Forward osmosis combined with sunlight helps desalinate salt water

11/12/2013 - 00:00

With energy-efficient desalination techniques, water-starved communities could produce fresh water from salty sources such as seawater and industrial wastewater. But common methods like reverse osmosis require pumping the water, which uses a substantial amount of energy. So some researchers have turned to forward osmosis, because in theory it should use less energy. Now a team has demonstrated a forward osmosis system that desalinates salty water with the help of sunlight (Environ. Sci. Technol.2013, DOI: 10.1021/es403266y).

Like reverse osmosis, forward osmosis removes solutes from water via a semipermeable membrane. But instead of pumping the water through the membrane, forward osmosis methods rely on osmotic pressure to drive water across it. To create this osmotic pressure, researchers place so-called draw agents, such as solutions of other salts or absorbent hydrogels, on the other side of the membrane. Once these materials draw fresh water across the membrane, researchers have to find a way to extract the water from them. Developing an energy-efficient way to do this last step has been a challenge for researchers.