Fouling Resistance and Ease of Cleaning Post Biofouling of Atmospheric Pressure Plasma Induced, Surface Nanostructured, Reverse Osmosis Membranes

Effective use of reverse osmosis (RO) membranes in brackish desalination and water reuse applications requires adequate suppression of membrane fouling and mineral scaling. In the present study, the recently developed atmospheric pressure plasma-induced graft polymerization (APPIGP) method was utilized to generate a high surface density of active surface sites on a polyamide membrane for subsequent graft polymerization using suitable water soluble vinyl monomers. Surface structuring via graft polymerization was then employed to form a brush layer of polymeric chains that are terminally and covalently attached to the polyamide surface of an optimized (with respect to flux and salt rejection) of a thin-film composite (TFC) polyamide (PA) membrane. The chemical and physical features of the resulting surface nano-structured (SNS) TFC-PA membrane was first tuned with respect to wettability, by the selected vinyl monomer chemistry, as well as the reaction conditions, to achieve the desired surface architecture. Performance evaluation of the SNS-TFC-PA RO membranes was subsequently carried out by examining their mineral salt scaling and biofouling propensities. Reduction in membrane mineral scaling propensity was quantified from flux decline studies using salt solutions supersaturated with respect to the target mineral salt scalant. Membranes effectiveness in retarding biofouling was assessed via flux decline studies with secondary treated municipal waste water effluent, permeability recovery by DI water and chemical (Na₂·EDTA) cleaning, and residual biofilm thickness. The results of the present study demonstrate that it is feasible to tailor-synthesize SNS-TFC-PA membranes of high permeability with the added benefit of reduced mineral scaling propensity and increased fouling resistance.