(625c) Surface Analysis and Biofouling Resistance of Nanostructured Reverse Osmosis Membranes

Water re-use could represent a significant sustainable water resource if upgraded to potable water quality. In this regard, reverse osmosis (RO) desalination is a promising technology for water desalination; however, despite modern advances in RO membrane technology, membrane mineral scaling and biofouling hinders the widespread use of RO membranes in brackish desalination and water re-use applications. This study focuses on the synthesis of a class of RO membranes with a dense hydrophilic polymeric surface brush layer that suppresses surface adhesion of organic, bacteria, and mineral foulants. The polymeric brush lower consists of covalently tethered and terminally-anchored water soluble chains whose segments are capable of a significant degree of Brownian motion. In order to assess the impact of the brush layer on nano-scale changes in surface topography, polyamide-silicon (PA-Si) surrogate surfaces were first developed to optimize the graft polymerization process. The UCLA atmospheric pressure plasma-induced graft polymerization (APPIGP) method was then utilized to generate a high surface density of active sites on a polyamide membrane support for subsequent graft polymerization onto the polyamide surface using suitable water soluble vinyl monomers. The resulting surface nano-structured (SNS)-PA-Si surfaces were characterized with respect to surface energy, roughness, and brush layer thickness. Performance evaluation of the SNS-thin-film composite (TFC)-PA RO membranes was subsequently carried out by examining their biofouling propensities, assessed via flux decline studies with secondary treated municipal waste water effluent, biofilm imaging with confocal laser scanning microscopy (CLSM), and extracellular polymeric substances (EPS) analysis. Additionally, the membrane effectiveness of permeability recovery was evaluated for cleaning regiments using DI water and chemical (Na₂·EDTA) cleaning. The present study demonstrated that it is feasible to tailor-synthesize the grafted brush layer to attain the desired tethered polymer layer topography and the level of surface free energy of hydration to promote biofouling resistance.