Remediation of Cd Contaminated Soil in Microbial Fuel Cells: Effects of Cd Concentration and Electrode Spacing

Abstract

A microbial fuel cell (MFC) was constructed to remediate cadmium (Cd) contaminated soil, and the effects of Cd concentration (0, 5, 20, and 100 mg/kg) and electrode spacing (3, 6, and 9 cm) on reactors were studied. The results showed that different Cd concentrations had no significant effect on the output voltage and internal resistance. However, the electrode spacing was inversely proportional to the MFC power generation and proportional to the charge transfer internal resistance (Rct) by the electrochemical impedance spectroscopy (EIS) test. The maximum power density was 22.93 mW/m2 (in MFC-0 mg/kg) and 22.71 mW/m2 (in MFC-3 cm), which was the best among the MFCs of different Cd concentrations and electrode spacing, respectively. After 50 days of operation, the maximum accumulation rate of Cd at the cathode was observed in MFC-5 mg/kg and MFC-3 cm, which were 130.00% and 107.70%, respectively. The kinetic analysis showed that high Cd concentrations and large electrode spacing could reduce the accumulation of Cd (ζCd) at the cathode as a result of the influence of soil respiration and cation migration, respectively. The results revealed that a MFC is a feasible option for remediating Cd contaminated soil, and the electrode spacing was the main determinant of the MFC performance and Cd accumulation rate, while the impact of the Cd concentration was minimal.