Concentration Polarization:

Concentration polarization results from the build up of highly concentrated solute on the membrane surface as compared to the bulk feed solution away from the membrane surface. This occurs since water permeation at the membrane surface leaves the more concentrated solute layer that must diffuse back within the bulk liquid. Concentration polarization raises the osmotic pressure at the membrane surface that causes a reduction in water flux and a rises in salt diffusion across the membrane. If the concentration of sparingly soluble salts within the boundary layer adjacent to the membrane surface exceeds solubility limits, precipitation or scaling will occur on the membrane surface. At such high concentrations, colloidal materials in the feed solution might also agglomerate and foul the membrane surface.