Comparative study about oxidation of trace N-nitrosamines by seven oxidation processes with a sensitivity improved determination method

Abstract

N-nitrosamines are highly toxic disinfection byproducts (DBPs) formed in drinking water treatment process. Moreover, they could permeate reverse osmosis (RO) membrane during water recycling. Herein, an improved detection method for simultaneously determining 9 N-nitrosamines was established, and 7 kinds of oxidation processes were examined for degradation of the 9 N-nitrosamines. Compared with conventional injection mode, pulsed injection technique improved signal to noise ratio (SNR) and peak area of N-nitrosodimethylamine (NDMA) by 2.1 and 3.77 times, respectively. Low method detection limits (MDLs) were achieved ranging from 0.3 to 1.5 ng/L. Based on the improved detection method, simultaneous oxidation of 9 N-nitrosamines with UV irradiation/UV based advanced oxidation processes (AOPs), O3/O3 based AOP, and permanganate and ferrate were comparatively investigated. Among these employed processes, O3/H2O2 was the most effective approach for the elimination of N-nitrosamines, and 36.6% (NDMA)-91.4% (NDBA) removal efficiency was achieved. In comparison, ozonation merely removed less than 20% of N-nitrosamines (except NDphA for 29.3%). Compared to UV irradiation, the removal efficiency of N-nitrosamines was improved by almost 10% in UV/Cl2 process, while the improvement in UV/peroxydisulfate (UV/PDS) process was not obvious. Permanganate and ferrate oxidations on N-nitrosamines removal were not significant. NDMA was found to be one of the most recalcitrant N-nitrosamines, therefore, it could be monitored as an indicator of N-nitrosamines in relevant treatment process. Finally, the risk of N-nitrosamines re-formation was found to be negligible when chloramination was applied after oxidation treatment.