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

Abstract

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.

Keywords:

• Chlorination
• Disinfection by-products
• N-nitrosamines
• Reclaimed water

Acknowledgments

This study has been financed by the Spanish Ministry of Science and Innovation, project CTM2011-28765-C02-02. A.G-R acknowledges a BR2011/27 research grant from the University of Girona. We would like to thank Lluis Sala and plant operators, from the Consorci de la Costa Brava for their help during sampling campaigns. We acknowledge the work carried out by Albert Vinyas in the development of the analytical methodology.