Predicting the performance of RO membranes

Theoretical and experimental recoveries are compared for spiral-wound and hollow-fiber membranes. The effect of ignoring concentration polarization and pressure drops is studied. Ignoring concentration polarization and pressure drops results in significant overestimation of the recovery. With spiral-wound membranes pressure drops were found to be less significant. In addition, a solution method based on integration was used for hollow-fiber membranes. Each of the water and salt fluxes is defined as an implicit function of two dimensions, namely length and radius, and this function is integrated over the whole of the membrane. The integration method resulted in recovery predictions closest to the average of the experimental data. The agreement between predicted and experimental salt rejection was less pronounced, the theoretical values being higher than the experimental.