Catalytic ozonation of 2-isopropyl-3-methoxypyrazine in water by γ-AlOOH and γ-Al₂O₃: Comparison of removal efficiency and mechanism

Taste and odor (T&O) is a serious problem in drinking water. The T&O compound, 2-isopropyl-3-methoxypyrazine (IPMP), generates an earthy-musty odor in water. In this study, catalytic ozonation by γ-AlOOH (HAO) or γ-Al₂O₃ (RAO) was used as an effective method for removing IPMP in water. The comparative removal performance and reaction mechanism of IPMP in catalytic ozonation with different aluminum oxides was investigated. The removal of IPMP in neutral water pH by catalytic ozonation in the presence of HAO or RAO was 94.2% and 90.0%, respectively. Both HAO and RAO exhibited the good stability and a low leaching of aluminum ions. The effect of water pH and typical anion experiments indicated that surface hydroxyl group was key reaction sites for HAO but not for RAO. From results of tert-butyl alcohol inhibition, R_ct values and ozone consumption efficiency in catalytic ozonation, OH was generated in the solution in HAO catalytic ozonation or around the surface of catalyst in RAO reaction. The roles of oxidants, including ozone molecules and OH, were analyzed quantitatively, confirming that the surface hydroxyl group was key site for ozone decomposition to generate OH in solution in HAO catalytic ozonation. Ozone was adsorbed physically on the surface and concentrated ozone played an important role in IPMP removal in RAO catalytic ozonation. The nitrogen-containing IPMP intermediates generated in catalytic ozonation were determined quantitatively and qualitatively.