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Biosensors play a very important role in pollutant monitoring, but there are still some problems such as stability, repeatability and low detection limits. Therefore, it is necessary to explore ways to increase the performance of biosensors. In this study, biochar-MFC sensors were constructed for heavy metals monitoring in constructed wetlands (CWs), and the correlation, repeatability and anti-interference were studied. At 1.0 M/L concentrations of heavy metals (Ni, Cu, Zn and Cr), CW with biochar as filler (B-CW) had an output voltage of 0.69 V, extending the detection limit of the sensor. B-CW had advantages in anti-interference and reproducibility. The results showed that B-CW had higher abundance of electrogenic bacteria than CW. Shewanella and Proteobacteria , main electricity-producing bacteria, increased 3-fold. The electrochemically active microorganism Shewanellaceae made up 6.2% of the B-CW microbial population, but was not detected in CW. The abundance of key genes AarC increased by 1295.8% in B-CW. More importantly, the abundance of extracellular electron transport chain related genes (MtrA , OmcA) increased significantly (p < 0.01). Biochar can promote oxidative phosphorylation, thus increasing the sensor's output voltage and detection range. This study is expected to provide support for the engineering application of MFC sensor in CWs. [Display omitted] • MFC-sensors can effectively detect heavy metals in constructed wetlands. • Extracellular electron transfer significantly increased in biochar system. • Biochar increased genes associated with oxidative phosphorylation by about 27%. • Biochar significantly enhanced the repeatability and anti-interference of the sensor. [ABSTRACT FROM AUTHOR]

To explore the application of biosensor in real-time monitoring of composite heavy metal polluted wastewater in view of the low performance of MFC sensor, this study used sodium alginate to immobilize biochar to the anode of MFC biosensor, and conducted a study on the sensor performance and related biological processes. The results showed that under the optimal HRT conditions, the output power of the MFC-sensor (BC-300) was 0.432 W/m3 after biochar modification, which was much higher than the highest power density of CG and BC-0 of 0.117 and 0.088 W/m3. The correlation coefficient was greater than that of the control group at the plating wastewater concentration of 0.1–1.0 M and had a wider detection range, and the time to recover the output voltage was 1/3 of that of the control group. The biochar significantly promoted the sensitivity, interference resistance, recovery and anti-interference performance of the MFC-sensor. The intrinsic mechanism was that the composition and structure of biochar lead to a 1.53 fold increase in the abundance of electrogenic microorganisms and the abundance of functional genes such as cytochrome c (MtrABC, CymA, Cox, etc.) and flavin (riba, Rib B, gdh, ushA, IDH, etc.) increased by about 1.03–3.20 times, which promoted the shift of electrons from intracellular to extracellular receptors and significantly improved the electron transfer and the energy metabolism efficiency. The results of this study can provide a reference for the application of MFCsensor to the detection of complex heavy metal effluents. [Display omitted] • Biochar enhanced the correlation, sensitivity and resilience of the MFC sensor. • Microbiological mechanism of biochar enhanced sensor performance was revealed. • The relationship between energy metabolism and biochar in MFC sensor was elucidated. • Electron transfer efficiency and gene abundance affected the performance of sensor. [ABSTRACT FROM AUTHOR]