Membrane fouling by turbidity constituents of beer and wine: characterization and prevention by means of infrasonic pulsing Original Research Article

During microfiltration of fermented beverages such as beer and wine, colloidal turbidity constituents play an important role in membrane fouling and therefore hinder the permeate flux. This paper studies polymeric membrane fouling by turbidity constituents of beer and wine and proposes a fouling prevention method to improve permeate flux. The model turbidity suspensions, based on gelatin and tannic acid, were microfiltered in a stirred cell using 0.2 μm cellulose acetate (CA), polyvinylidene di-fluoride (PVDF) and polycarbonate (PC) membranes under constant pressure (0.79 bar) and agitation (1350 rpm). Fouling caused by either a separate protein solution or a separate polyphenol solution was considerably lower than the fouling caused by a solution of both at the same concentration, which suggests that fouling is mainly caused by light scattering complexes formed by polyphenols and proteins. In all cases, during the microfiltration of model turbidity suspensions, the internal fouling mechanism dominated first and this was later followed by a period of external fouling. It was shown that membrane fouling depends strongly on the initial turbidity of the solution. A lower turbidity of the model solution resulted in a lower final total resistance. The initial turbidity also influenced the duration of the initial period of internal fouling. For the lower turbidity model solutions internal fouling lasted longer. An infrasonic pulsing was applied to remove foulant cake and improve permeate flux during microfiltration of model turbidity suspensions, and wine and beer samples. In infrasonic pulsing, high frequency pulses of permeate are periodically sent back in the direction of the membrane at a lower pressure than the transmembrane pressure. This causes the membrane to vibrate rapidly and removes a portion of the foulant cake. The model turbidity suspension (33±2 NTU) was filtered through a flat-sheet PVDF membrane at a transmembrane pressure of 0.65 bar. In the experiments with infrasonic pulsing a 0.2 duty cycle (Φ) was used. The improvement in net permeate flux depended on the infrasonic pulse frequency. For the highest frequency (6.67 Hz) net permeate flux improved fourfold in comparison with long-term permeate flux in normal cross-flow. These data fitted very well to the theoretical model first published by Czekaj [Reducción del Ensuciamiento de Membranas Poliméricas en Procesos de Microfiltración Tangencial de Suspensiones Biológicas Mediante Utilización de Infrasonidos y de la Técnica de Flujo Transversal, PhD Thesis, Universitat Rovira i Virgili, Spain] Experiments with wine and beer samples filtered through a PS hollow fiber membrane yielded approximately 2.4 and 2.1 times larger permeate fluxes with infrasonic pulsing than with normal cross-flow.