An integrated constructed wetland-Microbial fuel cell system with sewage sludge-biochar to enhance treatment and energy recovery efficiencies

Constructed wetlands and microbial fuel cells (CW-MFCs) are a promising green and sustainable wastewater treatment technology. However, the power production performance of CW-MFCs has long been limited by lowperformance cathodes. In this study, we designed two CW-MFC systems using cheap and readily available sewage sludge biochar (SSB) as the substrate for the experimental units. The integration of SSB significantly facilitated the removal of chemical oxygen demand, ammonium nitrogen, total nitrogen, and total phosphorus. Moreover, SSB enhanced the electrochemical performance of the air cathode, resulting in higher power density (44.64 mW/ m2) and lower internal resistance (900.00 Omega) compared to gravel-integrated CW-MFC (0.88 mW/m2, 2057.14 Omega). In addition, a typical electroactive bacterium-Geobacter was enriched in the SSB-integrated CW-MFC system. The iron oxides and graphic nitrogen of the SSB favor the growth of Geobacter, and the redox-active groups on the surface of SSB accelerate the extracellular electron transfer process, contributing to the enhancement of treatment performance. Meanwhile, the metal and nitrogen doping improves the oxygen reduction reaction activity and conductivity of SSB, enhancing the cathode area of CW-MFC and improving the energy recovery. Overall, these results demonstrated that SSB-integrated CW-MFC can be a competitive technology for effective wastewater treatment and energy recovery.