Extracellular electron transfer-coupled heavy metal reduction in biogeobattery: Perspectives and challenges

The natural bioelectrochemical phenomenon termed biogeobattery has exhibited a great ability to enlarge the effective remediation area to even meter-scale by the conductive electroactive bacteria (EAB) and native minerals matrix, which would be an evolution of heavy metal remediation by bioelectrochemistry in future. In this review, starting from the introduction of elementary parts of the biogeobattery, the progress of key conduits, cytochromes, and connectors for extracellular electron transfer (EET)-coupled heavy metal in the biogeobattery networks are discussed. Given that the shortage of enriched organics and conductive conditions in the natural biogeobattery has been identified as the main challenges for rapid metal reduction, the potential of native inorganic Fe/S/NH4 as electron donors to drive the EET are discussed. Meanwhile, establishing conductive networks by minerals and carbon materials additives are evaluated to enhance the EET in the biogeobattery. Particularly, in order to manipulate the formation of the networks, an applicable high-resolution analytical method is first proposed here to further decipher the EET-coupled heavy metal reduction process. Overall, this review would contribute to the real application of bioelectrochemistry to reduce heavy metals from soils efficiently.