A critical review of the symbiotic relationship between constructed wetland and microbial fuel cell for enhancing pollutant removal and energy generation

Constructed wetland technology (CW) is a mature, low-cost, and environmentally sustainable method frequently used for wastewater treatment. Recently, there has been significant research into Microbial Fuel Cell (MFC) technology due to its potential for simultaneous bioenergy generation and wastewater treatment. The fundamental physical processes within CW and MFC are highly complementary, and combining them offers a number of tantalising possibilities for greatly improving wastewater treatment methods. Recent findings have demonstrated a number of beneficial symbiotic interactions that improve overall system performance within an integrated CW-MFC system. Notably, CW operation is enhanced by improvements in the electrochemically active bacteria population at the electrode surfaces, consequently boosting wastewater treatment efficiency. Similarly, the MFC can utilise the natural redox gradient present within CW to assist bioelectricity generation. In this review article, the performance of integrated CW-MFC systems was discussed in comparison with both standalone MFC and CW systems based on criteria that the review identified as significant. The review shows that the combination of CW and MFC increases wastewater treatment efficiency by phytoremediation, MFC power generation is enhanced by the action of the wetland plants, and wetland greenhouse gas emissions are reduced due to the dominance of electrogenic bacteria. Consequently, a CW-MFC can achieve higher efficiency for contaminant removal and bioelectricity generation compared to standalone CWs and MFCs. However, in view of the physical size and operational life span of wastewater treatment systems required for domestic or metro-politan applications, the CW-MFCs presented within the literature are small and have only been studied over short periods of time. Large-scale controlled trials and long-term studies are urgently needed to provide more definitive evidence that can enable CW-MFC technology to advance to the point of successful implementation.