Use of models in the design of cross-flow microfilters for the purification of protein from bio-mixtures

In order to enhance the purification efficiency of protein from binary bio-mixtures, the parameters for the design of cross-flow microfilters were examined by using models. The filtration flux, the cake thickness, the protein rejection coefficient and the protein purification flux for two different geometrical-shape microfilters, two-parallel-plate (TPP) and circular porous tube (CPT) type filters, under various cross-flow velocities and filtration pressures were calculated and are discussed here. The major factors affecting cake formation as well as the overall filtration resistance were found to be the hydrodynamic forces exerted on the depositing microbial cells. Therefore, the filtration rate increased with the increase of the cross-flow velocity and filtration pressure under a wide range of conditions. Nevertheless, two competitive effects, the cake thickness and the sweeping factor on the membrane surface, should be taken into consideration in order to evaluate the exact rejection coefficient and purification flux of proteins. The cross-flow velocity can be set at 0.7–0.9 m/s for a TPP filter to minimize the protein rejection and maximize the filtration rate and purification flux. Furthermore, the effects of the filter length, the clearance of TPP filters and the hydraulic diameter of CPT filters on the filtration rate and the protein rejection coefficient are also discussed. The filtration rate and the purification flux did not show significant variation along the cross-flow direction except in the filter inlet region; in contrast, decreasing the clearance or hydraulic diameter of filters was found to be an efficient way to enhance the performance of cross-flow microfiltration. According to the results of this study, the separation rate and purification efficiency can be improved by increasing the cross-flow velocity and using a TPP filter.