Magnetite nanoparticles accelerate the autotrophic sulfate reduction in biocathode microbial electrolysis cells

The aim of this study was to investigate the effect of magnetite nanoparticles on the performance of autotrophic sulfate-reducing biocathode in microbial electrolysis cell (MEC). The biocathodes in MECs were start-up using cathode medium with and without magnetite nanoparticles addition (with initial iron content of 0.64 mM), respectively. With magnetite, the sulfate reductive rate reached 152 +/- 7.0 g m(-3) d(-1), which was improved by 122% than the MEC without magnetite. The electron recovery efficiencies in MECs with and without magnetite were 56.1% and 29.6%, respectively. With the effect of magnetite, the peak currents in cyclic voltammograms of the biocathode were about two times higher than that without magnetite, indicating its higher electrochemical activity. Analyses of the scanning electron microscope and the energy dispersive spectrometer showed that pilus-like substance and iron-sulfide were formed on the magnetite-biocathode. Confocal laser scanning microscopy showed the increase of the biomass, thickness, and viability of biofilm in the biocathode with magnetite compared to those without magnetite. The relative abundance of Desulfovibrio sp. was 72.2% in the biocathode with magnetite compared to 27.5% without magnetite. The conductive magnetite could affect the development of electrochemical active biofilm directly and accelerate sulfate reduction in the MEC. (C) 2018 Elsevier B.V. All rights reserved.