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 (•OH) and sulfate radical (•SO) 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 (•OH and •SO) and OPEs. This issue was solved by selecting three OPEs as model compounds, the oxidation of these OPEs in UV/HO and UV/KSO 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/HO and UV/KSO processes easily, the oxidation rates increased with increasing HO and KSO dosage. The oxidation rates of three OPEs have been studied using competition experiments in the UV/HO and UV/KSO processes. The bimolecular reaction rate constants of TCEP, TCPP and TDCPP with •OH were 2.50 × 10, 3.95 × 10 and 2.94 × 10 respectively; while •SO were 3.00 × 10, 1.82 × 10 and 2.06 × 10 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.