An adsorption water purifier with in situ photocatalytic regeneration

Abstract Simple devices are described for the purification of water combining adsorption of organic impurities with in situ photocatalytic oxidation regeneration of the adsorbent/photocatalyst. The adsorbent was silica gel and the photocatalyst was Degussa P25 TiO 2 in one purifier and colloidal TiO 2 on silica gel in the other. The adsorbent/photocatalysts were arranged in the annuli of hollow cylinders, with tubular fluorescent lamps occupying the central cavity. Apart from the central illumination the purifiers were analogous to chromatographic columns. The arrangement permitted more uniform distribution of light to the photocatalyst, better access of water to the photoactivated catalyst, improved contact time between impurities in the water and the photoactivated surface, and continuous regeneration of the adsorbing surface, by destructive photocatalytic oxidation. A single pass at 20 ml min −1 under 20-W illumination reduced the phenol concentration from 940 μg liter −1 , in the influent, to 940 ng liter −1 in the effluent stream, i.e., a 99.9% removal of phenol.