INTERNAL FOULING OF MICROPOROUS CROSS-FLOW FILTRATION MEMBRANES WITH DILUTE LATEX SUSPENSIONS

The cross-flow filtration of latex with a modal particle diameter of b etween 1.8 and 3 mu m on two membranes nominally rated at 0.45 and 1.2 mu m pore size has been studied. Characterization by a Coulter porome ter suggested that the average membrane pore diameters were 0.57 and 1 .8 mu m. The full pore distribution of the finer membrane contained po res apparently of diameters below the size of the challenge suspension . However, in both cases particles penetrated the membrane and no filt er cake was formed. This caused internal membrane fouling. Scanning el ectron micrographs showed that the membranes were, in fact, of cellula r structure with pores of diameter 5 times that of the characterizatio n tests and displaying a high degree of interconnectivity of the inter nal cells. The highly interconnected nature of the pore network inside the membrane made individual pore blockage unlikely and provided the means by which high filtration efficiencies could be achieved when fil tering particles smaller than the diameter of the surface openings of the membrane.