The production of biodiesel results in leftover glycerol, which is typically disposed of as waste. Although glycerol is loaded with sugar that could be processed into ethanol (another biofuel), the refinement of glycerol is expensive and inefficient. A research team at Michigan State University, led by Professor Gemma Reguera, has engineered a bacteria combination that converts glycerol to ethanol, hydrogen, and CO2, giving the dual benefit of cleaning wastewater and producing additional fuels.
Dr. Reguera’s team started with Geobacter, a bacterium that eats toxic waste and excretes benign byproducts. Through repeated selective breeding, they developed a strain of Geobacter that could survive in high levels of glycerol. Then they added a bacterium that ferments glycerol into ethanol; its byproduct is consumed by the Geobacter, which releases CO2 and hydrogen, both of which can be collected. The two organisms work together, cleaning wastewater and producing ethanol. A bonus: the hydrogen can then be used in fuel cells.
I asked Dr. Ruguera about the carbon footprint of this process. She responded, “Our technology converts the glycerol in the waste water into bioethanol, so the process is carbon neutral. However, the bioethanol can replace the petrochemical methanol in the transesterification reaction that makes biodiesel, reducing the overall carbon footprint of making biodiesel. And added benefit is that any non-ethanol byproduct of glycerol fermentation in our platform is removed as CO2 and H2, basically cleaning up the waste water and allowing the plant to recycle it, rather than paying to dispose of it at a water treatment plant. That also reduces the overall carbon footprint of biodiesel production.”
Producing fuel requires energy and results in byproducts. It’s good to know that microbiologists are contributing to the effort by creating organisms that convert some of those byproducts into more fuel.