Field and Laboratory Validation of Photoactivated Adsorption for Removal of Arsenic in Groundwaters

The project discussed in this final report is based on earlier studies performed at the University of Wisconsin — Madison regarding MCL of arsenic and treatment methods. Earlier studies involved two different treatment approaches. In one, a magnesium aluminate spinel was investigated as an alternative adsorbent for As (V). This spinel was observed to maintain its adsorption capacity for arsenate up to pH 7 as compared to y-alumina (synthesized as a surrogate for activated alumina), which loses capacity at pH 6, a value that 1s typical of many activated aluminas [Rosenblum and Clifford, 1984; Clifford, 1999]. A second study involved the successful use of photocatalytic oxidation to convert As (III) to As (V) in synthetic laboratory solutions.

This project was proposed as a continuation of these earlier studies and incorporated five main tasks. Task 1: Characterize the adsorption chemistry of arsenic on a commercial activated alumina, specifically focusing on the effect of competitive and cooperative adsorption (1.e., the effect of having other components present in the source water being treated) on the removal of arsenic. Task 2: Optimize the performance of a composite photocatalytic/adsorption medium containing two components, one a titania-based active photocatalyst to photooxidize As (III) to As (V) and the other an alumina-based adsorbent to remove photogenerated As (V) as it formed. Task 3: Develop methods to coat this composite on a near-UV transparent substrate for use in a waveguide photoreactor. (In a waveguide photoreactor, the activating light 1s carried through a transparent substrate and activates a coating of photocatalyst on the substrate whenever the light reflects off the substrate and the underside of the photocatalyst. This approach should illuminate the reactor and photocatalyst more uniformly than in a conventional photoreactor.) Task 4: Field test the waveguide photoreactor at a drinking water treatment plant in a small community with arsenic-contaminated water. Task 5: Develop a cost-benefit analysis for the performance of this system as compared to other commercial systems for arsenic treatment.