A multi-barrier osmotic dilution process for simultaneous desalination and purification of impaired water

Osmotically driven membrane processes use chemical potential difference between two aqueous solutions as a driving force for separation and concentration of feed streams or for recovery of energy. Forward osmosis was extensively studied in recent years and demonstrated that it can be successfully utilized in many applications of water treatment. In a new approach, the salinity difference between seawater and impaired water, such as reclaimed water, is used as a driving force for osmotic dilution of seawater before desalination. The osmotic dilution approach may provide at least four major benefits related to water and energy resources. These include lower energy desalination of seawater, multi-barrier protection of drinking water, reduction in reverse osmosis membrane fouling due to impurities in impaired water, and beneficial reuse of impaired water. The osmotic dilution process was investigated on both bench- and pilot-scales. Both secondary and tertiary treated effluents from a domestic wastewater treatment plant and impaired surface water were used as feed water to the process. Flux decline was minimal and under specific flow condition it was observed that membrane fouling was negligible. Additionally, the multiple membrane barriers provided high rejection of both organic and inorganic solutes and of trace organic chemicals.