Oxidative degradation of N-Nitrosopyrrolidine by the ozone/UV process: Kinetics and pathways

N-Nitrosopyrrolidine (NPYR) is an emerging contaminant in drinking water and wastewater. The degradation kinetics and mechanisms of NPYR degradation by the O-3/UV process were investigated and compared with those of UV direct photolysis and ozonation. A synergistic effect of ozone and UV was observed in the degradation of NPYR due to the accelerated production of OH center dot by ozone photolysis. This effect was more pronounced at higher ozone dosages. The second-order rate constants of NPYR reacting with OH center dot and ozone was determined to be 1.38 (+/- 0.05) x 10(9) M-1 s(-1) and 0.31 (+/- 0.02) M-1 respectively. The quantum yield by direct UV photolysis was 0.3 (+/- 0.01). An empirical model using Rct (the ratio of the exposure of OH center dot to that of ozone) was established for NPYR degradation in treated drinking water and showed that the contributions of direct UV photolysis and OH. oxidation on NPYR degradation were both significant. As the reaction proceeded, the contribution by OH center dot became less important due to the exhausting of ozone. Nitrate was the major product in the O-3/UV process by two possible pathways. One is through the cleavage of nitroso group to form NO center dot followed by hydrolysis, and the other is the oxidation of the intermediates of amines by ozonation. (C) 2015 Elsevier Ltd. All rights reserved.