POLARIZATION AND BACK EMF IN ELECTRODIALYSIS

Polarization and limiting current in electrodialysis (ED) are mass tra nsfer phenomena usually described in terms of greatly rising electrica l resistance of the depleted film. A simple and universally applicable technique has been developed to examine these. In actual operating co nditions, direct measurement of the back electromotive force in a spir ally wound electrodialysis (SPED) module suggests that the increase in ohmic resistance is minimal; the main mechanism is a large fall in th e net e.m.f. From experimental results it is possible to evaluate memb rane surface concentrations and hydrodynamic boundary layer thickness directly.