Photocatalytic oxidation of arsenite to arsenate using a continuous packed bed photoreactor

The aim of this work was to evaluate the effectiveness of TiO2 pellets for the photocatalytic oxidation of As(III) to As(V) under UV light with simultaneous adsorption of As(V) in a continuous packed bed photoreactor. In particular commercial cylindrical pellets of TiO2 were used as photocatalyst. Experimental photocatalytic tests were carried out in a cylindrical pyrex photoreactor (irradiated by UV-LEDs) which operates in continuous mode in order to treat aqueous solution contaminated with arsenic at different initial As(III) concentration. Preliminary tests conducted in a batch configuration showed that TiO2 pellets adsorb As(V) produced from the photoreaction, without leading to a deactivation of the active sites and evidencing that the As(V) produced is completely released into the solution. Moreover, TiO2 pellets maintained an excellent photoactivity and durability after several cycles making it a very promising catalyst to be employed in continuous reactors for the photocatalytic treatment of water polluted by arsenic, obtaining 98% As(III) oxidation yield after only 15 min of UV-LEDs irradiation. Moreover, the use of a continuous packed bed reactor filled with the stable TiO2 catalyst pellets irradiated by UV light allows to reach a steady state As(III) concentration without any deactivation phenomena. Finally, with 1 mg L-1 As(III) initial concentration, no As(V) release was observed from TiO2 surface during the irradiation time evidencing that the total arsenic removal could be achieved thanks to the photocatalytic properties and adsorption ability of the TiO2 pellets.