Landfill leachate management toward zero liquid discharge: Molecular-level characterization, process selectivity, and engineering regulation of DOM

Landfill leachate is a high-strength wastewater generated during municipal solid-waste disposal, and its composition and biodegradability vary strongly with landfill age. Dissolved organic matter (DOM) constitutes the dominant organic pool in leachate and influences treatment efficiency, toxicity, contaminant complexation, membrane fouling, concentrate management, and process sustainability. Recent ultrahigh-resolution mass spectrometry, especially Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), combined with multidimensional spectroscopy, enables molecular-level characterization of leachate DOM and tracking of its evolution during landfill aging and treatment. This review synthesizes molecular-level evidence on leachate DOM evolution, transformation, and engineering regulation within a molecular evolution–process selectivity–engineering regulation framework. Available evidence indicates that, during landfill aging, leachate DOM shifts from protein- and aliphatic-enriched mixtures toward a more oxygenated, aromatic, heteroatom- or halogen-bearing, and persistent pool, and this age-dependent evolution underlies declining biodegradability and reshapes process selectivity. We further synthesize process-selective DOM behaviors across physicochemical separation, advanced oxidation, and biological conversion, and highlight paired mass differences-based reactionomics and interpretable machine learning to link molecular fingerprints with transformation pathways and key operational metrics. Finally, we highlight the need to clarify DOM–microbial interactions, reduce method-related biases, and translate molecular descriptors into practical monitoring and operating conditions. Overall, this review argues for moving leachate treatment beyond bulk-metrics-based process stacking toward molecularly informed treatment-train design under stringent discharge limits and management strategies directed toward zero liquid discharge.