One of the critical issues for the application of low-pressure membrane processes (microfiltration, MF or ultrafiltration, UF) as pre-treatment processes for freshwater preparation is membrane fouling due to natural organic matter (NOM). The aim of this preliminary study is to contribute to a better understanding of the fouling phenomena occurring on a regenerated cellulose UF membrane fouled with a humic acid cake deposit. The originality of this work is based on a double approach on surface analysis at both macroscopic and microscopic scales. It is presently reported that humic acid fouling is mainly governed by cake formation, which plays a major role in flux decline via the well-known model of resistances in series. We obtained that the adsorbed resistance is 2% of the total resistance while the cake resistance is 52% of the total resistance, which is higher than that of the virgin membrane. From field emission gun scanning electron microscopy (FESEM) it was found for the first time that the humic acid cake is well organized, and particularly in fractal forms. The fractal dimension (FD) of the cake is determined as 2.52, which is in good agreement with the theoretical fractal dimension of particle-cluster aggregation underlying diffusion-limited aggregation (FD=2.51). This new microscopic fouling index decreases with the presence of cake and can be correlated with the decrease of the hydraulic permeability. The classical silt density index (SDI) and the new modified fouling index (denoted MFI-UF) were obtained and also proved the presence of the cake. To complete this approach transmembrane streaming potential (denoted SP) measurements were conducted with a new homemade apparatus developed in our lab and presented for the first time in the present article, helped us to observe also a penetration of low molecular fractions of humic acid inside the membrane. Indeed the displacement of the isoelectric point (iep) of the membrane from 2.3 to 1.5 for the virgin and fouled membranes, respectively, permitted to illustrate this penetration. This newly designed SP apparatus is a semi-automatic tool assisted by a software denoted as proFluid 1.2. Furthermore, preliminary experiments with seawater were realized in order to estimate the influence of seawater filtration on the hydraulic permeability and SP parameters for the RC 100-kDa membrane.

Les technologies à membranes sont en plein développement;toutefois, les problèmes de colmatage limitent cette expansion. Les acides humiques présents dans les eaux naturelles induisent des chutes de production des membranes et sont à l'origine de fortes diminution des durées de vie des matériaux filtrants. L'objectif principal de ce travail a été de développer une approche originale du colmatage de membranes basses pression d'ultrafiltration (UF) en cellulose régénérée susceptibles d'être employées comme pré-traitement avant l'opération d'osmose inverse, lors de la préparation d'eau destinée à la consommation à partir de la ressource eau de mer. L'originalité de ce travail est de proposer plusieurs outils d'autopsie de cette membrane à deux échelles, l'une macroscopique (par des mesures de perméabilité hydraulique, dont sont déduites les résistances de colmatage et l'indice de colmatage MFI-UF) et microscopique (par la détermination de la dimension fractale des particules d'acides humiques et leurs agrégats déposés à la surface de la membrane). De plus, un nouvel appareillage semi-automatique de la mesure du potentiel d'écoulement permet également de réaliser des investigations à l'intérieur de la structure de la membrane afin d'y déceler le cas échéant la présence de matière organiques naturelles. La dernière partie est consacrée à une étude préliminaire réalisée sur de l'eau de la côte atlantique.