D (+)-Glucosamine (DGA) based polyesteramide TFC NF membrane for the pretreatment of reverse osmosis seawater desalination

Reverse osmosis is an effective seawater desalination way extending the available sources of fresh water, but challenged by the gypsum scaling. Herein, D (+)-glucosamine (DGA) was rationally selected and utilized to prepare a novel polyesteramide (PEA) NF membrane that can reject SO42− but release Ca2+. Then it was employed in the pretreatment of seawater reverse osmosis to spatially isolate SO42− and Ca2+, thus removing the “foundation” for forming gypsum. Compared to the referenced NF270, the optimized sample denoted as DGA-PEA-NF has a looser structure with stronger negative charge, as well as a higher resistance to both organic fouling and chlorine attack. During the pretreatment of seawater, both the water permeability and SO42−/Ca2+ selectivity of the DGA-PEA-NF membrane were much higher than those of NF270; the seawater permeance and SO42−/Ca2+ selectivity of DGA-PEA-NF were 10.25 L m−2·h−1·bar−1 and 7.62, respectively, while those of NF270 were only 5.11 L m−2·h−1·bar−1 and 2.08. Consequently, the DGA-PEA-NF membrane effectively reduced the gypsum scaling both in NF and RO stages rather than just transferring the fouling problem forwards to NF stage. The implementation of this research is expected to provide guidance for a targeted fabrication of NF membranes, as well as support for the sustainable development of seawater desalination.