pH-Dependent Ozonation of 2,6-Dichloro-1,4-benzoquinone: Linking Oxidation Performance and Gas–Liquid Mass Transfer for Sustainable Water Treatment

This study evaluates the pH-dependent ozonation of 2,6-dichloro-1,4-benzoquinone to optimize sustainable oxidation strategies for water treatment. Experiments were conducted over a wide pH range under controlled temperature and ozone dosage. DCBQ was fully degraded within minutes following first-order kinetics, regardless of pH. Acidic to neutral systems experienced a progressive pH decrease due to the formation of oxygenated transformation products, whereas strongly alkaline conditions remained stable due to buffering effects. Aromaticity removal followed a second-order kinetic and increased with pH, reflecting enhanced aromatic ring cleavage under alkaline conditions. Color was rapidly eliminated for all tested pH values, while turbidity remained low at pH ≤ 10 but increased under extreme alkalinity due to colloidal aggregation. While previous studies have examined the influence of pH on ozone reaction pathways, its combined effect on ozonation performance and gas–liquid mass transfer remains largely unexplored. Dissolved ozone measurements enabled estimation of the gas–liquid mass transfer coefficient, which decreased linearly with increasing pH, revealing a direct coupling between pH-controlled ozone reactivity and transfer efficiency. Overall, pH 9–10 was identified as the optimal operational range, balancing effective aromaticity removal, ozone stability, and minimal turbidity, thus providing practical strategies for the treatment of chlorinated quinones in water.