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Household sewage called a vast new energy resource

Jan. 5, 2010
Courtesy of the American Chemical Society
and World Science staff

In a find­ing that gives new mean­ing to the ad­age, “waste not, want not,” sci­en­tists are re­port­ing that house­hold sew­age has far more po­ten­tial as an al­ter­na­tive en­er­gy source than pre­vi­ously thought. 

They say their dis­cov­ery, which raises the es­ti­mat­ed po­ten­tial en­er­gy in wastew­a­ter by al­most a fifth, could spur ef­forts to ex­tract meth­ane, hy­dro­gen and oth­er fu­els from this vast, un­tapped re­source.

Their re­port ap­pears in En­vi­ron­men­tal Sci­ence & Tech­nol­o­gy, the re­search jour­nal of the Amer­i­can Chem­i­cal So­ci­e­ty.

Au­thors Eliz­a­beth S. Hei­drich of New­cas­tle Uni­vers­ity in the U.K. and col­leagues said sew­age treat­ment plants in the Un­ited States use about 1.5 pe­r­cent of the na­tion’s elec­tri­cal en­er­gy to treat 12.5 tril­lion gal­lons of wastew­a­ter a year.

In­stead of just pro­cess­ing and dump­ing this wa­ter, they sug­gest that in the fu­ture treat­ment facil­i­ties could con­vert its or­gan­ic mo­le­cules in­to fu­els, trans­form­ing their work from an en­er­gy drain to an en­er­gy source. They es­ti­mate that a gal­lon (about 4 liters) of wastew­a­ter con­tains enough en­er­gy to pow­er a 100-watt light bulb for five min­utes.

Only one oth­er study had been done on wastew­a­ter’s en­er­gy po­ten­tial, ac­cord­ing to Hein­drich and col­leagues. She be­lieves the re­sults were too low be­cause some en­er­gy-rich com­pounds were lost to evapora­t­ion. 

Her team freeze-dried wastew­a­ter to con­serve more of its en­er­gy-rich com­pounds. Us­ing a stand­ard de­vice to meas­ure en­er­gy con­tent, they found that the wastew­a­ter they col­lect­ed from a wa­ter treat­ment plant in North­east Eng­land con­tained nearly 20 per cent more than re­ported pre­vi­ously.


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In a finding that gives new meaning to the adage, “waste not, want not,” scientists are reporting that household sewage has far more potential as an alternative energy source than previously thought. They say their discovery, which increases the estimated potential energy in wastewater by almost 20 percent, could spur efforts to extract methane, hydrogen and other fuels from this vast and, as yet, untapped resource. Their report appears in Environmental Science & Technology, the research journal of the American Chemical Society. Authors Elizabeth S. Heidrich of Newcastle University in the U.K. and colleagues said sewage treatment plants in the United States use about 1.5 percent of the nation’s electrical energy to treat 12.5 trillion gallons of wastewater a year. Instead of just processing and dumping this water, they suggest that in the future treatment facilities could convert its organic molecules into fuels, transforming their work from an energy drain to an energy source. Based on their research, they estimate that one gallon of wastewater contains enough energy to power a 100-watt light bulb for five minutes. Only one other study had been done on wastewater’s energy potential, according to Heindrich and colleagues. She believed the results were too low because some energy-rich compounds were lost to evaporation. In the new study, the scientists freeze-dried wastewater to conserve more of its energy-rich compounds. Using a standard device to measure energy content, they found that the wastewater they collected from a water treatment plant in Northeast England contained nearly 20 per cent more than reported previously.