Design of a Three-Stage Membrane Brine Concentrator Using Conventional Nanofiltration Modules Toward Zero Liquid Discharge in Wastewater Reclamation

A membrane brine concentrator (MBC) can reduce the concentrate volume entering thermal processes for zero liquid discharge (ZLD). Previous LSRRO-based studies have largely focused on high-salinity brines using modified or specifically selected low-salt-rejection membranes. This study examined the extent to which water recovery could be increased in wastewater reclamation using conventional nanofiltration (NF) modules in MBC processes. Two brackish water reverse osmosis (BWRO) modules and two NF modules were tested in 2000–40,000 mg/L NaCl. NE4040-90 provided the best balance between salt-concentrating performance and required pressure. An NF module model was developed using experimentally estimated water permeability, salt permeability, and mass-transfer coefficient. It reproduced permeate concentration and feed pressure with normalized root-mean-square errors of 5.73% and 1.20%, respectively. The developed NF module model was then iteratively coupled with the upstream BWRO simulation to evaluate an integrated two-stage BWRO and three-stage MBC process. Compared with conventional BWRO, the integrated system increased overall recovery from 81.0% to 95.9%, reduced concentrate flow from 32 to 7 m3/h, predicted a final concentrate concentration of 51,396 mg/L, and maintained permeate concentration at 34 mg/L while remaining below the 41.4 bar pressure limit. The reduced concentrate load lowered total specific energy consumption from 4.5 to 1.6 kWh/m3 of wastewater feed under the adopted ZLD assumptions. Conventional NF modules therefore provide a practical option for high-recovery wastewater reclamation toward ZLD.