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±0.8kJmol^-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 (k_obs=0.18min^-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.