DESALINATION ELSEVIER Desalination 147 (2002) 205-212 www.elsevier.com/locate/desal Understanding the steric and charge contributions in NF membranes using increasing MWCO polyamide membranes A. Wahab Mohammad*, Nora’aini Ali Dept. Chemical Engineering and Process, Universiti Kebangsaan Malaysia, 43600 I/KM Bangi, Selangor, Malaysia Fax + 60 (03) 89296148; email: wahabm@vlsi.eng.ukm.my Received 4 February 2002; accepted 1 April 2002 Abstract Various studies have shown the importance of steric and charge effects in NF membranes. Most of the studies, however, were done using NF membranes of different polymeric materials. In this study we have used three membranes made of polyamide with MWCO ranging from 200-2000 to investigate the significance of steric and charge effects upon the separation performance of NF membranes. The characterization of the membranes using uncharged solutes and salt solution shows that the membrane characteristics did not follow the expected pattern based on the increasing MWCO. The rejection performance of the membranes against various categories of salts/charged organic solute was then compared to the model prediction using DSPM. Membrane BM02D was found to have a combination of high steric and charge effects, which explain why the rejections of all solutes were in the range above 80% irrespective of concentrations. For BM20D and BMOSD, the pattern of rejections was quite varied and inconsistent, which made it quite difficult to assess the relative contribution of steric and charge effect between the two membranes. Keywords: Steric; Charge density; Nanofiltration; Mechanism; Nemst-Planck 1. Introduction Nanofiltration (NF) membranes, which have properties in between those of ultrafiltration (UF) and reverse osmosis (RO), have found applications in many areas, e.g. desalting, water *Corresponding author and wastewater treatment especially in rejecting ions and charged organic pollutants. Due to the charged (mostly negative) nature of the mem- branes, the separation performance is influ- enced not only by the steric effect, but also the charge or Donnan effect. Up to now, a lot of Presented at the International Congress on Membranes and Membrane Processes (ICON), Toulouse, France, July 7-12, 2002. 00 1 I-91 64/02/$- See front matter 0 2002 Elsevier Science B.V. All rights reserved PII: SO01 I-9 164(02)00535-O