Show Me the Salt

Capacitive deionization has intrigued desalination experts since its original announcement, but they say they're still waiting to see real-world results. "There's a lot of hope for the process, but a long way to go," says David Furukawa of Separation Consultants in Poway, CA, a former president of the International Desalination Association.

"I don't know if you can go into large-scale production" without a better understanding of how the process works, adds Ron Linsky, executive director of the National Water Research Institution in Fountain Valley, CA.

"A lot of desalination technologies have come and gone, promising the world and delivering almost nothing," adds Ian Watson of RosTek Associates in Tampa, one of the experts who contributed to the federal roadmap. When it first debuted, "this one looked good." He's very interested, but reserving judgment on capacitive deionization until the technology starts producing large volumes of fresh water in real-world applications. Watson says that he awaits the results of CDT's work on brackish water with interest but the "proof is in the eating." He also notes that the capital cost of the aerogel modules precludes high-volume seawater desalination.

The competition is still the tried-and-true reverse osmosis process, which has prospered while "crazy ideas" have come and gone, says Lisa Henthorne, vice president and membrane technology leader at environmental consultancy Metcalf & Eddy in Naples, FL. Reverse osmosis membranes have steadily improved; you get 27 times as much water for your capital investment as you got in 1980, she says.

"Hundreds of new desalination and water supply purification ideas are generated every year in the field and in the laboratory," notes the Desalination and Water Purification Technology Roadmap, a report issued earlier this year by the U.S. Department of the Interior.

And whether based on capacitive deionization, reverse osmosis or any other desalination technology, inland water projects face another severe challenge--disposing of the leftover brine concentrate. "You have to keep it away from fresh water supplies," points out Furukawa. Most states don't allow it to be injected in deep wells, and evaporation ponds take considerable land. Researchers are looking at creative solutions to contain the concentrate, or turn it into useful products.

According to the federal roadmap, half of U.S. population growth is forecast to occur in California, Texas, and Florida--"regions already experiencing water shortages." Moreover, the roadmap adds, "only with cost-effective and efficient revolutionary technologies will the nation be able to meet its future (25+ years out) demand for safe, sustainable, and affordable water."

It's too early to predict how much of a part capacitive deionization will play in desalination versus the well established rival technologies--not only reverse osmosis but also the thermal techniques popular in the Middle East, where energy is cheap, or the other approaches that crop up each year in labs worldwide. But the new technology's commercial emergence highlights the advanced alternatives now poised to meet a basic human need.

Experts agree on one point: demand for water is soaring, and it will only be met by broad, deep, and continuously improving desalination efforts. "We've been blessed and spoiled, I suppose, by copious quantities of very low cost water," says Furukawa. "That cost is going up."