Exploring the fate and oxidation behaviors of different organic constituents in landfill leachate upon Fenton oxidation processes using EEM-PARAFAC and 2D-COS-FTIR

In this work, the changes of different organic constituents in landfill leachate were tracked in Fenton oxidation processes with different operation parameters including H₂O₂ doses, pH, and the ratios of [H₂O₂]/[Fe] via fluorescence excitation emission matrix - parallel factor analysis (EEM-PARAFAC) and two-dimensional correlation spectroscopy (2D-COS). One tryptophan-like (C1), one fulvic-like (C2), and one humic-like (C3) components were identified in the leachates. The removal behaviors of the individual fluorescent components were dependent upon the operation conditions, suggesting the existence of unique characteristics with respect to the responses to the oxidation mechanisms, which were likely altered by different operation conditions. For all tested conditions, a greater extent of removal was consistently found for C3 versus C1 and C2 except for the relatively high pH ranges (>6.0), in which C2 presented the highest removal rates. 2D-COS combined with synchronous fluorescence spectra exhibited the preferential oxidation sequence in the order of C3 > C1 > C2 with higher H₂O₂ doses. 2D-COS coupled with Fourier transform infrared (2D-COS-FTIR) showed that aromatic functional groups were initially oxidized, followed by the removal of carboxylic groups and the formation of inorganic functional groups and aldehyde or ketonic groups. Hetero 2D-COS maps further revealed the close association between the aromatic groups and C3, and between the carboxylic groups and C1. This study utilizing 2D-COS provided new insights into the dynamic behavior of heterogeneous landfill leachate in Fenton oxidation processes under varying operation conditions.