Abstract
The chapter intends to discuss an application of hydrogel material as draw agent for a forward osmosis desalination system. This refers to systems that allow a continuous process of extraction of desalinated water with low energy costs and minimal environmental pollution. One of the most prominent properties of hydrogel materials is their ability to spontaneously absorb large quantities of water from saline solution separated by a semipermeable membrane. This process is energetically favorable due to the difference in the chemical potentials of water in the solution and hydrogel. Thermodynamic equilibrium between hydrogel and external saline solution corresponds to the strictly defined amount of water retained by the hydrogel in the given conditions. The excess pressure of water in hydrogel relative to the pressure of the pure external in this state is defined as the osmotic pressure difference. In contrast to the absorption of water molecules by hydrogel, their extraction is usually a process that requires large energy consumption and disruption of the continuity of the desalination cycle. However, known several opportunities to overcome this bottleneck and they are discussed in detail.