Removal of multiple nitrosamines from aqueous solution by nanoscale zero-valent iron supported on granular activated carbon: Influencing factors and reaction mechanism

Due to their significant absorption and reduction abilities, nanoscale zero-valent iron (nZVI)/granular activated carbon (GAC) composites are very effective for the degradation of organic contaminants and heavy metals. However, to date, there is no systematic study on the applicability of nZVI/GAC for the removal of multiple highly toxic nitrosamines from water supplies. For this study, nZVI/GAC was synthesized and applied to the degradation of multiple nitrosamines. The effects of initial nitrosamine concentration, composite dosage, contact duration, competition with coexistent elements, and reaction mechanisms during the nitrosamine removal process from aqueous solutions were investigated. Compared with bare nZVI and GAC, the removal rates of six nitrosamines via nZVI/GAC were initially very rapid. The highest removal ratios of the six nitrosamines were 76.1% (N-nitrosodimethylamine, NDMA), 84.7% (N-nitrosomethylethylamine, NMEA), 89.8% (N-nitrosodiethylamine, NDEA), 93.5% (N-nitrosodi-n-propylamine, NDPA), 95.7% (N-nitrosodi-n-butylamine, NDBA), and 80.4% (N-nitrosomorpholine, NMor). The nitrosamine degradation kinetics data agreed well with the pseudo-second-order model (R-2(2) > 0.99), the rate constant k(2) for nitrosamine (200 ng/L) removal by nZVI/GAC increased in the order of NDBA (0.3675) > NDPA (0.0254) > NMEA (0.0109) > NDEA (0.0105) > NDMA (0.0101) > NMor (0.0077). In the presence of cations, anions, and humic acid (HA) the removal of the six nitrosamines was inhibited at each concentration. Furthermore, the removal ratios and K-2 of the five linear nitrosamines by nZVI/GAC partially scaled with structure, LogK(ow), and Henry's constant, particularly between K-2 and these properties (R-2 > 0.80). The reaction mechanism revealed that nitrosamines were adsorbed by GAC and then reduced by Fe-0, where the reductive products were primarily secondary amines, nitrate, and nitrite. This study serves to improve our understanding, and further characterizes the removal of multiple nitrosamines by nZVI/GAC. (c) 2018 Elsevier B.V. All rights reserved.