Conversion of a substrate carbon source to formic acid for carbon dioxide emission reduction utilizing series-stacked microbial fuel cells

Carbon dioxide (CO2) is now known to be a major cause of global warming, and the reduction of its atmospheric concentration has therefore become a critical issue. The amount of CO2 discharged from the degradation process of waste organic substances is both tremendous and neglected. Here, an environmentally friendly method to achieve the fixation of the CO2 released from the degradation of waste carbonaceous substances has been investigated. A series-connected microbial fuel cell (MFC) stack is used to electro-reduce the CO2 to formic acid in situ utilizing the electricity generated from the degradation of the carbonaceous substances in the anodic chambers of the MFC stack. Consequently, formic acid at 4.27 mg L−1 h−1 is produced, and a Faraday efficiency of 64.8% is achieved. This technology will be helpful in recycling and reusing the carbon in wastewaters or wastes in the absence of external energy input, thereby promoting the virtuous cycle of carbon.

► An MFC-stack-driven MEC is used to electro-reduce CO2 to formic acid.
► The MFC-generated electricity is utilized in situ to reduce the MFC-produced CO2.
► Formic acid at 4.27 mg L−1 h−1 is produced with a Faraday efficiency of 64.8%.