Effect of pH on rejection of different species of arsenic by nanofiltration

Arsenic in drinking water attracts attention because some of the drinking water resources contain considerable concentration of arsenic to cause adverse health effects. The application of nanofiltration (NF) to drinking water treatment for arsenic removal was examined with negatively charged NF membranes. Experiments were conducted with ground water to which arsenate, arsenite and dimethyl arsinic acid (DMMA) were added. The concentrations of three different species were measured by the ion chromatography-inductively coupled plasma-mass spectrometry (IC/ICP/MS) method by which speciation and quantification of arsenic compounds with high sensitivity is possible at the same time. Arsenate rejection was almost steady, while rejection of arsenite increased with pH. Compared to the rejection of chloride ion, arsenic compounds except DMMA generally gave lower rejection. The reason for rejection change with pH was explained by the extended Nernst Planck. equation in which chemical equilibrium of arsenic compounds was taken into account.