Enhanced arsenite removal through surface-catalyzed oxidative coagulation treatment

• Published in: Chemosphere (Oxford) Vol. 150; pp. 650 - 658
• Main Authors: Li, Yue, Bland, Garret D., Yan, Weile
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.2016
• Subjects: Adsorption; arsenates; Arsenic; Arsenite; arsenites; Arsenites - analysis; Arsenites - chemistry; Catalysis; Coagulants; Coagulation; colloids; Drinking water treatment; Fe(III) hydroxide; Ferric chloride; Ferric Compounds - chemistry; Ferrous Compounds - chemistry; Flocculation; groundwater contamination; humic acids; Humic Substances - analysis; hydrogen peroxide; Hydrogen Peroxide - chemistry; iron; oxidants; Oxidation; Oxidation-Reduction; phosphates; Radicals; superoxide anion; Surface Properties; Surface-mediated oxidation; United States Environmental Protection Agency; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - chemistry; Water Purification - methods; Water quality; water treatment; Drinking water treatment; Fe(III) hydroxide; Surface-mediated oxidation; Arsenite; Coagulation
• DOI: 10.1016/j.chemosphere.2016.02.006
• ISSN: 0045-6535

Arsenic being a naturally-occurring groundwater contaminant 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) or H2O2-assisted 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 the production of reactive oxidants capable of As(III) oxidation. Fe(II)-assisted coagulation brought about small improvements in As(III) removal compared to treatment with Fe(III) coagulant alone, however, its arsenic removal efficiency is strongly dependent on pH (observed optimal pH = 7–9). Addition of H2O2 together with ferric chloride led to a significant enhancement in arsenic retention at pH 6–8, with final arsenic concentrations well below the U.S.EPA regulatory limit (10 μg/L). H2O2-assisted oxidative coagulation can attain reliable As(III) removal over a broad pH range of 4–9. Radical quenching experiments reveal the participation of superoxide radical in As(III) removal in the oxidative coagulation systems. Phosphate (at > 0.1 mM) strongly suppresses As(III) removal efficiency, whereas carbonate and humic acid pose a minor impact. Overall, 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 achieve improved As(III) removal efficiency. •The addition of Fe(II) or H2O2 during Fe(III)-based conventional coagulation was evaluated for enhanced As(III) removal.•H2O2-amended coagulation can significantly enhance As(III) removal than the conventional or Fe(II)-amended coagulation systems.•H2O2-amended coagulation holds a reliable As(III) removal performance over pH 4–9.•Among common background solutes examined, phosphate poses the greatest impact on As(III) removal during H2O2-amended coagulation.•Overall, addition of a small dose of H2O2 can be a viable method to enhance As(III) removal in drinking water treatment processes.