Fermentation process converts biomass into liquid fuels, hydrogen

By Erin Voegele | July 17, 2012

An innovative biofuel production process created by Michigan State University researchers uses microbes to produce both liquid biofuels and hydrogen from biomass feedstock. According to information released by the university,An innovative biofuel production process created by Michigan State University researchers uses microbes to produce both liquid biofuels and hydrogen from biomass feedstock

MSU microbiologist Gemma Reguera is leading the project. Her team has developed bioelectrochemical systems known as microbial electrolysis cells (MECs) using two types of bacteria; one that breaks down and ferments agricultural waste into ethanol, and a second that removes all the waste fermentation byproducts while generating electricity.

Reguera explained that bacteria have evolved for millions of years to degrade lignocellulose in nature. They do this, she said, by cooperating with each other to completely degrade organic matter into CO2. Essentially, the bacteria are more efficient as a group in degrading biomass than they are individually.

To conduct the research, Reguera and her team used a chemical pretreatment process to mimic the first steps in lignin solubilization and lignocellulose destabilization in nature. The next step was to screen natural cellulolytic bacterial isolates to identify those that could efficiency degrade the pretreated corn stover and ferment it into ethanol. “Among those we identified one (Cellulomonas uda) that produced non-ethanol fermentation products that could be converted into electricity by another bacterium (Geobacter sulfurreducens) in an electrochemical device,” Reguera said. G. sulfurreducens produces electricity by extracting electrons from the non-ethanol fermentation byproducts and transferring them to an electrode. “With some electrical input, we can provide sufficient energy to the system so the electrons react with protons in the fermentation broth to make hydrogen,” Reguera continues. “When H2 is the output of a system, we refer to the electrochemical system as a MEC. The beauty of this process is that it takes less energy to produce H2 electrochemically in a MEC than to produce it fermentatively using bacteria or by electrolysis.” Electrolysis is how hydrogen is produced from water.

Hydrogen has a low volumetric energy density, she continues. This means that a lot of energy is present in a small volume of the fuel. Reguera estimates that 2.2 pounds of hydrogen gas contains roughly the same amount of energy as 1 gallon of gasoline. She also points out that hydrogen can be burned with nearly zero emissions.

The production technology developed by Reguera and her team not only results in a highly valuable hydrogen coproduct, the process could also increase the efficiency of biofuel production as well. “Ethanol is produced in the fermentation broth along with fermentation byproducts, which accumulate and drop the pH of the broth and slow down the hydrolysis and fermentation,” she said. “Not only are we removing them and stimulating the hydrolysis and fermentation, we are also ‘cleaning up’ the broth and facilitating ethanol recovery through distillation.”

To date, the process has been evaluated on the bench scale. “Right now we are using bench-scale prototypes that process small volumes so we can generate data reproducibly and timely,” Reguera said. “We like to keep these scales while we optimize other important parameters that affect the performance of the system. For example, we have begun to optimize the platform to process industrially-relevant solid loadings and to increase ethanol titers. This also involves developing improved strains.” According to Reguera, her team intends to scale-up the MEC platform in the future.

It is also possible, she said, that the concept could be expanded to include other forms of biofuel, such as butanol. Ethanol is being used as a proof of concept because it offers good standards of comparison in energy recovery, Reguera continued.