ARSENIC REMOVAL BY RO AND NF MEMBRANES

Bench-scale experiments were performed to assess the effectiveness of reverse osmosis (RO) and nanofiltration (NF) membranes in removing ars enic (As) from synthetic freshwater and source water. The authors exam ined the effects of operational conditions (applied pressure and feedw ater temperature) and solution chemical composition (As oxidation stat e, pH, and presence of co-occurring inorganic solutes). Both As(V) and As(III) were effectively removed from synthetic freshwater by RO and tight NF membranes over a wide range of operational conditions. The re latively large molecular weight (>125 g/mol) of the As species governe d their separation behavior. Applied pressure had little effect on As removal, but an increase in feedwater temperature decreased As removal by a small percentage. Removals of As(III) and As(V) were comparable, with no significant preferential rejection of As(V) over As(III). Var iations in solution pH from 4 to 8 also did not affect the removal of As species by the membranes tested, despite changes in the speciation and charge of As (V). Co-occurring inorganic solutes had only a slight effect on As removal. Removal of As from source water was comparable to that obtained with synthetic freshwater, despite the presence of tu rbidity, natural organic matter, and a variety of co-occurring solutes .