Modeling concentration polarization in reverse osmosis processes

Accurate prediction of concentration polarization (CP) phenomena is critical for properly designing reverse osmosis (RO) processes because it enhances trans-membrane osmotic pressure and solute passage, as well as surface fouling and scaling phenomena. The objective of this study was to compare available analytical CP models to a more rigorous numerical CP model and experimental CP data. A numerical concentration polarization model was developed to enable local description of permeate flux and solute rejection in crossflow reverse osmosis separations. Predictions of channel averaged water flux and salt rejection by the developed numerical model, the classical film theory model, and a recently proposed analytical model were compared to well-controlled laboratory scale experimental data. At operating conditions relevant to practical RO applications, film theory and the numerical model accurately predicted channel-averaged experimental permeate flux and salt rejection data, while the more recent analytical model did not. Predictions of local concentration polarization, permeate flux, and solute rejection by film theory and the numerical model also agreed well for realistic ranges of RO process operating conditions.