BACKGROUNDUltrafiltration is used as tertiary treatment in wastewater treatment plants (WWTP) for wastewater reclamation. However, membrane fouling is the main drawback of the process. In this work a new effluent organic matter fractionation procedure with adsorption resins (XAD-8, XAD4 and IRA-958) has been applied without recovering the adsorbed fractions. In this way, strong and weak hydrophobic and charged hydrophilic substances of the dissolved organic matter (DOM) were removed for further ultrafiltration, in order to know the most fouling fraction. For this, secondary effluents of two WWTP and two membranes with different molecular weight cut-offs (100 kDa and 3 kDa) were used in ultrafiltration experiments in a laboratory plant. RESULTSThe hydrophobic substances (especially the strong hydrophobics) predominated over the hydrophilic compounds. Membrane fouling was higher for the membrane with the highest molecular weight cut-off (100 kDa). Thus, flux decline was around 25-47% higher than that measured for the 3 kDa membrane. The charged hydrophilic substances (CHi) were identified as the most fouling compounds with 100 kDa membrane. Reversible fouling was predominant. CONCLUSIONSThe proposed fractionation system enabled determination of the contribution of the different fractions to the DOM. (c) 2017 Society of Chemical Industry