(777b) Surface Modification of Forward Osmosis Membranes for Improved Fouling Resistance

Forward Osmosis (FO) utilizes the osmotic pressure difference between two solutions of different concentration to drive water permeation across a semipermeable membrane. As an emerging membrane technology, FO holds promise in a variety of applications, including seawater desalination, wastewater reclamation and osmotic membrane bioreactors. Despite significant advances in FO membrane development, membrane fouling, due to adsorption of organic molecules on the membrane surface, remains a major technical problem, decreasing process performance and membrane life. Here we report the fabrication, characterization and testing of thin film composite (TFC) FO membranes containing polyethylene glycol (PEG) surface grafts for improved fouling resistance. The membranes comprise a microporous polysulfone support over which a polyamide selective layer is synthesized by interfacial polymerization. To facilitate PEG grafting, a second interfacial polymerization is carried out between ethylene diamine and acyl chloride groups on the nascent polyamide layer, yielding a selective layer rich in primary amine groups. The resulting amine-rich active layer is functionalized with PEG diglycidyl ether, whose epoxide groups readily react with primary amines. Surface characterization by ATR-FTIR spectroscopy and zeta-potential measurements shows the presence of PEG and amine groups on the membrane surface, and contact angle measurements demonstrate that the PEGylated active layer is more hydrophilic than that of control polyamide membrane surfaces (whose active layer does not contain a grafted PEG layer). We report dynamic fouling experiments using alginate as model organic foulant, showing that membrane fouling is significantly reduced in the case of PEGylated membranes, due to the presence of a PEG barrier that hinders foulant adsorption. Finally, we use AFM adhesion force measurements to demonstrate that the interaction energy between a carboxylated colloidal probe and the PEGylated membrane is significantly weakened as compared to the control polyamide surface.