Formation potential of N-nitrosamines during the disinfection of treated wastewaters with sodium hypochlorite

This study investigated the formation of eight N-nitrosamines (N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA), N-nitrosomorpholine (NMOR), 1-nitrosopyrrolidine (NPYR), 1-nitrosopiperidine (NPIP), and N-nitrosodibutylamine (NDBA)) after the chlorination (with NaOCl) of wastewater effluents from two wastewater treatment plants (WWTPs) located in North East Spain. Two different WWTPs, one with nitrification-denitrification process (CB1) and the other without (CB2) have been chosen. The concentrations of individual N-nitrosamines in non-chlorinated tertiary treated wastewater effluents ranged from <LOD to 75 ng L-1. That range increases to 114 and 1092 ng L-1 after chlorinating tertiary-treated wastewater samples at 5 and 15 mg L-1 of free chlorine, respectively. NDEA and NMEA are the most abundant compounds in both non-chlorinated and chlorinated secondary and tertiary-treated wastewater effluents. The disinfection of tertiary treated wastewater at 5 mg L-1 of free chlorine gave a total N-nitrosamines concentration of about 300 ng L-1 in samples from the two studied WWTPs. Total N-nitrosamine concentrations in chlorinated secondary treated wastewater samples were significantly higher than those obtained from the chlorination of tertiary treated wastewaters (p < 0.05). This may be due to the capacity of the tertiary treatment processes for removing N-nitrosamines precursors. The experiments have revealed that in addition to NDMA, relatively high concentrations of other N-nitrosamines are produced when treated wastewater effluents are disinfected with chlorine for agricultural irrigation purposes.