Ultrafiltration of two microalgae species, Chorellasp. and Porphyridium purpureum, has been performed in two filtration units of different configurations: a module generating a classical tangential-plane flow and another one inducing a swirling decaying flow. The swirling motion is generated by a unique tangential inlet at the bottom of an annulus. Permeation flux obtained in each ultrafiltration unit depends on the filtered species, and specific deposits are associated to each species and module. Enhancement in permeation flux in the swirling configuration compared with that obtained in the plane unit can reach 40% during the ultrafiltration of Porphyridium purpureum and is negligible for the suspensions of Chlorella sp. The experimental data revealed the significant role of the soluble compounds in the medium culture in terms of flux limitation. It seems that the soluble products and their interactions with the microalgal cells are strongly involved in the fouling mechanism.

This work consists of evaluating the performances of a new membrance separation process: an annular, swirling, decaying flow induced by a tangential inlet. For this purpose, we have compared the permeation flux obtained in swlrling flow with that of a crossflow. We ultrafiltered a model suspension of bentonite in order to compare the performances of the two modul es for different operating conditions. Parameters such as flow rate, Reynol ds number and wall velocity gradient were studied, and this last one appears to be a significant hydrodynamic parameter to compare the configurations. Indeed, this ccount the flow field nature and, more precisely, the shear stress at the membrane surface. improvement of the permeation flux induced by the swirling, decaying flow in comparison with that observed in cross-flow can reach more than 30% under specific conditions. The study of the energy consumption of these two cells allows us to confirm the interest of the swirling, decaying flow in order to design new types of membrane separation modules.Mots c l b : ultrafiltration, hcoulement tourbillonnaire, koulement tangentiel plan, gradient p e vitesse, bentonite, consommation energhtiqu 248

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