Cut-off properties of porous membranes for microfiltration depend upon the pore-size distribution of those membranes, because the suspended particles are rejected by the porous membranes based on the size difference between the particle and the membrane pores. Therefore the control of pore size distribution during the membrane preparation is important to achieve a high reliability of the microfiltration processes. In this review, we summarized the conventional preparation methods of three kinds of porous membranes, that is, polymeric, ceramic and metallic membranes, and pointed out that the ceramic membrane has a bright prospect of developing the new industrial fields of microfiltration, although the efficient preparation method of this membrane to supply inexpensively has not been developed yet.

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The continuous microfiltration in the paper is a 0.2 micrometer hollow fiber filter that automatically backwashes with air at either preset time interval or pressure drop.
The CMF is operated in direct flow mode or cross blow mode at a low pressure producing a high flux. Surface river water, secondary sewage water and another process water can be treated in higher quality by the CMF, compared with concentional water treatment process.

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In pharmaceutical industry, micro-filtration is used for bacterial cell separation, sterilization filtration and etc. Recently, cross flow micro-filtration is used for biomass separation of fermentation broth instead of precoat filtration.
In this review, some cross flow micro-filtration data is shown and discussed its performance.

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Membranes of cellulose acetate derivatives-cyanoethyl cellulose acetate (CACN), hydroxypropyl cellulose acetate (CAHP) and cellulose acetate (CA) have been prepared. The reverse osmosis separation of aliphatic acids, alcohols and amines have been made. It was found that for n-alkyl organics, the solute rejections (Ra) firstly increased with the increase of carbon numbers of n-alkyl organics and reached a maximum when the organic molecule contained about three carbon atoms, and then decreased or kept stable. The order of solute rejections for organics with different structures was n-< iso--sec-<tert-because of the steric hindrance. The effect of oprating pressure on the properties of reverse osmosis have also been investigated and it was found that the solute rejections and the fluxes of solution increased with the increas of the operating pressure in the experimental extent. An analysis of experimental data with Spiegler-Kedem's transport model has been carried out and the membrane constants such as reflection coefficient σ, solute and hydraulic permeabilities ω and Lp for several organic solutes have been obtained

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A theory of membrane transport previously developed by us (Makino et al. Biophys. Chem. 35 (1990) 85; 38 (1990) 231; 43 (1992) 89) taking into account both of membrane volume and partition kinetic is extended to the situation in which a membrane consists of two submembranes. Such division of the membrane explicitly takes into account solute diffusion within the membrane phase. Equations are proposed which determine the time course of solute concentrations in the respective phases. Interestingly, overshoot phenomena can be observed in both submembranes under some conditions. Criteria for overshoot are given.

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Among natural polymers, sericin, which is nowadays abandoned, was selected as a membrane material, and polypeptide membrane was prepared from it. The sericin membrane gave a relatively sharp molecular weight cut-off profile in ultrafiltration. It was suggested that the present membrane could possibly be used as a hemofiltration membrane. Through the present study, it was made clear that sericin might be applicable as a membrane material among natural polymers.

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The virus removal filter shows two distinguishable performances of predictable and reproducible virus removability under the high recovery rate of proteins. These characteristics are realized in BMM (R) through the multi-layer pore structure and source material of regenerated cellulose.

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