In the present work, a ultrafiltration (UF) low pressure membrane (LPM) made of polyvinyl chloride (PVC) was used with an inline poly-ferric sulfate coagulation in a full scale drinking water treatment plant. The organic foulants and their accumulation behavior in the membrane filtration were investigated during a whole year operation. The evolutions of the surface morphology of the membranes were characterized by scanning electronic microscopy (SEM) and atomic force microscopy (AFM). The results revealed that the cake layer and pore blocked were responsible for the flux declining. Moreover, the roughness of the surface of the membranes continuously increased with the filtration. In order to identify the constitutes of organic foulants, attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR), high pressure size exclusion chromatography (HPSEC) and fluorescence excitation-emission matrix (EEM) spectrometry were used to examine the desorbed organic matters from the fouled membranes. The results showed that humic substances kept a very stable situation, indicating that it would not be important in the formation of the combined organic fouling layer. Protein/protein-like substances and soluble microbial product-like (SMP-like) substances were the dominant components in the organic fouling layer in a long-term ultrafiltration of surface water used as a drinking water source. A decrease of protein/protein-like substances and an increase of SMP-like substances with the filtration time were found, which could be attributed to the transition from proteins to SMP in the fouling layer. Thus, the increase of SMP-like substances in the fouling layer would play a significant role on the accumulation of irreversible fouling. (C) 2012 Elsevier B.V. All rights reserved.