Revealing the microbial mechanism of Fe0 and MnO2 mediated microbial fuel cell-anaerobic digestion coupling system and its energy flow distribution

Abstract

Microbial fuel cell-anaerobic digestion (MFC-AD) is a new sludge treatment technology with multi-path energy recovery. In this study, Fe0 and MnO2 with gradient concentration were added to investigate its effects on the sludge reduction, electrochemical performance, extracellular polymeric substances (EPS) of sludge, microbial community, electron distribution and energy flow of the MFC-AD system. Results showed that the highest sludge reduction 59% (49%), was obtained at 10 g/L Fe0 (5 g/L MnO2) adding and its total energy recovery efficiency increased by 100% (71%) compare to the control. Different Fe0 and MnO2 concentrations lead to different microbial mechanisms: at 10 g/L Fe0 or 5 g/L MnO2, it prefers to promote extracellular electrons transfer, favoring the Geobacter, Shewanella and Acinetobacter enrichment, while at 5 g/L Fe0 or 0.5 g/L MnO2 it plays a more important role in substrate metabolism of anaerobic digestion, with Clostridium, Roseomonas lacus, and Methylocystis enriched. Correspondingly, the electron quantity distribution from biomass to recovered energy ends (Current, CH4 and VFAs), was influenced by Fe0 and MnO2 concentration, indicating the controllability of the energy flow.