Double-barrier forward osmosis membrane for rejection and destruction of bacteria and removal of dyes

In this paper, a novel FO membrane with antibacterial and antifouling properties was prepared for the first time by forming a multifunctional negatively-charged active layer via the surface amidation reaction with two antibacterial agents, namely, sulfamethoxazole (SMX) and trimethoprim (TMP). The membranes modified by SMX and TMP showed superior water flux , the highest reaching 31.86 (±1.2) LMH for M-T-2, and a lower reverse salt flux (7.74 gMH), which significantly improved the FO performance. In addition, the SMX and TMP immobilized on the FO membrane formed an electrostatic repulsive force towards the negatively-charged bacteria, and showed the inherent destruction capabilities for bacteria when in contact, constructing a double barrier for the fouling of bacteria. As an example, M-T-2 membrane showed good anti-bacteria performance (OD value of 0.058) in the actual municipal sludge wastewater, meanwhile maintaining good water permeability (88% of the initial flux). Furthermore, the prepared membrane owned suitable antifouling and antibacterial ability in the negatively-charged dye wastewater, achieving the efficient removal of more than 95.5% of the dyes. These results show that the modification of the active layer with antibacterial agents can significantly improve the application prospect of FO membranes.