Degradation of N-nitrosodimethylamine (NDMA) in water by UV/O₃

Experiments were carried out under various conditions to study the effects of ozone dosage, solution pH and initial concentration of N-nitrosodimethylamine (NDMA) and humic acid on degradation of NDMA by UV/O₃. Results indicated that NDMA could be completely decomposed to form intermediates within 20 minutes. The degradation of NDMA by UV/O₃ was found to follow pseudo-first-order kinetics. Reaction rates of NDMA degradation did not fluctuate with pH increasing from acid to neutral but dramatically decreased in basic aqueous solution. NDMA initial concentration did not have an obvious effect on NDMA degradation. However, the presence of humic acid inhibited NDMA degradation. Methylamine (MA), dimethylamine (DMA), NO₂⁻ and NO₃⁻ were focused on as NDMA degradation intermediates. Degradation of NDMA by UV/O₃ promoted the conversion from DMA to MA and from NO₂⁻ to NO₃⁻, respectively. With the help of tert-butanol and sodium azide, both ¹O₂ and ∙OH were verified to be reactive species present in the process of NDMA degradation by UV/O₃. The mechanism of NDMA degradation by UV/O₃ was discussed based on the products detected in the present study and the previous literature. Several possible pathways of NDMA degradation were proposed.