Four flat-sheet membrane modules, which were operated under four different filtration modes but with the same treatment capacity, were used to treat synthetic wastewater in a submerged membrane bioreactor (MBR). Particle size distribution (PSD), gel filtration chromatography (GFC), capillary suction time (CST), and three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy were used to characterize membrane fouling properties. The high instantaneous flux induced faster fouling rate and continuous filtration mode was the most applicable filtration mode in this study. The average particle size of all foulants was smaller than that of bulk sludge; and the higher the instantaneous flux was adopted, the larger the average particle size of foulants would be. Only macromolecule substances were detected in all the foulants. The macromolecule substances in the influent were degraded by microorganism and retained by membrane, and small molecular substances could pass through membrane pores to enter the effluent. The membrane foulants had poorer dewaterability compared to the mixed liquor confirmed by CST measurement. Although there were several peaks associated with protein-like fluorophores, fulvic acid-like substances and humic acid-like organics in soluble microbial products (SMP) and extracellular polymeric substances (EPS) sample, it was found that the dominant fluorescence substances in membrane foulants were protein-like substances. (C) 2010 Elsevier Ltd. All rights reserved.