Autonomous forward osmosis process employing an amine-modified support layer for production of potable water

Although ammonium bicarbonate enables the forward osmosis (FO) process to function as a standalone water treatment method due to its easy separation and regeneration of the draw solution, ammonium leakage from the draw solution represents a limitation of the FO process because it reduces the osmotic pressure and waste resource gradients. This study investigated a double-sided rejective FO membrane with a positive and tight amine layer on the support layer to prevent ammonium transport and evaluated the membrane under various operational cycles and feed and draw solution concentrations to determine its reusability and feasibility in seawater desalination. The modified support layer was optimized with 5 % polyetherimide (PEI) and 3 % trimesoyl chloride (TMC), and the modified support layer increased the surface potential from −36.52 to over 35 mV due to the 1.4 fold increase in the quantitative amine structure. At extremely high feed salt concentrations (45,000 ppm), the reverse ammonium flux (RSF_A) of the double-sided rejective FO was reduced by 59.53 % compared to virgin FO with comparable initial water flux (J_W) values (virgin FO: 1.96 LMH, modified FO: 2.71 LMH). Owing to the strong chemical bonds of the polyamide-based amine layer, the low RSF_A of the double-sided rejective FO was maintained during the 5th operational cycle, and the J_W remained stable based on the stable positive surface potential. In seawater desalination, double-sided rejective FO showed comparable water production and less ammonium loss (approximately 32.56 %) relative to virgin FO. This study proposes new forms of FO membranes to overcome water scarcity concerns.