Microbial electrochemical buffer zones enable PFAS detoxification and hidden risk mitigation in reclaimed water

Ecological buffer zones (EBs), such as constructed wetlands (CWs), represent an eco-friendly technology have been increasingly studied for their potential in treating per- and polyfluoroalkyl substances (PFAS) in contaminated water. However, the reclaimed water from EBs systems can be directly discharged remains uncertain, and the ecological impacts and environmental risks associated with this practice are still poorly understood. This study investigated the performance of activated carbon (AC), graphite (GP), and sludge biochar (SB) as anode electrodes in microbial fuel cell-ecological buffer zones (MFC-EBs) for perfluorooctanoic acid (PFOA) removal, and simultaneously examining the ecological behavioral and molecular-level impacts of MFC-EB effluent on zebrafish. Results demonstrated that the activated carbon closed-circuit MFC-EB (MAC-EB) achieved optimal removal efficiencies for both PFOA (70.22 %) and total nitrogen (TN, 99.8 %), while the SB anode generated the highest power density (1.447 mW/m²). Furthermore, the MFC-EBs effluent significantly mitigated oxidative damage in zebrafish compared to zebrafish exposed to synthetic wastewater directly. Transcriptomic evidence revealed systemic oxidative overload in zebrafish exposed to raw PFOA-contaminated wastewater, with severe dysregulation of stress-responsive gene expression under prolonged high-concentration exposure. In contrast, the MFC-EBs system significantly mitigated metabolic and immunological disturbances compared to open-circuit operation. This study demonstrates that the MFC-EBs system achieves efficient PFOA removal and significantly reduces its ecological risks to aquatic organisms, providing a feasible research framework for establishing early-warning strategies of water ecosystem safety.