Compositional characteristics of dissolved organic matter during coal liquefaction wastewater treatment and its environmental implications.

The variations in the structural components of dissolved organic matter (DOM) during coal liquefaction wastewater (CLW) treatment are still unclear at present, limiting the further improvement and application of CLW treatment processes. In this study, the changes of DOM composition during air flotation, catalytic oxidation, biofiltration, ozonation, anoxic/oxic (A/O), and membrane bioreactor (MBR) which were applied in the full-scale CLW treatment, were investigated by three-dimensional excitation-emission matrix fluorescence and ultraviolet-visible spectroscopy. The dissolved organic carbon and chemical oxygen demand of the raw CLW reached 1965.2 mg/L and 5310.0 mg/L, respectively, with humic acid-like substances being as the dominant component (63.1%), and protein-like substances contributing a small amount (5.3%). Air flotation could treat humic acid-like substances more effectively. Catalytic oxidation and ozonation efficiently removed macromolecular aromatic substances with aliphatic chain substituents, resulting in the notable enhancement of the biodegradability of the organics. The DOM removal efficiency of biofiltration and A/O reached 86.0% and 92.3%, respectively, and simultaneously complex macromolecular substances with a high degree of aromaticity were formed. This study could provide a theoretical basis for optimizing the technical parameters and further improving the treatment efficiency of CLW.