The influence of different kinds of pre-treatment on the performance of a polyamide nanofiltration membrane

Although pre-treatment of membranes is often used to ensure the reliability of experimental data, it also has the potential to improve many aspects of membrane performance. This study investigates the influence of chemical pre-treatment and wetting on membrane flux and retention. The results show that chemical pre-treatment, with either a phosphate buffer or alkaline cleaning agents, enhances the flux and lowers the retention. Wetting at 40°C after membrane cleaning increased the flux and retention, whereas wetting at 50°C decreased the flux and increased the retention. No effect of pre-treatment with NaOH, at pH 9.8 or 10.4, was observed. The influence of NaCl on flux and surface contact angle was also evaluated, and pre-treatment with 0.20 M NaCl(aq) was shown to increase the flux but to have no effect on surface contact angle. The origin of the positive effect of chemical pre-treatment on membrane flux appears to lie in the ion–membrane interactions within the membrane, where time and temperature are of importance. This would explain our finding that some of the positive effects of cleaning agents and NaCl on membrane flux are quickly lost after increasing the processing temperature during pure water flux measurements.