Factors affecting N-nitrosodimethylamine formation from poly(diallyldimethyl-ammonium chloride) degradation during chloramination.

Siying Tan,Xiaoyu Li,Qiuhong Yuan,Shaojie Jiang

doi:10.1098/rsos.180025

Siying Tan, Xiaoyu Li + Show 2 more

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https://doi.org/10.1098/rsos.180025

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Abstract

Poly(diallyldimethylammonium chloride) (polyDADMAC) has been shown to be an important precursor of the probable human carcinogen N-nitrosodimethylamine (NDMA) when in contact with chloramine. In this study, we conducted an orthogonal experiment design to evaluate the effects of pH values, ammonia, bromide, natural organic matter (NOM) and monochloramine dosages on the formation of NDMA from polyDADMAC during chloramination. Meanwhile, single-factor experiments of pH, bromide and NOM prove the results of orthogonal experiment. The results supported that pH was the most critical factor affecting NDMA formation from polyDADMAC during chloramination, and the highest NDMA formation from polyDADMAC occurred at pH near 7 due to released DMA from polyDADMAC degradation and the critical importance of low concentrations of dichloramine in water. In the presence of excess bromide, the NDMA formation was enhanced significantly at all different pH values owing to bromochloramine, which has higher electronegativity of the brominated nitrogen atom than monochloramine or dichloramine. The NDMA formation from polyDADMAC in the presence of NOM was 41.7% lower than NDMA formation in the absence of NOM. The overwhelming majority of NDMA formation from polyDADMAC under simulated conditions was lower than the current advisory levels (i.e. 9 ng l−1 in Ontario, 10 ng l−1 in California).

Highlights

N-nitrosodimethylamine (NDMA), one of emerging nitrogenous disinfection by-products [1,2,3], has generated significant concern due to its high probable human carcinogenesis [4,5]
In the presence of natural organic matter (NOM), NDMA formation was less than in the absence of NOM, whereas residual DMA concentration stayed constant, which was consistent with the results of orthogonal experiments. These results indicate that the presence of NOM did not affect DMA released from polymer-bound tertiary amines and polymer-bound quaternary ammonium groups of polyDADMAC solution, but hindered the reaction between DMA and NHCl2 to form NDMA
The NDMA formation of polyDADMAC increased with bromide ion concentration, and the presence of bromide enhanced NDMA formation at all pH values due to the formation of a more reactive component, NHBrCl

Summary

Introduction

N-nitrosodimethylamine (NDMA), one of emerging nitrogenous disinfection by-products [1,2,3], has generated significant concern due to its high probable human carcinogenesis [4,5]. Owing to the significant health risk of NDMA, previous researches have been conducted in recent years to identify the precursors and formation mechanisms during the process of disinfection. Among NDMA potential precursors, anime-based water treatment polymers, such as poly(epichlorohydrin dimethylamine) (polyamine), poly(diallyldimethylammonium chloride) (polyDADMAC) and cationic polyacrylamide, have received considerable attention due to their usage in water and wastewater treatment [11,12,13,14,15]. Zeng et al [17] classified the precursors of NDMA from untreated polyDADMAC into three pools, free secondary or tertiary amines, polymer-bound tertiary amines and polymer-bound quaternary ammonium groups serving as the intended functional groups within polymers, and their average contributions of NDMA formation were 16 ± 2%, 25 ± 5%, and 57 ± 11%, respectively

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