Novel insights into the control of N-nitrosodimethylamine (NDMA) and bromate formation during heterogeneous catalytic ozonation

N-nitrosodimethylamine (NDMA) and bromate (BrO₃^-) have been found to be disinfection by-products during ozonation, which need to be solved urgently. In this study, O₃/Al₂O₃, O₃/MnOx/Al₂O₃ and O₃/β-FeOOH/Al₂O₃ were used to investigate the control of NDMA and BrO₃^- formation during the ozonation of daminozide (DMZ) and Br^-. During ozonation alone, NDMA formation decreased from 0.66 to 0.37 μM with increasing ozone dosages (20–100 μM) without tert-butanol (TBA). Greater control efficiency for NDMA formation was observed during the O₃/Al₂O₃ process (0.55–0.21 μM), which was attributed to the high hydroxyl radical (•OH) yield, and NDMA formation during the O₃/MnOx/Al₂O₃ and O₃/β-FeOOH/Al₂O₃ processes changed negligibly (∼0.63 and ∼ 0.65 μM, respectively). The formation of NDMA was affected by different concentrations of Br^-, HCO₃^–, tannic acid, and humic acid, which was attributed to the competition for ozone or •OH. During ozonation process, the addition of catalysts could effectively control BrO₃^- formation due to the decomposition of HOBr and the adsorption or reduction of BrO₃^- by catalysts. The control efficiencies of BrO₃^- formation were in the order of O₃/β-FeOOH/Al₂O₃ > O₃/MnOx/Al₂O₃ > O₃/Al₂O₃ > ozonation alone. In a real water sample without Br^-, significant control of NDMA was observed in the presence of the catalysts. In a real water sample containing Br^-, NDMA formation decreased in the presence and absence of catalysts, and a great control capacity for BrO₃^- formation was exhibited during the O₃/Al₂O₃, O₃/MnOx/Al₂O₃ and O₃/β-FeOOH/Al₂O₃ processes. Therefore, the addition of catalysts can be utilized to control disinfection by-products during ozonation.