Application of microbial fuel cell technology to the remediation of compound heavy metal contamination in soil

Exploring the removal rules of MFC on composite heavy metal pollution is very important for the future development and field application of MFC. We constructed a three-chamber soil MFC and the results showed that with the gradual deterioration of soil heavy metal contamination from single heavy metal to metals in different oxidation states (e.g., copper (II), lead (II), and chromium (III) compounds), the internal resistance of the soil MFC increased by 2.16–2.71 times, which significantly inhibited the power production performance of the MFC. After 59 days of remediation, the migration removal efficiencies of total Cu, total Cr and total Pb from the soil under composite conditions were 36.69%, 52.35% and 19.67%, respectively. The main removal mechanisms included both electromigration and diffusion, where electromigration contributed 74.41%, 31.48% and 97.67% to the removal of total Cu, Cr and Pb, respectively. The removal of composite heavy metals was affected by adsorption-desorption competition and synergism. The competition of Pb for specific adsorption sites in soil leads to the increase of mobility of Cr and Cu, which is conducive to migration and removal. The migration of Cu and Pb ions to the cathode inhibited the diffusion of Cr to the anode; however, it drove the synergistic migration of Pb ions to the cathode. For the heavy metals migrated from the soil into the catholyte, only Cu²⁺ with high redox potential is reduced to copper at the cathode.