Coupling PFOA defluorination with Fe0-mediated CO2 methanation: Metabolic pathways in PET microplastic niches

Perfluorooctanoic acid (PFOA) is a persistent emerging contaminant that has attracted increasing attention due to its recalcitrance and toxicity. This study demonstrates the efficacy of a zero-valent iron (Fe 0 ) mediated biogas upgrading system for simultaneous PFOA degradation and methane production, with PET microplastics playing a secondary role in the degradation process. At a PFOA dosage of 0.3 mg/L, defluorination efficiencies ranging from 21.22% to 31.98% were achieved after five biogas upgrading cycles (approximately 25 days), accompanied by enhanced CO 2 methanation performance (ultimate CH 4 content >95%). At a PFOA concentration of 10 mg/L, analysis of extracellular polymeric substances (EPS) revealed a significant decrease in protein content within the reactors. Molecular docking models and reactive oxygen species (ROS) analyses suggested that the binding of PFOA to specific amino acid residues mitigated its cytotoxicity. The microbial community in the Fe 0 -mediated reactor was dominated by Methanosaeta , a strictly acetoclastic methanogen. Furthermore, metagenomic analysis indicated the upregulation of key genes associated with methanogenesis and fluoride transport under Fe 0 mediation. Characterization of infrared spectrum and fluorinated metabolic intermediates suggested that PFOA degradation proceeded primarily via stepwise decarboxylation pathways. This study not only confirms the roles of Fe 0 and PET microplastics in PFOA removal but also reveals the synergistic metabolic coupling between defluorination and methanogenesis, therby elucidating the mechanisms of Fe 0 -enhanced PFOA degradation.