Rate constants for the reaction of hydroxyl and sulfate radicals with organophosphorus esters (OPEs) determined by competition method

Advanced oxidation processes (AOPs), such as hydroxyl radical (center dot OH) and sulfate radical (center dot SO4) mediated oxidation, are proved to be effective methods to remove the organophosphorus esters (OPEs) in wastewater effluents. However, few studies have reported about the bimolecular reaction rate constants between free radicals (center dot OH and center dot SO4) and OPEs. This issue was solved by selecting three OPEs as model compounds, the oxidation of these OPEs in UV/H2O2 and UV/K2S2O8 process were studied. Tris(2-chloroethyl) phosphate (TCEP), tris(1-chloro-2-propyl) phosphate (TCPP), and tris(2,3-dichloropropyl) phosphate (TDCPP) can hardly be oxidized through direct irradiation methods using UV lamp, with the oxidation rate less than 30% after 7 h' irradiation. However, TCEP, TCPP, and TDCPP undergo degradation via UV/H2O2 and UV/K2S2O8 processes easily, the oxidation rates increased with increasing H2O2 and K2S2O8 dosage. The oxidation rates of three OPEs have been studied using competition experiments in the UV/H2O2 and UV/K2S2O8 processes. The bimolecular reaction rate constants of TCEP, TCPP and TDCPP with center dot OH were 2.50 x 10(10), 3.95 x 10(10 )and 2.94 x 10(10) respectively; while center dot SO(4 )were 3.00 x 10(7), 1.82 x 10(7) and 2.06 x 10(7) respectively. Results showed that the simplified kinetic model involves only steady state concentration of free radicals and the molecular reaction rate contents are available for calculating the oxidation rates of OPEs in ultrapure water.