Performance of Nanostructure RO/NF Membranes

Thin-film composite polyamide membrane has been the dominant membrane used for reverse osmosis and nanofiltration since its development by Cadotte and co-workers. However, in inland brackish water desalination (including desalting of treated municipal wastewater), fouling (due to both inorganic salt scaling and organic fouling) of RO/NF membranes pose a major bottleneck to increasing process efficiency. A new class of surface nano-structuring polyamide thin-film composite (SNS-PA-TFC) membranes were synthesized via atmospheric pressure plasma induced graft polymerization (APPIGP) [4]. Surface activation was achieved by exposing the surface to an impinging atmospheric plasma source, followed by free radical graft polymerization (FRGP) in an aqueous monomer solution. Surface nano-structured polyamide thin-film composite (SNS-PA-TFC) membranes were prepared in a three step process. SNS-PA-TFC membrane performance was evaluated with respect to gypsum scaling using a laboratory plate-and-frame RO (PFRO) system. The PFRO system was equipped with an optimal membrane imaging hardware and software to allow direct visual observations of the membrane surface and detection of mineral scale on the RO membranes under high pressure. Gypsum scaling tests demonstrated that the SNS-PA-TFC membranes had significantly lower scaling propensity compared to LFC1 membrane. Current efforts are underway to simultaneously tune the polymer brush layer structure (and polymer type) to increase organic and bio-fouling resistance of the membranes while maintaining (or even increasing) the present level of reduced scaling propensity and high permeability.

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