Nanotechnology for Robust Reverse Osmosis Production of Freshwater

The human appetite for clean freshwater is getting larger, as the global supply of groundwater supplies is decreasing. It has been obvious for several decades that better ways of producing freshwater from brackish and salt water would be needed. Finally, thanks to work done at UCLA with maturing nanotechnology methods, it is getting easier to design and manufacture more efficient and robust membranes for reverse osmosis.

The new membrane, developed by civil and environmental engineering assistant professor Eric Hoek and his research team, uses a uniquely cross-linked matrix of polymers and engineered nanoparticles designed to draw in water ions but repel nearly all contaminants. These new membranes are structured at the nanoscale (the width of human hair is approximately 100,000 nanometers) to create molecular tunnels through which water flows more easily than contaminants.

Unlike the current class of commercial RO membranes, which simply filter water through a dense polymer film, Hoek’s membrane contains specially synthesized nanoparticles dispersed throughout the polymer — known as a nanocomposite material.

“The nanoparticles are designed to attract water and are highly porous, soaking up water like a sponge, while repelling dissolved salts and other impurities,” Hoek said. “The water-loving nanoparticles embedded in our membrane also repel organics and bacteria, which tend to clog up conventional membranes over time.”

With these improvements, less energy is needed to pump water through the membranes. Because they repel particles that might ordinarily stick to the surface, the new membranes foul more slowly than conventional ones. The result is a water purification process that is just as effective as current methods but more energy efficient and potentially much less expensive. Initial tests suggest the new membranes have up to twice the productivity — or consume 50 percent less energy — reducing the total expense of desalinated water by as much as 25 percent.

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The new nanotech membranes are also less subject to bacterial and particulate fouling, which limits the lifetime of current reverse osmosis membranes. With the development of more efficient and longer-lasting nano-membranes, all that will be needed is the energy to drive the high pressure pumps that force the water through the membrane.

Presently, the Persian Gulf oil states are the main users of reverse osmoses desalination/water purification. With more efficient methods, there is no reason why most seaports and coastal areas cannot produce more of their water from desalination.