Ozone-persulfate molecular energy-level matching regulates dissolved organic matter degradation and transformation in leachate aerobic effluent

Ozone-persulfate coupling can enhance ozonation for wastewater treatment, but its activation mechanism and component-specific degradation pathways governing COD removal in real wastewater remain unclear. Herein, ozone-persulfate coupling for treating composting leachate aerobic effluent was studied, via DFT, radical quantification, and spectroscopy. Based on results, the energy-level matching mechanism governing the molecular interactions between ozone and persulfate species (PS and PMS) was first reported. PS enabled pronounced O-O bond elongation (1.323 to 1.702 Å) for radical-assisted activation, whereas PMS favored initial O₃ association (adsorption −1.704 vs. −0.985 eV; orbital gap 1.451 vs. 1.875 eV). O₃/PS (7.60 × 10–10 M·s) produced more SO₄·⁻ than O₃/PMS (6.14 × 10⁻¹⁰ M·s), which achieving higher COD (71.33 %) and TOC (59.70 %) removal, reducing oxidation cost from 1.40 to 0.33 USD kg⁻¹ COD. O₃/PS induced broader functional group changes, suppressed carbonyl accumulation, and exhibited stronger SO₄·⁻-driven selectivity for humic-like C2. O₃/PS transformed protein-like/low-excitation humified fluorophores before fulvic/humic-like components, whereas O₃/PMS transitioned from protein/fulvic/low-excitation humic-like to aromatic humic structures. These findings link structure-activation-reactivity to radical exposure, temporal responses, and component selectivity, providing mechanistic guidance for ozone-persulfate process optimization and application.