Reduction of S0 deposited on electroactive biofilm under an oxidative potential

Abstract

The inevitable deposition of S0 on the electroactive biofilm (EAB) via anodic sulfide oxidation affects the stability of bioelectrochemical systems (BESs) when an accidental discharge of sulfide occurred, leading to the inhibition of electroacitivity, because the potential of anode (e.g., 0 V versus Ag/AgCl) is ~500 mV more positive than the redox potential of S2−/S0. Here we found that S0 deposited on the EAB can be spontaneously reduced under this oxidative potential independent of microbial community variation, leading to a self-recovery of electroactivity (> 100 % in current density) with biofilm thickening (~210 μm). Transcriptomics of pure culture indicated that Geobacter highly expressed genes involving in S0 metabolism, which had an additional benefit to improve the viability (25 % – 36 %) of bacterial cells in biofilm distant from the anode and the cellular metabolic activity via electron shuttle pair of S0/S2−(Sx2−). Our findings highlighted the importance of spatially heterogeneous metabolism to its stability when EABs encountered with the problem of S0 deposition, and that in turn improved the electroactivity of EABs.