Unveiling the underlying mechanisms of performance loss induced by compaction in SWRO membranes

Improving the compaction resistance of seawater reverse osmosis (SWRO) membranes is critical for enhancing seawater desalination efficiency. However, the specific mechanisms of performance degradation resulting from compaction effects in SWRO membranes remain unclear. To elucidate the dominant factors contributing to the decline in permeate flux caused by membrane compaction, the 60-day continuous performance of self-made and commercial LG membranes under cross-flow filtration conditions was studied. The micro- and sub-micro structural morphology of the membranes was characterized using X-ray scattering in combination with SEM, TEM, and AFM. During long-term operation, macropores of the polysulfone substrate were compacted, but no significant changes were observed at the sub-microscopic level. In addition, the macroscopic structure of the polyamide separation layer was not notably affected. However, in both the self-made and LG membranes, the polyamide inter-chain molecular spacing was decreased after compaction, with reductions of 0.07 Å and 0.04 Å, respectively. This reduction explains the decrease in flux of the self-made and LG membranes of 42.10 % and 32.55 %, respectively, along with the increased salt rejection. These results reveal the key mechanisms behind the decrease in permeability during the compaction process from a sub-microscopic perspective, providing valuable insights for the development of pressure-resilient, high-performance SWRO membranes.