Electrofiltration of Biomaterials
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Solid–liquid separation of biomaterials is still a problem that has not sufficiently been solved on the technical scale. Most biological compounds like cells and biopolymers exhibit comparatively high electrical surface charges. These allow for the application of electrical forces strong enough to overcome hydrodynamical forces. The contribution given here describes an innovative filter chamber, which makes use of this property. In this so-called press electrofiltration, an electrical field is superimposed onto a conventional dead-end filtration with membranes on both sides of the filtration chamber. The electrical field induces an electrophoretic flux of charged biomaterials towards the oppositely charged electrode. Thus, a big filter cake can be built up on the membrane at this side, while dewatering happens at the membrane next to the other electrode. Here only a thin surface layer is formed. One special feature of this newly designed filter chamber is the separation of the electrodes by flushing chambers. These allow for the removal of electrolysis gases, as well as for pH and temperature control. After reviewing the mathematical description of electrofiltration, the chapter highlights the advantages of this approach by describing different application examples. These range from dewatering of biopolymers, namely polysaccharides and proteins, to removal of cells from product up to fractionation of different polymer colloids from each other. Each example is extensively discussed on the basis of given data for model systems and for real fermentation suspensions. It is outlined that press electrofiltration is especially worthwhile for fine, highly charged particles as being present in biosuspensions. One unique selling point is the high final biopolymer concentration, which can be reached. For transfer of these examples to processes in fermentation or food industries useful general guidelines are given at the end of the chapter.