivation by both disinfectants increased with increasing gas concentration, contact time and relative humidity (RH). Inactivation was found impractical at humidity levels below 70%. The concentration X time, or the CT concept, was valid only under limited conditions. A diffusion limited disinfection model was proposed to mechanistically explain the deviations from the linear CT rule. The experiments with different surface materials showed that the type of surface on which the spores rest may affect the inactivation rate significantly. In the aqueous phase, the CT concept was applicable to the inactivation rate data for both disinfectants. Ozone was shown to be much more effective than chlorine dioxide in inactivating spores in the aqueous phase. The presence of the main growth nutrients was found to be essential for the growth and the resistance of the spores. The presence of several cations, especially magnesium and manganese, in the growth medium was required to create spores with high resistance against the gaseous disinfectants. In conclusion, this research provides the groundwork for application of ozone and chlorine dioxide for remediation of an enclosed space that is subject to contamination by biological agents. In addition, it offers valuable kinetic and mechanistic information on the inactivation patterns of B.subtilis spores by ozone and chlorine dioxide in both the gaseous and the aqueous phases