Sewage holds untapped power

James Cheng /

At a sewage treatment plant in Renton, Wash., biodegradable solid waste powers a 1-megawatt fuel cell. A new study suggests that wastewater contains 20 percent more energy-rich compounds than previously thought.

Wastewater streaming out of our households contains nearly 20 percent more potential energy than previously believed, a new study has found.

If confirmed, the results could spur efforts to extract methane, hydrogen and other fuels from this largely untapped resource.

“Given the huge amount of wastewater globally and the potential energy stored within it, it is important that this potential energy should be determined,” Elizabeth Heidrich and her colleagues at Newcastle University in Britain report in the latest issue of Environmental Science and Technology.

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The team felt the estimates from the only other study analyzing the energy potential of wastewater were too low, primarily because too many energy-rich compounds were lost in the oven-drying method that was used to capture them.

For their study, Heidrich and her colleagues freeze-dried wastewater to conserve more of its energy-rich compounds. They then measured the energy content of the compounds and found them to be 20 percent more than previously reported.

While the technologies used to extract these compounds and then turn them into energy require further development, her team concludes that converting wastewater into fuels could transform sewage from an energy drain to an energy source.

In the U.S., for example, sewage treatment plants use about 1.5 percent of the nation’s electrical energy to treat 12.5 trillion gallons of wastewater a year. According to Heidrich and colleagues’ calculations, one gallon of wastewater contains enough energy to power a 100-watt light bulb for five minutes.

If this works out, household wastewater will join an energy-making party already started by vintners and brewers. Another experiment is using biodegradable solid waste captured at a sewage treatment plant in Renton, Wash., to power a 1-megawatt fuel cell power plant.

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In addition to Heidrich, the authors of “Determination of the Internal Chemical Energy of Wastewater,” published online Dec. 9 by Environmental Science and Technology, include T.P. Curtis and J. Dolfing.

John Roach is a contributing writer for Connect with the Cosmic Log community by hitting the “like” button on the Cosmic Log Facebook page or following’s science editor, Alan Boyle, on Twitter (@b0yle).


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