Michel Moutounet

Fouling of organic microfiltration membranes by wine constituents: importance, relative impact of wine polysccharides and polyphenols and incidence of membrane properties

Abstract Microfiltration experiments, along with biochemical analyses and scanning electron microscopy observations, were used to investigate the ability of wine soluble constituents to foul organic cross-flow microfiltration membranes, to weight the respective impact of polysaccharides and polyphenols and to determine the incidence of membrane surface polarity in fouling. Three organic membranes were used, presenting similar rated average pore size and differing by their pore size distribution and their polarity. Though much smaller than the membrane average pore size, wine polysaccharides and polyphenols induced sharp flux declines within the first minutes of the process that could not be attributed to adsorption alone. Results suggested that flux losses were related to the aggregation of wine constituents at the pore entrance and on the membrane surface, induced by permeation fluxes. On the whole, polysaccharides had a higher impact on membrane permeability than polyphenols. Due to its strong incidence on polyphenol deposition, membrane polarity had a large impact on the building of the fouling deposit. However, the amounts of deposited polysaccharides and polyphenols alone could not account for the differences observed between membranes in terms of fluxes. Considering the mechanism proposed for membrane fouling (interactions between wine constituents) these differences were well explained by the differences in the pore size distribution of the three membranes.

Contribution to the understanding of fouling build-up during microfiltration of wines

Abstract The aim of the present study was to investigate the respective impact of wine dissolved constituents, colloids and particles on the fouling of an organic microfiltration membrane. Microfiltration runs with a crude and centrifuged red wine, with model solution of particles recovered from centrifugation and with permeates from microfiltration experiments were thus compared. Particle concentration and size distribution were determined by Coulter-counter analyses while colloidal size-range constituents were evidenced by means of dynamic light scattering (DLS) experiments. Examination of fouling kinetics, along with scanning electron microscopy (SEM) observations of the membrane surface, evidenced that microfiltration performances were governed by colloids and small particles. These constituents induced sharp initial flux declines, related to both internal and external fouling. The evolution of the overall membrane resistance during wine processing was governed by external fouling. It was mainly reversible and attributed to polarisation of the retained species on the membrane front face. In accordance with previous works, a substantial irreversible fouling also developed. Membrane fouling by large particles and permeates set-up in a quite different way. With large particles, fouling developed due to the formation of a coherent cake, which was resistant to re-dispersion. Processing of the permeates led to the formation of a surface cake of aggregated organic matter. These whole results were discussed with the aim to better understand mechanisms implied in the fouling build-up during microfiltration of wine.