Transmembrane streaming potential

Figure 9.6 (a) Zeta potential versus NaCI concentration for PS-Uf (O) and PS-Uf-DEAE-dextran fouled ( ) membranes determined from transmembrane streaming potential. 

In practice, the cross membrane filtration potential is modified by a very brief jump of transmembrane pressure and, in consequence, of the permeate rate, which creates a jump of filtration potential, too (Fig. 2). For a given pH, that procedure is repeated with different pressure jump values. The streaming potential is obtained by dividing filtration potential jump value by transmembrane pressure jump value. The same test done at different pH, enables to determine the isoelectric point of a membrane (Fig. 3) and to have an idea on electrostatic charges density and sign. 

Figure 9.5 (a) Transmembrane (filtration) streaming potential vs applied pressure ... 

Dialysis is a diffusion-based separation process that uses a semipermeable membrane to separate species by vittue of their different mobilities in the membrane. A feed solution, containing the solutes to he separated, flows ou one side of the membrane while a solvent stream, die dialysate, flows on die other side (Fig. 21. -1). Solute transport across the membrane occurs by diffusion driven by the difference in solme chemical potential between the two membrane-solution interfaces. In practical dialysis devices, no obligatory transmembrane hydraulic pressure may add an additional component of convective transport. Convective transport also may occur if one stream, usually the feed, is highly concentrated, thus giving rise to a transmembrane osmotic gradient down which solvent will flow. In such circumstances, the description of solute transport becomes more complex since it must incorporate some function of die trans-membrane fluid velocity. 

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