Reverse osmosis (RO) is a well-established process for water desalination and effluent treatment and it is anticipated that its application could be extended to complex mixtures of industrial effluents. Pilot-scale experiments using a spiral-wound thin-film composite (TFC) polyamide membrane were carried out to investigate the potential of RO for processing a composite effluent, which was a mixture of various wastewaters from bulk drug and pharmaceutical factories. Separation performance was evaluated at various feed pressures (0-70 bar) and feed concentrations (2-30 g dm(-3)), and was found to improve with increasing pressure. High rejection of dissolved solids (similar to98%), COD, BOD and almost complete removal of color were achieved with reasonable flux rates and water recovery. The effect of concentration polarization and fouling on flux and rejection rates as functions of time was evaluated. An approximate cost estimate for an aerobic process vis-A-vis a RO membrane process for treatment of the composite effluent is presented. (C) 2003 Society of Chemical Industry.