Arsenic adsorption characteristics of biogenic iron oxides in comparison to chemogenic iron oxides

Abstract

Iron-based adsorbents are attractive agents for remediation of arsenic contaminated water. This study characterized biogenic iron oxides (BIO) samples, which were obtained from a biological water treatment plant, from the physicochemical and biological aspects, and examined their As(V) and As(III) adsorption capability in comparison to that of chemogenic iron oxides (CIO). The BIO samples contained large amounts of Fe, Mn and PO4 3and were dominated with Leptothrix spp., a typical iron-oxidizing bacteria, suggesting the formation of Fe and Mn oxides precipitation with large surface area on Leptothrix cell surface. Batch adsorption experiments of As(V) and As(III) (100 to 1500 μg/L each) with BIO and CIO (5 mg-Fe/L), and the regression of the experimental data by Langmuir and Freundlich isotherms revealed that BIO is more effective than CIO regarding the aqueous arsenic removal, irrespective of the species and concentrations of arsenic. The maximum arsenic adsorption capacities of BIO were 34.25 µg-As(V)/mg-Fe and 28.99 µg-As(III)/ mg-Fe, respectively, which were 2.7 times larger than those of CIO. Because BIO can be generated continuously by biological oxidation of Fe coexisting in arsenic contaminated water, it can be concluded that BIO-based adsorption would be a promising arsenic remediation technology for Asian developing countries where drinking water source is heavily contaminated with arsenic and contains a high concentration of iron.