Arsenic removal from drinking water using anion exchange and iron coagulation-microfiltration

Lowering of the arsenic MCL from 50 to 10 mug/L has spurred an increased interest in developing technologies for arsenic removal from drinking water. This study focused on two of the several best available technologies (BATs) listed by the EPA for arsenic removal, namely, ion exchange and iron coagulation-microfiltration. Most, if not all, BATs are much more effective at arsenate removal than arsenite. In an arsenite oxidation study, of the seven oxidants studied for As III oxidation, chlorine and permanganate were effective under all conditions. The effectiveness of ozone was diminished in the presence of other interfering reductants (IfR), whereas monochloramine and chlorine dioxide were ineffective. When dissolved oxygen was not limiting, a MnO2-based solid oxidizing media provided quantitative arsenite oxidation. However, limiting-DO and interfering reductants resulted in incomplete oxidation.; Conventional sulfate-selective resins produced longer run lengths (when compared with nitrate or monovalent-selective resins). Very fast flow rates were used without sacrificing arsenic removal efficiency. A key finding was that spent brine containing high concentrations of arsenic and sulfate could be reused for regeneration several times, as long as its chloride level was maintained.; Arsenic run lengths were found to be strongly influenced by resin capacity. When normalized for capacity, sulfate selectivity was found to be the only variable that influenced arsenic run lengths. Using experimentally determined separation factors at high ionic strength, EMCT model correctly predicted field observations that spent brine could be reused effectively and that a resin, regenerated with spent brine, did not significantly leak arsenic or sulfate upon subsequent exhaustion.; A compact iron coagulation-microfiltration treatment process was designed that eliminated the need for a flocculation step for arsenic removal. Arsenic removals were found to be strongly dependent on pH, mainly due to competition for adsorption sites from silica. Extended 3--5 day operation successfully demonstrated consistent removals below 2 mug/L without fouling the microfiltration membrane.