Molecular insights into dissolved organic matter post electrokinetic-persulfate treatment: Heteroatom induced resistance

The application of electrokinetic-enhanced in situ chemical oxidation remediation of contaminated sediments has attracted increasing attention. However, the molecular changes in dissolved organic matter (DOM) during these remediation processes remain unexplored. To address the gap, we explored the molecular transformation of DOM subjected to electrokinetic (EK)-persulfate treatment. The findings revealed that DOM transitioned from a reduced to an oxidized state, marked by the removal of low O/C molecules and the formation of high O/C molecules. Heteroatom-containing molecules accumulated and constituted the dominant fraction among the resistant molecules post-treatment. N-containing and Cl-containing molecules displayed elevated N/C and Cl/C ratios during the treatment, decomposing into smaller and N-rich or Cl-rich molecules, while S-containing molecules exhibited a decrease in S/O ratios. Oxygen addition reaction and dealkyl group reaction were identified as the two most common transformation pathways, contributing to the increased oxidation and resistance of DOM molecules. This study deepens our understanding of DOM transformation using EK-persulfate treatment and aids in assessing the potential risks associated with resistant molecules in its practical application.