EFFECTS OF LIGHT-INTENSITY AND TITANIUM-DIOXIDE CONCENTRATION ON PHOTOCATALYTIC STERILIZATION RATES OF MICROBIAL-CELLS

Photocatalytic sterilization of Escherichia coli (bacterium) or Saccha romyces serevisiae (yeast) was conducted with a rectangular bubble-col umn photoreactor (40 mm in width, 40 mm in breadth, and 250 mm in heig ht) containing slurried TiO2 semiconductor particles. The profiles of cell deactivation with sterilization time could be expressed in fair a greement with experimental data, based on a series-event model and a s econd-order kinetics with respect to the concentrations of microbial c ells and oxidative radicals generated by photoexcitation of TiO2 parti cles. Sterilization rate constants for the microbes were determined un der various conditions of TiO2 concentrations (0-5 x 10(-1) kg/m(3)) a nd average light intensities (0-223 W/m(2)) in the photoreactor. Linea r relationships were obtained between the rate constants and average l ight intensity at TiO2 concentration of 1 x 10(-2) kg/m(3). When incid ent 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 a nd TiO2 concentration were interpreted considering a fraction of TiO2 particles adhered to the cells in slurry.