Recent developments in the application of hydrogels as draw agents in the forward osmosis desalination process

The shortage of water resources has been one of the most worrying world crises. Thus, one promising way to address the need for water is desalination. In recent years, forward osmosis has been an emerging technique in water treatment applications, especially desalination. This is due to the enhanced quality of water production, which resulted from reduced fouling propensity and high salt rejection. However, the selection of an ideal draw agent for the forward osmosis desalination process is still a challenging issue. Draw agents for forward osmosis desalination should be distinguished with their high osmotic pressure, low reverse solute flux, and facile regeneration. Lately, hydrogels have offered some advantages, such as negligible reverse solute flux and their capability to capture large amounts of water. These merits made different types of hydrogels, like thermoresponsive, electroresponsive, magnetic responsive, gas-responsive, multi-responsive, green, and other hydrogels’ classes, be recognized as draw agents for forward osmosis desalination. In this review, we will describe how hydrogels could be applied as drawing agents for the forward osmosis desalination approach and their operational advantages and drawbacks. In addition, we will display and discuss the recent research output that aimed to improve the performance of hydrogels as draw agents for the forward osmosis desalination.