Optimization on a new hybrid Forward osmosis-Electrodialysis-Reverse osmosis seawater desalination process

Standalone membrane desalination processes are largely influenced by thermodynamic irreversibility-driven energy loss. It is one of the reasons that many studies focus on integrated membrane systems, in addition to creating process flexibility. A new Forward osmosis-Electrodialysis-Reverse osmosis (FO-ED-RO) hybrid system employs FO element upstream to ED-RO system for an access to draw solutions with higher electrical conductivity, aiming at reducing energy consumption and inheriting various advantages of ED system. Various draw solutes candidates, including sodium chloride, are selected primarily based on conductivity, and are further analyzed for best draw solute selection. Then, the optimum values for energy consumption, unit process sizes, and total unit production cost are determined by a simulation based on various FO membranes, modules and FO recovery ratio. As a result, in terms of total unit water production cost, the best draw solute is ammonium chloride with 0.514 USD/m³. The results prove that the new hybrid process is competitive in seawater desalination with respect to the established RO as well as other hybrid systems. Meanwhile, the study also recommends pursuing a research on cheap, yet high electric conductive draw solutes and low cost-low resistance ED membranes, to consolidate the applicability of the process.