Synergistic and antagonistic effects in the photoelectrocatalytic disinfection of water with TiO2 supported on activated carbon as a bipolar electrode in a novel 3D photoelectrochemical reactor

A novel photoelectrochemical three-dimensional reactor was designed and used to evaluate the photoelectrocatalytic inactivation of bacteria (E. coli) in water using a commercial anode of RuOx/Ti and an illuminated photocatalyst of GAC-TiO(2 )composite as bipolar electrode. Due to the complexity of the process, the individual phenomena potentially involved in the inactivation mechanism (adsorption, photolysis, electrolysis and photocatalysis) have been evaluated to establish the possible additive, synergistic or antagonistic results of their different combinations. The main oxidizing species formed during the processes (chlorine species and hydroxyl radicals) have been analyzed to elucidate the mechanism. Results show that the use of granular activated carbon (GAC) and GAC-TiO2 composites as third bipolar electrode improves the efficiency of conventional electrocatalysis, but mainly due to the removal effect of the adsorption of bacterial onto the solid particles, and not through a direct impact on the electrochemical generation of disinfecting species. When the GAC-TiO(2 )composite electrode is illuminated with UV-A light, a significant improvement in the bacterial inactivation efficiency is also observed due to the sum of the adsorption of bacteria and the generation of reactive oxygen species (especially hydroxyl radicals) by the TiO2 photocatalyst. It has been proven that in the electrochemical processes the formation of chlorine species is favored while hydroxyl radical's generation is favored in the TiO2 photocatalytic system. However, the combination of the photocatalytic process with the electrochemical process (photoelectrocatalytic disinfection) presents a remarkable antagonism derived from the mutual annihilation of the hydroxyl radicals with the chlorine species.