What is concentration polarisation in relation to Reverse Osmosis?
Concentration polarisation (CP) is the term that describes the tendency of the solute to accumulate at membrane solution interference within a concentration boundary layer or stringent liquid film. This layer contains near stringent liquid, since at the membrane surface itself the liquid velocity must be nil. This implies that the only mode of transport within this layer is diffusion, which is around two orders of magnitude slower than convective transport in the bulk liquid region. Rejected materials thus build up in the region adjacent to membrane, increasing their concentration over the bulk value. This build up occurs exponentially with increasing flux. This thickness of the boundary layer, on the other hand, is determined entirely by the system hydrodynamics, decreasing in thickness when turbulence is promoted. For pressure driven processes, the greater the flux, the greater the build up of solute at interface. The greater the solute build up, the higher the concentration gradient
