Delineating Nitroxyl Formation Pathways from Chloramines and Free Chlorine and Cascades of Reactive Nitrogen Species to N-Nitrosamines and N-Nitramines

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Disinfection is a critical unit operation used in water treatment to protect the public from waterborne diseases. Chloroamines are utilized to disinfect about one-half of the drinking water produced in the United States. The use of chloramines in water disinfection provides several advantages. Because they are less reactive and more stable than chlorine, chloroamines have much less tendency to form disinfection by-products by reacting with dissolved organic matter (DOM). In addition, chloramines provide longer-lasting disinfection and better protection against microorganism regrowth and contamination as treated water is delivered through the distribution pipe networks. However, recent research has linked the presence of the cancer-causing compound N-nitrosodimethylamine (NDMA)in drinking water to reactive nitrogen species (RNS) that are formed in chloramine systems used in water disinfection. The goal of this research is to investigate the role of RNS in the formation of NDMA in chloroamine water disinfection systems. The successful completion of this project will benefit society through the development of new knowledge and insight to control and mitigate the formation of NDMA in chloramine water disinfection systems. Further benefits to society will be achieved through student education and training including the mentoring of a doctoral student and an undergraduate student.Reactive nitrogen species (RNS) have long been postulated to form in chloramine systems used in water disinfection. However, the identification of these RNS and delineation of their roles in the formation of toxic disinfection by-products (DBPs) such as N-nitrosodimethylamine (NDMA) has remained elusive. Thus, there is a critical need to identify RNS formed from chloramines and free chlorine and delineate the subsequent RNS cascades that initiate NDMA formation in drinking water. The goal of this project is to address these knowledge gaps. To achieve this goal, the PI propose to test the hypothesis that that nitroxyl is the “missing link” in understanding NDMA formation via (1) dichloramine hydrolysis and (2) the reactions of monochloramine or hypochlorous acid with hydroxylamine. The project will integrate batch kinetic experiments and modeling to (1) evaluate the formation and role of peroxynitrite as a parent nitrosating agent, (2) delineate nitroxyl formation pathways from chloramines and free chlorine, and (3) determine the proportion of N-nitrosamines (e.g. NDMA) and N-nitramines formed through the nitroxyl pathway under typical chloramination conditions used during water disinfection. The kinetic experiments will measure and quantify the concentrations of the relevant reactive species including reactants (free chlorine, chloramine species, precursors, and dissolved oxygen), RNS intermediates, stable products (nitrous oxide, nitrogen gas, nitrite, and nitrate), and N-nitrosamines and N-nitramines. Thus, the successful completion of this project has the potential for transformative impact through the development of new fundamental knowledge that could enable the control and mitigation of the formation of toxic DBPs such as NDMA in chloramine water disinfection systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.