The Decomposition Kinetics of Monocrotophos in Aqueous Solutions by the Hydrogen Peroxide–Ozone Process

Abstract

Decomposition of monocrotophos in an aqueous solution by the hydrogen peroxide–ozone (H2O2–O3) process was studied under various solution pHs and H2O2–O3) molar ratios. Experimental results indicated that monocrotophos could be almost completely (>95%) decomposed by the H2O2–O3) process within 20 minutes. Formation of carbon dioxide was observed, followed by the formation of nitrate and phosphate. A simplified kinetic model, consisting of three two‐step consecutive reactions based on elemental mass balances, was found to accurately describe the temporal behaviors of reacting species during the decomposition of monocrotophos in aqueous solution by the H2O2–O3) process. In most experiments, acidic conditions favored the disappearance of monocrotophos, possibly because of breakage of the carbon–carbon double bond to form various organic intermediates, but mineralization of organic intermediates by free radical hydroxyl (OH·) attack was more favored in alkaline conditions. The decomposition of monocrotophos by the H2O2–O3) process was found to be significantly affected by the mode of H2O2 addition. For the batch mode of H2O2 addition, increased H2O2 dose reduced the decomposition rate, possibly because large amounts of H2O2 added initially served as a scavenger for OH· free radicals. For the continuous mode of H2O2 addition, increased H2O2 dose accelerated reaction rates of monocrotophos until an optimum H2O2–O3) molar ratio was reached, which was found to vary for different solution pHs.