Two Peas in a Pod: Sustainable Electrochemical Solutions for Waste and Water Reuse

Satisfying the energy demands of the world population will require the development of technologies for waste and water reuse. Glycerol-containing wastewater is, for example, the major waste product of the biodiesel producers and bioethanol refineries, and it has become an economical and environmental liability to the industry. Purifying, concentrating, and selling the glycerol is no longer a profitable option and producers must pay to dispose of the wastewater as a hazardous waste. Electrochemical platforms show promise for the processing of wastewater and, if driven by customized consortia, they could be used to simultaneously generate added-value products from the organic waste. Hence, we developed an electrochemical reactor for the treatment of glycerin wastewater and the generation of ethanol, which can be used as alcohol feedstock for the transesterification reaction of oils to make the biodiesel industry fully petroleum independent. The electrochemical reactor was driven by the synergistic metabolisms of the exoelectrogen Geobacter sulfurreducens and the bacterium Clostridium cellobioparum, which fermented glycerol into ethanol at high yields (90%) and produced fermentative byproducts that served as electron donors for Geobacter. The synergistic interactions of the microbial catalysts stimulated glycerol consumption and ethanol production. At the same time, the fermentation byproducts were converted into cathodic H₂, which facilitated the stripping of ethanol and resulted in clean waste streams that could be reused in upstream reactions. The platform was further improved to process glycerol loadings typical of biodiesel wastewater and to improve ethanol productivity. Furthermore, other alcohols could be produced to improve the economics of the electrochemical platform and address the needs of the producers in a fluctuating market. The results highlight the potential of electrochemically systems to simultaneously treat wastewater and harness the energy in the waste to generate bio-based feedstocks, fuels, and/or specialty or commodity chemicals.