GM invests in 'trash to ethanol' start-up

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Nearly all ethanol today is made from corn or sugar cane. Ethanol advocates say that cellulosic ethanol, made from wood chips, grasses, agricultural residue, and other wastes, is more environmentally sound and doesn't compete with food sources. The Department of Energy is funding about 20 cellulosic ethanol trials, and the recently passed energy bill mandates that by 2022, 20 billion out of 36 billion gallons a year of biofuels come from non-corn feedstocks.

Rather than use specially designed enzymes for fermentation, Coskata uses naturally occurring micro-organisms it licensed from the University of Oklahoma to make ethanol.

GM's investment is part of a second round of funding, which was originally backed by venture firms Khosla Ventures, Advanced Technology Ventures, and GreatPoint Ventures.

Its process starts by putting carbon-based materials into a gasification chamber where heat and pressure turn feedstock into syngas, a combination of carbon monoxide, hydrogen, and carbon dioxide.

That gas combination is then scrubbed to remove particulates and then moved into a bio-fermentation vessel where micro-organisms metabolize the syngas and turn it into ethanol.

Its process is flexible enough to work with a range of renewable sources, including grasses, wood chips, and even old tires. The company says its bioreactor uses plastic tubes, rather than dropping the entire mixture into a single tank, to maximize exposure to the microbes, a design which keeps overall costs down.

"Our calculations indicate that for virtually any carbon-containing feedstock handled in large bulk, we will be able to convert it without subsidies at under a dollar a gallon," said Coskata President and CEO Bill Roe, who added that current processes are about twice as expensive. "We believe that's what's going to drive consumer interest."

Coskata has a water-recovery step that allows it to use less than 1 gallon of water for each gallon of ethanol produced. That compares to 3 to 5 gallons of water per gallon of corn-based ethanol.

Roe said that Argonne National Laboratories measured the "energy balance" of its process and found that it can produce 7.7 times as much energy in the end product as it takes to make it. Its fuel produces 84 percent less carbon dioxide than gasoline, when measured from production to use.

Those numbers compare favorably to switchgrass, an experimental ethanol source. A recent multi-year study from the Proceedings of the National Academy of Sciences found that switchgrass contains five times the energy required to grow it and produces 94 percent less greenhouse gases.

Coskata, named after a nature preserve near Nantucket, Mass., is one of several racing to bring cellulosic ethanol to market cost-effectively.

"It really points to the potential for this family of technology to be large-scale and really environmentally beneficial," said the NRDC's Greene. "There's a much higher probability of success through this shot gun approach."

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