Search

Refractory organic matter in membrane bioreactor effluent resulting from landfill leachate treatment has a complex composition. This paper identified the transformation mechanism of organic matter in a flocculation-ultraviolet (UV)/peroxymonosulfate (PMS) system at the molecular level using electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. The results showed that the flocculation system was able to remove a large amount of dissolved organic matter (DOM) with high oxidation and unsaturation/saturation. UV radiation displayed a relatively strong reactivity for DOM with an electron-rich structure, which it can transform into DOM with lower aromaticity through photolysis and photosensitivity, although the effectiveness of the transformation was poor. In comparison, due to the action of reactive oxygen species, the UV/PMS system can enable reactions such as demethylation, dehydrogenation, decarboxylation, dehydroxylation, ring cleavage, and decarbonylation. It can remove approximately 60% quantity of the total DOM and produce DOM featuring a higher degree of oxidation and saturation than that of the UV system alone. The results showed that the UV/PMS system was a complementary of flocculation in DOM removal from the membrane bioreactor effluent, while the system also resulted in a large number of sulfuric compounds; thus, requiring further evaluation of its ecological effects. [Display omitted] • Flocculation removed most oxidized DOM and newly-produced sulfuric and aliphatic DOM. • UV radiation decreased the aromaticity of electron-rich DOM. • The combination of UV/PMS and flocculation ahieved effective DOM removal. • Sulfuric compounds were produced in the treated leachate, needing further evaluation. [ABSTRACT FROM AUTHOR]

During leachate treatment, molecular information regarding the completely removed, partially removed, less-reactive, increased, and produced parts of dissolved organic matter (DOM) remains unknown. This study applied ESI FT-ICR MS to investigate the transformation characteristics of leachate nanofiltration concentrate (NFC) DOM during a combined flocculation–O 3 /H 2 O 2 process. The NFC contained 5069 compounds in four main classes (CHO, CHON, CHOS, and CHONS compounds). The DOM number decreased to 4489 during flocculation and to 2903 after the O 3 /H 2 O 2 process. During flocculation, the completely and partially removed DOM was mainly low-oxygen unsaturated and phenolic compounds. Saturated DOM was produced and remained in the flocculated effluent. During the O 3 /H 2 O 2 process, the completely and partially removed DOM were mainly low-oxygen unsaturated and phenolic compounds that were mainly in a reduced state. Flocculation can remove many (condensed) aromatic compounds, and methylation and hydrogenation reactions occurred during flocculation. In the O 3 /H 2 O 2 process, dearomatization, demethylation, carboxylation, and carbonylation reactions further achieved the degradation of DOM that was resistant to flocculation. Overall, the combined flocculation-O 3 /H 2 O 2 process collectively eliminated a broader range of DOM than the single processes could achieve. The results of this study provide an in-depth understanding of DOM transformation in an NFC treatment. [Display omitted] • Transformation of NFC DOM in flocculation-O 3 /H 2 O 2 process was studied by FT-ICR MS. • Removed, less-resistant, and produced parts of NFC DOM in flocculation-O 3 /H 2 O 2 were determined. • A Kendrick mass defect theory was used to study DOM transformation of NFC. • Flocculation-O 3 /H 2 O 2 collectively eliminated a broader range of DOM. [ABSTRACT FROM AUTHOR]