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Although Castellaniella species are crucial for denitrification, there is no report on their capacity to carry out denitrification and anode respiration simultaneously in a bioelectrochemical system (BES). Herein, the ability of a mixed inoculum of electricigenic Castellaniella species to perform simultaneous denitrification and anode respiration coupled with cathodic metals recovery was investigated in a BES. Results showed that 500 mg/L NO 3 - -N significantly decreased power generation, whereas 100 and 250 mg/L NO 3 - -N had a lesser impact. The single-chamber MFCs (SCMFCs) fed with 100 and 250 mg/L NO 3 - -N concentrations achieved a removal efficiency higher than 90% in all cycles. In contrast, the removal efficiency in the SCMFCs declined dramatically at 500 mg/L NO 3 - -N, which might be attributable to decreased microbial viability as revealed by SEM and CLSM. EPS protein content and enzymatic activities of the biofilms decreased significantly at this concentration. Cyclic voltammetry results revealed that the 500 mg/L NO 3 - -N concentration decreased the redox activities of anodic biofilms, while electrochemical impedance spectroscopy showed that the internal resistance of the SCMFCs at this concentration increased significantly. In addition, BES inoculated with the Castellaniella species was able to simultaneously perform heterotrophic anodic denitrification and cathodic metals recovery from real wastewater. The BES attained Cu 2+ , Hg 2+ , Pb 2+ , and Zn 2+ removal efficiencies of 99.86 ± 0.10%, 99.98 ± 0.014%, 99.98 ± 0.01%, and 99.17 ± 0.30%, respectively, from the real wastewater. Cu 2+ was bio-electrochemically reduced to Cu 0 and Cu 2 O, whereas Hg 0 and HgO constituted the Hg species recovered via bioelectrochemical reduction and chemical deposition, respectively. Furthermore, Pb 2+ and Zn 2+ were bio-electrochemically reduced to Pb 0 and Zn 0 , respectively. Over 89% of NO 3 - -N was removed from the BES anolyte during the recovery of the metals. This research reveals promising denitrifying exoelectrogens for enhanced power generation, NO 3 - -N removal, and heavy metals recovery in BES., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

The impact of nickel (Ni 2+ ) on the performance of anodic electroactive biofilms (EABs) in the bioelectrochemical system (BES) was investigated in this study. Although it has been reported that Ni 2+ influences microorganisms in a number of ways, it is unknown how its presence in the anode of a BES affects extracellular electron transfer (EET) of EABs, microbial viability, and the bacterial community. Results revealed that the addition of Ni 2+ decreased power output from 673.24 ± 12.40 mW/m 2 at 0 mg/L to 179.26 ± 9.05 mW/m 2 at 80 mg/L. The metal and chemical oxygen demand removal efficiencies of the microbial fuel cells (MFCs) declined as Ni 2+ concentration increased, which could be attributed to decreased microbial viability as revealed by SEM and CLSM. FTIR analysis revealed the involvement of various microbial biofilm functional groups, including hydroxyl, amides, methyl, amine, and carboxyl, in the uptake of Ni 2+ . The presence of Ni 2+ on the anodic biofilms was confirmed by SEM-EDS and XPS analyses. CV demonstrated that the electron transfer performance of the anodic biofilms was negatively correlated with the various Ni 2+ concentrations. EIS showed that the internal resistance of the MFCs increased with increasing Ni 2+ concentration, resulting in a decrease in power output. High-throughput sequencing results revealed a decrease in Geobacter and an increase in Desulfovibrio in response to Ni 2+ concentrations of 10, 20, 40, and 80 mg/L. Furthermore, the various Ni 2+ concentrations decreased the expression of EET-related genes. The Ni 2+ -fed MFCs had a higher abundance of the nikR gene than the control group, which was important for Ni 2+ resistance. This work advances our understanding of Ni 2+ inhibition on EABs, as well as the concurrent removal of organic matter and Ni 2+ from wastewater., (Copyright © 2022. Published by Elsevier Ltd.)