Free Radical Chemistry of Advanced Oxidation Process Removal of Nitrosamines in Water

Abstract

Absolute rate constants and degradation efficiencies for hydroxyl radical reactions with seven low-molecular-weight nitrosamines in water have been evaluated using a combination of electron-pulse radiolysis/absorption spectroscopy and steady-state radiolysis/GCMS measurements. The hydroxyl radical oxidation rate constants were found to depend upon nitrosamine size and to have a very good linear correlation with the number of methylene groups in these compounds. This correlation, given by In(k x OH) = (19.72 +/- 0.14) + (0.424 +/- 0.033) (#CH2), suggests that hydroxyl radical oxidation predominantly occurs by hydrogen atom abstraction from constituent methylene groups in each of these nitrosamines. In contrast, the hydrated electron reduction rate constants measured for these compounds were remarkably consistent, with an average value of (1.67 +/- 0.22) x 10(10) M(-1) s(-1). These reduction kinetic data are consistent with this predominantly diffusion-controlled reaction occurring at the N-NO moiety in these carcinogens. From steady-state radiolysis measurements under aerated conditions, specific hydroxyl radical degradation efficiencies for each nitrosamine were evaluated. For larger nitrosamines, the efficiency was constant at 100%; however, for the smaller alkyl substituted species, the efficiency was significantly lower, with a minimum value of only 80% determined for N-nitrosodimethylamine. The reduced efficiency is attributed to radical repair reactions competing with the slow peroxyl radical formation.

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

“…S2 shows the ratio of the reaction rate constants of NPYR and pCBA with OH using the relative rate methodology. The ratio of k OH,NPYR /k OH,pCBA was 0.276, and thus k OH,NPYR was calculated to be 1.38 (± 0.05) Â 10 9 M À1 s À1 , which was comparable to the literature value of 1.75 (± 0.07) Â 10 9 M À1 s À1 obtained by pulse radiolysis (Landsman et al, 2007). In summary, Table 1 compares the molar absorptivities, quantum yields, rate constants of NPYR and NDMA reacting with OH, ozone and quantum yields by the direct photolysis at 254 nm.…”

“…For example, photodecomposition, advanced oxidation (e.g. O 3 /H 2 O 2 , UV/H 2 O 2 , UV/TiO 2 ), reverse osmosis and chemical reduction processes have been considered and verified being capable of removing nitrosamines from water efficiently (Gui et al, 2000;Stefan and Bolton, 2002;Sharpless and Linden, 2003;Mezyk et al, 2004;Lee et al, 2005aLee et al, , 2005bDavie et al, 2006;Landsman et al, 2007;Lee et al, 2007;Plumlee and Reinhard, 2007;Frierdich et al, 2008;Zhou et al, 2012;Mestankova et al, 2014). In addition to its wide application as a mean for disinfection, UV irradiation is an effective process to decompose nitrosamines including NDMA and NPYR (Stefan and Bolton, 2002;Lee et al, 2005a;Xu et al, 2009).…”

“…Hydrogen abstraction was found as the first step of NDMA oxidation by OH, followed by the release of the NO group and the formation of methylamine (MA), nitrite (NO 2 e ) and nitrate (NO 3 e ) (Lee et al, 2007). The rate constant of NPYR reacting with OH produced from linear accelerator electron-pulse radiolysis has been reported 2-time higher than that of NDMA with OH (Landsman et al, 2007). We therefore hypothesized that the simultaneous exposure to UV and ozone (hereafter referred to as the O 3 /UV process) might be more effective than to UV irradiation only in degrading NPYR, in which process NPYR can be degraded by both UV and OH.…”

Occurrences of nitrosamines in chlorinated and chloraminated drinking water in three representative cities, China

“…Several alternative disinfectants such as O 3 are able to produce nitrosamines, but usually at lower concentrations than chloramines (Najm and Trussell, 2001;Andrzejewski et al, 2008). In contrast, UV and advanced oxidation processes have both been investigated as possible strategies to decrease or eliminate nitrosamine in water (Stefan and Bolton, 2002;Lee et al, 2005;Landsman et al, 2007). In fact, NDMA levels of P5 decreased to 3.5 ng/L in finished water after LPUV/OCl − treatment.…”

Photodegradation of N-nitrosodiethylamine in water with UV irradiation

“…Landsman et al [25] evaluated the absolute rate constants and degradation efficiencies for hydroxyl radical reactions with seven low-molecular-weight nitrosamines by using the combination of electron-pulse radiolysis/absorption spectroscopy and steady-state radiolysis/GC-MS measurement. The removal rate of NDEA by hydroxyl radicals was (86.0±3.3)%, and the reaction rate constants of NDEA with hydroxyl radicals and hydrated electrons were (6.99±0.28)×10 8 (mol·L −1 ) −1 ·s −1 and (1.61±0.12)×10 10 (mol·L −1 ) −1 ·s −1 , respectively.…”