Transient critical flux due to coupling of fouling mechanisms during crossflow microfiltration of beer

Models of fouling during beer clarification, previously validated for dead-end filtration, are combined with a model describing the build-up of the cake layer of yeast cells via shear-induced diffusion induced by crossflow. For describing shear-induced diffusion, we have taken the most recent model, which is based on the effective temperature concept. Via scale analysis we show that (1) effects of polydispersity are negligible and (2) the cake layer growth model still be reduced to the earlier model of Romero and Davis, albeit with different parameter values. The adapted Romero and Davis model has been coupled to the earlier reviewed models of fouling by aggregates and macromolecules, for which we have performed computer simulations. In this paper we report on striking results on the downstream movement of the critical point, xcr, where the cake layer starts building up. We show that this is due to strong coupling between the cake layer build-up and the other fouling modes. Hence, this means that the concept of critical flux can not be viewed any more as a time-invariant value. This finding has implications beyond the application of beer, and especially for biotechnological broths which have similar composition of beer.

► Crossflow microfiltration model of Romero and Davis is still allowed to use for complex feeds as beer.
► Due to interaction between cake and membrane fouling, the cake layer moves downstream.
► For complex feeds the critical flux is not a time-invariant concept.