New biofuel fermentation tech yields over 70% energy recovery

New biofuel process creates 20 times more energy than existing methods

By: Anne Seccombe
Examiner.com
July 15, 2012

A new biofuel production process created by Michigan State University researchers produces 20 times more energy than existing methods.

The results, 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.

Dr Gemma Reguera, an Assistant Professor at MSU with PhDs in both biology and microbiology and a post-doctoral Fellowship at Harvard, runs a laboratory which studies the adaptive responses of microbes to their natural environment and exploits this knowledge to find novel biotechnological applications for microbial processes. Her team 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 byproducts or nonethanol 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, said Reguera, an Ag Bio Research scientist who co-authored the paper with Allison Spears, MSU graduate student.

“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 said. “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 said.

“When the MEC generates hydrogen, it actually doubles the energy recoveries,” she said. “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 fiber expansion process, an advanced pretreatment technology pioneered at MSU. AFEX is an already proven method that was developed by Bruce Dale, MSU professor of chemical engineering and materials science.

Dale 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.

(C) Copyright 2012 Anne Seccombe. This material may not be published, rewritten or redistributed without the express permission of the author. All rights reserved.

More Information:
Allison M. Speers, Gemma Reguera. Consolidated Bioprocessing of AFEX-Pretreated Corn Stover to Ethanol and Hydrogen in a Microbial Electrolysis Cell.Environmental Science & Technology, 2012; : 120628130731000 DOI: 10.1021/es3008497