Enhancing nanofiltration membranes performance by melamine modification for emergency treating deteriorated water quality in drinking water source

New nanofiltration membrane with larger volume output is one of the key parameters for selection in drinking water treatment applications. Moreover, evaluating the separation performance of NF membranes is crucial for ensuring the continued safety of effluent water quality when responding to sudden changes in water quality. In this study, the melamine, a highly reactive monomer containing a triazine ring, participates in the interfacial polymerization reaction between the piperazine and 1,3,5-benzenetricarbonyl trichloride, thus providing an opportunity to tune the polyamide layer properties. The reaction with melamine changes the structural parameters and decrease the diffusion rate of piperazine, while introducing more intermolecular hydrogen bonds in new hybrid polyamide layer compared to the conventional polyamide layer. These strong intermolecular hydrogen bonds are crucial for enabling high Na2SO4 rejection in melamine-modified membranes. This strategy resulted in membrane permeance of 2.5 times that of commercial membranes (VNF1 and NF270) and unmodified membrane in a complex mixed salts solution, with Cl−/SO42‒ selectivity factor increasing form 7.5 to 44.6. Furthermore, the new membrane can remove most dissolved substances from ultrafiltration effluent in treating drinking water source (Hulukou Reservoir) impacted by sudden shale gas wastewater spill, ensuring the safety of the treated water. The purified water quality parameters are inferior to those of the VNF1 and NF270 membranes, but slightly superior to the unmodified membrane. However, water recovery experiments revealed that all membranes suffered from severe scaling issues. Overall, the results suggest that melamine may be utilized to tune the performance of nanofiltration membrane through the scalable one-step polymerization procedure, providing an effective strategy for preparing high-performance membranes.