Mapping Fragmentation Pathways: Assessing Degradation Potential of Individual Organic Fractions in Concentrated Leachate Using E⁺/Ozonation

Electro-ozonation (E+/ozonation) was used to degrade recalcitrant dissolved organic matter (DOM) in high-salt concentrated leachate (CL), but individual DOM molecules with varying oxidizability and their degradation mechanisms in different E+/ozonation remain unexplored. This study revealed the DOM oxidizability from molecular insight and their fragmentation-pathway mechanism by modifying the graph-DOM-based mode in Ti-based E+/ozonation. Ti4O7-E+/ozonation achieved a high-efficiency CODCr removal of 74.5%, detecting 1570 DOM precursors, 1037 resistant, and 614 products. Key molecular properties, such as molecular weight, S, C, N, and O/C, were identified as influencing DOM oxidizability. The primary nonheteroatom-involved pathways among the 42 transformation pathways were the oxygen reaction, the reaction of the dealkyl group, and carboxylic acid. More loss of the –COO group was observed in Ti4O7-E+/ozonation by Kendrick mass defect (KMD), further revealing the transformation between homologous DOM. Fragmentation pathways were refined using a machine-learning framework on graph networks based on 42 one-step paired mass distance (PMD) pathways and KMD multistep pathways, highlighting the role of absorbed •OH and O2•- in complex DOM transformations. This modified model offers the potential for predicting DOM reactivity in such a complex matrix under different treatment conditions, leading to more efficient degradation strategies.