Improved understanding of dissolved organic matter transformation in concentrated leachate induced by hydroxyl radicals and reactive chlorine species

Concentrated leachate (CL) is commonly featured with high salt and dissolved organic matters (DOM). In this study, molecular transformation of DOM was revealed to identify the reactive mechanisms with (non-) radical reactive species in ozonation, electrolysis and E+-ozonation processes. Chlorine ions were efficiently activated into non-radical reactive chlorine species (RCS) with 245.7 mg/L, which was more dominant in electrolysis. Compared to ozonation, C-center dot OH was increased from 2.6 x 10(-4) mg/L into 5.8 x 10(-4) mg/L and the generation of Cl center dot/ClO center dot could be concluded according to the decline of non-radical RCS in E+-ozonation process. For chromophoric and fluorescent DOM, aromatic compounds and polymerization degree dramatically decreased in E+-ozonation. Lipid-like and CRAM/lignin-like compounds were substantially degraded, as center dot OH and ClO center dot/Cl center dot shows an affinity towards oxygen-containing organic compounds via single electron transfer by attracting O-H bonds. Especially, carbon/hydrogen/oxygen (CHO-containing) compounds were readily to be degraded with the removal efficiency of 92.5 %, 97.0 % and 98.4 % in electrolysis, ozonation and E+-ozonation, respectively. Moreover, nitrogen atoms have a negative effect on DOM degradation, and thus, carbon/hydrogen/nitrogen and carbon/hydrogen/nitrogen/sulfur (CHN- and CHNS-containing) compounds were considered as refractory compounds. This paper is expected to shed light on the synergetic effect in E+-ozonation and transformation of refractory DOM in CL treatment.