A series of reverse osmosis (RO) bench-scale experiments were conducted using cross-flow cells at a municipal wastewater treatment plant. The experiments were used to observe the accumulation of effluent organic matter (EfOM) on the membrane surfaces over time and to compare two pretreatment options including a membrane bioreactor (MBR) and conventional activated sludge with tertiary membrane filtration (CAS-TMF). The membrane surfaces after filtration from 3 to 36 days were characterized by quantifying organic species, especially proteins and polysaccharides using Fourier-transform infrared reflectometry (FTIR), correlative microscopy using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The results suggest that the MBR resulted in less RO fouling. It was also found that observations of fouling within the first few days of operation were distinctive from observations following operations after a month or more, suggesting that short-term studies are unable to predict long-term fouling trends. It was also found that proteins were the predominant foulant found on the surface within the first 2 weeks, but polysaccharide deposition became much higher than proteins after 4 weeks of operation. An examination into the underlying fouling mechanisms is provided. (C) 2011 Elsevier B.V. All rights reserved.