Fabrication of mesh-embedded double-skinned substrate membrane and enhancement of its surface hydrophilicity to improve anti-fouling performance of resultant thin-film composite forward osmosis membrane

Abstract

Forward osmosis (FO) has been postulated as a potential viable alternative to conventional pressure-driven membrane treatment processes for water treatment, wastewater reclamation and desalination. Nevertheless, FO suffers from inherent drawbacks such as internal concentration polarization (ICP) and membrane fouling. Its practicality is further limited by the operational dilemma of either experiencing a more severe dilutive ICP in active-layer-facing-feed-solution (AL-FS) orientation or suffering a higher fouling propensity in active-layer-facing-draw solution (AL-DS) orientation, especially with the conventional asymmetric single-skinned FO membranes. Aiming at alleviating the problem of internal fouling while still exploiting the lower ICP and higher water flux of the AL-DS orientation, this study has demonstrated the fabrication of a flat-sheet mesh-incorporated double-skinned substrate membrane for thin-film composite (TFC) FO membrane. Through a progressive substrate membrane surface modification via polydopamine (PDA) deposition, this study explicitly correlates the increment of substrate membrane surface hydrophilicity to the improved fouling resistance and fouling reversibility of resultant TFC-FO membrane in the AL-DS orientation. The effects of foulant types (i.e., alginate and silica), cross-flow rates (i.e., high flow and low flow) and membrane orientations (i.e., AL-DS and AL-FS) have also been systematically studied to better understand FO operation characteristics and enhance its practical applications. The PDA modified double-skinned membrane developed in this study, e.g., TFC-Psf-6, has demonstrated more than 93.0% of water flux recovery in the AL-DS orientation after cleaning as well as significantly surpassing the performance over unmodified double-skinned TFC-Psf-0 (81.7%) and single-skinned TFC-Psf-S (61.7%) under the same testing condition.