Electron Transfer–Driven Biogeochemical Reactors for Circular Phosphorus Management in Onsite Wastewater Treatment Systems

Traditional evaluations of phosphorus (P) management in onsite wastewater treatment systems (OWTS) rely on short-term sorption metrics that treat filter media as static materials with finite capacities. However, field evidence shows that laboratory-derived predictions often fail to capture sustained phosphorus retention under realistic operating conditions. Here we synthesize current understanding and reconceptualize OWTS filters as dynamic, redox-active biogeochemical reactors in which phosphorus behavior emerges from coupled mineral, microbial, and interfacial processes. Across calcium-, aluminum-, iron-, zeolite-, carbon-, and mixed-media systems, long-term phosphorus stabilization is governed by the interplay of mineral precipitation, surface redox cycling, microbial mediation, and progressive mineral–organic transformations. In this framework, apparent “sorption capacity” reflects not irreversible exhaustion, but continuous reorganization among reactive phases and transformation pathways. Electron transfer processes provide a unifying mechanism linking mineral reactivity and microbial metabolism, enabling partial regeneration of reactive surfaces while coupling phosphorus transformations to carbon, nitrogen, sulfur, and oxygen cycles. Embedding OWTS within broader soil–water biogeochemical networks shifts phosphorus management from equilibrium sorption concepts toward system-level, nonequilibrium reactivity. This perspective provides a foundation for designing resilient, multifunctional media capable of sustained phosphorus retention beyond conventional capacity-based constraints.