Effect of pH and importance of ozone initiated radical reactions in inactivating Bacillus subtilis spore

The effect of pH on the inactivation of Bacillus subtilis spores with ozone in a batch reactor was examined in association with the role of OH radicals. The exact effect OH radicals have on ozone inactivation of microorganism is not well understood, although a direct reaction of molecular ozone has sometimes been emphasized. This study reports a novel observation that the presence of OH radicals plays a significant role in microbial inactivation. Considering the dependence of the ozone decay rate on pH, the observed C̄ T values for achieving a 2 log inactivation using the modified Chick-Watson model was 40% lower at pH 8.2 compared to that at pH 5.6. In the presence of OH radical scavengers (tert-butanol), the observed change of C̄ T with pH was within 10%. This difference could be explained by the significant role of OH radicals.