Kinetics of the photocatalytic disinfection of Escherichia coli suspensions

Abstract

The photocatalytic inactivation of E. coli suspensions has been successfully modelled with kinetic equations based on a simplified reaction mechanism using three parameters: kinetic constant (k), pseudo-adsorption constant (K) and inhibition coefficient (n). This model has been used to fit complex bacterial inactivation curves with shoulder and tails regions in addition to the classical log-linear behaviour. Experiments performed with increasing concentrations of titania, using TiO2/SiO2 photocatalysts and waters with different composition indicates that the most sensitive parameters are the kinetic and the pseudo-adsorption constant, whereas the values of the inhibition coefficient do not seem to be influenced by the experimental conditions in the range studied. The chemical composition of the water strongly influences the efficiency of the disinfection process. However, the effect of different inorganic anions has been found to be produced at very different concentration levels and by different mechanisms, which also affects the values of the kinetic and pseudo-adsorption constants in different ways. Similarly, low concentrations of humic substances inhibit the disinfection process whereas the same concentration of sucrose does not affect at all. Consequently, the macroscopic analysis of real waters based on conductivity and total organic carbon measurements must be carefully considered, as differences in the nature of the inorganic and organic substances present in similar waters could lead to unexpected results.