Separation of trace toxic metallic constituents from effluent streams by membrane processes has been under investigation in our laboratory. Removal of zinc sulfate and lead nitrate in low concentration, especially in the millimolar range, using cellulose acetate and TFC-polyamide membranes assembled in plate-n-frame modules is reported in this paper. Separation data are presented as a function of concentration and pressure in single and mixed solute systems at low feed flow rates. Under the experimental conditions for dilute feed solutions, a decline in solute separation at very low concentrations as well as at high pressures are noticed. The solute and solvent transport across the membranes are analyzed in terms of pure water permeability constant (A) and solute transport parameter using Kimura-Sourirajan’s transport equations as applied to very dilute feed systems. Solute separation is predicted for various product permeation velocities and compared with experimental data.