Molecular-level transformation of refractory organic matter during flocculation-ultraviolet/peroxymonosulfate treatment of MBR-treated landfill leachate.

Abstract

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.