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Fuel from sewage can be profitable: study

May 23, 2010
Courtesy of the American Chemical Society
and World Science staff

Sew­age sludge could be used to make bio­die­sel fu­el in a pro­cess that’s with­in a few pe­r­cent­age points of be­ing cost-com­pet­i­tive with con­ven­tion­al fu­el, a new re­port in­di­cates.

A four pe­r­cent re­duc­tion in the cost of mak­ing this al­ter­na­tive fu­el would make it “com­pet­i­tive” with tra­di­tion­al pe­tro­le­um-based die­sel fu­el, ac­cord­ing to the au­thor, Da­vid M. Karg­bo of the U.S. En­vi­ron­men­tal Pro­tec­tion Agen­cy. 

Sew­age sludge, shown at a waste-water treat­ment plant, may pro­vide a new source of biodie­sel fu­el that is cost-competitive with con­ven­tion­al die­sel. (Im­age cour­te­sy iStock)


How­ev­er, he cau­tions that there are still “huge chal­lenges” in­volved in re­duc­ing the price and in sat­is­fy­ing likely reg­u­la­tory con­cerns. The find­ings by Karg­bo, who is with the agen­cy’s Re­gion III Of­fice of In­nova­t­ion in Phil­a­del­phia, ap­pear in En­er­gy & Fu­els, a jour­nal of the Amer­i­can Chem­i­cal So­ci­e­ty.

Tra­di­tion­al pe­tro­le­um-based fu­els are in­creas­ingly be­set by en­vi­ron­men­tal, po­lit­i­cal and supply con­cerns, so re­search in­to al­ter­na­tive fu­els is gain­ing in pop­u­lar­ity.

Con­ven­tion­al die­sel fu­el, like gas­o­line, is ex­tracted from pe­tro­le­um, or crude oil, and is used to pow­er many trucks, boats, bus­es, and farm equip­ment. An al­ter­na­tive to con­ven­tion­al die­sel is bio­die­sel, which is de­rived from al­ter­na­tive sources to crude oil, such as veg­e­ta­ble oil or an­i­mal fat. How­ev­er, these sources are rel­a­tively ex­pen­sive, and the high­er prices have lim­it­ed the use of bio­die­sel.

Kargbo ar­gues that a cheape­r al­ter­na­tive would be to make biodie­sel from mu­nic­i­pal sew­age sludge, the sol­id ma­te­ri­al left be­hind from the treat­ment of sew­age at wastew­a­ter treat­ment plants. The Un­ited States alone pro­duces about sev­en mil­lion tons of sew­age sludge yearly. 

To boost biodie­sel pro­duc­tion, sew­age treat­ment plants could would have to use mi­crobes that pro­duce high­er amounts of oil than the mi­crobes cur­rently used for wastew­a­ter treat­ment, Karg­bo said. That step alone, he added, could in­crease bio­die­sel pro­duc­tion to the 10 bil­lion gal­lon mark, which is more than tri­ple the na­tion’s cur­rent biodie­sel pro­duc­tion ca­pacity.

“Cur­rently the es­ti­mat­ed cost of pro­duc­tion is $3.11 per gal­lon of biodie­sel. To be com­pet­i­tive, this cost should be re­duced to lev­els that are at or be­low [re­cent] petro die­sel costs of $3.00 per gal­lon,” the re­port says.

How­ev­er, the chal­lenges that re­main in both low­er­ing this cost and in sat­is­fy­ing reg­u­la­tory and en­vi­ron­men­tal con­cerns re­main “huge,” Kargbo wrote. Ques­tions sur­round meth­ods of col­lect­ing the sludge, separa­t­ion of the bio­die­sel from oth­er ma­te­ri­als, main­tain­ing bio­die­sel qual­ity, and un­wanted soap forma­t­ion dur­ing pro­duc­tion, and the re­mov­al of phar­ma­ceu­ti­cal con­tam­i­nants from the sludge.

None­the­less, “bio­die­sel pro­duc­tion from sludge could be very prof­it­a­ble in the long run,” he added.


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Sewage sludge could be used to make biodiesel fuel in a process that’s within a few percentage points of being economically competitive with conventional fuel, a new report indicates. A four percent reduction in the cost of making this alternative fuel would make it “competitive” with traditional petroleum-based diesel fuel, according to the author, David M. Kargbo of the U.S. Environmental Protection Agency. However, he cautions that there are still “huge challenges” involved in reducing the price and in satisfying likely regulatory concerns. The findings by Kargbo, who is with the agency’s Region III Office of Innovation in Philadelphia, appear in Energy & Fuels, a journal of the American Chemical Society. Traditional petroleum-based fuels being increasingly beset by environmental, political and supply concerns, scientists, research into alternative fuels has gained in popularity. Conventional diesel fuel, like gasoline, is extracted from petroleum, or crude oil, and is used to power many trucks, boats, buses, and farm equipment. An alternative to conventional diesel is biodiesel, which is derived from alternatives to crude oil, such as vegetable oil or animal fat. However, these sources are relatively expensive, and the higher prices have limited the use of biodiesel. Kargbo argues that a cheaper alternative would be to make biodiesel from municipal sewage sludge, the solid material left behind from the treatment of sewage at wastewater treatment plants. The United States alone produces about seven million tons of sewage sludge yearly year. To boost biodiesel production, sewage treatment plants could would have to use microbes that produce higher amounts of oil than the microbes currently used for wastewater treatment, Kargbo said. That step alone, he said, could increase biodiesel production to the 10 billion gallon mark, which is more than triple the nation’s current biodiesel production capacity. “Currently the estimated cost of production is $3.11 per gallon of biodiesel. To be competitive, this cost should be reduced to levels that are at or below [recent] petro diesel costs of $3.00 per gallon,” the report adds. However, the challenges that remain in both lowering this cost and in satisfying regulatory and environmental concers remain “huge,” Kargbo wrote. Questions surround methods of collecting the sludge, separation of the biodiesel from other materials, maintaining biodiesel quality, and unwanted soap formation during production, and the removal of pharmaceutical contaminants from the sludge. Nonetheless, “biodiesel production from sludge could be very profitable in the long run,” he added.