Microbial fuel cells (MFCs) are devices generating electrical current from a wide range of organic substrates by using bacterial metabolism. Integrations of MFCs into wastewater treatment plants seem to be the most likely application of this technology. Due to the fact that the current flow in a MFC is fundamentally produced by the metabolic activity of microorganisms, it would be desirable to elucidate the capacity of the microbial systems to optimize the energy extraction processes in MFCs. In this study, the correlation between the parameters X-BH (active heterotrophic biomass) and X-BA (active autotrophic biomass) from the established activated sludge model number 1 (ASM1) and the measured current flow in MFCs was investigated for the first time. The simulation protocol based on ASM1 shows a good congruence between measured and simulated effluent values for the wastewater treatment plant. Comparisons between the measured current densities and the simulated concentrations of active biomass showed linear correlations at substrate pulses and at different residence times of the substrate. Therefore, it can be concluded that the model parameter X-BH and X-BA of the ASM1 can be used to estimate the current output of a MFC in wastewater treatment plants. The identified correlations can be used to optimize operating conditions and to generate high current outputs of the MFCs based on simulations. (C) 2017 Elsevier Ltd. All rights reserved.