Ofloxacin removal, electrochemical performance, and antibiotic resistance gene responses in a FeO/C–Shewanella oneidensis MR-1 enhanced constructed wetland–microbial fuel cell with different cathodes

Ofloxacin (OFL) contamination can promote antibiotic resistance gene (ARG) enrichment, yet it remains unclear whether cathode configuration in constructed wetland–microbial fuel cells (CW-MFCs) can simultaneously affect OFL removal, electrochemical performance, and ARG-related microbial responses. To address this question, a CW-MFC incorporating a FeO/C– Shewanella oneidensis MR-1 enhanced bioanode was operated with three cathode materials: granular activated carbon (GAC), graphite plate (GP), and carbon felt (CF). Their effects on OFL removal, conventional pollutant removal, and electrochemical performance were evaluated, together with microbial community responses and the relative abundances of mexB and aac(6′)-Ib-cr under different OFL loads. During 45 d of cathode comparison at 1000 μg/L OFL, the GAC-based system achieved the highest time-averaged OFL removal efficiency (89.2%) and the highest average voltage output (approximately 364.5 mV), whereas the GP configuration exhibited a slightly higher peak power density during polarization testing. Increasing OFL loading was accompanied by marked microbial community restructuring and enrichment of both target ARGs. However, the S. oneidensis MR-1-augmented CW-MFC consistently showed lower mexB and aac (6′)-Ib-cr abundances than the conventional wetland and the non-inoculated FeO/C system. These findings indicate that cathode configuration was associated with differences in treatment and electrochemical performance, while FeO/C– S. oneidensis MR-1 bioaugmentation was associated with greater OFL stress tolerance and lower relative abundances of the two target ARGs.