Microbial fuel cells implemented in constructed wetlands: fundamentals, current research and future perspectives

A microbial fuel cell (MFC) is a device that generates electricity from the microbial degradation of organic and inorganic substrates. Constructed wetlands (CWs) are natural wastewater treatment systems that constitute a suitable technology for the sanitation of small communities. The synergy between MFCs and CWs is possible because of the presence of organic matter in CWs due to wastewater characteristics and the naturally generated redox gradient between the upper layer of CWs treatment bed (in aerobic conditions) and the deeper layers (completely anaerobic). As a result of MFC implementation in CWs (MFC-CW), it is possible not only to produce an energy surplus while wastewater is treated but also to improve and monitor the overall treatment process. Moreover, the implementation of MFCs may exert other beneficial effects on CWs, such as a decrease of surface treatment requirements, reduction of greenhouse gas emissions or clogging. Finally, MFCs implemented in CWs would be also a suitable bioelectrochemical tool for the assessment of treatment performance without any additional cost involved in the process. Overall, though considered to be at an infancy stage, MFC-CW represents a promising synergy between technologies that may reduce energy costs and enhance treatment performance and monitoring while wastewater is treated. The envisaged main challenges for maximizing the synergy between both technologies are linked to the optimization of both operational and design criteria in CW and MFC cell architecture and materials.

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