Modeling study of the effects of intrinsic membrane parameters on dilutive external concentration polarization occurring during forward and pressure-retarded osmosis

In membrane-based desalination systems, the mass transfer coefficient is a critical determinant when estimating changes within the boundary layers. However, it is pivotal to recognize the substantial role of intrinsic membrane parameters that can significantly influence the formation of boundary layers by modulating the water and salt fluxes. In this context, we investigated the effects of intrinsic membrane parameters on dilutive external concentration polarization (dECP) during forward osmosis (FO) and pressure-retarded osmosis (PRO). In particular, the Péclet number is utilized to evaluate the degree of dECP. The results revealed that the effects of the membrane parameters on dECP differ completely in accordance with the membrane orientations or magnitude of hydraulic pressure. Moreover, this study emphasizes that the reduction of solute permeability, i.e., improving the selectivity, should be the priority of FO/PRO membrane optimization because solute permeability is the only parameter that simultaneously suppresses both the internal concentration polarization and dECP. Hence, the results of the current study are expected to serve as valuable guidelines for future FO/PRO membrane optimization research.