Chapter 4. Metal Recovery Using Microbial Electrochemical Technologies

The demand for mineral and energy resources is increasing. Resources are sourced from finite geological deposits. Therefore the development of more sustainable routes is paramount. Industrial, municipal and agricultural wastewaters are potential sources of metals and energy can be recovered from oxidising waste organic matter but conventional methods are not technically or economically feasible. Bioelectrochemical systems (BES) have the potential to overcome these problems. Integrated BES can combine wastewater treatment, energy generation and resource recovery. Organic waste generated annually by humans globally contains ca. 600–1200 TWh of energy. BES can harvest energy as electricity from wastewater but the coulombic yields and power outputs are uncompetitive with alternative systems for electricity production from waste. Alternative uses of energy recovered from wastewaters by BES include resource recovery from waste streams (e.g. metals), offering wastewater treatment while valorising a waste stream for valuable product recovery. This chapter focuses on electrochemical metal recovery from wastes, noting also (bio)electrochemical synthesis of high-value organic compounds on the cathode, and biological electricity production from wastewaters at the anode. We review how fundamental microbial processes can be harnessed for resource recovery and the environmental benefits, and consider scale-up, environmental and economic costs and benefits of BES technologies for resource recovery.