Halonitromethanes (HNMs) and nitrosamines constitute two important classes of disinfection byproducts (DBPs) that can form during water treatment. HNMs have orders of magnitude higher cytotoxicity and genotoxicity than any of the regulated organic DBPs, while nitrosamines pose cancer risk at very low levels (i.e., ng/L). The PI?s recent research has shown that HNM formation was significantly higher during ozonation-chlorination as compared with other typical disinfection scenarios used in drinking water treatment. It was also demonstrated that the HNM formation increased with an increase in dissolved organic nitrogen (DON) content in water. However, little is known about the role of DON components and the identity of precursors causing HNM formation. Furthermore, the formation of nitrosamines during ozonation is controversial. Though previous studies have shown that ozonation decreased N-nitrosodimethylamine (NDMA) formation, recent works have reported an appreciable amount of NDMA formation after ozonation in both lab studies and full scale ozonation plants. Therefore, it will be critically important to investigate the formation of HNMs and nitrosamines during ozonation, and to understand the factors controlling their formation and speciation.
The PI seeks to systematically investigate formation of HNMs and nitrosamines during ozonation, and to gain insight to their potential precursors and formation mechanisms. We hypothesize that the formation of N-DBPs is precursor specific, and different precursors/ mechanisms will involve in the formation of HNM or nitrosamines. Therefore, in this study, various formation mechanisms have been postulated and experimental plans are proposed to investigate the proposed mechanisms. The PI and coworkers will initially perform experiments with a set of carefully selected model nitrogenous organic compounds (Task 1). Reaction intermediates will be analyzed to examine the proposed formation mechanisms and to gain insight to the formation of HNMs and nitrosamines (Task 2). A monitoring study (Task 3) in selected natural waters is also planned to examine the relationship(s) between the precursors (based on Task 2 and 3) and the DBPs (HNM or Nitrosamines). The proposed work is novel because it will be the first time that the proposed mechanisms will be investigated. The findings are expected to provide important information about the potential role(s) of different organic nitrogen components in natural waters in the formation of HNMs and nitrosamines during ozonation.
Understanding the formation of HNMs and nitrosamines is vital for finding strategies to control these compounds. There are approximately 250 ozonation plants in the US, and some of them are quiet large (500-800 MGD), serving very large populations. Research results will provide important information for ozonation plants worldwide (e.g., ozonation is widely implemented in Europe). An appreciable number of utilities in the US have been exploring alternative approaches to comply with the stringent requirements of the Stage 2 D/DBP Rule. Ozonation is one of the available alternatives. Therefore, the findings will be important for utilities considering ozonation. The knowledge from this work will improve our understanding of the nature of HNM and nitrosamine formation and directly impact practitioner?s ability to control the formation of these compounds in treatment facilities. The USEPA and state regulatory agencies can benefit from the results in developing both present and future procedures for managing these compounds. Implementing this project will also promote training and education of a wide range of students with diverse backgrounds and levels. The PI will offer a Creative Inquiry research course through this project, a unique program of Clemson University bringing undergraduate students from different departments studying various disciplines to work in small team-projects and earn college credits. Participating students will learn about water treatment processes, applied chemistry (i.e., DPB formation) and how to conduct scientific research. The project will also allow opportunities for high school and undergraduate students, particularly from underrepresented groups.
