Identifying transformation of dissolved organic matter in treatment of coal chemical wastewater for zero liquid discharge.

Accumulation of refractory dissolved organic matter (DOM) poses a critical challenge to stable operation of zero liquid discharge (ZLD) systems in the coal chemical industry. Conventional water quality parameters (e.g., COD and TOC) provide limited insight into DOM compositional complexity, which constrains the targeted selection and optimization of treatment processes. Molecular-level evolution of DOM across the full-scale ZLD system and its implications for process control remain poorly understood. In this study, the fate and transformation of DOM were elucidated in a full-scale ZLD plant treating coal chemical wastewater (CCW). Results revealed that biological treatment shifted DOM toward more saturated and reduced state, accompanied by a substantial decline in oxidized aromatic components, whereas tryptophan-like biogenic metabolites persisted in the treated effluent. Membrane based concentration processes were accompanied by distinct DOM fingerprints in concentrates. High-molecular-weight and sulfur-rich compounds were accumulated in the nanofiltration concentrate (NFC), whereas low-molecular-weight halogenated N-heterocycles were enriched in the ultra-high-pressure reverse osmosis concentrate (UHPROC). UV254 and BIX illustrated exploratory associations with selected aromaticity- and oxidation-related molecular descriptors. This study not only provides mechanistic insights into transformation of DOM in CCW but also suggests engineered strategies for targeted intensification optimization of ZLD system.