Photocatalytical inactivation of E. coli:: effect of (continuous-intermittent) light intensity and of (suspended-fixed) TiO2 concentration

A detrimental effect on the survival of bacteria Escherichia coli KI2 was observed after photocatalytic exposure. The reactions have been carried out in a batch photoreactor using mainly titanium dioxide (TiO2) P-25 Degussa as a catalyst. Illumination was produced by a Hanau Suntest lamp. Some parameters, such as light intensity, extend of continuous irradiation, catalyst concentration and temperature have a positive effect on disinfection. Intermittent illumination results in an increase in the time required for E. coli inactivation. No bacterial growth was observed after illumination of a contaminated TiO2 suspension. In contrast, without catalyst, illuminated bacteria recovered its initial concentration after 3 h in the dark. Bacterial inactivation in the absence of catalyst was more affected than that with catalyst when increasing light intensity from 400 to 1000 W/m(2). TiO2 concentrations higher than 1 g/l do not significantly increase the initial inactivation rate for both intensities. However, at 1000W/m(2) a modification of TiO2 concentration ranging between 0.25 and 1.5g/l did not affect the total inactivation time, as with 400 W/m(2). Water turbidity negatively affects the photocatalytic inactivation of bacteria. TiO2 immobilized on Nafion((R)) membranes inactivates E. coli with efficiencies close to those observed for bacterial suspension containing the same concentration of suspended TiO2. For fixed TiO2 on glass, the dose (W min/m(2)) necessary for the total inactivation decreases by increasing the fixed TiO2 amount. Fixed TiO2 P-25 was more active to photocatalytic inactivation when compared with immobilized rutile and anatase. However fixed rutile enhances E. coli inactivation as anatase. The effect of temperature and turbidity were made using wastewater sample. (C) 2003 Elsevier Science B.V. All rights reserved.