Driving synergistic Fe-N-Plastic co-metabolism and functional microbial symbiosis via nZVI@RA for enhanced decontamination in constructed wetlands

Nanoplastics (NPs) significant challenges to nitrogen removal in constructed wetlands (CWs). Although nano-zero valent iron (nZVI)-based composites have shown potential in enhancing pollutant removal, the integrated mechanisms governing iron, nitrogen, and plastic metabolism, as well as their influence on the microbial network remain poorly understood. Here, we developed recycled aggregates-supported nZVI (nZVI@RA) and systematically investigated its impact on microbial nitrogen metabolism and plastic degradation within CWs. The results revealed that nZVI@RA profoundly reshaped the microbial symbiotic network, promoting Exiguobacterium and Bacillus as dominant genera and facilitating synergistic interactions. Mechanistically, nZVI@RA enhanced iron metabolism and electron transfer, leading to the upregulation of key genes and enzymes involved in nitrogen transformation (e.g., amoABC and nirKS) and NP degradation (e.g., styA and styC). These processes, coupled with superior adsorption capacity, improved removal efficiencies of COD (64.57 ± 3.57 %), TN (70.79 ± 4.19 %), and NPs (92.46 ± 3.66 %). Structural equation modeling revealed strong correlations between iron metabolism, microbial activity (0.82), nitrogen metabolism (0.51), and plastic degradation (0.40) in the nZVI@RA system, underscoring the central role of iron cycling. This study elucidates the critical function of nZVI@RA in orchestrating microbial interactions and optimizing pollutant removal, providing a foundation for advanced CW design.