Date of Award
Doctor of Philosophy (PhD)
Environmental Engineering and Earth Science
Freedman, David L.
Ladner, David A.
To comply with the increasingly stringent disinfection by-product (DBP) regulations in the United States, many water treatment plants have been switching from chlorination to chloramination in the last decade. Although chloramination reduces the formation of regulated DBPs such as trihalomethanes and haloacetic acids, it causes the formation of nitrosamines. Nitrosamines are a class of compounds that are probable human carcinogens, mutagens and teratogens at concentrations as low as 0.2 ng/L. In particular, N-nitrosodimethylamine (NDMA) is the most frequently detected nitrosamine in distribution systems in the United States. Although, nitrosamines are currently not regulated by the USEPA, they have been recently identified as a group of contaminants highlighted for possible regulatory action. Although several studies have investigated the formation mechanisms and important precursors for nitrosamines (especially NDMA), there is still much more to learn about their formation pathways. The main objective of this research was to systematically examine nitrosamines formation from amines to gain insight into the formation mechanisms of nitrosamines (especially NDMA) and examine the interactions of these precursors with different oxidants. Specifically, the research focused on: (i) the formation potential of nitrosamines from amino acids (AAs) under different disinfection conditions, (ii) the roles of tertiary structure on the formation of NDMA during chloramination, (iii) the importance of chloramine species in the NDMA formation, and (iv) the interaction of various precursors with different oxidants (chlorine, chlorine dioxide and ozone) and their consequent effect on NDMA formation. The research approach consists of three phases. First phase consisted of identifying the important nitrosamine precursors and understanding the effect of precursor structure on the conversion yield. Primary and tertiary amines were selected as the target compounds and results are presented in Chapters V and VI. Then in the second phase the roles of chloramine species in NDMA formation was examined as presented in Chapter VII. Finally, controlling NDMA formation, practically as critical as understanding the fundamentals of those reactions, was investigated using different oxidants in Chapter VIII. AAs were selected initially as nitrosamine precursors since they are rich in nitrogen, reactive and shown to form of other classes of DBPs (trihalomethanes, halonitromethanes, etc.). Nine AAs (alanine, aspartic acid, cysteine, glutamic acid, glycine, lysine, histidine, proline and serine) were selected based on their structures (i.e., acidity vs. basic, polar vs. nonpolar, hydrophilic vs. hydrophobic), and tested under different oxidation conditions for their formation of nitrosamines. NDMA yields of all nine AAs during chloramination were below the minimum reporting levels. However, during ozonation alone and ozonation followed by chloramination, the formation of several nitrosamines (including N-nitrosopyrrolidine and N-nitroso-di-n-butylamine) at very low molar conversion yields (25%). Espe cially, strategies for controlling the discharge of those types of contaminants would lead to decreases in NDMA precursor's levels in source waters. (ii) The precursor's structure also influences the chloramine species (mono- vs. di-) responsible for NDMA formation. The dominant chloramine species responsible for NDMA formation was found as dichloramine in selected natural waters. The utilities may opt to minimize the formation of dichloramine in their distribution systems (e.g., maintaining higher pH) to control NDMA formation. However, it should be noted that some NDMA formation may still be observed due to monochloramine. (iii) Pre-oxidation strategies can be an effective method for utilities to control NDMA formation as long as the formation of regulated DBPs (trihalomethanes, haloacetic acids, chlorite and bromate) are within the allowable limits. Chlorine has shown reduction in NDMA formation for most of the precursors (except polymers). On the other hand, chlorine dioxide and ozone may lead to decreases or increases in NDMA formation depending on the characteristics of the precursors. Preliminary testing is suggested for utilities for selecting the appropriate oxidant type, to optimum dose and contact times for controlling NDMA formation.
SELBES, MERIC, "THE EFFECTS OF AMINE STRUCTURE, CHLORAMINE SPECIES AND OXIDATION STRATEGIES ON THE FORMATION OF N-NITROSODIMETHYLAMINE" (2014). All Dissertations. 1316.