In situ modification of membrane elements for improved boron rejection in RO desalination

The study presents in situ modification of a spiral-wound seawater reverse osmosis (SWRO) membrane elements using sorption of hydrophobic long-chain aliphatic amine molecules as a generic approach to increasing selectivity, in particular, boron removal. Spiral-wound seawater SW30 elements modified using decylamine and dodecylamine showed 2–4 times lower boron passage for the modified elements at the expense of a moderate drop in permeability. Autopsy indicated no change in surface morphology and chemistry, suggesting immobilization of the modifying molecules within the active layer. Overall, the reported in situ modification of the SWRO element resulted in a superior trade-off between permeability and boron passage and no change in salt rejection, as compared to regular polyamide membranes. The enhanced selectivity toward boron5 removal could potentially help eliminate or reduce the costs related to the second pass in sea water desalination.