Conductive wire-activated iron-carbon potential: Self-driven bio-electrochemical system for efficient nitrogen and phosphorus removal from wastewater.

iron-carbon (IC) materials were packed as fillers into the anoxic and micro-aerobic zones of a biological filter, and for the first time, these two zones were electrically connected via a conductive wire to enable electron transfer from the micro-aerobic zone to the anoxic zone. Microorganisms in the anoxic zone utilized the cross-regionally transferred electrons to drive nitrate denitrification, thereby enhancing the denitrification efficiency, reducing the requirement for external carbon sources, and simultaneously achieving high total phosphorus (TP) removal. This configuration constitutes a novel self-driven bio-electrochemical system (SD-BES). A SD-BES trickle filter was established at a wastewater treatment plant, in which a current density of up to 45.7 mA m⁻³ was achieved. The system demonstrated a total nitrogen (TN) removal efficiency of 81.2% and a TP removal efficiency of 93.9%. Integrated analysis of microbial diversity and functional genes revealed significant enrichment of electrochemically active bacteria (e.g., Geothrix) and iron-autotrophic denitrifying bacteria (e.g., Dechloromonas), along with a marked increase in the abundance of key functional genes associated with nitrogen metabolism. The intensity of IC micro-electrolysis in the micro-aerobic zone consistently exceeds that in the anoxic zone, providing a natural potential difference for the cross-regional transfer of electrons. The wire serves as a bridge for electron transfer, and the enrichment of functional microorganisms enables the cross-regional transferred electrons to be utilized in an efficient pollutant removal process. The incorporation of a conductive wire in this study offers a novel application approach and theoretical basis for IC-assisted simultaneous nitrogen and phosphorus removal from wastewater.