Desalination 199 (2006) 81–83 Presented at EUROMEMBRANE 2006, 24–28 September 2006, Giardini Naxos, Italy. Membrane processes for water disinfection: investigation on bacterial transfer mechanisms Nathalie Delebecque a,b , Christel Causserand a *, Christine Roques b , Pierre Aimar a a Laboratoire de Génie chimique, Université Paul Sabatier, 118 route de Narbonne, 31062 Toulouse cedex 09 email: caussera@chimie.ups-tlse.fr b Laboratoire de Bactériologie, Microbiologie et Virologie Industrielle EA 3036, Université Paul Sabatier, 35 chemin des Maraîchers, 31062 Toulouse cedex 04 Received 19 October 2005; accepted 6 March 2006 1. Introduction Microbiological water quality is one of the major concerns to potable water production. By providing an effective barrier to pathogens, membrane processes are able to fulfil the disin- fection final step, until the membrane integrity is not compromised. Nevertheless, several stud- ies point out that bacteria are able to pass through porous membrane structure, even in the case of nominal pore size smaller than bacterial size [1–3]. The aim of the present study is to improve the understanding of the bacterial trans- fer mechanisms through the porous membrane structure. 2. Results and discussion Dead-end filtration, in an Amicon stirred cell device, of several bacterial suspensions upon different membrane supports showed that in the case of Escherichia coli (strain ATCC 10536), cellulose ester membranes with largest pore size of 0.22 m m or polycarbonate track-etched mem- branes of nominal pore size of 0.4 mm leaked coliforms to some extent. By considering bacterial dimensions (2 ´ 1 m m), transport mechanisms based upon physical sieving do not enable us to explain those phe- nomena. As a consequence, two main assump- tions ought to be taken into account and the first one deals with the presence of a small number of abnormally large size as compared to the average pore rating and which are not detected by the current available characterization meth- ods (water permeability, tracers rejection) [3,4]. To improve fine membrane characterisation, the bacterial log removal value obtained with challenge testing upon membranes with small created imperfections is compared to the results of the direct integrity test performed upon the same membrane. The second assumption focuses on the microor- ganisms’ physiological behaviour during filtration. Indeed, some reports indicate that microorganisms are deformable under mechanical stress and that *Corresponding author. doi:10.1016/j.desal.2006.03.147 0011-9164/06/$– See front matter © 2006 Published by Elsevier B.V.