Forward osmosis, reverse electrodialysis and membrane distillation: New integration options in pretreatment and post-treatment membrane desalination process

Integration of emerging membrane processes [i.e., forward osmosis (FO), membrane distillation (MD), reverse electrodialysis (RED)] and mature membrane processes [i.e., reverse osmosis (RO)] can address the need for efficient desalination solutions. Utilization of different membrane units in pre- and post-treatment stages allows lowering the energy requirements and environmental impacts of the process wastes. FO as pretreatment unit before RO can reduce the energy consumption because it does not require hydraulic pressure as in microfiltration and ultrafiltration. On the other side, RO effluents can further be utilized as MD feed solution for higher water recovery, while waste heat can be exploited as temperature gradient to drive MD. Moreover, salinity gradient energy can be harvested by RED from brines of RO or MD. This additional energy can partially compensate total energy need for desalination process. Also, due to dilution of retentate streams, the environmental effect of brine disposal can be minimized.