Effect of nickel (II) on the performance of anodic electroactive biofilms in bioelectrochemical systems

•The effect of Ni2+ on the performance of anodic EABs was investigated.•Ni2+ decreased microbial viability and resulted in a shift in microbial community.•Ni2+ decreased biocatalytic activity and power generation of BES.•Ni2+ resulted in a decrease in Geobacter and an increase in Desulfovibrio.•Ni2+ decreased the expression of extracellular electron transfer-related genes. The impact of nickel (Ni2+) on the performance of anodic electroactive biofilms (EABs) in the bioelectrochemical system (BES) was investigated in this study. Although it has been reported that Ni2+ 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 Ni2+ decreased power output from 673.24 ± 12.40 mW/m2 at 0 mg/L to 179.26 ± 9.05 mW/m2 at 80 mg/L. The metal and chemical oxygen demand removal efficiencies of the microbial fuel cells (MFCs) declined as Ni2+ 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 Ni2+. The presence of Ni2+ 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 Ni2+ concentrations. EIS showed that the internal resistance of the MFCs increased with increasing Ni2+ 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 Ni2+ concentrations of 10, 20, 40, and 80 mg/L. Furthermore, the various Ni2+ concentrations decreased the expression of EET-related genes. The Ni2+-fed MFCs had a higher abundance of the nikR gene than the control group, which was important for Ni2+ resistance. This work advances our understanding of Ni2+ inhibition on EABs, as well as the concurrent removal of organic matter and Ni2+ from wastewater. [Display omitted]