On-line monitoring of repeated copper pollutions using sediment microbial fuel cell based sensors in the field environment

Most microbial fuel cells (MFCs) based sensors rely on exoelectrogenic bacteria to sense contaminants. However, these sensors cannot monitor repeated pollutions unless the exoelectrogenic bacteria are recovered or reinoculated. To overcome this drawback, a novel sediment microbial fuel cell (SMFC) based sensor was developed for online and in situ monitoring of repeated Cu2+ shocks to the overlaying water of paddy soil. The SMFC sensor was operated for a period of eight months in the field environment and a group of CuCl2 solutions ranging from 12.5 to 400mg L-1 Cu2+ were repeatedly applied on sunny and rainy days in different seasons. Results show that the SMFC sensor generates one voltage peak in less than 20 s after each Cu2+ shock, regardless of the seasons and weather conditions, and the voltage increments frombaseline to peak exhibit linear correlation (R-2 > 0.92) with the logarithm of Cu2+ concentrations. Repeated Cu2+ pollutions do not decrease the baseline voltage, indicating that the activity of exoelectrogenic bacteriawas not significantly inhibited. Soil adsorbed and inactivated approximately 99% of total Cu2+. Only1% of total Cu2+ was the toxic exchangeable fraction, of which the concentrations were 0.73, 0.23, and 0.22 mg kg(-1) in the surface (0-3 cm), middle (3-6 cm), and bottom (6-11 cm) layers, respectively. The abundance of 16S rRNA gene transcripts of exoelectrogenic bacteria-associated genera is the lowest in the surface layer (2.86 x 10(11) copies g(-1)) and the highest in the bottom layer (7.99 x 10(11) copies g(-1)). Geobacter, Clostridium, Anaeromyxobacter, and Bacillus are the most active exoelectrogenic bacteria-associated genera in the soil. This study suggests that the SMFC sensor could be applied inwetlands to monitor the repeated discharge of Cu2+ and other heavy metals. (c) 2020 Elsevier B.V. All rights reserved.