Efficiency of Ozone Quenching Agents at Different Temperature, pH, and Hydrodynamic Conditions

Quenching of excess aqueous ozone (O₃) residual is needed to avoid off-gassing and oxidative damage to downstream components. Eight quenching agents (QAs), calcium thiosulfate (Ca-Thio), sodium bisulfite (Na-Bi), hydrogen peroxide (H₂O₂), sodium thiosulfate (Na-Thio), sodium metabisulfite (Na-Metabi), potassium metabisulfite (K-Metabi), sodium sulfite (Na-S), and ascorbic acid (AscAcid) were tested at varying pHs (7.5, 7.9, and 8.5) and temperatures (4°C, 15°C, and 23°C). Temperature had significant effects on initial quenching (≤30 s), with less occurring at 4°C than 23°C; but with extended contact time this trend reversed. Quenching efficiency was not substantially affected by pH. Ca-Thio and Na-Thio were inefficient but quick, had lower mass requirements, and minimal handling concerns. Na-Metabi, Na-Bi, and Na-S were quick and efficient, but K-Metabi was the only QA that quenched (26–31%) less O₃ than stoichiometry at all conditions. These sulfite-based QAs had more handling concerns and greater mass requirements. H₂O₂ was slower than other QAs but 2–9× quicker than predicted by rate coefficients and efficient when given longer contact time (≤5 min). H₂O₂ had some handling concerns but the lowest mass requirements (assuming 5 min contact time) and creates desirable AOP conditions. AscAcid consistently quenched (22–113%) more O₃ than the stoichiometric ratio but had higher mass requirements, except in colder temperatures. Hydrodynamics, QA-diffuser design, and supply chain were also important considerations.