Concentration polarization and fouling

Concentration polarization is often the reason for the serious limitation of the membrane processes due to its negative influence on the transmembrane flux. Many theoretical studies on this polarization phenomena have resulted in mathematical models for concentration polarization. In most of them, solutions are sought for the coupled nonlinear system of the equations of continuity and motion. Each of these solutions makes use of some assumptions in order to simplify the equations which represent the phenomenon.Different kinds of flow systems have been constructed in order to reduce the concentration polarization. The aim of these flow systems has mainly been to improve the mass transport from the membrane surface back to the bulk solution.Fouling often is a result of concentration polarization, but can also have other reasons.The attention that was drawn to fouling ten to fifteen years ago mostly consisted of recognizing the fact as such and to roughly identify the foulant. Later, efforts to avoid the negative effects have basically followed the paths of altering the composition of the feed solution by a pretreatment to change or get rid of the foulant, to change the hydrodynamics of the membrane module or to alter the membrane itself.However, unveiling the basic mechanisms of fouling attracted little attention until the late seventies when for example fouling of an RO sea water desalination membrane could be subdivided into four consecutive steps.Also, studies of the chemistry and physics of fouling have being performed on whey lately and revealed in closer detail some of the responsible phenomena.