Arsenic is a naturally-occurring groundwater contaminant and its presence in drinking water supply is subject to stringent water quality regulations. Coagulation and adsorption are widely used methods to treat arsenic-contaminated water, however, these treatments have been reported to be less efficient for the removal of arsenite (As(III)) than arsenate (As(V)). In this study, the feasibility of in situ oxidation of As(III) during coagulation was investigated in two systems: Fe(II)-assisted or H2O2-assited oxidative coagulation treatment using ferric chloride as the coagulant. This setup exploits the catalytic property of the fresh formed Fe(III) hydroxide colloids in coagulation suspension to mediate production of reactive oxidants capable of As(III) oxidation. With Fe(II) -assisted oxidative coagulation, small improvements in As(III) removal were observed compared to treatment with Fe(III) coagulant alone. However, the arsenic removal efficiency is strongly dependent on pH, with optimal As(III) uptake obtained within a narrow pH range (pH 7- 9). Addition of H2O2 together with ferric chloride led to a significant enhancement in arsenic retention. The final arsenic concentration was well below the U.S. regulatory limit (10 μg/L) at a H2O2 dose of 1 mg/L or more. This H2O2-assisted oxidative coagulation can attain stable As(III) removal over a broad pH range of 4 to 9. The effect of background anions was also investigated. The results suggest that a low dose addition of H2O2 along with ferric coagulant is a feasible method for the existing water treatment facilities to attain improved As(III) removal efficiency.

Enhanced arsenite removal during Fe(III)-based Oxidative Coagulation Treatment

251st National Meeting (2016)

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