Microbial electrosynthesis for CO2 conversion and methane production: Influence of electrode geometry on biofilm development

Abstract

[EN] Electromethanogenesis is a process of microbial electrosynthesis (MES) in whichelectroactive microorganisms reduce carbon dioxide (CO2) to produce methane (CH4), using a cathodeas an electron donor. The efficiency of this reaction is greatly determined by the establishment of arobust microbial community on the biocathodes, which eventually affects the global performance of thebioreactor. Moreover, the development of the biofilm depends on several characteristics of theelectrodes, more specifically their material and geometry. Since electrode geometry is a crucialparameter, this study aims at evaluating the sole influence of the electrode shape by installingcarbon-based electrodes with two different constructions (brush and carbon felt) of biocathodes in anelectromethanogenic reactor for CO2capture. The overall performance of the reactors showedcoulombic efficiencies around 100%, with high-quality biogas reaching methane concentrations above90%. The results reveal that the electrode geometry affects the individual biocathode performance, andthe carbon brush showed a bigger contribution to current generation and electrical capacitance,exhibiting higher peak hydrogen production compared to the carbon felt, which could be reflected inhigher CO2capture and methane generation. Both geometries showed a greater proliferation of archaeaover bacteria (between 53 and 85%), which was more significant on the brush than on the carbon felt.Archaea community was dominated byMethanobacteriumin carbon felt electrodes and codominatedwithMethanobrevibacterin brush electrodes, while bacteria analyses showed a very similar communityfor both geometries