Reduction of N-Nitrosodimethylamine with zero-valent zinc

Abstract

N-Nitrosodimethylamine (NDMA) is known as the disinfection by-product and the pollutant in the source water. Reduction with zero-valent zinc (Zn(0)) was investigated as a potential technology to treat NDMA. The results showed that Zn(0) was effective for NDMA reduction at initial pH 7.0. There were lag period and rapid period during the process, the corresponding zero-order rate constant (kzero) was 2.968 ± 0.245 μg L−1 h−1 ([Zn(0)]0 = 10g L−1),the mass normalized pseudo-first-order rate (kM) was 0.1215 ± 0.0171 L g−1 h−1. The reactivity of zinc on NDMA removal was consistent with the zinc corrosion rate. NDMA had little effect on the corrosion of zinc. Lower solution pH benefited the reduction of NDMA with Zn(0). The consumption of the oxygen and the localized acidification should be the cause of the shift from lag to rapid reaction period in the aerobic experiments. 1,1-dimethylhydrazine (unsymmetrical dimethylhydrazine, UDMH), dimethylamine (DMA) were detected as the products of NDMA degradation. The nitrogen mass balance at 24 h was 56%, the loss can be due to the formation of ammonium, the degradation of UDMH and other unmeasured products. DMA formed during the degradation of UDMH with Zn(0), the nitrogen loss could be caused by the formation of unmeasured products. Catalytic hydrogenation is proposed to be the mechanism based on the results and the redox properties of zinc and NDMA. One reduction process is: the active hydrogen atoms initially cleave and reduce the N=O bond in NDMA, generating UDMH. Then the N–N bond in UDMH is cleaved to form DMA and ammonium.