AWWA ACE58141

The oxidation status of arsenic in source waters significantly affects the adsorption capacity of adsorbents. Many arsenic removal processes have been found to be ineffective for arsenite, As(III), which is uncharged at the pH of drinking water. Removal of As(III) is generally accomplished by oxidizing it to arsenate, As(V), which can be removed by adsorption or ion-exchange mechanisms. Previous researchers have found that the TiO2/ultraviolet photocatalytic process effectively converts As(III) to As(V). However, most of the research was performed with TiO2 nano-particle suspensions. Removal of these particles later in the treatment process could be problematic. During the authors' testing, a TiO2/Al2O3 mixed oxide was developed which has been shown to effectively remove As(III) without requiring a separate oxidation process. A heterogeneous photocatalytic adsorbent (Al2O3/TiO2) was synthesized by sol-gel techniques. This composite acts as a photocatalyst that can oxidize As(III) to As(V), with the latter species being adsorbed by the adsorbent. The materials (Al2O3/TiO2) were mixed as a stable suspension (sol) that was used to coat glass beads. After the coated beads were fired, the resulting thin films served as both a photocatalyst and an adsorbent. Includes 24 references, figures.