Performance and mechanism of constructed wetland-microbial fuel cell systems in treating mariculture wastewater contaminated with antibiotics

Mariculture wastewater has raised great concerns owing to its potential impact on the sustainability of coastal environments and aquaculture practices. In this study, constructed wetlands coupled with microbial fuel cells (CW-MFCs) were constructed to evaluate their ability to treat mariculture wastewater that has been contaminated with antibiotic sulfadiazine (SDZ). The results showed that both open- and closed-circuit CW-MFCs (R1 and R2) had comparable removal efficiencies for NH4+-N, total inorganic nitrogen (TIN), chemical oxygen demand (COD), and total phosphorus (TP). Compared with R3, which had no SDZ, R2 was less efficient at removing NH4+N and TP, and also presented inhibited electricity generation. R2 in closed-circuit mode was more efficient at removing SDZ than R1 in open-circuit mode. However, R2 also had a higher relative abundance of antibiotic resistance genes (ARGs) in the anode region and cathode effluent than R1, indicating that the closed-circuit CWMFC system was inferior to the open-circuit system in controlling ARGs. High-throughput sequencing analysis suggested that the presence of SDZ and being in closed-circuit mode both increased the diversity of the microbial community, which in turn led to changes in the removal efficiency of SDZ and the system's ability to generate electricity. The potential hosts of the three ARGs at the phylum level were mainly from Proteobacteria, Desulfobacterota, Patescibacteria, Firmicutes, Actinobacteriota, and Spirochaetota. Notably, some genera related to sulfur transformation in Desulfobacterota showed strong positive correlations with ARGs. This study is beneficial to expand the application of CW-MFCs in the treatment of antibiotic-contaminated mariculture wastewater.