A steady state model is formulated for a two step membrane separation processes (ultrafiltration followed by nanofiltration) for treatment of the liming effluent collected from a tannery. The extent of polarization on the membrane surface is quantified. The model parameters are determined by fitting of the calculated results of permeate flux and permeate concentration with the corresponding experimental data. Solution diffusion and osmotic pressure model are combined for continuous, cross-flow membrane processes. Three flow regimes, namely, laminar, laminar with promoter and turbulent are investigated. The effective osmotic coefficient, solute diffusivity, solute permeability through the membrane have been estimated for liming effluent of a tannery. For both ultrafiltration and nanofiltration, the extent of polarization increases with tramsmembrane pressure and decreases with cross-flow rate. (C) 2009 Elsevier B.V. All rights reserved.