Bacterial biofuel bioreactor
By David Manly
Jul. 30, 2012 – Researchers from Michigan State University (MSU) have been able to create a biofuel process that produces energy at more than 20 times the rate of current methods. Gemma Reguera, a microbiologist and a co-author of the study, says that the trick is that they are using microbes to do the hard work.
The study was recently published in Environmental Science and Technology, and Reguera says that a key step in the research was due to the development of a bioelectrochemical system known as a microbial electrolysis cell (MEC). By using these MECs, Reguera was able to harness the natural power of microorganisms to digest plant matter and create useable energy.
In nature, she says, waste is generated by a living organism and is quickly removed by another and used for energy. “I hypothesized that we could harness this efficient and synergistic process through careful selection of two bacteria cooperating with each other.”
To prepare the biomass (the researchers used corn stover), Reguera treated it with an ammonia fiber expansion process or AFEX developed by Bruce Dale, a professor of chemical engineering and materials science also at MSU. This process mimics the natural degradation of the plant cells to expose the cellulose, the useable part of the plant, which could be turned into ethanol.
The next step was to determine which microorganisms would be best utilized within the MEC, which consisted of testing numerous different bacteria. “We identified Cellulomonas uda,” she said, “which produced the non-ethanol fermentation products that could be converted into electricity by another bacterium, Geobacter sulfurreducens, in an electrochemical device.”
By using a modified bioreactor with an electrode, the researchers were able to create a bioprocessing unit that fit their needs. “C. uda grows using the AFEX-corn stover and produces ethanol,” says Reguera. “At the same time, it produces the ‘food’ for G. sulfurreducens, which grows on the electrode while removing the non-ethanol products and converting it into CO2, protons and electrons.”
Instead of using the by-products to create direct electricity, the researchers use them to generate hydrogen gas by having the electrons react with protons within the fermentation broth of the MEC. By doing this, the researchers were able to increase the total energy recovery process even more.
“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 (achieved using water),” says Reguera. “Hydrogen has many advantages over electricity, the main one is that it can be stored until needed for use … and it is also a clean fuel that can be burned with little to zero emissions.”
She adds that every step of the bioelectrochemical process was designed and optimized to work flawlessly. However, the work is far from finished. Their next steps are to improve the process even further with new catalysts to improve processing time, with the goal of reaching an industrial-level of scale.