Surface modification of nanofiltration membrane for enhancing salt rejection and scaling remediation in brackish groundwater desalination application

This study examines the surface modification of a commercial nanofiltration (NF) membrane using spray coating for brackish groundwater desalination. The NF membrane is coated with 5 wt% PEG and 10 wt% GTMAC to establish a pseudo-zwitterionic surface and improve the NF membrane's salt rejection and anti-scaling efficacy. Several characterization methods are employed to characterize the surface of pristine and modified NF membranes. The characterization results confirm that the membrane surface was successfully modified with PEG and GTMAC. Cross-flow filtration studies show increased permeate flux for the PEG-NF membrane compared to the NF membrane. Additionally, the GTMAC-PEG-NF membrane exhibits a stable flux over an extended period, highlighting its improved performance relative to the NF membrane. Moreover, the initial overall salt rejection for the GTMAC-PEG-NF membrane is 56 %, higher than the NF membrane (37.5 %). Ion chromatography results show significant improvements in mono- and divalent ion rejection for the GTMAC-PEG-NF membrane compared to the NF membrane. The real-time monitoring results with optical coherence tomography (OCT) reveal predominant surface crystallization on the pristine NF membrane, while bulk crystallization primarily occurs on the modified membranes. These changes in the scaling mechanism are due to the alteration of surface properties after the modifications, including surface charge, roughness, and hydrophilicity. In conclusion, this study demonstrates the significant promise of enhancing the performance of NF membranes by surface modification through GTMAC-PEG coating.