Fuel from Sewage

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.

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.

World Science

Detail...

Comets

Comets may have come from other solar systems.

Many of the best known comets, in­clud­ing Hal­ley, Hale-Bopp and Mc­Naught, may have been born or­bit­ing oth­er stars, ac­cord­ing to a new the­o­ry.

The pro­pos­al comes from a team of as­tro­no­mers led by Hal Lev­i­son of the South­west Re­search In­sti­tute in Boul­der, Co­lo., who used com­put­er sim­ula­t­ions to show that the Sun may have cap­tured small icy bod­ies from “si­b­ling” stars when it was young.


Sci­en­tists be­lieve the Sun formed in a clus­ter of hun­dreds of stars closely packed with­in a dense gas cloud. Each star would have formed many small icy bod­ies, Lev­i­son and col­leagues say—comets. These would have aris­en from the same disk-shaped zone of gas and dust, sur­round­ing each star, from which plan­ets formed.

Most of these comets were slung out of these fledg­ling plan­e­tary sys­tems due to gravita­t­ional in­ter­ac­tions with newly form­ing gi­ant plan­ets, the the­o­ry goes. The comets would then have be­come ti­ny, free-float­ing mem­bers of the clus­ter.

The Sun’s clus­ter came to a vi­o­lent end, how­ev­er, when its gas was blown out by the hot­test young stars, ac­cord­ing to Lev­i­son and col­leagues. The new mod­els show that the Sun then gravita­t­ionally cap­tured a large cloud of comets as the clus­ter dis­persed.

“When it was young, the Sun shared a lot of spit with its sib­lings, and we can see that stuff to­day,” said Lev­i­son, whose re­search is pub­lished in the June 10 ad­vance on­line is­sue of the re­search jour­nal Pro­ceed­ings of the Na­tio­n­al Aca­de­my of Sci­en­ces.

“The pro­cess of cap­ture is sur­pris­ingly ef­fi­cient and leads to the ex­cit­ing pos­si­bil­ity that the cloud con­tains a pot­pour­ri that sam­ples ma­te­ri­al from a large num­ber of stel­lar sib­lings of the Sun,” added Mar­tin Dun­can of Queen’s Uni­vers­ity, Can­a­da, a co-author of the stu­dy.

The team cites as ev­i­dence a bubble-shaped re­gion of comets, known as the Oort cloud, that sur­rounds the Sun, ex­tend­ing half­way to the near­est star. It has been com­monly as­sumed this cloud formed from the Sun’s proto-plan­e­tary disk, the struc­ture from which plan­ets formed. But be­cause de­tailed mod­els show that comets from the so­lar sys­tem pro­duce a much more ane­mic cloud than ob­served, anoth­er source is needed, Lev­i­son’s group con­tends.

“More than 90 per­cent of the ob­served Oort cloud comets [must] have an extra-so­lar orig­in,” as­sum­ing the Sun’s proto-plan­e­tary disk can be used to es­ti­mate the Oort Cloud’s in­dig­e­nous popula­t­ion, Lev­i­son said.

World Science

Detail...

Solar System

Solar system’s distant ice-rocks come into focus
Be­yond where Nep­tune—of­fi­cially our so­lar sys­tem’s fur­thest plan­et—cir­cles the Sun, there float count­less faint, icy rocks.

They’re called trans-Nep­tu­ni­an ob­jects, and one of the big­gest is Plu­to—once clas­si­fied as a plan­et, but now des­ig­nat­ed as a “d­warf plan­et.” This re­gion al­so sup­plies us with comets such as fa­mous Com­et Hal­ley.

Now, as­tro­no­mers us­ing new tech­niques to cull the da­ta ar­chives of NASA’s Hub­ble Space Tel­e­scope have added 14 new trans-Nep­tu­ni­an ob­jects to the known cat­a­log. Their meth­od, they say, promises to turn up hun­dreds more.


“Trans-Neptunian ob­jects in­ter­est us be­cause they are build­ing blocks left over from the forma­t­ion of the so­lar sys­tem,” said Ce­sar Fuentes, form­erly with the Har­vard-Smith­son­ian Cen­ter for As­t­ro­phys­ics and now at North­ern Ar­i­zo­na Uni­vers­ity. He is the lead au­thor of a pa­per on the find­ings, to ap­pear in The As­t­ro­phys­i­cal Jour­nal.

As trans-Nep­tu­ni­an ob­jects, or TNOs, slowly or­bit the sun, they move against the star­ry back­ground, ap­pearing as streaks of light in time ex­po­sure pho­tographs. The team de­vel­oped soft­ware to scan hun­dreds of Hub­ble im­ages for such streaks. Af­ter prom­is­ing can­di­dates were flagged, the im­ages were vis­u­ally ex­am­ined to con­firm or re­fute each disco­very.

Most TNOs are lo­cat­ed near the eclip­tic—a line in the sky mark­ing the plane of the so­lar sys­tem, an out­growth of the fact that the so­lar sys­tem formed from a disk of ma­te­ri­al, as­tro­no­mers say. There­fore, the re­search­ers search­ed for objects near the eclip­tic.

They found 14 bodies, in­clud­ing one “bi­na­ry,” that is, a pair whose mem­bers or­bit each oth­er. All were more than 100 mil­lion times faint­er than ob­jects vis­i­ble to the un­aided eye. By meas­ur­ing their mo­tion across the sky, as­tro­no­mers cal­cu­lat­ed an or­bit and dis­tance for each ob­ject. Com­bin­ing the dis­tance, bright­ness and an es­ti­mat­ed re­flec­ti­vity al­lowed them to cal­cu­late the ap­prox­i­mate size. The new­found TNOs range in size from an es­ti­mat­ed 25 to 60 miles (40-100 km) across.

Un­like plan­ets, which tend to orbit very near the ecliptic, some TNOs have or­bits quite tilted from that line. The team ex­am­ined the size dis­tri­bu­tion of ob­jects with both types of or­bits to gain clues about how the popula­t­ion has evolved over the past 4.5 bil­lion years.

Most smaller TNO’s are thought to be shat­tered re­mains of big­ger ones. Over bil­lions of years, these ob­jects smack to­geth­er, grind­ing each oth­er down. The team found that the size dis­tri­bu­tion of TNOs with flat ver­sus tilted orbits is about the same as ob­jects get faint­er and smaller. There­fore, both popula­t­ions have si­m­i­lar col­li­sion­al his­to­ries, the re­searchers said.

The study ex­am­ined only one-third of a square de­gree of the sky, so there’s much more ar­ea to sur­vey. Hun­dreds of ad­di­tion­al TNOs may lurk in the Hub­ble ar­chives at high­er eclip­tic lat­i­tudes, said Fuentes and his col­leagues, who plan to con­tin­ue their search. “We have prov­en our abil­ity to de­tect and char­ac­ter­ize TNOs even with da­ta in­tend­ed for com­pletely dif­fer­ent pur­pos­es,” Fuentes said.


World Science

Detail...