A dual process strategy bridging fermentation and electrochemistry is enabling the production of mid-chain carboxylic acids (MCCAs) — important and valuable precursors to a number of products — using inexpensive organic waste streams from breweries, distilleries and dairies. Developed by a research team at Johns Hopkins University’s (JHU; Baltimore, Md.; www.jhu.edu) Whiting School of Engineering, led by Michael Betenbaugh, professor of chemical and biomolecular engineering, the process is one of 17 projects selected for federal funding under the U.S. Dept. of Defense’s BioMADE initiative.
“We’re testing these different waste streams under very acidified conditions to see if we can take anaerobic bacteria in our bioreactors, which normally produce short-chain carboxylic acids and single-carbon compounds, and get longer, medium-chain carboxylic acids, which are much more economically valuable,” explains Will Brakewood, graduate researcher at JHU. Key to chain elongation is the ability to stop methanogenesis in the organisms to cease methane production and instead shift to the production of longer-chain compounds, as well as microbial resilience and the continuous removal of toxic byproducts. Downstream of the bioreactors is a proprietary electrolysis process to extract and purify the produced MCCAs.
(From L-R): Yayuan Liu, Michael Betenbaugh, Robert Price, Shilva Shretha (Source: JHU)
“An electrical gradient pushes these MCCAs across the electrolyzer’s membrane, which allows us to significantly concentrate them and purify them, and get a much cleaner waste stream,” says Brakewood. Furthermore, adds Betenbaugh, there is a potential to capture “waste” from the electrolyzer, such as hydrogen gas and hydroxide ions, and recycle them back into the bioreactor to help with pH control and product removal in the reactor.
“Because this product is toxic to our microorganisms at certain concentrations, it starts inhibiting the process itself. So, when our bioreactors are connected with this extraction unit, where it provides in situ product recovery, we continuously remove product from our bioreactor, so that we can keep pushing our microbes to make more of these desired products,” explains Shilva Shrestha, assistant professor of Environmental and Health Engineering.
The bioreactor portion of the process has been demonstrated in 7-L bioreactors, and the team expects eventually to scale up to a 250-L pilot plant. The integrated system with downstream electrolysis has been demonstrated at the 1-L scale.
“We’re using well-tested equipment for the bioreactor side and novel ways of integrating upstream and downstream processing. We’re trying to optimize the upstream and downstream independently, find out the key parts that connect the two, before scaling up the integrated system,” says Betenbaugh. Scaleup partners on the project include Technology Holding LLC (Lehi, Utah; www.tekholding.com) and CleanJoule (Salt Lake City, Utah; www.cleanjoule.com).