Mechanisms on the impacts of humic acids on persulfate/Fe2+-based groundwater remediation

Persulfate (PS) has been increasingly applied for in situ chemical oxidation of organic contaminants in groundwater, while the impacts of humic acids (HAs) on the efficiency of persulfate/Fe2+-based remediation are not well understood. This study examined the effects of HAs originating from different places, including three commercial HAs and two soil HAs, on 2,4-dinitrotoluene (DNT) degraded by PS/Fe2+. DNT degradation by PS/Fe2+ was dependent on the types and concentrations of HAs and pH in solution. The positive correlation between the first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs and the conditional stability constant (KM) indicates that the complexation of HAs with Fe3+ was beneficial to the degradation of DNT. The first order kinetic rate constant of DNT degradation by PS/Fe2+/HAs correlated well with their absorbance intensity of HAs at 465 or 665 nm. High positive correlation coefficients indicated that π-electrons of HAs strongly influenced DNT degradation, which was consistent with the results provided by solid-state 13C NMR spectra. Two-dimensional correlation spectroscopy (2DCOS) analysis confirmed that the fulvic-like fraction of HAs is prior to the humic-like fraction complexed with Fe3+.