Nanofiltration is a process that successfully purifies effluents containing salts. The production of surfactants, for example, results in an effluent that contains 7 to 8 percent by weight of sodium chloride. Biodegradation of surfactant effluents is only partially successful, and a subsequent filtration process is necessary to reduce the chemical oxygen demand (COD). Laboratory investigations tested the effectiveness of cross flow nanofiltration for removing salts and reclaiming surfactants. Tests demonstrated that nanofiltration membranes manufactured by Dow Chemical and Membrane Products Kiryat Weizmann Limited reduced the COD content of the effluent by more than 98 percent. Tests of naonfiltration systems using wound module geometries demonstrated that salt removal efficiencies depended on the salt concentration of the effluent. Salt content of less than 1 percent was obtained by diluting the partially desalinated effluent and subjecting it to dialfiltration. A pilot plant comprised two concentrating stages and 12 Filmtec 4040 membrised two concentrating stages and 12 filmtec 4040 membrane elements with NF-45 Dow Chemical nonfiltration membranes. Desalination levels achieved during pilot plant trials were approximately 90 percent, indicating that a commercial scale plant would require more than two concentrating stages. An economic analysis of operating costs indicated that such an installation could operate profitably. 5 refs.