Heat-activated persulfate oxidation of diuron in water

Heat-activated persulfate oxidation of diuron, a commonly found herbicide in groundwater, was evaluated in this study. Sulfate radicals SO4- was the principal oxidizing agent responsible for the diuron degradation. The diuron decomposition exhibited a pseudo-first-order kinetics pattern at all the conditions tested. The observed rate constants determined at 50–70 °C well fit the Arrhenius equation, yielding an activation energy of 166.7 ± 0.8 kJ mol−1. Temperature, persulfate dose, initial diuron concentration, pH, and three common groundwater solutes (CO32-,HCO3-, and Cl−), to different degrees, influenced the degradation. Typically, high temperature, high persulfate dose, and low initial diuron concentration increased the decomposition rate of diuron. At the tested pH range of 5.5–8.1, the highest degradation rate (kobs = 0.18 min−1) occurred at pH 6.3. The three groundwater anions inhibited the diuron decomposition with the following order: CO32->HCO3->Cl-. The major oxidation products in this study were C15H15ON3Cl4 (P3, m/z = 376.2), C16H16O4N3Cl4 (P4, m/z = 420.3), and C17H17O7N3Cl4 (P5, m/z = 465.4), different from those produced during hydroxyl radical-induced advanced oxidation. The in situ chemical oxidation (ISCO) technology can be achieved in practice through combination with in situ thermal remediation.