Extracellular polymeric substances-derived geobattery-like nano-bio interface improves nanoscale zero-valent iron biocompatibility and triggers extracellular electron transfer for microbial denitrification in low carbon-to-nitrogen wastewater

Nano zero-valent iron (nZVI) has emerged as an inorganic electron donor for denitrification in low carbon‑to‑nitrogen (C/N) wastewater, but its low electron utilization efficiency and nanotoxicity limit practical implementation. Inspired by microbial self-protection mechanisms, a robust bio–nano interface was engineered by coating nZVI with extracellular polymeric substances (EPS) from Shewanella oneidensis MR-1 (EPS@nZVI). The EPS@nZVI microbial combined system achieved 97.6% nitrate removal at a C/N ratio of 2, significantly outperforming systems with bare nZVI (60.2%). Mechanistically, the EPS coating served a dual function by acting as a redox-active “geobattery” while mitigating nZVI-induced nanotoxicity. By buffering electrons from rapid Fe⁰ corrosion, the EPS synchronized abiotic electron release with microbial uptake, redirecting electrons from hydrogen evolution to efficient biological utilization. Meanwhile, the EPS corona functions as a biocompatible shield that mitigates oxidative stress and membrane damage, thereby maintaining a metabolically active microbial community and foundational carbon metabolism. Multi-omics analyses revealed that EPS@nZVI selectively enriched electroactive taxa such as Geobacter, upregulated extracellular electron transfer and denitrification pathways, and reprogrammed microbial metabolism from stress response toward efficient energy harvesting. Collectively, the enhanced extracellular electron transfer efficiency and biocompatibility enabled by EPS@nZVI jointly governed the improved nitrate-reduction performance. This work demonstrates a bio-inspired strategy to rationally design nanomaterials that bridge the nano-bio interface, synchronizing abiotic electron supply with microbial metabolism for environmental remediation.