Ozonation and peroxone oxidation of benzophenone-3 in water: Effect of operational parameters and identification of intermediate products

The goal of this study was to bring forward new data and insights with respect to the effect of operational variables and reaction pathways during ozonation and peroxone oxidation of the UV filter compound benzophenone-3 (BP3) in water. A systematic parameter study, investigating the effect of the ozone inlet concentration, temperature, pH, H2O2 and t-butanol addition in a lab-scale bubble reactor, showed the promising potential of ozonation towards BP3 degradation. pH showed to be a major process parameter, with half-life times (5.1–15.0 min) being more than two times shorter at pH 10 compared to neutral and acid conditions. This indicates the important role of hydroxyl radicals as supported by the addition of H2O2 and t-butanol as HO· promoter and scavenger, respectively. Ozonation intermediate products were identified by liquid chromatography coupled to quadrupole-time-of-flight mass spectrometry (HPLC–QqTOF-MS/MS). Demethylation and non-selective HO· attack proved to be the major reaction mechanisms. Where available, identified intermediates were confirmed using analytical standards, and concentration profiles along the ozonation process were determined through selective targeted MS/MS analysis. Benzophenone-1 (BP1), also being a UV-filter compound, and 2,2′-dihydroxy-4-methoxybenzophenone (DHMB) revealed to be the major BP3 degradation products, showing a maximum concentration at about the half-life time of BP3. Highlights: ► Ozonation shows to be a promising technology for the elimination of BP3. ► New data are obtained on the effect of process parameters on BP3 removal. ► Conditions favoring hydroxyl radical formation accelerate the degradation process. ► The reactivity is higher through radicalar pathways compared to direct ozonation. ► Seven major transformation products of BP3, including BP1 and DHMB, are identified