Arsenic removal from drinking water through a hybrid ion exchange membrane – Coagulation process

Abstract

A hybrid process targeting arsenic (As) removal from drinking water was developed in this study, consisting of arsenate transport through an anion exchange membrane followed by coagulation. The main advantage of this ion exchange membrane (IEM) process is improved drinking water quality through the prevention of secondary contamination by coagulants and pH-controlling agents, a design feature that was successfully confirmed experimentally. This study describes: (1) the selection of an appropriate anion exchange membrane for transporting monovalent and divalent forms of arsenate, (2) the effects of iron (Fe) vs. aluminium (Al) coagulants on the process, (3) the long-term efficacy of the IEM process and (4) a comparison of the IEM process effectiveness with conventional coagulation/filtration. Al was found to be more effective than Fe at preventing membrane scaling, likely due to the contrasting charges of the precipitates, which are repelled from the positively charged membrane in the case of Al, unlike Fe. Arsenate was removed below the maximum contaminant level (6.6 ± 2.8 ppb) during periods with and without Al addition, where minimal operational maintenance was required. The high quality drinking water that is achievable and its ease of operation make the IEM process attractive for treating As-containing water supplies.