Nanofiltration of single and mixture solutions containing anionics and nonionic surfactants below their critical micelle concentrations (CMCs)

Nanofiltration (NF) of linear alkyl benzene sulfonate (LABS), sodium dodecylether sulfate (SLES) as anionic surfactants and of nonylphenol ethoxylate (NPE) as nonionic surfactant for selected concentrations below CMC (critical micelle concentration) was carried out using various membranes as NF PES10, N 30F and XN 45. Membrane fouling was observed in the order of XN 45 > NF PES10 > N 30F for LABS, SLES and mixture solutions, while the order was as NF PES10 > N 30F > XN 45 for NPE solution. The most fouled membrane, XN 45, exhibited the least fouling on the surface in opposition to N 30F. In single solutions, the highest rejection of LABS and SLES was obtained around 97–98% by NF PES10 and N 30F, whereas when XN 45 was used, the rejection rate was around 93%. In mixture solution, the rejection rates were observed to be around 97 and 98% by NF PES10 and N 30F, respectively, which were quite different from XN 45 rejection rates. The enhancement of rejections compared to the adsorption of single surfactants, except for NPE-XN 45 couple, could have been taken place by synergism between nonionic and anionics as a function of both stronger interactions between surfactants and surface and, more effective physical separation forces based on micellation. In NPE-XN 45 couple, NPE was rejected predominantly under the effect of binding LABS, which had the highest feed concentration in mixture, on the membrane surface. Consequently, it was determined that, XN 45 for nonionic (NPE) and NF PES10 for anionics (LABS and SLES) and mixture solution (LABS + SLES + NPE) performed the best performance in NF of single and mixture surfactant solutions.