Modeling of arsenic rejection considering affinity and steric hindrance effect in nanofiltration membranes

Rejection characteristics of arsenic compounds such as arsenite, dimethyl a rsinic acid, and arsenate were examined regarding the effect of pH change i n nanofiltration. Rejection mechanism of arsenic compounds was explained by comparing experimental rejection with calculation of the Extended Nernst-P lanck model coupled with steric hindrance model. Nanofiltration membranes o f the same material show similar rejection characteristics of arsenic compo unds in different species. Steric hindrance and electrostatic effect in the nanofiltration membranes was well described by the model because the rejec tion of chloride, sulfate and arsenate ions, which exist in ionized forms a t a wide pH range showed quite good agreement between model calculation and experimental result. The rejection of dimethyl arsenic acid and arsenite r equired the consideration of mutual interaction between membrane material a nd solutes as well as steric hindrance and electrostatic effect. A system w ith ultra low-pressure nanofiltration membrane coupled with pre-oxidation d evice was suggested for the treatment of arsenic in groundwater in Banglade sh.