Investigation of Gas-Phase Ozone as a Potential Biocide

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Abstract
Ozone has been used as a germicidal agent for drinking water since 1903, and its activity in the aqueous phase is well documented. However, despite the wide use of ozone generators for indoor air treatment, there is little research data on ozone's biocidal activity in the gas phase. This article presents experimental data on the effect of ozone on both vegetative and spore-forming fungi as well as a spore-forming bacterium. Dried suspensions of the test organisms were exposed to a range of ozone concentrations from 3 to 10 ppm in 50-L Teflon-coated stainless steel chambers. A two-phase study was performed. The first phase was an extensive series of tests on the efficacy of ozone itself. Tests using organisms deposited on glass slides to minimize losses of ozone were carried out under conditions of high (90%) and low (30%) relative humidity (RH). For the organisms used in this study, ozone concentrations in the range of 6 to almost 10 ppm were required for significant kill. Organisms exposed under high RH conditions were generally more susceptible to ozone. The second phase of tests employed actual building materials as the test surfaces. No microbial kill was demonstrated on any of the building materials even at 9 ppm ozone.