Membrane-based forword osmosis desalination



In forward osmosis (FO), natural osmotic pressure differences serve as the driving force for water transport through a semi-permeable membrane. In a typical forward osmosis separation, the feed solution, i.e., saline water, passes through one side of a semipermeable membrane, and a draw agent with high osmotic pressure flows on the other side of the membrane. Due to the naturally driven osmotic flow, water permeates through the membrane from the feed solution to the draw agent side. After the forward osmosis process, the water and the draw agent are separated to obtain the purified water product and to regenerate the draw agent for reuse in the forward osmosis process. Thermo-responsive hydrogels containing ionic groups are a class of materials that can be potentially utilized as draw agent for forward osmosis desalination. The ionic groups provide high osmotic pressure, which induces the water flow through the membrane in the process. In the last step of the FO process, by increasing temperature, the hydrogel is forced to shrink, whereby the absorbed water is recovered, and the hydrogels are then regenerated.