Longevity of iron-activated persulfate oxidation for the remediation of 2,4-dinitrotoluene-contaminated groundwater

To evaluate the longevity of the iron-activated persulfate (PS) oxidation degradation of 2,4-dinitrotoluene (2,4-DNT), zero-valent iron (ZVI), and three different micron-scale iron oxides were used as catalysts for the activation of PS. It was revealed that 2,4-DNT was degraded more effectively by ZVI and maghemite (γ-Fe₂O₃) compared to that of hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) catalyst treatments. Denitration of 2,4-DNT and oxidation of nitro groups as nitrate occurred by Fe⁰/PS and γ-Fe₂O₃/PS. When the 2,4-DNT removal rate was 1%, the generated sulfate concentrations of Fe⁰/PS and γ-Fe₂O₃/PS were 2.08 mg/L and 1.27 mg/L, respectively. Only micron scale γ-Fe₂O₃ could activate PS for 2,4-DNT removal. ZVI was cycled and able to activate PS through multiple rounds. The size of the corrosion products of ZVI was more than 100 nm, and the particle size gradually increased in the cycling process. The first cycle of Fe⁰ resulted in 45% removal of 2,4-DNT in 360 min. The 2,4-DNT removal efficiency (68.15%) increased after the second cycle, reaching the best removal efficiency in the fourth cycle. Oxidation products formed during degradation covered the ZVI surface, forming a shell. Adsorption of organic pollutants to this shell aids in the removal efficiency of 2,4-DNT and longevity of ZVI in groundwater.