Dissolved organic matter (DOM) in sewage effluent and its transformation during pilot wastewater treatment processes (WWTPs) was characterized and compared using size exclusion chromatography (SEC) as well as other organic matter analytic methods. DOM in effluents from an artificial wastewater, a landfill leachate, a saline wastewater, and DOM collected from surface water were also tested for comparison. As for pilot WWTPs operating with the same actual wastewater feed, the DOM transformation was comparable: low MW (< 500 Da) and middle MW (> 5000 Da) organic materials decreased, while humic-like substances with MW of 650 Da, 1700 Da and 2000 Da and large MW organic materials (SMPs) with MW > 10,000 Da were aggregated. DOM in effluents from different sewage displayed their own characteristic SEC chromatograms. The properties of sewage effluent were influenced by the wastewater source, operation parameters and the inflow style of the biological treatment process. The only intensity difference in the SEC chromatogram was observed for effluents from WWTPs operating with the same actual wastewater feed. (C) 2011 Elsevier B.V. All rights reserved.