The effect of sulfamethoxazole on nitrogen removal and electricity generation in a tidal flow constructed wetland coupled with a microbial fuel cell system: Microbial response

This study aims to investigate the effect of sulfamethoxazole (SMX) concentration on nitrogen removal efficiency and electricity generation in tidal flow constructed wetlands coupled with microbial fuel cells (TFCW-MFCs) used for synthetic wastewater treatment for 240 days and the microbial response to system performance using high-throughput sequencing. The efficiency of inorganic nitrogen removal was slightly lower in the presence of 10 μg/L SMX (period B) than in the control (period A), whereas a substantially increased NH₄⁺-N removal efficiency (63.8% → 80.3%) and decreased NO₃⁻-N removal efficiency (72.6% → 43.1%) were seen with subsequent exposure to 50 μg/L SMX (period C); this may be primarily related to lower relative abundances of enzymes nitrite reductase (NADH) (EC 1.7.1.15) and nitrate reductase (EC 1.7.99.4) during period C. The maximal voltage (524.5 mV) occurred in period B and was attributed to electroactive bacteria, namely, Dechloromonas and Geobacter, the communities of which were different from those in other periods and were greatly enriched for all substrates and anodes. Notably, there were obvious differences in the compositions of nitrogen transformation functional bacteria under low and high SMX exposure, especially for Nitrosomonas, which resisted changes in period B but peaked in period C. Moreover, network analysis predicted NH₄⁺-N and NO₃⁻-N removal by Rhodobacter and suggested that bioelectricity production and SMX reduction were significantly influenced by Azospirillum, Euglena and Nitrosospira. Together, these findings provide a theoretical reference for the concurrent enhancement of nitrogen and antibiotic removal and power generation in TFCW-MFCs and will facilitate their application for wastewater treatment.