Beer clarification by cross-flow microfiltration - effect of surface hydrodynamics and reversed membrane morphology

The separation characteristics in beer microfiltration is based on a fine balanced retention of particles (yeast cells, debris, and coagulated protein-polyphenol complexes) and transmission of dissolved macromolecules (proteins, carbohydrates, colour and flavour compounds) to achieve beer clarification whilst preserving the 'wholesome' quality of the filtered beer. The required porous transmission of large amount of macromolecular species led to an unavoidable and complex membrane fouling in terms of fouling constituents, formation and structure, which are the major obstacles to obtaining an economically viable flux and consistent permeate quality. This paper describes an experimental study of beer clarification by cross-flow microfiltration with the aim of increasing a low permeation rate to an economically acceptable level by employing and optimising some flux-enhancement techniques. These include, (i) modification of bulk feed flow hydrodynamic conditions by superimposing a helical-flow pattern and a two-way reversing flow pulsation; (ii) application of an automated high frequency backflush programme with controllable frequency and backpulse strength; and (iii) filtration at reversed membrane morphology to allow the open substructure of the asymmetric ceramic membrane (Ceramem) to face the feed flow and thereby a reversed transmembrane pressure (TMP) gradient. The increased bulk-flow turbulence generated by flow pulsation was found disappointingly ineffective, and the superimposed helical flow pattern was only marginally better. The backflush technique was a more effective method and application of an optimised backflush programme at normal cross-flow conditions achieved 410% flux increase. The most dramatic flux improvement was achieved when the filtration was carried out with high frequency backflush at a reversed membrane mounting configuration. The author attributed the large flux increase to a mechanism of reversible 'particle holding and releasing' by the open sub-structure of the membrane under the influence of high frequency backflush, which greatly reduced fouling in the critical membrane phase. (C) 2001 Elsevier Science B.V. AM rights reserved.