Daminozide (DMNZD) has been found to be an important ozone-reactive N-nitrosodimethylamine (NDMA) precursor; however, the influence of humic acid (HA) on NDMA formation from daminozide during ozonation is unclear. In this study, the impacts of HA on NDMA formation from daminozide at various oxidation conditions (ozone dosages, pH) and other water components (bicarbonate ion (HCO3−), sulfate ion (SO42−)) were investigated. In addition, its implications for water treatment plants are discussed. The results indicated that low levels of HA (≤0.6 mg L−1) facilitated NDMA formation and its molar yield was maximized at 0.1 mg L−1 HA (8.5%), while a high concentration of HA (>0.6 mg L−1) had an inhibition role. The NDMA amount increased with increasing pH and showed a peak at pH 8. With 0.1 mg L−1 HA, NDMA was raised from 3.0% to 23.1% with ozone increasing from 0.5 to 4 mg L−1; HCO3− competed with daminozide for ozone and cut down NDMA formation, whereby 160 μM HCO3− reduced NDMA conversion from 8.5% to 6.5%; however, with the increase in SO42− from 0 to 20 μM, NDMA conversion was augmented from 8.5% to 17.8%. Based on the results of LC/MS/MS and GC/MS analyses, NDMA transformation pathways with/without HA are proposed.
Removal of chlorpheniramine in a nanoscale zero-valent iron (nZVI) induced heterogeneous Fenton system was investigated. The removal efficiency of chlorpheniramine depended on its initial concentration, initial pH, H 2 O 2 concentration and nZVI dose. Chlorpheniramine (⩽15 mg/L) was completely removed after 60 min oxidation under the following optimal conditions: initial pH = 3.0, H 2 O 2 concentration = 0.1 mM and nZVI dose = 22.4 mg/L. The degradation of chlorpheniramine fitted well with the pseudo first-order kinetics model, and the rate constants ( k obs ) were obtained ( R 2 > 0.9). Several degradation intermediates of chlorpheniramine were detected and confirmed, including 4-hydroxy-4-methyl-2-pentanone, 2-methylaminopyridine, 4-chlorophenol, 2-propionylpyridine, 2-acetylpyridine, 4-chlorophenyl-2-pyridyl ketone, dimethylamine (DMA) and N-nitrosodimethylamine (NDMA). Based on the identified intermediates, a tentative degradation pathway of chlorpheniramine in the nZVI/H 2 O 2 system was proposed. After nZVI/H 2 O 2 reaction, 52.2% of NDMA formation potential (FP) from chlorpheniramine was reduced. Therefore, nZVI as the catalyst used in the heterogeneous Fenton system is not only an alternative to remove chlorpheniramine, but also effective in reducing NDMA FP.
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