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Environment

Cleaning Wastewater While Generating Electricity

Device combines microbial fuel cell with reverse electrodialysis

by Lila Guterman
March 5, 2012 | APPEARED IN VOLUME 90, ISSUE 10

When researchers combine two electricity-generating technologies, synergy creates efficient cleaning of wastewater and surprisingly high energy production. Last year, Bruce E. Logan and Younggy Kim, of Pennsylvania State University, sandwiched a so-called reverse electrodialysis stack inside a microbial fuel cell to generate up to 3.6 W per m2 of cathode surface (Environ. Sci. ­Technol., DOI: 10.1021/es200979b). The microbes on the fuel cell’s anode oxidize organic matter in water. Meanwhile, the ion-exchange membranes that form the stack harness gradients in salinity to produce electricity. Then Logan and Kim, with graduate student Roland D. Cusick, struck on using ammonium bicarbonate, rather than sodium chloride, to generate the salinity gradient. The device generated more energy—5.6 W per m2—and became easier to recharge because moderate temperatures, such as those captured from waste heat, can concentrate the bicarbonate salt solution (Science, DOI: 10.1126/­science.1219330). When the researchers tested the device with domestic wastewater, rather than with solutions of acetate, they still could generate 2.9 W per m2, and the cell’s bacteria quickly ate through the dissolved organic matter. “The two processes alone do so much less,” Logan says, “but when put together, do so much more.”

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