Kinetic study of diuron oxidation and mineralization by persulphate: Effects of temperature, oxidant concentration and iron dosage method

Abstract

The elimination of pesticides by persulphate activated with Fe 2+ showed high oxidation rates due to the oxidation effectiveness of persulphate free radicals (SO 4 −). Effects of iron addition policy, reaction temperature and persulphate concentration were studied employing diuron as target pollutant. Different amounts of Fe 2+ (from 5 to 86 mg) were used, either adding this iron source at the beginning of the reaction or continuously feeding Fe 2+ for 30, 60 and 120 min. The effect of persulphate concentration was studied at 500 and 735 mg/L. Reactions were carried out at 20 and 50 °C with an initial diuron concentration of 20 mg/L. The effectiveness of the process was evaluated based on the degradation of diuron and total organic carbon (TOC) removal. Not only the total amount of Fe 2+ used but also the mode of addition of this activator seemed to have big influence on diuron oxidation and mineralization. An increase of the temperature improved the oxidation and mineralization rate. Using stoichiometric amounts of persulphate and iron complete diuron removal and 64% of TOC conversion were achieved at 50 °C by continuously adding the iron solution. A kinetic model capable of describing diuron oxidation and mineralization was proposed and successfully validated. Finally, diuron degradation by persulphate was lower if radical scavengers, as carbonate ions (500 mg/L NaHCO 3), are present in the media.