Microbial fuel cell (MFC) anodes are anaerobic bioreactors. Processes such as fermentations and methanogenesis are likely competitors to electricity generation. This work studied the pathway of glucose conversion in continuous microbial fuel cell anodes with an adapted bacterial community. The study revealed that the majority of glucose is first fermented to hydrogen and acetate. Both are then used as substrates for bacterial electricity generation. When methanogens are present methane production occurs at a rate that slightly increases with the current. Methanogenesis and electricity generation compete for hydrogen, causing increased fermentation rates. In a rather young anodic biofilm on granular graphite, methanogenesis can be suppressed by aerating the anode compartment for one hour. Only short-term inhibition can be achieved applying the same technique on a well established biofilm on granular graphite. This study shows that fermentative processes are not detrimental to current generation, and that direct oxidation of glucose does not play a major role in mixed population conversions in a MFC anode.
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