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

• Published in: Environmental science & technology 2007-08, Vol.41 (16), p.5818-5823
• Main Authors: Landsman, Nicholas A, Swancutt, Katy L, Bradford, Christine N, Cox, Casandra R, Kiddle, James J, Mezyk, Stephen P
• Format: Article
• Language: English
• Subjects: Applied sciences; Biochemistry; Cobalt Radioisotopes; Drinking water and swimming-pool water. Desalination; Efficiency; Electrons; Environmental science; Exact sciences and technology; Free radicals; Free Radicals - chemistry; General purification processes; Hydrogen-Ion Concentration; Hydroxyl Radical; Kinetics; Nitrosamines - chemistry; Nitrosamines - isolation & purification; Nutrient removal; Oxidation; Oxidation-Reduction; Pollution; Wastewaters; Water; Water - chemistry; Water treatment and pollution
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es070275f

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 measure ments. 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 ln(k • 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) × 1010 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.