The objectives of this research were to investigate the combined and individual influence of hydrophobic and hydrophilic fractions of NOM on the fouling of thin-film composite nanofiltration (NF) membranes. and also the roles of solution chemistry on the permeate flux and fouling. Combined fouling is compared to the individual fouling behaviors (i.e., alginate or humic acid alone). Experiments were conducted using a "cross-flow" pilot-scale membrane unit with a full circulation mode. Fouling experiments were performed with individual and combined humic acid and alginate. The results demonstrated that increasing organic concentration increased greatly the rate and extent of flux reduction. Individual alginate fouling was more detrimental than individual humic acid fouling, and alginate exhibited greater flux decline than humic acid fouling alone at the same conditions. A higher flux decline was observed with increasing proportions of aliginate in combined fouling. In other word, there are antagonistic effects during combined fouling because the charge functional groups of two above foulants are negative and increase electrostatic repulsion between two foulants and also foulant-membrane. The flux reduction increased with increasing ionic strength. foulant concentrations, and with lower pH, This observation implies the importance of interaction between various foulants for deeper understanding of fouling phenomena. The membrane fouling was largely dependent on organic properties and fractions. (C) 2009 Elsevier B.V. All rights reserved.