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In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm− 2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture. In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm− 2. The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 Ω·cm2 and 34 Ω·cm2, respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the Butler–Volmer relationship that needs further exploration. ; The authors wish to acknowledge funding from the European Union Seventh Framework Programme (FP7/2012-2016) project 'Bioelectrochemical systems for metal production, recycling, and remediation' under grant agreement no. 282970. AtH is supported by a NWO VENI grant no. 13631. OS was supported by the French environmental agency ADEME, by the Region Bretagne and by Rennes Metropole when doing the experiments. This work was performed in the cooperation framework of Wetsus, Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is co-funded by the Dutch Ministry of Economic Affairs and Ministry of Infrastructure and Environment, the European Union Regional Development Fund, the Province of Fryslân, and the Northern Netherlands Provinces.

This study investigated the effect of pre-fermented urine on anode performance of a two-chambered microbial electrolysis cells (MECs) compared to raw urine. Pre-fermentation of urine was performed by anaerobic digestion. The effect of this pre-fermentation on anode performance of a MEC was assessed by measuring the removal of chemical oxygen demand (COD), current density and Coulombic efficiency (CE). The MEC using fermented urine achieved a higher average current density (218±6mAm2) and a higher CE (17%). Although no significant differences were observed in the COD removal efficiency between both urines, the MEC using fermented urine displayed the highest COD removal rate (0.14±0.02gL1d1). The organic compounds initially found in both urines, as well as the metabolic products associated to the biodegradation of the organic matter were analyzed by proton nuclear magnetic resonance (1H NMR). The main compounds initially identified in the raw urine were urea, creatinine and acetate. In the fermented urine, the main compounds identified were methylamine, acetate and propionic acid demonstrating the effectiveness of the anaerobic fermentation step. ; This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469 unit and COMPETE 2020 (grant number POCI-01-0145-FEDER-006684) and BioTecNorte operation (grant number NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020 - Programa Operacional Regional do Norte. This research has received funding from the European Union's Seventh Programme for research, technological development and demonstration (grant number 308535). The authors also would like to acknowledge the support of Wetsus, European Centre of Excellence for Sustainable Water Technology. ...