A View from Kevin Bullis
A Biofuel Milestone
A one-step process for converting cellulose into ethanol produces high concentrations of the fuel.
This week Qteros, a startup in Marlborough, MA, announced a major milestone. The company, which was a microbiologist founded after discovering an organism that devours woody biomass and other cellulosic materials and excretes ethanol, has shown that the bacteria it uses can produce high concentrations of ethanol. The company says this makes its process for converting cellulosic plant materials into ethanol “more economical than any other process to date.”
Increasing the concentration of ethanol lowers the cost of ethanol production in many ways. As the bacteria break down plant matter, they produce a beer-like broth containing ethanol and water. The lower the concentration of ethanol in the water, the more expensive it becomes to distill pure ethanol (more water is needed for the process, and the processing plant needs to be bigger and more expensive).
Qteros’s chief technology officer, Kevin Gray, says that for making ethanol from cellulosic sources, the target is to produce a broth with 5 percent ethanol by weight. This is well above the less than 1 percent by weight that the company’s organism produced when the company first started working with it, he says. Now Qteros researchers, by optimizing the conditions in which they grow the organism and the nutrients they provide, have increased the broth concentration to 7 percent ethanol by weight (9 percent by volume).
Gray says the new numbers are remarkable because the bacteria are a species of Clostridium, a type of bacteria notorious for low tolerance for ethanol, typically surviving in concentrations of only 2.5 to 3 percent. The concentrations are still far lower than those in corn ethanol production, which can be 18 percent ethanol by weight. But with cellulosic ethanol, the feedstock produces less-concentrated sugar, so such high concentrations aren’t possible, according to Gray.
The high concentrations could save roughly 30 percent or more on the cost of the process, compared to the minimum desired level of 5 percent, Gray says. This will add to the other main advantage of Qteros’s organism: it produces both the enzymes needed to convert cellulose into sugar and the mechanisms for fermenting sugar to produce ethanol. Most other processes must use costly enzymes produced by one organism paired with another organism for fermentation.
Work remains to be done, however, before the process can be successfully commercialized. Gray says the rate of ethanol production still needs to be increased and the cost of the nutrients decreased.
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