Nitrogen gas could lower cellulosic production costs — study 

Source: Amanda Peterka, E&E reporter • Posted: Thursday, February 5, 2015

Nitrogen gas may be key to producing cost-competitive cellulosic ethanol, according to a new study by Indiana University researchers.

Microbes that convert plant sugars to ethanol can use nitrogen gas instead of costly industrial fertilizer, researchers say in the study published online Monday in the journal Proceedings of the National Academy of Sciences.

Unlike corn ethanol, cellulosic ethanol is made from nonfood crops such as grasses, wood and inedible agricultural residues. Cellulosic ethanol yields more greenhouse gas savings than conventional ethanol, but the inputs needed to produce it are lacking in nitrogen. Cellulosic producers typically add nitrogen-rich fertilizer to fermentation vats to increase their yields.

Researchers found that Zymomonas mobilis, a bacterium that can convert plant sugars to ethanol, can use nitrogen gas as a nitrogen source. They found that using straight nitrogen gas in conjunction with the bacterium resulted in similar yields of ethanol as the yields that are produced when costlier conventional nitrogen supplements are used.

“To our surprise the ethanol yield was unchanged when the bacteria used N2,” Indiana University biologist and lead author James McKinlay said in a statement. “In fact, under certain conditions, the bacteria converted sugars to ethanol much faster when they were fed N2.”

Ethanol facilities can produce their own nitrogen gas and potentially save more than $1 million a year by using gas instead of fertilizer, the study predicted. The actual plant material and enzymes that are needed to break down tough plants parts into component sugars would still remain a big expense, however, in the cellulosic ethanol production process.

The IU team filed a provisional patent with the U.S. Patent and Trademark Office related to the results. They cautioned, though, that it’s still too early in the process to determine how the results would play out on a commercial scale.

“More work needs to be done to assess how this approach can be integrated and optimized on an industrial scale, but all of the data we’ve collected thus far are very encouraging,” McKinlay said.

The study was funded by an Oak Ridge Associated Universities Ralph E. Powe Junior Faculty Enhancement Award, a Department of Energy grant and the College of Arts and Sciences at Indiana University.