Persulfate activation by inherent soil constituents for sulfamethoxazole degradation: Synergistic roles of iron minerals and organic matter

Abstract

Persulfate (PS)-based in situ chemical oxidation has attracted extensive attention for remediating organic-contaminated soils. The inherent Fe minerals can act as the activators of PS in the degradation of soil organic contaminants, but the combined effects of Fe minerals and organic matter (OM) remained elusive. Here, we investigated sulfamethoxazole (SMX) degradation by PS in complex soil system. Results showed that SMX degradation by PS in soil could reach 70.7 %. Notably, the removal of free Fe oxides led to a 12.6 % decrease in SMX degradation, while OM removal resulted in a more substantial 28.0 % decrease in SMX degradation, implying that inherent OM played more pivotal roles in SMX degradation than Fe minerals. Furthermore, the synergistic roles of OM and Fe mineral facilitated SMX degradation through the formation of surface complexes between Fe minerals and OM with -HOH and -COO groups, as analyzed by fourier transform ion cyclotron resonance mass spectrometry. Specifically, the presence of OM promoted the reductive dissolution of Fe minerals, leading to the generation of surface-bound Fe(II). Then this Fe(II) formed a complex with OM, which was favorable for the PS activation to produce reactive species. The dominant roles of radicals, particularly ^•OH in SMX degradation were collectively evidenced by multiple methods, including quenching test, chemical-probing test, electron paramagnetic resonance, analysis of degradation products, and density functional theory calculations. These findings provide valuable insights into the interactions between Fe mineral and OM for PS activation in remediation of organic-contaminated soils.