Combined Effects of Coagulation and Ozonation Treatment on Landfill Leachate DOM Biodegradability

Coagulation significantly alters molecular characteristics and oxidizability of dissolved organic matters (DOM), while the linkage between DOM molecular characteristics and fragmentation pathways were unclear for the following processes. Here, four typical coagulation processes were employed to improve DOM molecular properties in leachate, and their subsequent impact on oxidizability in ozonation was identified. The results indicate that Polyaluminum chloride (PAC), Polyferric sulfate (PFS), Polyaluminium ferric chloride (PAFC) and Polymerized aluminum ferric silicate (PSAF) can all reduce the COD and TOC levels of the leachate concentrate through coagulation and precipitation, with PAC achieving the highest removal efficiency. PAC-ozonation effectively removes aromatic and unsaturated compounds, significantly improving DOM composition and enhancing conditions for subsequent oxidation. In contrast, PFS shows the poorest removal of aromatics (2.92%) and polycyclic aromatics (9.81%), along with the highest NOSC (−0.5036) and lowest (DBE-O)/C (−0.0051), indicating greater oxidation resistance. Only 11% of COD was further removed by ozonation after PFS treatment, suggesting limited reactivity of the residual DOM. Machine learning analysis of molecular transformation networks further confirmed that PFS treatment produced the fewest conversion pathways following ozonation. This indicates the choice rules and relationship between coagulation and ozonation for landfill leachate. This work provides an effective strategy to enhance leachate treatability and reduce energy and reagent consumption in subsequent processes, thereby contributing to more sustainable and cost-effective landfill leachate management.