oa Co2 Capture and Transformation to Ethanol using Dehydrogenase Cascade at Cathode in Bioelectrochemical System (BES): Role of Carbonic Anhydrase

Industrial revolution, a consequence of the rapid economic growth, has contributed to ever increasing demand for energy and has resulted in about 40% rise in the atmospheric concentration of carbon dioxide, from 280 ppm in 1750 to 400 ppm in 2015. Abundant use of fossil fuels has become a cause of concern due to their adverse effects on the environment, particularly related to the emission of carbon dioxide (CO2), a major contributor of GHG. In this context, CO2 capture and is storage or transformation gained significance in the recent research scenario. Various matured CO2 capture technologies such as amine based capture, needs high energy input, especially in desorption process and are also not sustainable in nature. Alternatively, carbonic anhydrase (CA) proved to be more efficient in capturing CO2 at faster rate and also needs less energy input for desorption process. However, utilization of the captured CO2 is more important rather than its capture, to close the carbon cycle and recycle it. In this direction, bioelectrochemical system (BES) is presenting an exciting opportunity with a possibility of simultaneous CO2 capture and biotransformation to value-added products in a sustainable way. Both microbes and enzymes were studied as catalyst in BES, though the application of enzymes is less foreseen. Present study demonstrates the biotransformation of CO2 to ethanol using a cascade of dehydrogenases [formate dehydrogenase (FateDH), formaldehyde dehydrogenase (FaldDH) and alcohol dehydrogenase (AlcDH)] together on the electrode of BES. Further to that, carbonic anhydrase (CA) was also included in the cascade and found that the product yield increased by 15% contributing to ethanol production rate of ∼0.6 kg/m³/h along with current density of ∼2 A/m². When the FaldDH was excluded from the cascade also, there is no reduction in productivity of ethanol. It was surprising to get ethanol instead of methanol but based on literature, it is also possible for the production of ethanol directly from formic acid, which is economically more viable.