This research investigated the application of H2O2/UV oxidation for source water pretreatment, and membrane cleaning to improve the performance of nanofiltration processes. It further examined the nature and mechanisms of membrane fouling by natural organic matter (NOM), and membrane cleaning using different chemical agents, by employing several surface characterization techniques. These techniques included attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The study revealed that significant improvement could be achieved in the efficiency and economics of nanofiltration for removing NOM and synthetic organic chemicals (SOCs) by employing source water pretreatment and membrane cleaning strategies. The H2O2/UV oxidation of source water prior to nanofiltration showed potential for the following: (i) mitigation of flux decline due to membrane fouling, (ii) removal of the pesticide alachlor and hydrogen sulfide, and (iii) improvement in membrane cleanability. Nonetheless, careful control of the preoxidation conditions was exercised to arrive at a reasonable compromise between fouling mitigation and NOM rejection. (C) 2004 Elsevier B.V. All rights reserved.