Collections > Electronic Theses and Dissertations > Anion Exchange Resins as Sources of Nitrosamines and Nitrosamine Precursors
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Nitrosamines are a family of potent chemical carcinogens including, among others, N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-propylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA). NDMA and other nitrosamines have been identified as disinfection byproducts. They are regulated in the State of California and are candidates for Federal regulation. Anion exchange resins, used for the removal of anionic contaminants from drinking water, consist of polymer networks with positively charged amine groups. Resins are often synthesized using trimethylamine (TMA), triethylamine (TEA), tri-n-propylamine (TPA) or tri-n-butylamine (TBA) which can react with chloramines to form NDMA, NDEA, NDPA and NDBA, respectively. Drinking water treatment plants using anion exchange resins have been found to have higher levels of NDMA in finished waters. The objective of this research was to investigate the potential relationship between the use of anion exchange resins in drinking water treatment and the presence of nitrosamines and nitrosamine precursors in finished waters. A wide array of resins, representing those commonly used in practice, was investigated through bench-scale batch contact experiments, bench-scale continuous-flow column experiments, and measurements at water utilities using anion exchange for treatment. In the batch experiments, resins were found to release nitrosamines and their precursors after one hour of contact. Resins manufactured with TEA or TBA were found to release NDMA precursors in addition to NDEA or NDBA precursors. In column experiments, resins released high nitrosamines and precursors in the first 10 bed volumes of flow. Regeneration with NaCl resulted in a spike in precursor release, as did flow interruptions. The introduction of chlorine or preformed monochloramine resulted in increases in nitrosamines. Explanations for the presence of precursors and their increased release during regeneration and flow interruption are offered, and a mechanism for nitrosamine formation via reactions with free chlorine and monochloramine is proposed. A study of ten full-scale treatment plants using anion exchange resins found that three contained nitrosamines and five contained precursors in their anion exchange effluents. Experiments suggested that resins can be washed clean of any residual nitrosamines and precursors, and field observations confirmed that resins that have been in place for longer periods of time release lower levels of precursors.