New membrane makes fresh water from sea and sewage feasible.

New membrane makes fresh water from sea and sewage feasible.

Jul 20, 2010

Yin Yip, N, A Tiraferri, WA Phillip, JD Schiffman and M Elimelech. 2010.
High performance thin-film composite forward osmosis membrane. Environmental Science & Technology http://dx/doi.org/10.1021/es1002555.

Synopsis by Adelina Voutchkova
A special membrane turns salty sea water into fresh water, paving the way for large-scale desalination that would provide desperately needed drinking water.

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Researchers at Yale University have developed a custom membrane that can clean and purify water from oceans, salty ground water or sewage water with far less energy input than currently is required to do a similar job.

The membrane may be a big step forward in reaching the goal of reliable and affordable sources of fresh water.  Finding sustainable sources of clean drinking water is a major global challenge, especially in most of the developing world. The need is apparent in both urban areas, due to growing population and demand, and rural regions, where sometimes scarce water supplies are quickly drying up.

As fresh water becomes more scarce, desalination and filtering will be increasingly necessary to satisfy the world’s unquenchable thirst for this precious commodity. Yet, neither of the existing desalination technologies – distilling sea water water vapors by boiling then collecting the water vapors or reverse osmosis where water is pushed through membranes to filter the salt – are feasible on a large scale. Both require high amounts of energy to either boil the water or create pressure.

A newer approach does not require external heat or pressure but lacks an adequte membrane to filter the water. The techique uses a mixture of dissolved carbon dioxide and ammonia gas in water on one side and salty or dirty water on the other side of the membrane. The gas/water mixture draws the clean water through the membrane and leaves the salt and dirt on the other side. A small amount of heat is then applied to drive off the carbon dioxide and ammonia, leaving just pure, fresh water.

However, no current membranes can stand up to the ammonia.

Now, researchers report that they have developed one – a thin-film composite forward osmosis membrane. They describe the elaborate technology in the journal Environmental Science and Technology. The membrane is permeable enough to allow water to flow freely through it but resistant enough to keep the ammonia and chemicals in sewage from passing through it.

This landmark development is a beginning. More research is needed to bring down the costs of the membranes and make this technology accessible in all parts of the world.