Development of a Five-Chemical-Probe Method to Determine Multiple Radicals Simultaneously in Hydroxyl and Sulfate Radical-Mediated Advanced Oxidation Processes.

Advanced oxidation processes (AOPs), such as hydroxyl radical (HO • )- and sulfate radical (SO 4 •- )-mediated oxidation, are attractive technologies used in water and wastewater treatments. To evaluate the treatment efficiencies of AOPs, monitoring the primary radicals (HO • and SO 4 •- ) as well as the secondary radicals generated from the reaction of HO • /SO 4 •- with water matrices is necessary. Therefore, we developed a novel chemical probe method to examine five key radicals simultaneously, including HO • , SO 4 •- , Cl • , Cl 2 •- , and CO 3 •- . Five probes, including nitrobenzene, para -chlorobenzoic acid, benzoic acid, 2,4,6-trimethylbenzoic acid, and 2,4,6-trimethylphenol, were selected in this study. Their bimolecular reaction rate constants with diverse radicals were first calibrated under the same conditions to minimize systematic errors. Three typical AOPs (UV/H 2 O 2 , UV/S 2 O 8 2- , and UV/HSO 5 - ) were tested to obtain the radical steady-state concentrations. The effects of dissolved organic matter, Br - , and the probe concentration were inspected. Our results suggest that the five-probe method can accurately measure radicals in the HO • - and SO 4 •- -mediated AOPs when the concentration of Br - and DOM are less than 4.0 μM and 15 mg C L -1 , respectively. Overall, the five-probe method is a practical and easily accessible method to determine multiple radicals simultaneously.