Decoupling denitrification from the tricarboxylic acid cycle through extracellular pseudocapacitive electron flux.

Disruption of the anthropogenic nitrogen cycle has strained planetary boundaries to critical thresholds, driving an urgent demand for carbon-neutral water infrastructure. Conventional biological denitrification is inherently constrained by stoichiometric dependence on organic carbon, resulting in an unsustainable trade-off between aquatic nutrient remediation and carbon footprint. This study presents a decarbonized respiratory metabolism paradigm that circumvents the tricarboxylic acid cycle via the battery-like pseudocapacitance property of electroactive humic acid (eHA), a non-sacrificial energy carrier reclaimed from municipal waste sludge. Exhibiting a specific capacity of 11.62 mmol e- g-¹, eHA acts as a microbial battery that supplies over 75% of the total reducing equivalents. This system achieves nitrogen removal efficiencies exceeding 92% without reliance on external organic carbon input. Such metabolic decoupling substantially mitigates N2O emissions and drives a functional specialization dominated by Thaufigera via interfacial electron capture. By bridging urban metabolism with planetary health, this regenerative framework offers a transformative pathway for climate-neutral nutrient management.