Researchers from Michigan State University (MSU) develop a new biofuel production process that generates 20 times more energy than currently known methods. The process highlights a novel use of microbes to produce ethanol and hydrogen from agricultural wastes.
Gemma Reguera, MSU microbiologist, is the co-author of the study along with Allison Spears, MSU graduate student. Their study makes use of bioelectrochemical systems known as microbial electrolysis cells or MECs.
A microbial electrolysis cell uses bacteria to degrade and ferment agricultural wastes in the form of chemically pretreated corn stover, a common feedstock for biofuels. The fermentation process produces ethanol with an average energy recovery of 35 to 40 percent.
Other microbial fuel cells have been previously tested. However, the maximum energy recovery from corn stover was only around 3.5 percent.
The MEC platform is unique because it uses a second bacteria, Geobacter sulfurreducens. These bacteria remove all the waste fermentation byproducts or non-ethanol materials while generating electricity.
Reguerra asserted that each step of the process was custom-designed to give optimal results. The fermentative bacterium was carefully selected to produce ethanol efficiently, and to generate byproducts that could be metabolized by the electricity-producing bacterium. The growth and metabolism of the fermentative bacterium was also enhanced by removing the fermentation byproducts.
The electricity generated by the second bacterium was not harvested as an output. It was used to produce Hydrogen in the MEC. This enabled the MEC to double the total energy recovery output to 73 percent.
The MEC uses corn stover treated by the ammonia fiber expansion (AFEX) process. AFEX is an advanced pretreatment method pioneered in MSU by Bruce Dale, MSU professor of chemical engineering and materials science.
Dale is currently working in developing AFEX for commercial scale.
Similarly, Reguera is continuing work to optimize MCE for commercial applications. Her goal is to develop decentralized systems that can help process agricultural wastes. These systems could be customized at small to medium scales such as compost bins and small silages to provide farms with an attractive method to recycle wastes while generating electricity.
This study can be read in the current issue of Environmental Science and Technology.