Top Paper in Environmental Technology: Saltwater power an anode at the other. The flow of sodium and chlorine ions across the membranes sets up an electric current that produces energy. Post and Hamelers calculated that mixing 1 cubic meter (m3) of freshwater with 1 m3 of salt water could yield 1.5 megajoules of energy. When they investigated the efficiency of their reverse electrodialysis setup, they found that more than 80% of the energy could be recovered. Compare this with the efJan Post was just fooling ficiency of coal-fired around in his consulting power plants, which harfirm’s laboratory one day vest only 38-50% of the when inspiration struck. A energy released by burncivil engineer with DHV in ing coal, and it is easy to Amersfoort (The Nethersee why their idea was lands), he suddenly enviworth pursuing, Hamelers sioned how energy could says. be derived from the mix“Currently we are getBert Hamelers (left) and Jan Post raise a glass to the Rhine ing of salt water and ting a lot of attention for River, which generates 2000 MW of power when it mixes freshwater. Post apour idea because a 75with seawater at its mouth. proached Bert Hamelers, year-old dike in the north an environmental engiof the country, the Afsluitwith a degree in chemical engineer at Wageningen University, dijk, needs to be improved,” neering. When Post made his ofwho took Post on as a Ph.D. Hamelers says. One of the profer, “I wondered: should I start student. posals is to build a reverse elecwith a civil engineer?” Hamelers “I still remember that trodialysis plant at this location admits. The project required momentsI was in our lab and with a possibility of generating knowledge of physical chemistry had a bad Internet connection,” 300 megawatts (MW) of electricthat typically is not part of the Post recalls. Unable to work on ity. This could supply a large part curriculum for civil engineers. But the computer, but required to reof the electricity demand for Post was a perfect fit because he main in the laboratory for the homes in the northern part of was so motivated, and his civil safety of a colleague, Post wonThe Netherlands, he notes. A kiloengineering background brought dered, “What can I do in the lab watt-scale pilot project there is a fresh and useful perspective, today?” He started playing with a estimated to launch by the end of Hamelers says. desalination unit, switching it on this year, Post says. Scientists in the 1950s had and off and thinking about —JANET PELLEY proven the concept of deriving osmosis. electrical power from adding salt “I was struggling with the queswater to freshwater, but no one tion: why does it take so much had ever measured how much energy to desalinate water?” Post energy could actually be harsays. He claims it was not so diffivested, Hamelers explains. He and cult to imagine the opposite: Post constructed a reverse elecmaybe adding seawater to freshtrodialysis stack consisting of alwater to make it more salty would ternating anion- and cationgenerate energy. The discovery so exchange membranes separating fascinated him that he could not thin compartments of river water leave it alone. “Jan came around and seawater, sandwiched beat the right time,” Hamelers says. tween a cathode at one end and He had been discussing the potential of salt water and freshwater mixing as an energy source with Cees Buisman, scientific director of Wetsus, a research institute in Leeuwarden. A partnership between Wetsus and the university was in the works, but they were looking for a skilled student
2194 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / April 1, 2009
GITTE SCHOBER
“Energy Recovery from Controlled Mixing Salt and Fresh Water with a Reverse Electrodialysis System” by Jan W. Post and Hubertus V. M. Hamelers, Sub-Department of Environmental Technology, Wageningen University (The Netherlands); and Cees J. N. Buisman, Wetsus, Centre for Sustainable Water Technology, Leeuwarden (The Netherlands), 2008, 42 (15), 5785-5790; DOI 10.1021/es8004317.
10.1021/es9004224
2009 American Chemical Society
Published on Web 03/04/2009
