Research progress on interspecies electron transfer mechanisms and their regulation in denitrification systems

Denitrification is a critical process for advanced nitrogen removal in wastewater treatment， fundamentally governed by microbially driven electron transfer and electron allocation. As research has shifted from macroscopic treatment metrics toward microscopic regulation， elucidating denitrification mechanisms from an electron-flow perspective has emerged as a major research frontier. This review systematically summarized the theoretical framework of electron flow in denitrification systems， compared intracellular electron transport pathways and energy allocation characteristics between heterotrophic and autotrophic denitrifiers， and highlighted the central role of the quinone pool in electron collection and redistribution. Furthermore， from the perspective of interspecies microbial interactions， recent advances in indirect interspecies electron transfer （IIET） and direct interspecies electron transfer （DIET） were summarized， and competitive as well as cooperative interactions among microorganisms in mixed systems during electron donor and electron acceptor utilization were analyzed. Building on this framework， the impacts of carbon source characteristics， pH， oxidation-reduction potential （ORP）， and coexisting contaminants on electron transport chains and electron allocation pathways were further discussed. Finally， in light of current limitations in the in situ quantification of electron fluxes， future research directions were proposed， including the development of multi-scale in situ characterization techniques， novel electron-conductive materials， and intelligent electron-flow regulation models.