Concentration polarization in pressure driven processes

When pressure is applied to the feed side of a membrane during the filtration process, the solute is partially or totally retained by the membrane and will accumulate on the surface, while the solvent passes through the membrane more freely. Due to the membrane’s solute retention, the concentration of the solute in the permeate (Cp) is lower than the concentration in the bulk (Cb) 1.

The concentration of the solute gradually increases on the surface of the membrane, due to solute accumulation from convective flow. At some point, the convective solute flow to the surface of the membrane will be balanced by the solute flux through the membrane and the diffusive flow from the membrane surface to the bulk. A concentration polarization profile, in which the concentration at the membrane surface (Cm) is typically higher than the Cb, will be established in the boundary layer.