Reinforced biofilm-mediated electron transfer and perfluorooctanoic acid removal: Neglected macrophyte roles in iron-biochar-based constructed wetlands.

This study evaluated how macrophytes regulated biofilm-mediated electron transfer and perfluorooctanoic acid (PFOA) fate in iron-carbon (IC)-based constructed wetlands (CWs). Compared with unplanted systems, Iris pseudacorus markedly enhanced intracellular electron transfer and energy metabolism, increasing final electron transport system activity by 51.3%, and raising ratio of oxidized nicotinamide adenine dinucleotide to reduced nicotinamide adenine dinucleotide by up to 5.9-fold and adenosine triphosphate content by 308.1% in IC layer after long-term PFOA exposure. Plants increased alpha diversity, optimized microbial community, and enriched functional microorganisms (like Geobacter and Shewanella) and up-regulated genes (belonging to Complex I/III/V, extracellular polymeric substance synthesis, and quinone), which were closely related to electron transfer and iron/sulfur-cycling. Consequently, macrophytes contributed to higher PFOA removal in IC-based CW (74.0-92.6%) than unplanted group (41.5-71.3%), with increased defluorination rate (by up to 30.7%), greater degradation contribution (28.5%), lower short-chain PFCA accumulation, and continuously enhanced nutrient removal. These findings innovatively proposed macrophytes as key regulators for sustainable PFOA treatment in IC-based CWs.