Photocatalytic inactivation of Escherichia coli and Lactobacillus helveticus by ZnO and TiO2 activated with ultraviolet light

The photocatalytic inactivation of Gram negative Escherichia coli and Gram positive Lactobacillus helveticus by both TiO2 and ZnO with 365-nm ultraviolet (UV) light was studied in a batch reactor. Almost all the initial E coli cell (10(8) CFU/ml) were inactivated in 40 min in the presence of 2 g/l ZnO. Photocatalytic inactivation of bacteria was found to follow first order kinetics with the highest rate constants being 4.5 x 10(-1) and 2.2 x 10(-1)/min for E coli and L. Helveticus, respectively, treated with 2 g/l ZnO. A similar bactericidal tendency was found in the UV-TiO2 system, where the rate constants were 3.7 x 10(-1) and 1.8 x 10(-1)/min for E coli and L. Helveticus, respectively. The use of air as the purging gas, providing a stronger oxidising environment to both strains, gives a higher catalytic effect on bacteria inactivation than that of nitrogen. (C) 2003 Elsevier Science Ltd. All rights reserved.