Membrane foulants including external foulants and internal foulants were systematically characterized in a full-scale membrane bioreactor (MBR) for supermarket wastewater treatment in this study. Three-dimensional excitation emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analyzer were used to characterize the membrane foulants. The results indicated that the organic substances with fluorescence characteristics in both external and internal foulants were identified as protein-like substances and soluble microbial by-product-like materials by EEM technology. The GFC analysis exhibited that the external foulants had much broader distributions of molecular weight (MW) than the effluent and the internal foulants. Analyses of MW distributions suggest that the external and internal foulants were formed due to distinct fouling mechanisms. Besides proteins and polysaccharides, the oil substances were identified on the fouled membranes by the FT-IR analysis. SEM and EDX analyses indicated that the foulants covering the membrane surfaces comprised not only organic substances but also inorganic elements including Mg, Ca, Na, Al, K, and Si. (c) 2011 Elsevier Ltd. All rights reserved.