A forward osmosis-nanofiltration (FO-NF) integrated new system in flat-sheet cross-flow module was designed to separate reusable water from coke-oven wastewater with reduced concentration polarization and high flux using low energy. Investigations were carried out under different sets of operating conditions of pressure, cross-flow rate, pH of the feed solution and run time for better understanding of the phenomena of concentration polarization and reverse salt diffusion in the new system. A set of polyamide composite membranes were investigated to screen out the best performing ones (NF-2 for forward osmosis and NF-1 for draw solute recovery) for the final experiments. While investigating effects of different draw solutions (DS) on the water flux and rejection of target contaminants, 1.5 M NaCl was found to be the best for forward osmosis. Removal of about 96-98% of cyanide, phenols, NH4+-N and chemical oxygen demand from real coke-oven could be achieved along with pure water flux of 46 L/(m(2)h) in FO system under optimized conditions. Downstream nanofiltration module ensured continuous recovery and recycle of 99% of the draw solute while ensuring recovery of reusable water at the rate of 45 L/(m(2)h). (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.