Enhancing the degradation of 2,4-dinitrotoluene using zero-valent magnesium in the presence of persulfate and hydrogen peroxide

Abstract

The degradation of 2,4-dinitrotoluene (DNT) by persulfate and hydrogen peroxide in the presence of zero-valent magnesium (Mg(0)) was examined in a series of batch experiments. The degradation of DNT by Mg(0) alone was limited to 32 % after 24 h due to the rapid oxidation of Mg(0) and the formation of a passivation layer in the presence of oxygen. However, the combination of Mg(0) with persulfate or hydrogen peroxide greatly enhanced the degradation of DNT to 65 % and 90 % after 24 h, respectively. Quenching experiments with radical scavengers and electron paramagnetic resonance spectroscopy analysis showed that sulfate (SO₄⁻·) and hydroxyl (OH·) radicals were responsible for the enhancement of DNT degradation in the Mg(0)-persulfate/hydrogen peroxide systems. Analyses of total organic carbon and 5-day biochemical oxygen demand revealed that non-mineralized by-products remained in the systems and that the biodegradability of the non-mineralized by-products was significantly enhanced. To further enhance the degradation of DNT using the Mg(0)–persulfate/hydrogen peroxide systems, stepwise dosing of Mg(0) was employed, leading to DNT degradation rates of 83 % and 77 % after 2.5 h with persulfate and hydrogen peroxide, respectively. Co-catalysis of Mg(0) with Fe(0) also significantly improved the DNT degradation in the persulfate/hydrogen peroxide systems, with the complete degradation of DNT after 4 h. The sonication of Mg(0) also led to the complete degradation of DNT after 2 and 3 h with persulfate and hydrogen peroxide, respectively. Our results suggest that Mg(0) is a promising reductant and an effective catalyst for the degradation of DNT in persulfate/hydrogen peroxide systems.