Ozone/membrane hybrid process for arsenic removal in iron-containing water

Abstract

In this study, the efficiency of arsenic removal by UF and NF membrane after ozonation was investigated. Furthermore, the role of iron in the removal of arsenic was studied. We found that more than 99% of As(III) was oxidized into As(V) with a 1.0 mg/L dose of ozone. The oxidized As(V) was partially removed (20% removal) by UF, and completely removed using NF. The effect of pH on As(V) removal by NF was evaluated. The As(V) was completely removed by NF at pH 9, but the removal rate decreased to 80% at an acidic pH (pH 4). A variation of pH affected the predomination of arsenic species, altering the overall removal rate of NF. The effect of co-existing iron species on arsenic removal was investigated under the condition of pH 7 by adding 5.0 mg/L FeCl(3) to the initial concentration of 100 mu g/L arsenic. More than 40% of As(V) could be eliminated simply through co-precipitation with the iron precipitate. After UF membrane filtration, up to 99% of As(V) could be removed. The enhanced removal efficiency of As(V) was due to the precipitate As(V) with Fe(III) hydroxide being effectively filtrated onto the UF membrane, which was not observed in the case of the iron-free water.