BACKGROUNDThis work is focused on the assessment of the performance of mini-scale air-breathing microbial fuel cells (MFCs), by monitoring the evolution of the bio-electrogenic activity for a period of 40 days and by comparing the microorganisms populations developed in each of the MFCs after this period. RESULTSFive MFCs were operated at sludge ages ranging from 1.4 to 10.0 days. Results showed the superb performance of the MFC operating under a sludge age of 2.5 days. Desulfuromonas, Syntrophothermus, Solitalea, Acholeplasma, Propionicimonas, Desulfobacula and Sphaerochaeta are proposed as potentially responsible for the bio-electrogenic activity. CONCLUSIONSMicrobial population analysis through Illumina amplicon sequencing demonstrated that despite all MFCs being seeded with the same mixed culture inoculum, the biological cultures developed in the suspension and the biofilm are completely different and depend strongly on sludge age. (c) 2017 Society of Chemical Industry