Investigation of fouling mechanisms governing permeate flux in the crossflow microfiltration of beer

The local phenomenology associated with membrane fouling has been investigated experimentally at laboratory scale for the crossflow microfiltration (CMF) of beer. Two downstream membrane processes were involved: clarification and sterilisation of beer. Fouling mechanisms were interpreted and compared for two types of beer (clarified beer and rough beer), filtered through a track-etched 0.2 mu m polycarbonate membrane. Flux decay was analysed by using the combination of the constant pressure blocking filtration laws with the measurement of membrane resistances arranged in series. It was found that for both types of beer the permeate flux was governed by two identical fouling mechanisms: an internal fouling of pores at the initial stages of filtration that conforms to the standard blocking model, followed by an external surface fouling conforming to the cake filtration model. It was shown that the predominant membrane resistance arises from the buildup of a loosely bound and reversible fouling layer over the membrane surface (representing more than 80% of the total filtration resistance). Macrosolutes and colloids are likely to be involved both in the progressive pore plugging and in the external fouling layer (in combination with the yeast cells cake in the case of rough beer), because of their high tendency to interact with porous material. Thus the relevance of using the so-called classical filtration laws for the investigation of fouling mechanisms in terms of total resistance of the membrane in beer CMF has been demonstrated.