Characterization of Natural Organic Matter as Precursor for N-nitrosamines: Hydrophobicity, Molecular Weight and Fluorescence

Natural organic matter (NOM) in source water originated from Luan River and Yellow River, North China was isolated and fractionated with XAD resins and ultra-filtration membranes. The raw water samples and fractions were disinfected with sufficient monochloramine to determine their N-nitrosamines formation potentials. Fluorescence Excitation-Emission Matrix (EEM), molecular weight (MW), dissolved organic carbon (DOC), Specific Ultra-Violet Absorbance at 254nm (SUVA254), Ammonia, nitrate, nitrite, and dissolved organic nitrogen (DON) were also measured for the raw water and each fraction. The results showed that the hydrophilic fraction accounted for majority of NOM in these two raw water samples. The NOM fraction below 3k Da in the raw water samples from the Luan River and the Yellow River accounted for about 68% and 78% of the total DOC, respectively. The hydrophilic fraction showed much higher N-nitrosamines formation potentials than the corresponding hydrophobic in both samples. Meanwhile, the NOM fraction with MW below 1k Da had higher contribution to N-nitrosamines precursor than that with higher MW. It was observed that the much higher N-nitrosamines formation potential was related with the fractions with much lower DOC/DON ratio and much lower SUVA254 values. The EEM results were used to monitor changes of NOM composition before and after chloramination. However, it was very hard to establish the quantitative relationship between the change of EEM intensity and N-nitrosamines formation. In addition, The EEM results showed the notable existence of soluble microbial products like materials and aromatic proteins (BOD5), which indicated that the river water might have been contaminated by wastewater discharge. The professionals in the water treatment plants should care about the high risk of N-nitrosamines formation brought by wastewater discharge upstream.