Surface modification of thin film composite forward osmosis membrane using tris(2-aminoethyl)amine for enhanced ammonium recovery

In this study, we aimed to develop a forward osmosis (FO) thin film composite (TFC) membrane which could retain NH4+ from wastewater. The conventional TFC membrane has a microporous polymer support and a selective layer for salt rejection; however, the polyamide selective layer is known to not be able to reject NH4+. Our strategy was to develop tris(2-aminoethyl)amine (TAEA)-modified TFC membranes via secondary interfacial polymerization, and the modification factors were optimized. The NH4+ rejection of the optimized membrane significantly increased from 64.9 % (pristine TFC) to 94.7 %. TAEA modification resulted in a smoother surface and thinner polyamide selective layers. The mechanism of NH4+ rejection during FO operation was investigated and was found to be influenced by membrane surface carboxylic group density and the polyamide crosslinking, cation exchange between the draw and feed solutions, and size sieving. In conclusion, the TAEA-modified membrane showed high selectivity against NH4+ and applicability for NH4+ recovery. In the future, the TAEA-modified membrane may be applied for NH4+ enrichment and recovery from real wastewater systems.