BACKGROUNDThis work is focused on the optimization of the performances of air-cathode microbial fuel cells (MFC) by changing the solid retention time (SRT) of the suspended biomass culture. RESULTSFive MFCs inoculated with activated sludge obtained from a municipal wastewater treatment plant were fed with a highly-concentrated acetate solution (10 000 ppm COD) and operated over two-month tests in order to determine how SRT may influence the performances of the bio-electrogenic cells. The MFC operated at SRTs of 2.5 days was found to outperform the other cells, operated at SRT of 1.4, 5.0, 7.4 and 10.0 days. In order to evaluate the possibility of using SRT as a manipulated parameter for the regulation of the operation of MFC, the SRT of the other MFCs was changed from their initial value up or down to 2.5 days. CONCLUSIONSAs a result of the change in the SRT, production of electricity of the cells increased significantly in all cases, highlighting the relevance of SRT control in the optimization of the performances of MFCs. By operating at SRT 2.5 days, the current density was 4.2 A m(-2), the COD consumption rate was 1.53 g COD d(-1) L-1 and the COD transformed by electrogenic microorganisms was estimated at 1.5%. (c) 2016 Society of Chemical Industry