Diuron abatement using activated persulphate: Effect of pH, Fe(II) and oxidant dosage

The high oxidation efficiencies of the free radicals (SO4−), in combination with the slow rate of consumption of the oxidant, make this process very effective for the degradation of organic herbicides. Effects of pH, persulphate and Fe(II) concentration on the destruction of diuron by heat-assisted persulphate were examined in batch experiments. All the experiments were performed at 50 °C and an initial diuron concentration of 0.09 mM. The effectiveness of the process was evaluated based on the degradation of diuron and total organic carbon (TOC) removal. Under the reaction conditions, the diuron conversion is enormously influenced by the presence of Fe(II) in solution which rapidly produces the sulphate radical. Fe(II) concentration significantly accelerates diuron degradation at the first stages where the Fe(II) is oxidized to ferric iron. Increasing the persulphate concentration from 1 to 2.1 mM at natural pH accelerated the oxidation rate of diuron, which achieved 60% oxidation in 180 and 90 min, respectively. For the higher persulphate concentration (2.1 mM), complete diuron oxidation was achieved at 0.72 mM Fe(II) concentration in a few minutes. Additionally, diuron degradation by persulphate in bicarbonate-buffer solution was slower, most likely due to the presence of bicarbonate ions (radical scavengers).