Performance of TiO 2 photoanodes toward oxidation of methanol and E. coli inactivation in water in a scaled-up photoelectrocatalytic reactor

The aim of this work was to demonstrate the possibility of using scaled-up photoanodes to inactivate bacteria and oxidise organic compounds as disinfection tertiary treatment of wastewaters. Scaled-up nanoparticulate titania photoanodes were immobilised on conductive glass by dip-coating (141.4 cm2). Photoelectrocatalysis led to a higher disinfection rate in comparison to photocatalysis for all experiments, giving rise to an increase in values of bacterial inactivation kinetic constant from 1.45 up to 2.18 × 104 CFU L−1 min−1 in 0.1 M Na2SO4 and from 1.73 up to 2.23 × 104 CFU L−1 min−1 in simulated wastewaters when using a TiO2 thickness layer of 0.88 ± 0.12 μm and applying +1.0 V. In contrast, photocatalytic oxidation of methanol was not improved when an electric potential bias is applied. It is suggested that electrostatic attraction of negatively charged bacteria to the positively biased photoanodes leads to the enhancement observed. When scaling-up a TiO2/ITO (Indium Tin Oxide) electrode, the change in the way of illumination of the photoreactor has to be carefully taken into account. It led to significant differences in bacterial inactivation, which was noticeably diminished when using a photoreactor with scaled-up photoelectrodes illuminated from the back side of the photoanode. No differences were found out for methanol oxidation. This may be explained by the differences in size between both pollutants, leading to differences in their transport through the TiO2 layer and their feasibility to interact with OH radicals.