The long-term effect of Fe3O4 in activating persulfate to degrade refractory organic contaminants for groundwater remediation

Highly reactive metal-based materials for persulfate activation have been intensively studied for treatment of groundwater contaminants. However, the long-term efficacy of the readily available metal-oxide additives, which can be more important for groundwater remediation practice, has received minimal attention. In this study, the results of preliminary experiments demonstrated that Fe3O4 was superior to seven metal oxides (MnO, Fe2O3, MnO2, CuO, Cu2O, CoO, NiO) and zero-valent iron for activating persulfate to degrade 1,2-dichloropropane. Experiments were then conducted to examine the long-term effects of Fe3O4-activated persulfate degradation of four contaminants, i.e., 1,2-dichloropropane, 1,1,2-trichloroethane, 1,4-dioxane, and methyl tert-butyl ether (MTBE). The system achieved complete removal of the contaminants in approximately 72 h, which was contrasted to a removal efficiency less than 35 % in the absence of Fe3O4. Highly efficient use of persulfate for contaminant degradation was observed with insignificant production of soluble Fe before depletion of the contaminants. Production of sulfate radical (SO4•−) and hydroxyl radical (HO•) via surface reactions was likely the process responsible for the degradation. Ten and five cycles of 1,2-dichloropropane degradation experiments were conducted in deionized water and actual groundwater. These results suggested that the Fe3O4 could retain 80 % of its original activation capacity after 5 cycles, but partial oxidation of Fe3O4 eventually occurred. Production of some Cl-containing degradation-resistant intermediates from degradation of 1,2-DCP was observed and could be mitigated under specific conditions. The results show that Fe3O4 has a long-term effect in activating persulfate for contaminant degradation, which is promising for applications such as permeable reactive barriers and nanoparticle injection for groundwater remediation.