Nitrogen may offer better bioethanol solution

Biologists believe they have found a faster, cheaper and cleaner way to increase bioethanol production by using nitrogen gas.

For a number of years supporters of bioethanol have been attempting to create a fuel-energy source that could compete with gasoline and corn ethanol as an affordable alternative to petroleum products. According to the latest research, a breakthrough may finally have arrived to achieve that goal.

In a report published last month by Indiana University, biologists believe they have found a faster, cheaper and cleaner way to increase bioethanol production by using nitrogen gas, the most abundant gas in Earth's atmosphere, in place of more costly industrial fertilizers. The discovery could save the industry millions of dollars and make cellulosic ethanol—made from wood, grasses and inedible parts of plants—more competitive with corn ethanol and gasoline.

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The news comes at a good time for supporters of cellulosic ethanol. With the price of oil drastically lower in recent weeks than it has been in years, support for all types of ethanol has been faltering. On the heels of the U.S. oil company's success with the hydraulic fracturing boom and, lately the falling prices of crude oil, concerns that interest and support of ethanol and bioenergy could suffer have been rising.

While this latest research doesn't preclude a decline in widespread support for the ethanol industry, it does go a long way in illustrating that new research may yet prove useful in achieving in replacing fossil fuels with alternative energy products.   

Timely breakthrough

This latest breakthrough by biologists at Indiana University (IU) comes at a time when fertilizer prices have skyrocketed, and it helps solve a perplexing problem with the cellulosic process.

The raw materials for cellulosic ethanol are low in nitrogen, a nutrient required for ethanol-producing microbes to grow, so cellulosic ethanol producers are estimated to spend millions of dollars annually on nitrogen fertilizers like corn steep liquor and diammonium phosphate. But an IU team led by biologist James B. McKinlay has found that the bioethanol-producing bacterium Zymomonas mobilis can use nitrogen gas (N2) as a nitrogen source, something that the more traditional baker's yeast cannot do.

"When we discovered that Z. mobilis could use N2 we expected that it would make less ethanol. N2 utilization and ethanol production demand similar resources within the bacterial cell so we expected resources to be pulled away from ethanol production to allow the bacteria to grow with N2," McKinlay said. "To our surprise the ethanol yield was unchanged when the bacteria used N2. In fact, under certain conditions, the bacteria converted sugars to ethanol much faster when they were fed N2."

Inexpensive substitute

Knowing the bacterium could use N2 without hindering ethanol production, the team reasoned that N2 gas could serve as an inexpensive substitute for nitrogen fertilizers during cellulosic ethanol production.

"Until recently, ethanol has been produced almost entirely from food crops, but last year there was a surge in cellulosic ethanol production as several commercial facilities opened," McKinlay said. "Cellulosic ethanol offers more favorable land use and lower carbon emissions than conventional ethanol production. Even so, cellulosic ethanol is struggling to be cost-competitive against corn ethanol and gasoline."

The largest cost contributors to cellulosic ethanol production are the cellulosic plant material and the enzymes needed to degrade the plant material into sugars that are converted into ethanol, so they have received the most attention.

"But we recognized nitrogen fertilizers as smaller, yet considerable, cost contributors that could potentially be more readily addressed," he said.

They estimated that using N2 gas, which can be produced on-site at production facilities, in place of costly nitrogen supplements could save an ethanol production facility over $1 million dollars a year. Using N­2 gas could also have environmental benefits such as avoiding carbon dioxide emissions associated with producing and transporting the industrial fertilizers.

"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.

A provisional patent in relation to the study has been filed with the United State Patent and Trademark Office, he added.

The research was published last week in the journal Proceedings of the National Academy of Sciences by McKinlay and three past and present members of his laboratory team including graduate student Timothy A. Kremer, postdoctoral fellow Breah LaSarre, and former research associate Amanda L. Posto.

McKinlay is an assistant professor in the IU Bloomington College of Arts and Sciences' Department of Biology.

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