Identification of hydroxyl and sulfate free radicals involved in the reaction of 1,4-dioxane with peroxone activated persulfate oxidant.

This research investigates the formation of free radical intermediates in an advanced oxidation processes (AOP) capable of destroying recalcitrant contaminants. The AOP studied is marketed as OxyZone® and relies on the premise of successful persulfate activation by peroxone (hydrogen peroxide plus ozone) and the formation of free radicals. The goal of this research was to determine which radicals are involved in the treatment of the model contaminant, 1,4-dioxane, which is a ubiquitous, recalcitrant organic groundwater pollutant difficult to destroy by conventional oxidants. In a parallel study, the peroxone activation persulfate (PAP) solution investigated herein rapidly degraded 1,4-dioxane. The degradation rates of 1,4-dioxane were measured as a function the oxidant:contaminant ratio. Its degradation products or mechanism were not investigated, however. Electron paramagnetic resonance (EPR) spectroscopy spin trapping was used to identify radicals produced in the oxidant solution, its active ingredients, and their possible interplay. The data presented herein indicate that the combination of hydrogen peroxide and dissolved ozone in the presence of persulfate results in the co-occurrence hydroxyl and sulfate radicals and possibly superoxide/hydroperoxyl radicals. These findings progress our understanding of the chemical radicals formed during PAP treatment of aqueous phase contaminants, such as 1,4-dioxane.