Microbial ecology approach of anodic biofilms for the study of scaled-up microbial fuel cells

Since 1911 when Potter described bacteria that could produce electrical currents interest in this ability and associatedtechnologies like microbial fuel cells (MFCs) has grown especially the last 20 years. Many MFCs have an anaerobic chamberfilled with the feeding solution where are immerged an anode and a cathode which is generally in contact with air for oxygensupply. After inoculation with bacteria (pure bacterial culture or from environmental sources such as wastewater), biofilmsdevelop on the anode and cathode. Some bacterial strains are able to use the anode as their terminal electron acceptor.These electrons travel via an external electric circuit to the cathode where the oxygen reduction occurs with or withoutbacterial participation.The application of MFCs for the production of energy from wastewater requires the scale-up of such devices which, for now,doesn’t allow electrical yield comparable to lab-scale MFCs. Our work was based on the hypothesis that typical scale-upefforts modify specific MFC parameters (substrate diffusion, geometry, hydraulic forces… ) which in turn affect the anodicbiofilm (microorganism selection, physical structure of the biofilm, electrons transport strategies… ) and that is one majorreason for electric yield variations. We investigated microbial ecology and electricity production of three MFCs of differentvolumes: 10 mL, 500 mL, 4 L operated under similar conditions and identical MFC parameters.Electrical production and microbial community structure (16S rRNA gene sequencing to evaluate the enrichment ofelectroactive bacteria species like Geobacter sulfurreducens or Shewanella oneidensis MR-1) and function (to examine foodweb and electron exchange functions) were monitored during the MFC start-up and operation. In parallel, the physicalstructure of the biofilms (such as density, thickness, bacterial distribution and nanowire (conductive pili) presence) wasstudied by microscopy techniques and proteomics analysis.