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The performance of a microfiltration (MF) membrane was compared with an anisotropic ultrafiltration (UF) membrane during cell harvesting of E.coli. The microfiltration membrane has very high surface porosity and thus very high water flux. When challenged with E.coli fermentation broth the MF membrane exhibited a much higher rate of initial flux decline and gave lower steady state flux than the UF membrane. Transmission Electron Microscopy was used to examine the nature of the deposits on the remaining membrane surface after use. The cake on the MF membrane was composed of E.coli cells densely packed into a biofilm while the deposit on the UF membrane was very thin and composed of macromolecules and fibrils and only few cells. These results showed that under cross-flow conditions cells were washed away from the smooth surface of the UF membrane but not from the surface of MF membrane.

It that appears decline with convection the one of the major problems causing the flux microfiltration membrane is the intial high of bacteria to the membrane surface. Strategies which could control this problem are: (i) operate at higher cross flow velocity. However, this may be inappropriate if very high cross flow velocities are required; other methods of creating high shear would be of interest (rotating modules etc), (ii) operate with modest to low transmembrane pressure, (iii) new or modified structures of microfiltration membranes with isoporosity or with precoated pores.