# Metal Recovery from Wastes: A Review of Recent Advances in the Use of Bioelectrochemical Systems
## 5 Conclusions  
The recovery of metals from wastes has become increasingly critical in addressing the dual challenges of growing metal demand and environmental pollution. Wastes offer a valuable secondary metal resource, particularly as conventional mineral extraction struggles to meet current demands. Proper waste treatment not only mitigates environmental pollution but also maximizes the recovery of metals and, when feasible, energy.  
While traditional methods such as pyrometallurgy and hydrometallurgy are effective, they often generate secondary pollution and come with significant operational costs. Incontrast, BESs present an environmentally and economically sustainable alternative. These systems combine microbial activity with electrochemical processes to recover metals while reducing or even generating energy. BESs have demonstrated the ability to recover metals such as copper, cobalt, chromium, and iron, among others. Double-chamber MFC bioelectrochemical systems remain the most commonly used because of their superior flexibility and precise control, which enable enhanced performance and efficient metal recovery.  
Despite significant advancements, large-scale implementation of BESs remains a challenge. The microbial catalysis that drives these systems often exhibits slow reaction kinetics, limiting productivity, especially at higher current densities. This kinetic constraint limits BES performance, requiring operation under milder conditions to maintain efficiency. While these conditions align with the energy-saving advantages of BESs, meeting higher demand or treatment rates comparable to other technologies requires significantly larger system configurations, such as stacked cells. This approach complicates practical implementation and increases CAPEX, posing additional barriers to scalability.  
Future advancements in BESs for metal recovery must address critical challenges to enhance their scalability, efficiency, and economic viability. Key priorities include optimizing reactor designs to maximize metal recovery rates, developing cost-effective and sustainable materials for electrodes and membranes, and improving the robustness of microbial communities to withstand industrial conditions. Economic evaluations underscore the importance of reducing operational costs, particularly by minimizing energy demands and material expenses, to ensure competitiveness with established technologies.  
The unique advantage of BESs lies in their dual ability to recover valuable resources while simultaneously remediating polluted environments. This combination positions BES as a promising solution for decentralized applications and niche markets where traditional technologies may be impractical or inefficient. Hybrid and modular systems, which integrate BESs with other technologies, represent a significant opportunity to expand their applicability and address scalability limitations.  
Conceptualization: M.T.P.P. and F.J.F.-M.; methodology: M.T.P.P., L.F.L.-F. and F.J.F.-M.; software: M.T.P.P., E.L.F. and J.V.; validation: L.F.L.-F., J.V. and F.J.F.-M.; formal analysis: M.T.P.P. and E.L.F.; investigation: M.T.P.P.; resources: F.J.F.-M.; data curation: M.T.P.P. and F.J.F.-M.; writing--original draft preparation: M.T.P.P.; writing--review and editing: L.F.L.-F. and F.J.F.-M.; visualization: E.L.F.; supervision: L.F.L.-F. and F.J.F.-M.; project administration: F.J.F.-M.; funding acquisition: F.J.F.-M. All authors have read and agreed to the published version of the manuscript.  
This article is part of the research project SBPLY/23/180225/000143 and was funded by the EU through ERDF and by Junta de Comunidades de Castilla-La Mancha (JCCM) through INNOCAM.  
No new data were created or analyzed in this study. Data sharing is not applicable to this article.  
The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.