Influence of intrinsic membrane variability and flexibility on mass transfer and polarization in osmotic-pressure-driven processes

Forward osmosis (FO) has garnered significant attention as an energy-efficient membrane process for water treatment and resource recovery. While previous studies have focused on membrane material development, the influence of operational conditions on intrinsic membrane properties remains underexplored. In this study, we systematically investigated how system-level parameters, namely temperature, transmembrane temperature difference, and cross-flow velocity (CFV), affect the intrinsic transport properties of a polyamide thin-film composite (TFC) FO membrane. Our findings reveal that water and solute permeability (A and B values), as well as the structural parameter (S value), vary considerably with operational changes, particularly in the presence of transmembrane thermal gradients. Notably, an increase in draw solution temperature led to enhanced internal concentration polarization (ICP), elevating the structural parameter and reducing effective performance. In contrast, increasing the feed solution temperature or CFV improved convective mass transfer and suppressed polarization effects. These results highlight that intrinsic FO membrane properties are not fixed material constants but are dynamically influenced by operating conditions. This study underscores the importance of contextualizing intrinsic property measurements and provides guidance for optimizing FO system design and performance evaluation under realistic conditions.