Nitrogen removal and microbial metabolic analysis in an iron-carbon based constructed wetland-microbial fuel cell for mariculture wastewater treatment

Mariculture wastewater is characterized by high salinity and rich nitrogen compounds, which pose significant threats to marine ecosystems. While conventional constructed wetlands (CWs) have demonstrated effective performance in treating freshwater aquaculture wastewater, their efficiency often decreases under high salinity conditions. Currently, studies on the integration of constructed wetlands with microbial fuel cells (MFCs) for seawater wastewater treatment remain limited. In this study, a CW-MFC system with iron-carbon (Fe-C) as the anode filler was constructed to investigate its performance in purifying mariculture wastewater, electricity generation, and microbial community dynamics. After nearly 30 days of operation, the CW-MFC showed excellent performance in removing target pollutants and generating electricity, with a COD removal rate of 95.84 ± 0.58 %, NH 4 + -N removal rate of 84.22 ± 2.68 %, and NO 3 - -N removal rate of 98.17 ± 0.28 %. During the stable period, the system maintained an average output voltage of 713.59 mV, with a power density of 111.27 mW/m². Denitrifying halophilic bacteria, including Halomonas and Alkalibacter , were abundantly enriched on the anode, which significantly improved the denitrification and nitrogen removal capacity of the system. Metagenomic analysis showed that the abundance of denitrifying enzyme genes in the anode of CW-MFC compared to the CW, and nitrogen-related metabolism significantly increased. The functional gene analysis revealed enhanced pathways related to nitrogen fixation, denitrification, and organic matter degradation. • Pollutant removal and power generation performance were significantly improved in the CW-MFC system. • The Fe-C anode filler enhanced electron transfer and denitrification, enriching halophilic bacteria (Halomonas, Alkalibacter). • The CW-MFC generated 713.59 mV, with a power density of 111.27 mW/m². • A high abundance of napAB and narGHI was found in the CW-MFC, contributing to enhanced nitrogen removal.