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N‑Nitrosodimethylamine (NDMA) Degradation by the Ultraviolet/Peroxodisulfate Process

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journal contribution
posted on 10.01.2019, 00:00 by Inmaculada Velo-Gala, María J. Farré, Jelena Radjenovic, Wolfgang Gernjak
This study investigates the photodegradation kinetics of N-nitrosodimethylamine (NDMA) by the ultraviolet (UV)/S2O82– process initiated by a medium-pressure mercury lamp in a collimated beam setup. Experiments were carried out to characterize the kinetics in the absence and presence of bicarbonate, chloride, and sulfate. The kinetic behavior adjusted well to first-order dependence, and the addition of 33.6 μM S2O82– increased the NDMA removal rate by 3–4 times compared to direct photolysis leading to a reduction of 1 order of magnitude for every 8.2 × 103 J m–2 of fluence. In the range investigated, the reaction rate increased linearly with peroxodisulfate concentration. The presence of inorganic carbon and chloride can negatively affect the efficiency of both the UV/S2O82– process and the conventional UV/H2O2 process, yet given that the reaction rate constants of Cl and HCO3 with the OH radical are 1 and 3 orders of magnitude higher, respectively, than with SO4•–, their scavenging effect is less pronounced in the UV/S2O82– process. In conclusion, the UV/S2O82– process efficiently removes NDMA from water even containing a low concentration of HCO3 and Cl anions such as reverse osmosis permeates.