Effects of Light Intensity and Titanium Dioxide Concentration on Photocatalytic Sterilization Rates of Microbial Cells

Photocatalytic sterilization of Escherichia coli (bacterium) or Saccharomyces serevisiae (yeast) was conducted with a rectangular bubble-column photoreactor (40 mm in width, 40 mm in breadth, and 250 mm in height) containing slurried TiO 2 semiconductor particles. The profiles of cell deactivation with sterilization time could be expressed in fair agreement with experimental data, based on a series-event model and a second-order kinetics with respect to the concentrations of microbial cells and oxidative radicals generated by photoexcitation of TiO 2 particles. Sterilization rate constants for the microbes were determined under various conditions of TiO 2 concentrations (0−5 × 10 -1 kg/m 3 ) and average light intensities (0−223 W/m 2 ) in the photoreactor. Linear relationships were obtained between the rate constants and average light intensity at TiO 2 concentration of 1 × 10 -2 kg/m 3 . When incident light intensity was kept constant (27 W/m 2 for E . coli or 238 W/m 2 for S . cerevisiae ), the correlations between the rate constants and TiO 2 concentration were interpreted considering a fraction of TiO 2 particles adhered to the cells in slurry.