Microbial And Enzymatic Electrosynthesis Of Renewable Chemicals: A Case Study Of Bioelectrochemical Conversion Of Co2 To Chemicals (2014)

Background Increasing renewable electricity leads to moments of overproduction coupled to points in time for which not enough production is available to fulfill the needs. In a scenario of 100% renewable energy, about 20% of the yearly production will need to be stored to keep the system in balance. Since the Antwerp-Rotterdam-Rhine-Ruhr (ARRR) cluster is the European region where the highest CO2-emissions are measured (highest production, but also highest population density and energy supply), this region is well positioned to focus on CO2 and &apos;peak shaving&apos; of renewable energy. Since it is also one of the biggest chemical clusters, the conversion of CO2 into new molecules makes sense guaranteeing that the final balance on energy use and CO2-emissions are lower than in the classical production. We have started an initiative to explore technologies for converting CO2, preferentially coupled to &apos;peak shaving&apos;, to building blocks for the chemical sector. Microbial Electrosynthesis Generation of electric current from the metabolism of organic substrates in microbial fuel cells (MFCs), using bacteria as electrocatalysts was reported. By converting the chemical energy stored in organic substrates to electricity, MFCs can reduce the operational cost of wastewater treatment plants. Recently, a new concept of microbial electrosynthesis has evolved where similar setups, generally known as bioelectrochemical systems (BES), are being used for the production of chemicals. Already the bioelectrochemical reduction of CO2 to acetate has been achieved, as well as the reduction of CO2 to methane and multi-carbon compounds. Efforts are underway to utilize a wide variety of substrates for production of an array of compounds. The key advantage here is the use of excess electricity that is often generated renewably, from solar cells and wind mills, all of which cannot be utilized immediately and can be fed into BES to produce chemicals. We will report our first results with specific bacteria towards bioelectrochemical conversion of CO2 to organic compounds. Acetogens like Sporomusa and Clostridium sps. were experimented for their CO2 reduction capacity at -0.6 V vs Ag/AgCl cathode potential. Adjustment of reduction potential and optimization of cell conditions were carried out in a fed batch reactor with an activated carbon cathode. Production of 67 mg/L ethanol with mixed culture as biocatalyst was the most remarkable achievement. Enzymatic Electrosynthesis Enzymes can also be used for chemical transformations including both the reduction and oxidation reactions. We are using CO2 as substrate for the production of methanol which will have a significant positive impact on environment as well as energy crisis. Electrosynthesis of formic acid was higher at an operational voltage of -1 V vs. Ag/AgCl (9.37 mg L-1 CO2) compared to operation at -0.8 V (4.73 mg L-1 CO2) which was strongly supported by the reduction catalytic current. Voltammograms also depicted a reversible redox peak throughout operation at -1 V, indicating NAD+ recycling for proton transfer from the source to CO2. Product saturation was observed after 45 minutes of enzyme addition and then reversibility commenced, depicting a lower and stable formic acid concentration throughout the subsequent time of operation.