Photoelectrocatalytic and photocatalytic disinfection of E-coli suspensions by titanium dioxide

This paper reports studies of the photoelectrocatalytic and photocatalytic disinfection of E. coli suspensions by titanium dioxide in a sparged photoelectrochemical reactor. Two types of titanium dioxide electrode have been used. 'Thermal' electrodes were made by oxidation of titanium metal mesh; 'sol-gel' electrodes were made by depositing and then heating a layer of titania gel on titanium mesh. Cyclic voltammetry was used to carry out an initial characterisation and optimisation of both electrode types. The best 'thermal electrodes'-i.e. those with the highest photocurrents-were prepared by heating titanium mesh at similar to700degreesC in air. For sol-gel derived electrodes, optimum performance was obtained by heating at similar to600degreesC. These electrodes were then used, in a gas sparged reactor, to disinfect E. coli suspensions with an initial concentration of 107 colony forming units (cfu) ml(-1). Films prepared by the oxidation of titanium metal were shown to be superior to sol-gel derived films. Direct experimental comparison demonstrates that the photoelectrochemical system is more efficient than photocatalytic disinfection effected by slurries of Degussa P25 titanium dioxide. Since in practical systems the TiO2 would be exposed to a variety of species additional to those that are targeted, we also examined the effects of H2PO4- and HCO3- ions on the measured disinfection rates. Phosphate addition poisons both the electrode and particulate-slurry systems and is only partially reversible. By contrast, although bicarbonate addition affects all three systems, the effects are reversible. (C) 2002 Elsevier Science B.V. All rights reserved.