Presented at the Conference on Desalination Strategies in South Mediterranean Countries, cooperation between Mediterranean Countries of Europe and the Southern Rim of the Mediterranean, sponsored by the European Desalination Society and Ecole Nationale d'Ingenieurs de Tunis, September 11–13, 2000, Jerba 0011-9164/01/$– See front matter © 2001 Elsevier Science B.V. All rights reserved Desalination 137 (2001) 241–250 Removal of chromate anions by micellar-enhanced ultrafiltration using cationic surfactants Lassâad Gzara, Mahmoud Dhahbi* Laboratoire de Physicochimie des Interfaces, BP 95, Institut National de Recherche Scientifique et Technique, 2050 Hammam-Lif, Tunisia Tel. +216 (1) 430044; Fax +216 (1) 430934; e-mail: mahmoud.dhahbi@inrst.rnrt.tn Received 1 August 2000; accepted 3 September 2000 Abstract Micellar-enhanced ultrafiltration (MEUF) of chromate anions (CrO 4 2– ) from aqueous streams has been studied at 30°C using twice cationic surfactants (cetyltrimethylammonium bromide and cetylpyridinium chloride). The solution is processed by ultrafiltration, using a membrane with pore sizes small enough to block the passage of the micelles and adsorbed ions. Rejection coefficients higher than 99% are reached in optimal conditions of pressure, feed concentration in cationic surfactant, and percent filtered volume. The rejection rate depends on the ionic strength and pH. The increasing of ionic strength decreases the retention of chromate ions and the permeate surfactant concentration. As long as the NaCl feed concentration is less than or equal to 100 mM, more than 88% of hexavalent chromium are retained and surfactant leakage was reduced. Keywords: Chromate removal; Cetyltrimethylammonium bromide; Cetylpyridinium chloride; Micelles; Membrane process; Water treatment; Micellar-enhanced ultrafiltration 1. Introduction The increasing contamination of urban and industrial wastewater by toxic metal ions is a _________________________ *Corresponding author. worrying environmental problem. These inorganic micro-pollutants are of considerable concern because they are non-biodegradable, highly toxic and have a probable carcinogenic effect. If directly discharged into the sewage