Molecular transformation of dissolved organic matter in high-temperature hydrogen peroxide oxidation of a refinery wastewater

Advanced oxidation processes have been extensively used in industrial wastewater treatment. However, the molecular transformation of dissolved organic matter (DOM) during oxidation process is poorly known. In this study, a refinery wastewater was oxidized at high temperature using H₂O₂. Negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was applied to analyze the molecular changes of DOM. 68 heteroatom class species including O_x, O_xS₁, O_xS₂, N₁O_x, N₂O_x, N₃O_x, and N₁O_xS₁ were assigned from a single spectrum of the raw water, in which O_x and O_xS₁ class species were dominant. The molecular composition changed during oxidation. Sulfur- and nitrogen-containing compounds were almost completely removed. The removal of oxygen compounds by oxidation and the new production of oxygen compounds were simultaneous. Chain scission and oxidation of O_x compounds were the major reactions. Abundant chlorinated compounds were detected in the oxidation product. These compounds are considered as reaction products of DOM molecules with chloride ions in the water.