The main purpose of this study is to understand the transient flux behaviors via membrane fouling in hybrid powdered activated carbon/microfiltration (PAC/MF) processes. Experiments were carried out for nickel solution at various surfactant adsorbent and membrane types and membrane pore sizes. Transient fluxes were modeled together using neural network (NN). A good agreement was obtained with correlation value of 0.986 and mean absolute error of 0.366 m(3)/m(2) h respectively. In hybrid processes three discriminable phase behaviors for the flux were determined as fast [0-40s] slow [40-1000s] and low stable [1000-4500s]. Considerable losses in the flux were determined during the first and the second phases while the flux reached a partial steady-state in the third phase. In the first and the third phases participation of surfactant-adsorbed PACs to the cake layer and/or interaction of surfactants and PACs in the cake with each other were found to be predominant ways for the fouling. Whereas in the second phase the interaction of surfactants with both membrane and cake layer was appeared more influential on transient flux behavior. (C) 2009 Elsevier B.V. All rights reserved.