Reactive Media for Arsenic Removal from Potable Water

James Farrell* 1 and Dhananjay Mishra 2
1Associate Professor / 2Graduate Research Assistant
Department of Chemical and Environmental Engineering
University of Arizona, Tucson, AZ 85721
farrellj@engr.arizona.edu / 520 621-2465 / fax 520 621-6048

Topic: Hazardous Contaminants

Keywords: arsenic, ferric hydroxides

This study investigated the use of iron and manganese containing mixed valent oxides as reactive adsorbent media for removing arsenic from potable water. Corrosion and dissolution of the media in oxygenated waters continuously generates Fe(III) and Mn(IV) species that remove arsenic via coprecipitation and adsorption onto freshly precipitated Fe(III)/Mn(IV) hydroxides. Column experiments were performed to determine the effectiveness of the media for arsenic removal over a range in empty bed contact times (EBCTs), influent arsenic concentrations, dissolved oxygen levels, solution pH values and silica concentrations. Corrosion and dissolution rates of the media as a function of the water composition were determined using batch and electrochemical methods. Corrosion and dissolution rates of the media were sufficiently slow to avoid column clogging over 90 days of operation. The reaction products formed in the columns had average As to Fe ratios that were more than four times higher than those achieved by commercially available granular ferric hydroxide media under similar conditions. The higher arsenic loadings can likely be attributed to a coprecipitation mechanism and the fact that freshly precipitated ferric hydroxides have higher arsenic adsorption capacities than aged materials. The planned use of the adsorbent media is in packed-bed filters in both large and small-scale treatment systems, as well as point-of-use filters suitable for an individual well-head or faucet. No regeneration of the adsorbent media is planned, and disposal of the spent media is expected to be as a nontoxic waste.