Research Article Dead-End Liposomal Electro-Filtration: Phenol Removal by Dioctadecyl Dimethyl Ammonium Chloride as a Case Study Among the important efforts that have been made for the removal of trace organ- ic molecules, sorption by micelles and subsequent membrane filtration is a pro- mising method which, however, still suffers from a number of disadvantages such as low efficiency and high energy consumption. In this article, we present the results of the sorption of phenol (as an important trace organic pollutant in industrial wastewater) to dioctadecyl dimethyl ammonium chloride (DODAC) liposomes, as well as the filtration properties of the resulting dispersion. Whereas the sorption of phenol by a 0.5 wt % DODAC dispersion at neutral pH and ambi- ent temperature was only 26–35 %, it increased to above 95 % at pH 11. Applying an electric field during the filtration process considerably improved both the fil- trate flow rate and the retention. An electric field of 5 V/cm increased the filtrate flow rate at 200 kPa 30-fold. Keywords: Dead-end filtration, Energy saving, Filtration Received: March 15, 2010; revised: April 07, 2010; accepted: April 15, 2010 DOI: 10.1002/ceat.201000115 1 Introduction The presence of ecotoxic substances such as pesticides and endocrine disrupters at low levels in wastewater streams has induced the wastewater treatment sector to focus on the mea- surement and removal of such micro-pollutants. In this con- text, phenolic compounds are of great importance because of their biotoxicity (toxicity for the protoplasm) and their effects on the odor as well as the taste of water and fish [1, 2], and due to their abundance in wastewater streams of various pro- cesses such as in organic chemicals, plastics, steel and petro- leum plants [2, 3]. There are many different methods for the removal of these micro-pollutants from wastewater streams, among which bio- logical treatment, adsorption, advanced membrane technolo- gies and reverse osmosis are the most widely used methods. While biological processes are not always able to remove these target molecules with satisfactory efficiency, membrane tech- nologies such as reverse osmosis are not very efficient with regard to energy consumption aspects. In addition, Lopez-Mu- noz et al. [4] found that the retention of phenolic compounds was limited to about 60 % with nanofiltration. An approach in this regard was micellar enhanced ultrafiltration (MEUF), which contains the solubilization of organic pollutants by mi- celles of surfactants followed by ultrafiltration of the mixture solution [5–9]. Different investigations have been performed on the interac- tion of phenolic compounds with surfactant molecules, and it is known from these studies that the main interactions between phenol and the surfactant micelles are hydrophobic interactions, as well as electrostatic interactions if cationic sur- factants are used [5, 10]. Two major shortcomings of the MEUF method in previous studies were the limited solubilization of micro-pollutants by micelles, which might be due to the rigid structure of the sur- factants [11], and the low efficiency of the filtration. In most cases, high retention values are only achievable at very high surfactant concentrations, which is associated with a more dra- matic drop in filtrate flow rate [8, 9]. Since the bottleneck of membrane filtration is the low filtrate flow rate due to fouling, electric field-enhanced filtration has been known for a long time as a more effective way of membrane filtration [12–15]; however, in practice, it is still not very common because of the four processes of electrophoresis, electroosmosis, electrolysis and viscosity reduction which may have opposite effects dur- ing the process [13]. The aim of this study is to improve the removal efficiency of low-molecular-weight pollutants by ad/absorbing them into cationic liposomes and filtering the dispersion afterwards. Firstly, micelles are replaced by liposomes, which according to Chem. Eng. Technol. 2010, 33, No. 8, 1321–1326 © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Maryam Hakimhashem 1 Hans Saveyn 1 Birgit De Bock 1 Paul Van der Meeren 1 1 Particle and Interfacial Technology Group, Ghent University, Gent, Belgium. – Correspondence: M. Hakimhashemi (maryam.hakimhashemi@ugent.be), Particle and Interfacial Technology Group, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium. Dead-end filtration 1321