The mini-pilot experiments of submerged membrane bioreactor (sMBR) for the drinking water treatment from a slightly polluted surface water supply was conducted for more than 110 days, with a hydraulic retention time of 0.5 h. Perfect ammonia removal (by 89.4%) were achieved by the sMBR through the biological nitrification. However, the capacity of the sMBR for organic matter removal was demonstrated to be low. The average removal efficiencies for TOC, CODMn, DOC, UV254, and corresponding THMFP and HAAFP were 28.6%. 33.5%, 21.5%. 15.1%, 34.1% and 24.7%, respectively, though much higher removal of 51.7% and 54.9% were obtained for BDOC and AOC, respectively. A sludge layer was observed on the OF membrane surface in the sMBR. The sludge layer could provide additional filtration for dissolved organic matter (DOM) in the mixed liquor, especially for organic molecules in the range of 5000-500Da. Fractionation of DOM indicated that the sludge layer together with the OF membrane had the ability to reject hydrophobic neutrals, hydrophobic acids, and weakly hydrophobic acids by 45.0%, 42.7% and 48.1%, respectively; whereas hydrophobic bases and hydrophilic organic matter were separated mainly by the OF membrane, with the efficiencies of 11.3% and 14.6%. respectively. (C) 2008 Elsevier B.V. All rights reserved.