- Metal contaminated wastewater posts great health and environmental concerns, but it also provides opportunities for precious metal recovery, which may potentially make treatment processes more cost-effective and sustainable. Conventional metal recovery technologies include physical, chemical and biological methods, but they are generally energy and chemical intensive. The recent development of bioelectrochemical technology provides a new approach for efficient metal recovery, because it offers a flexible platform for both oxidation and reduction reaction oriented processes. While dozens of recent studies demonstrated the feasibility of the bioelectrochemical metal recovery concept, the mechanisms have been different and confusing. This study provides a review that summarizes and discusses the different fundamental mechanisms of metal conversion, with the aim of facilitating the scientific understanding and technology development. While the general approach of bioelectrochemical metal recovery is using metals as the electron acceptor in the cathode chamber and organic waste as the electron donor in the anode chamber, there are so far four mechanisms that have been reported: (1) direct metal recovery using abiotic cathodes; (2) metal recovery using abiotic cathodes supplemented by external power sources; (3) metal conversion using bio-cathodes; and (4) metal conversion using bio-cathodes supplemented by external power sources.