Community analysis and long-term performance of microbial fuel cells fed individual fermentation endproducts

Microbial fuel cells were operated for more than one year with individual fermentation endproducts of lignocellulose fermentation. Reactors were fed acetic, formic, lactic or succinic acid, or ethanol. Successful colonizers of each reactor, characterized by 16S clone libraries, included Rhodobacteraceae (Paracoccus denitrificans), Geobacteraceae (Pelobacter propionicus), Bradyrhizobiaceae (Rhodopseudomonas palustris), and Peptococcaceae (Desulfitobacterium hafniense). Delta Proteobacteria dominated most reactors, with the microbe Pelobacter propionicus dominating reactors fed lactic or acetic acid and making up a substantial proportion of reactors fed ethanol or succinic acid. 16S sequence information identified strains with significant similarity to previously identified exoelectrogens including, various Geobacter species, Rhodopseudomonas palustris and Desulfitobacterium hafniense. There were large variations in reactor performance with the different substrates, with power densities ranging from 835 mW/m3 (acetic acid) to 62 mW/m3 (formic acid), and Coulombic efficiencies (CE) of 20.6 % (acetic acid) to 4.8 (formic acid). Cathode performance deteriorated over time, as demonstrated by increases of 4% (succinic acid) to 118% (ethanol) when new cathodes were used. These results provide valuable insights into the effects of long-term MFC operation on reactor performance, cathode deterioration, and anodic microbial diversity.