Zwitterionic surface modification of forward osmosis membranes using N-aminoethyl piperazine propane sulfonate for grey water treatment

Zwitterionic amide monomer (N-aminoethyl piperazine propane sulfonate, AEPPS) was used to modify the active layer of the thin-film composite (TFC) Forward Osmosis Membranes (FOMs) by either adding into the water phase before the interfacial polymerization (route 1) or grafting to the initial active separation layer after the interfacial polymerization (route 2). Their separation performance and anti-fouling property were investigated. Different from the literature results, the synthesized AEPPS was a mixture of isomers which is too complicated to be purified. Results showed that both fourier transform infrared spectroscopy and X-ray photo-electron spectroscopy confirmed that the zwitterionic materials were successfully incorporated into the FOMs. However, in a long-term FO fouling test by using grey wastewater as the feed solution, surface grafted zwitterionic FO membrane prepared after the interfacial polymerization (route 2) showed superior stable FO performance than the membrane prepared by imbedding the AEPPS inside the active layer (route 1). Imbedded AEPPS chemical inside the active layer could not prevent the adsorption of foulant, thus no relief in the fouling was observed. The results demonstrated that the zwitterionic material surface grafting after the interfacial polymerization way is a more efficient approach to prepare fouling resistant FOMs for treating greywater.