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Comparison of Hydroxyl Radical Generation for Various Advanced Oxidation Combinations as Applied to Foundries

The authors monitored hydrogen peroxide (H2O2), ozone (O3), and apparent hydroxyl radical (OH·) concentrations in the liquid phase, along with gas phase ozone when operating an advanced oxidation (AO) system that included H2O2, O3, sonication, and underwater plasma (UWAP). The OH· radical converted non-fluorescent terephthalic acid to fluorescent hydroxyterephthalic acid (HTA). As determined from HTA formation, when a 500 ppm H2O2 dose in tap water was combined with O3 and sonication, nearly twice as much OH· (0.72 ppm) accumulated than with H2O2 alone. When UWAP accompanied H2O2, O3, and sonication, these together generated 15–35% more OH· than when UWAP was excluded. When ozone was introduced into this AO system, the AO system decomposed almost all the O3. This research has been conducted as a part of a study that has appraised this advanced oxidation system (Sonoperoxone) in green sand foundries, where it has diminished volatile organic compound (VOC) and hazardous air pollutant (HAP) emissions by 20–75%; and clay and coal consumption by 20–35%.