Cost-oriented optimization of osmotic dilution based on concentration-dependent hydraulic pressure

Abstract

Osmotic dilution (OD) has been integrated with mainstream seawater reverse osmosis (SWRO) desalination technology to eliminate the worry about the draw solution regeneration and simultaneously lower the desalination cost. In this study, we further optimize the OD design with regard to mitigated water flux decline by introducing the concentration-dependent hydraulic pressure and developing one module-level techno-economic model. Analysis of the module-scale model firstly indicates that simply increasing the flowrate ratio of the feed solution stream to the draw solution stream is not economically applicable to mitigate the inherent water flux behavior in OD, potentially highlighting the significance of concentration-dependent hydraulic pressure. Accordingly, one-stage or multi-stage pressure-assisted forward osmosis (PAFO) followed by OD is evaluated its techno-economic advantage compared to the original OD process, respectively. Simulation results show that, for applied commercial FO membrane, OD combined with one-stage PAFO is the optimal design that balances the mitigated water flux decline with maximum saving and strongly depends on the permeate flow. But, future improved FO membranes necessitate the systematic exploration due to the fact that the optimal OD design is also affected by the membrane transport parameters. Therefore, this work can provide a protocol to optimize the OD design in seawater desalination.