Abstract
For the photochemical sterilization of thermoduric bacterial spores (Bacillus stearothermophilus), light-irradiation experiments were conducted with a square bubble-column photoreactor (4cm in width×4cm in depth×25cm in height) containing slurried TiO2 semiconductor particles (mean diameter : 21nm). Under the operational condition that TiO2 particles and dissolved oxygen coexisted in reaction mixture, the spores were effectively sterilized. In the present study, a maximal rate of spore sterilization was obtained under conditions of average light intensity in the reactor of 6. 0×105J·m-3, TiO2 concentration of 5×10-2kg·m-3 and dissolved oxygen concentration of 7.7×10-3kg·m-3.
Considering that oxidative radicals formed from dissolved oxygen via TiO2 photocatalysis cause the spores' death, the knetics of spore sterilization was analyzed on the basis of a second-order rate equation with respect to spore and oxidative radical concentrations, and a single-hit multitarget model. As a result, the elapse of spore sterilization could be expressed successfully and linear correlation was observed between determined rate constants of spore sterilization and average light intensity in the reactor.
