Iron-carbon enhanced constructed wetland microbial fuel cells for sulfamethoxazole wastewater treatment: Performance evaluation and mechanistic insights.

Sulfamethoxazole (SMX) is frequently found in aquatic environments, causing ecological toxicity and accelerating the spread of antibiotic resistance genes (ARGs). The conventional constructed wetlands (CWs) face challenges in removing antibiotics and recovering energy. Constructed wetland-microbial fuel cells (CW-MFCs) are a combination of constructed wetlands and bio-electrochemical technology, enhancing pollutant removal and bioelectricity production. In this study, an iron-carbon particle-enhanced CW-MFC (FCCW) was constructed for SMX removal. The decontamination performance, electrochemical properties, metagenomic profiles, ARG distribution, and transformation products of SMX were analyzed. The results showed that the FCCW displayed superiority in power generation performance with an average voltage of 286.16 mV, a peak power density of 5.40 mW·m-2, a peak current density of 32.48 mW·m2, and a low internal resistance of 382.10 Ω. The FCCW achieved the highest removal rates of TN (51.66±1.63%), NH4+-N (65.49±1.96%), TP (96.69±2.46%), COD (80.90±2.98%), and SMX (96.49±2.77%). Metagenomic analysis revealed that Proteobacteria and Actinobacteria dominated in the three systems and the iron-carbon particles increased the relative abundance of genes associated with energy metabolism and pollutant transformation. Additionally, the FCCW showed a more diffuse distribution of ARGs and no localized accumulation. The analysis of transformation intermediates showed that the FCCW may rely on a glutathione (GSH)-related conjugation pathway associated with lower accumulation of certain toxic intermediates. Overall, the enhanced performance of the FCCW was attributed to improved redox conditions, more efficient electron transfer, and changes in microbial functional composition. Therefore, the FCCW system offers a promising approach for in-situ electricity generation and stable pollutant treatment performance.