Bioelectricity-driven wastewater treatment: Coupling CW-MFC and CW-MEC systems with pyrite substrate for advanced treatment of low C/N ratio wastewater

The use of power generated by constructed wetland–microbial fuel cells (CW-MFCs) has recently attracted considerable attention. This study is the first to investigate the use of electricity generated by CW-MFCs to power constructed wetland microbial electrolysis cells (CW-MECs) for enhanced pollutant removal from tailwater with a low C/N ratio. Substrate optimization strategies to improve the electricity-generation performance of CW-MFCs were systematically investigated, and the performance of the CW-MFC and CW-MEC coupled system for advanced tailwater treatment was evaluated. The results demonstrated that CW-MFCs with a pyrite (PY) anode substrate exhibited higher voltage and current density than those with activated carbon (AC) or mixed pyrite–activated carbon (PA) substrates. The PY system achieved a 4.4-fold higher power density (93.98 mW/m³) than the AC system (21.29 mW/m³). Substrate optimization also influenced the microbial community structure and abundance in the CW-MFC anode zone. Specifically, the PA and PY systems showed a significantly (p < 0.05) higher relative abundance of electroactive bacteria (EAB) than the AC group, while the AC and PA systems harbored a higher relative abundance of denitrification-associated bacteria. Substrate type is a key environmental determinant driving microbial community differentiation. The CW-MFC and CW-MEC coupled system achieved removal efficiencies of 89.20 ± 1.80% for COD, 61.03 ± 0.60% for NH₄⁺-N, 94.82 ± 1.87% for NO₃⁻-N, and 83.60 ± 3.35% for total phosphorus (TP) from low C/N ratio tailwater. The self-powered CW-MFC and CW-MEC coupled system presents a transformative pathway toward energy-neutral advanced wastewater treatment, effectively addressing key challenges in sustainable water management.