A new way of making biofuel produces 20 times more energy than existing methods by adding bacteria that turn by products into electricity.
The results of a new study, published in the current issue of Environmental Science and Technology, showcase a novel way to use microbes to produce biofuel and hydrogen, all while consuming agricultural wastes.
Gemma Reguera, a Michigan State University microbiologist, has developed bioelectrochemical systems known as microbial electrolysis cells, or MECs, using bacteria to breakdown and ferment agricultural waste into ethanol.
Reguera’s platform is unique because it employs a second bacterium, which, when added to the mix, removes all the waste fermentation by-products or non-ethanol materials while generating electricity.
Similar microbial fuel cells have been investigated before. However, maximum energy recoveries from corn stover, a common feedstock for biofuels, hover around 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, says Reguera, an AgBioResearch scientist who co-authored the paper with Allison Spears, a Michigan State graduate student.
“This is because the fermentative bacterium was carefully selected to degrade and ferment agricultural wastes into ethanol efficiently and to produce by-products 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.”
The second bacterium, Geobacter sulfurreducens, generates electricity. The electricity, however, isn’t harvested as an output. It is used to generate hydrogen in the MEC to increase the energy recovery process even more, Reguera says.
“When the MEC generates hydrogen, it actually doubles the energy recoveries,” she says. “We increased energy recovery to 73 percent. So the potential is definitely there to make this platform attractive for processing agricultural wastes.”
Reguera’s fuel cells use corn stover treated by the ammonia fibre expansion process, an advanced pretreatment technology pioneered at Michigan State. AFEX is an already proven method that was developed by Bruce Dale, professor of chemical engineering and materials science, who is currently working to make AFEX viable on a commercial scale.
In a similar vein, Reguera is continuing to optimize her MECs so they, too, can be scaled up on a commercial basis. Her 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.
By. Layne Cameron