Bioelectric field drives ion migration with the electricity generation and pollutant removal

A bioelectric field was developed by electricigens that metabolize organics and emit electrons in a soil microbial electrochemical system (MES). The bioelectric field intensity and accumulated charge of the soil MES increased with the addition of ions, which substantially promoted charge transfer in the soil. In MESs with added Zn2+, the bioelectric field intensity increased to 175 ± 3 mV ⋅cm −1 from 26 ± 1 mV ⋅cm −1 in the controls, while the accumulated charge was enhanced by 9-fold. Compared to open circuit MESs, the removal of total petroleum hydrocarbons increased by 108%–166% in closed circuit ones. In the presence of a bioelectric field, cations were transferred from the anode to the cathode and apparently amassed near the cathode, especially in the presence of Na+, K+, Mg2+, Ca2＋ and Fe2/3+. For anions, the amount of NO3− decreased by half in treated soils, especially near the cathode. Unexpectedly, near the cathode, the contents of Cl− and SO42− increased to 176–807 mmol ⋅kg −1 from 256 to 314 mmol ⋅kg −1 in the original soil. This study verifies the effect of soluble ions on enhancing bioelectricity generation, reveals the quantitative profile of ion migration in the bioelectric field and proposes a potential method of soil desalinization by soil MESs with the advantages of electricity generation and pollutant removal.