Single Stage Reactors for Electrifying Bio-Methanation

As a combined solution for minimizing CO2 emissions and meeting global energy demands, upgrading CO2 to produce renewable natural gas is an emerging technology to utilize and store renewable energy. When this process is performed by efficient and product selective biocatalysts, conventional and energy intense thermal methanation technologies can be replaced by bio-methanation technology. The bio-methanogenesis process is typically performed with hydrogen produced externally in electrolyzers, but is severely limited by poor mass transport and solubility issues of molecular hydrogen. A system where both electrolysis and microbial conversion are combined in a single reactor helps overcome these problems. However, despite the outstanding opportunities of in-situ electro-bio-methanogenesis, there are challenges of electrified bioreactors that must be overcome, including microbial tolerance and enhancing the kinetics of in-situ hydrogen evolution. Thus, developments to achieve the balance between both biochemical and electrochemical requirements will allow these reactors to achieve optimum performance. The developments include maintaining physiological pH, effective separation of anode and cathode, improving charge transfer kinetics and reducing internal resistance. We have used our advanced manufacturing capabilities to design and fabricate components for developing electro-bioreactors from 0.1 W scale in sluggish H-cells to MW scale stacks of flow cell CO2 electrolyzers. This allows us to achieve the balance between both biochemical and electrochemical requirements mentioned above. In this study, we show how utilization of high surface area porous 3D electrodes can support maintaining biocompatible conditions near the vicinity of hydrogen evolving electrode at effective rates of electrolysis, while improving both efficiency and productivity of microbial methanogenesis. We have conducted studies to understand the effect of electrode geometry and surface area on energy efficiency and microbial health. Finally, we demonstrate the ability to produce pipeline-quality methane (>97% CH4) from CO2 for an extended period.