Water desalination by forward osmosis: draw solutes and recovery methods–review

Water production has become a serious concern nowadays due to many environmental and social factors. Conventional desalination processes are considered as energy-intensive, as energy consumption represents 50–60% of water production cost. As an example, multistage flash evaporation (MSF), requires 19.58–27.25 kWhe/m3, and reverse osmosis (RO) 1.5–6 kWhe/m3. Thus, developing forward osmosis (FO), a membrane technology for water desalination considered as a potentially energy-efficient process, has gained growing interest. However, the technology is facing serious limitations concerning the availability of a high-performance draw solution and membrane, which represent the core of the process. In addition to the lack of energy-efficient recoverable draw solutes, as the regeneration process represents the main energy consumption of the overall FO process. In this paper, an updated state of the art of newly developed draw solutes such as deep eutectic solvents, ionic liquids, smart materials, and classical FO draw solutes have been carried out. Finally, FO technology challenges, opportunities, and future prospects have been discussed. Draw solutes have been categorized according to their recovery methods, innovations and draw solutes strengths and limitations have been critically reviewed. The necessity of theoretical energy consumption and water production costs estimation have been outlined, in addition to pilot-scale testing to demonstrate the process feasibility. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.