New process makes safe water cheaper

In the Mason Laboratory on Hillhouse Avenue, a refrigerator packed with bottles contains a thin piece of plastic with the potential to revolutionize water desalination.

With support from environmental and chemical engineering professor Menachem Elimelech, graduate students Ngai Yin Yip GRD ’13 and Alberto Tiraferri GRD ’13, and postdoctoral researchers William Phillip and Jessica Schiffman have designed a membrane for forward osmosis, a water treatment process that uses very little energy. Since current methods of water desalination are expensive largely because they are energy intensive, Elimelech said developing the membrane is one of the key steps that will lower the cost of water desalination, which could help the nearly one-fifth of the world’s population that lacks access to drinking water.

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Carol Hsin
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Forward osmosis works by taking advantage of the way water naturally moves from areas of high concentration to low concentration, so it uses less energy to separate pure water from brackish water.
Carol Hsin
Forward osmosis works by taking advantage of the way water naturally moves from areas of high concentration to low concentration, so it uses less energy to separate pure water from brackish water.
Forward osmosis works by taking advantage of the way water naturally moves from areas of high concentration to low concentration, so it uses less energy to separate pure water from brackish water.
Carol Hsin
Forward osmosis works by taking advantage of the way water naturally moves from areas of high concentration to low concentration, so it uses less energy to separate pure water from brackish water.

“Water runs the world almost as much as oil does,” said Jeffrey McCutcheon GRD ’08, a former student of Elimelech who is now a chemical engineering professor at the University of Connecticut.

McCutcheon said as freshwater sources have become more and more scarce, regional conflicts over water are becoming more common. Using forward osmosis technology to extract pure water from seawater and waste water could alleviate these socio-political tensions, he said.

The current “state-of-the-art” water desalination technique is reverse osmosis, which uses primarily electrical energy to force water across a plastic membrane, Tiraferri said. Forward osmosis, on the other hand, takes advantage of the way water naturally moves from areas of high concentration to low concentration to separate pure water from brackish water, he said. Researchers at Yale and other institutions have been dissolving compounds in water to find cheap and safe chemical solutions that will draw water across a membrane.

“We cannot continue with current technologies being used for water desalination,” Elimelech said. “If we continue to use energy to desalinate water, it will accelerate climate change.”

In 2002, Robert McGinnis GRD ’09, who used to work in Elimelech’s lab, patented a solution made of dissolved ammonia and carbon dioxide gases. When brackish water and the ammonia and carbon dioxide solution are separated by a membrane, water will move to the side of the solution. After exposing the solution to a small amount of heat, the gases evaporate, leaving pure water in the container. Because most of the gases are collected and reused, Tiraferri said the gases do not need to be replenished often.

While Elimelech’s lab has long had the chemical solution for the forward osmosis process on hand, it was not complete because commercially available membranes, which are designed for reverse osmosis, are not suitable for forward osmosis, McCutcheon said. A membrane for forward osmosis needed to be impermeable to salts, but allow a large amount of water to pass through, McCutcheon said. Last May, the researchers in Menachem’s laboratory began working on making such a membrane.

“After over a hundred unsuccessful attempts, we achieved a breakthrough,” Yip said.

Although the researchers have created a suitable membrane, Yip said the technology must be mass-produced before it can be widely used. In order for forward osmosis to replace existing municipal water treatment processes, Phillip said more than 1.7 million square feet of membrane would be needed. The membranes made in the laboratory are about 20 cubic centimeters, he said.

With the solution and membrane both available, companies such as Oasys, a company spun off by the Yale Office of Cooperative Research, want to install the technology in water treatment plants. But this work will not be done by the Yale researchers, Phillip said.

“Now it’s not about research as much as it is about industry,” Tiraferri said.

In 2000, the United Nations set a goal of halving the number of people who do not have sustainable access to safe drinking water by 2015.

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