Microbial Fuel Cell Integrated in Biorefinery Converts Persistent Plant Debris into Valuable Resources
In a groundbreaking study led by Kimberly Gray, a civil and environmental engineer at Northwestern University, a sustainable and inexpensive two-step process has been developed to upcycle organic carbon waste, including lignin. This research, featured on the cover of the January issue of the journal ACS Sustainable Chemistry and Engineering, aims to convert organic waste, including lignins, into useful products through an efficient and environmentally friendly method.
Lignin, a fibrous, woody material present in all vascular plants and giving plants structural support, is often discarded as a byproduct in various industries. Most industries that use plants strip out lignin, leaving behind cellulose, a type of sugar, and burn lignin as a cheap fuel, wasting a potential renewable resource.
The new process utilizes a microbial electrolysis cell (MEC) with exoelectrogens, a type of bacteria that generates electrical energy by eating organic matter, as the catalyst. The biorefinery developed by the researchers cycles waste-filled water through the bacteria, degrading the organic carbon into carbon dioxide and generating electrons.
The extracted electrons flow from the bio-anode to the cathode (made of a carbon cloth), where they reduce oxygen to generate water. The process consumes protons, driving up the water's pH to turn it into a caustic solution. Exposing lignin to this bio-based caustic chemical causes lignin's polymers to break apart in a way that preserves the aromatic rings.
About 17% of the processed lignin turns into rings of carbon called flavonoids, an antioxidant-rich phytonutrient often found in supplements. The processed lignin can be used in high-value, plant-derived pharmaceuticals and antioxidant nutraceuticals. The rest of the processed lignin (about 80%) becomes carbon-based nanoparticles, which could be used for targeted drug delivery in humans or targeted nutrient delivery in plants.
Moreover, the MEC process can effectively treat wastewater to remove detrimental organic carbon, resulting in clean water. The MEC-based approach has many advantages, including being safer, less expensive, able to be used in ambient conditions, and capable of generating chemicals at the point of need. Using commercially available caustic substances to process lignin involves shipping and storing large amounts of toxic chemicals, which is expensive and hazardous for public health.
The study, "Valorization of lignin under mild conditions: Biorefining flavonoids and lignin nanoparticles," was supported by the Finite Earth Initiative of the McCormick School of Engineering at Northwestern University. The nanoparticles could offer a sustainable, plant-derived alternative for sunscreens and cosmetics. Roxelylyn and Richard Pepper Family Chair in Civil and Environmental Engineering and a professor at the McCormick School of Engineering, Gray, is hopeful that this research will lead to a more sustainable future in waste management and resource recovery.
