Self-sustained Bio-Fenton system driven by Shewanella oneidensis for efficient degradation of persistent organic pollutants under oxygen-limited conditions.

Persistent organic pollutants (POPs) pose severe environmental risks because of their chemical stability, bioaccumulation, and toxicity. The Bio-Fenton process, coupling microbial metabolism with Fenton chemistry to generate •OH in situ, offers a green and sustainable remediation strategy. However, its application is hindered by inefficient Fe(III) reduction and insufficient endogenous H2O2 production. In this study, we developed a self-sustained microbial Fenton system driven by Shewanella oneidensis MR-1 under oxygen-limited conditions. Fine-tuning the dissolved oxygen level enabled simultaneous Fe(III) reduction and H2O2 generation. Mechanistic investigations revealed that the metal-reducing (Mtr)-dependent extracellular electron transfer (EET) pathway and bd-type terminal oxidase cooperatively induced continuous Fenton activation. Engineered strains with enhanced EET and H2O2 biosynthesis exhibited a 1.70-fold higher Fe(II) production and 3.59-fold higher H2O2 accumulation. Using 1,4-dioxane (17.6 mg/L) as a model compound, over 84.5 % degradation efficiency was achieved, and the proposed oxidative pathway was also elucidated. Moreover, the system efficiently removed diverse pollutants, including trypan blue (10 mg/L), rhodamine B (5 mg/L), bisphenol A (10 mg/L), and benzopyrene (1 mg/L), with 73.3-92.3 % removal efficiencies. This Bio-Fenton strategy overcame the limitations of conventional Fenton systems by operating under neutral pH without external H2O2 or redox cycling, thereby offering a scalable and eco-friendly solution for the in situ remediation of POPs in hypoxic environments.