Degradation of 1,2,3-trichloropropane by unactivated persulfate and the implications for groundwater remediation

Degradation of 15 halogenated hydrocarbons by 5 unactivated in-situ chemical oxidation oxidants

Oxidants used in the ISCO technology usually require activation by activators to degrade contaminants. However, this study investigated degradation of 15 typical halogenated hydrocarbons by five common ISCO oxidants (PS, PMS, H2O2, KMnO4, SPC) without activation in both pure water and real groundwater. Unactivated PS could degrade 14 halogenated hydrocarbons, excluding tetrachloromethane. Unactivated KMnO4 could degrade chlorinated alkenes. Unactivated SPC could degrade 1,1,2,2-tetrachloroethane by a base-promoted second-order elimination reaction. PMS, H2O2, and SPC could be activated by the natural matrix constituents in groundwater, enabling them to degrade some halogenated hydrocarbons. Among the 15 halogenated hydrocarbons studied, only tetrachloromethane cannot be degraded by any oxidant due to its carbon being in its highest oxidation state. The experimental data in the pure water indicate that the overall degradation rate of unactivated PS for chlorinated alkanes increased with increases in the number of chlorine substituents. The degradation rate of unactivated PS for halogenated hydrocarbons decreased with increases in the carbon chain length. Chlorinated alkenes are more easily degraded than chlorinated alkanes while chlorinated alkanes are more readily degraded than brominated alkanes. The degradation rate of unactivated KMnO4 for chlorinated alkenes decreased with increases in the number of chlorine substituents and decreased with increases in the carbon chain length. Overal, results of this study show that unactivated ISCO is a promising and environmentally friendly in-situ remediation technology that may be a good candidate for the remediation of contaminated sites by halogenated hydrocarbons.

Abiotic natural attenuation of 1,2,3-trichloropropane by natural magnetite under O2 perturbation

1,2,3-Trichloropropane (TCP) is an emerging groundwater pollutant, but there is a lack of reported studies on the abiotic natural attenuation of TCP by iron minerals. Furthermore, perturbation by O2 is common in the shallow subsurface by both natural and artificial processes. In this study, natural magnetite was selected as the reactive iron mineral to investigate its role in the degradation of TCP under O2 perturbation. The results indicated that the mineral structural Fe(II) on magnetite reacted with dissolved oxygen to generate O2-· and HO·. Both O2-· and HO· contributed to TCP degradation, with O2-· playing a more important role. After 56 days of reaction, 66.7% of TCP was completely dechlorinated. This study revealed that higher magnetite concentrations, smaller magnetite particle sizes, and lower initial TCP concentrations favored TCP degradation. The presence of <10 mg/L natural organic matter (NOM) did not affect TCP degradation. These findings significantly advance our understanding of the abiotic natural attenuation mechanisms facilitated by iron minerals under O2 perturbation, providing crucial insights for the study of natural attenuation.