1 School of Environmental and Municipal Engineering, Tianjin Key Laboratory of Aquatic Science and Technology, Tianjin Chengjian University, Jinjing Road 26, Tianjin 300384, China.
2 School of Civil Engineering and Architecture, Taizhou University, Taizhou 318000, China.
3 Department of Building, Civil, and Environmental Engineering, Concordia University, 1455 de Maisonneuve Blvd. W. Montreal, Quebec, Canada.
4 School of Civil Engineering and Architecture, Taizhou University, Taizhou 318000, China. Electronic address: tingtingguo163@163.com.
5 School of Civil Engineering and Architecture, Taizhou University, Taizhou 318000, China. Electronic address: jianbguo@163.com.

Co-pollution of nitrate and tetracycline (TC) poses a critical barrier to efficient biological treatment due to impaired electron transfer, diminished microbial metabolic activity, and disrupted community structure. To address this challenge, this study synthesized an iron-nitrogen-doped carbon material (Fe-NC) featuring electron-withdrawing pyridinic nitrogen and Fe active sites. Under co-contaminated conditions, the nitrate and TC removal efficiencies of the TC/Fe-NC₂₀₀ system were 100 % and 96 %, which were 21.27 and 2.18 times higher than those of the TC system. Material characterization indicated that Fe-NC might act as an electron transfer station, promoting the removal of nitrate and TC through Fe³⁺/Fe²⁺ cycling. Electrochemical analyses showed that Fe-NC promotes the secretion of cytochrome c and flavin mononucleotide, accelerating extracellular electron transfer. Enzyme activity assays indicated that Fe-NC enhances intracellular electron transfer by activating key redox enzymes and upregulating associated gene expressions. Electron transfer system activity and metagenomic analysis further demonstrated that Fe-NC improves microbial respiration and increases the abundance of dominant taxa such as Bacteroidota (11.96 %) and Chryseobacterium (12.00 %), which support both TC degradation and microbial stress tolerance. These mechanistic insights establish a novel, bio-electroactive function for Fe-NC, in which the synergistic effects of Fe redox cycling and pyridinic nitrogen coordination led to improved electron flow, microbial function, and pollutant breakdown. This work not only reveals a previously unexplored pathway for biological co-removal of nitrate and antibiotics but also provides a scalable strategy for enhancing bioremediation efficiency in complex wastewater systems.