Ethanol, a promising biofuel to replace petroleum, may have increased potential to generate energy as result of a fermentation process developed by a Michigan State University microbiologist.

Gemma Reguera has developed a two-step process in which agricultural waste – in this case, corn stover – first undergoes a pretreatment process known as ammonia fiber expansion (AFEX). The AFEX process, which was pioneered by MSU professor of chemical engineering and materials science Bruce Dale, breaks down the cellulose and hemicellulose within the plant into efficiently fermentable sugars. Reguera then ferments the pre-treated mixture in a bioelectrochemical system known as a microbial electrolysis cell, or MEC, using two bacteria, Geobacter sulfurreducens and Cellulomonas uda, to produce ethanol.

While the energy-generating potential of microbial fuel cells has been investigated by other researchers in the past, Reguera’s process is unique because it employs a second bacterium to remove the waste fermentation byproducts or nonethanol materials while generating electricity. The electricity, however, isn’t harvested as an output. It is used to generate hydrogen in the fuel cell to increase the energy recovery process even more.

“When the microbial electrolysis cell generates hydrogen, it actually doubles the energy recoveries,” Reguera says. “We increased energy recovery to 73 percent. So the potential is definitely there to make this platform attractive for processing agricultural wastes.”

In previous microbial fuel cells, the maximum energy recovered has only been about 3.5 percent. Reguera’s platform, despite the energy invested in chemical pretreatment of the corn stover, averaged 35 to 40 percent energy recovery just from the fermentation process.

“This is because the fermentative bacterium was carefully selected to degrade and ferment agricultural wastes into ethanol efficiently and to produce byproducts that could be metabolized by the electricity-producing bacterium,” Reguera says. “By removing the waste products of fermentation, the growth and metabolism of the fermentative bacterium also was stimulated. Basically, each step we take is custom-designed to be optimal.”

Reguera’s goal is to develop decentralized systems that can help process agricultural wastes. Decentralized systems could be customized at small to medium scales (scales such as compost bins and small silages, for example) to provide an attractive method to recycle the wastes while generating fuel for farms.

Reguera’s fuel cell and Dale’s ammonia pretreatment system are currently being scaled up to become viable on a commercial basis. According to Tom Herlache, interim assistant director of MSU Technologies, “The new fuel cell technology provides a competitive, not-previously-available process for efficiently producing biofuels and electricity. While this process actually occurs in nature, until now, researchers have had difficulty effectively and efficiently duplicating it.”

Both Reguera and Dale are also AgBioResearch scientists.