抄録
Microporous membranes for depth filtration capture particles internally, and thus the compaction of the particle layer is partially repressed by the internal structure of the filter to yield a high permeation flux at a low transmembrane pressure. The standard blocking, fiber coating, and deep bed filtration models are typical ones for isotropic depth filters. On the other hand, filtration characteristics of asymmetric filters are much less investigated than that of isotropic ones. We filtered suspensions of polystyrene latex particles (incompressible, spherical, 0.54 µm in diameter) with an asymmetric depth filter, SE20 (nominal pore size ＝ 0.20 µm), at different transmembrane pressures and concentrations. The filtration resistance per unit weight of trapped particles with the depth filter was half of that with a screen filter in the filtration of latex particles. The particles were trapped first near the outlet side of the depth filter and then near the inlet side unlike the filtration models for isotropic depth filters. A filtration model was proposed for the filtration of latex suspension with the depth filter. The model suggested that the asymmetric depth filter showed high performance because the filaments in the filter increased the porosity of the particle layer in contact with them. The permeation flux was 3 ～ 8 times higher with the depth filter than with a screen filter at 10 ～ 150 kPa in the filtration of bacterial cell suspensions. Scanning electron microscopy revealed that the bacterial cells were captured dispersedly from the depth of 2/3 to the inlet side of the depth filter. The dispersed capture was effective to suppress the increase in filtration resistance in the filtration of bacterial cell suspensions with the asymmetric depth filter. The filtration model for the filtration of bacterial cell suspensions has not yet been established. Further studies are necessary to develop the universal filtration model for asymmetric depth filter membranes.
