Fuel from sewage can be profitable: study

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.