Recently, microbial fuel cells (MFCs) have been integrated with membrane bioreactors (MBRs), either in an internal or an external configuration, for wastewater treatment and energy recovery. In an external configuration, MFCs could be applied for an efficient sludge reduction since they can simultaneously address energy issue and environmental concerns associated with sludge treatment. In the present study, a potentiostatic controlled microbial fuel cell (MFC) was fed with activated sludge from a membrane bioreactor (MBR) at different total suspended solid (TSS) concentrations (1–10 gTSS L −1 ) in order to assess the electrochemical response of the system and the impact of the bioelectrochemical treatment on sludge characteristics and membrane fouling parameters. The MFC showed COD removals 30% higher than the control test and a reduction of volatile suspended solids (VSS) up to 43% with concomitant production of energy (maximum current density of 2.0 A m −2 ). The electricity production increased with the increase of TSS content. In both MFC and the control test, an increase of soluble microbial products (SMP) ratio in terms of proteins and carbohydrates (SMPp/SMPc) and an average 50% increase of sludge hydrophobicity were observed. This could limit membrane fouling in the case that the sludge is recirculated to the MBR. The electrochemical characterization indicated that both, acetate and sludge oxidation took place at a similar formal potential of −0.2 V vs. SHE indicating that both used the same electron transfer mechanism. Hence, this study shows that a MFC could oxidize, reduce and stabilise MBR sludge producing electricity and affecting membrane fouling parameters

The authors would like to thank the Spanish Ministry (CTQ2014-53718-R and CTM2015-71982-REDT) and the University of Girona (MPCUdG2016/137) for their financial support. LEQUIA has been recognised as consolidated research groups by the Catalan Government (2014-SGR-1168)