Kinetics and influence of water composition on photocatalytic disinfection and photocatalytic oxidation of pollutants.

This work is focused on the comparison between the photocatalytic inactivation of Escherichia coli and the photocatalytic oxidation of methylene blue, regarding the reaction kinetics and the influence of water composition. Disinfection profiles show an initial delay, in contrast with the exponential decay shown by the decolorization of methylene blue solutions. A serial-event mechanism is proposed for both disinfection and mineralization processes, the number of intermediate species being the main difference between them. Concerning the influence of water composition, inactivation of bacteria is more sensitive to the presence of inorganic ions and/or organic matter in the solution. In some cases opposite behaviours are observed, such as in the presence of chloride ions, which enhance the disinfection rate but decrease degradation activity for methylene blue. Consequently, the results obtained in the evaluation of photocatalytic processes for the degradation of chemical pollutants cannot be always extrapolated to the inactivation of microorganisms.