Enhanced performance of biochar-biosensor applied to heavy metals detection in constructed wetlands and biological mechanisms

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.