Inactivation of E. coli and S. aureus by novel binary clay/semiconductor photocatalytic macrocomposites under UVA and sunlight irradiation

The disinfection efficiency of several novel photocatalytic macrocomposites made of Ecuadorian clay mixed with two semiconductor materials (TiO2, ZnO) has been evaluated with Staphylococcus aureus and Escherichia coli as target bacteria. They have been tested under two irradiation sources (UVA lamp and sunlight) in different configurations. Two different semiconductor/clay ratios (60/40 and 80/20) were tested at 10-20 g & BULL;L-1 (with UVA) and 20-40 g & BULL;L-1 (with sunlight) composite loadings. With the presence of the photocatalyst, a four-to five-fold increase in the inactivation rate by UVA was observed with respect to single UVA inactivation, while the performance with sunlight reaches up to six-fold. The particular effect of nature, ratio and loading on the inactivation kinetics depends on the specific bacterial species tested. In this case, the inactivation of S. aureus was faster in comparison with E. coli, probably due to the interaction between bacteria and the catalytic material and the associated & zeta;-potential. In general, the 80% ZnO composites at maximum loading show the highest efficiency, comparable to that of nanosized semiconductors. The ability of these composites to maintain a high disinfection efficiency after three uses, together with their low cost and ease of recovery, make these composites an attractive option for wider use in water disinfection facilities.