Grantee Research Project Results
2002 Progress Report: Formation and Stability of Ozonation By-Products in Drinking Water
EPA Grant Number: R826833Title: Formation and Stability of Ozonation By-Products in Drinking Water
Investigators: Weinberg, Howard S.
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Hahn, Intaek
Project Period: November 1, 1998 through October 31, 2001
Project Period Covered by this Report: November 1, 2001 through October 31, 2002
Project Amount: $441,261
RFA: Drinking Water (1998) RFA Text | Recipients Lists
Research Category: Drinking Water , Water
Objective:
With less than 50 percent of the assimilable organic carbon generated by ozonation identified to date, the overall goal of this research project is to investigate new methodologies for targeting a series of new by-products. These methods, together with refined existing techniques, then would be employed to study the impact of water quality parameters on the formation and stability of these compounds in distributed drinking waters. The specific objectives of this research project are to: (1) investigate the relative occurrence of these by-products in treated drinking waters; and (2) determine water quality, treatment, and distribution system conditions, which influence their relative concentrations. Their kinetics of formation and stability need to be characterized to understand the underlying causes of the relative differences in by-product formation in different waters, and a controlled study needs to be conducted in which the various contributory factors are investigated.
Progress Summary:
In Year 4 of the project, we have expanded our suite of analytical methods to include multifunctional carbonyl-containing ozonation by-products and explored their formation, occurrence, and persistence in drinking waters. The specific target carbonyl-containing compounds now include: formaldehyde, acetaldehyde, cyanoformaldehyde, chloroacetaldehyde, dichloroacetaldehyde, bromochloroacetaldehyde, tribromoacetaldehyde, trans-2-hexenal, 5-keto-1-hexanal, 6-hydroxy-2-hexanone, glyoxal, methylglyoxal, dimethylgyoxal (2,3-butanedione), 1-hydroxyacetone, 5-hydroxy-2-pentanone, 6-hydroxy-2-hexanone, 4-hydroxybenzaldehyde, glyoxalic acid, pyruvic acid, ketomalonic acid, and 4-carboxybenzaldehyde.
For the analysis of hydroxyl carbonyls in water, two approaches were investigated; derivatization of the carbonyl with pentafluorobenzylhydroxylamine followed by either silylation with N-methyl-N-(tert-butyldimethylsilyl) trifluoroacetamide containing 1 percent tert-butyldimethylchlorosilane or methylation with iodomethane. Extraction of the double derivative was evaluated with both hexane and methyl tert-butyl ether (MtBE). After formation of the oxime, the MtBE or hexane extract was split into two aliquots; one was kept for direct analysis and the other for silylation. A comparison of the peak responses and extrapolation to a signal:noise value of five shows very similar quantitation limits for the two aliquots. Although the double derivatization approach is somewhat time intensive, it offers an opportunity to identify the presence of an OH- group within the by-product by formation of the silyl adduct that affords a distinctive fragment ion in an electron ionization mass spectrum.
The stability of hydroxycarbonyls was studied at room temperature with both synthetic spiked aqueous solutions and settled water from a local conventional surface water treatment plant. Aliquots were removed after different holding times of up to 2 weeks, and were extracted alongside fresh calibration samples. In the synthetic water, the compounds appear stable for at least 2 weeks. In settled water, however, hydroxyacetone and 4-hydroxybenzaldehyde are partly degraded after 1 week. After 2 weeks, only 6-hydroxyhexanone is still present at its original concentration.
A similar study was performed for the evaluation of methods for the analysis of ketoacids. Quantitation limits for each standard in settled water were established at 0.5 µg/L using methylation of the MtBE extracted oxime. In the synthetic water, all of the ketoacids are stable for 24 hours, but only 4-carboxybenzaldehyde remained stable for the complete 2-week holding time. In settled water, the ketoacids partly are degraded after 24 hours except for 4-carboxybenzaldehyde. After 1 week, all of the compounds are degraded in settled water. The implications for this are twofold. For analysis purposes, the aqueous samples must be kept cool and processed within a relatively quick turnaround time. In terms of impact on the consumer, it appears that even if these compounds are by-products of ozonation and enter the distribution system, it is likely that they will undergo a certain degree of degradation before reaching the consumer’s tap. It will be important, therefore, to answer the following questions:
(1) Are hydroxyl compounds formed by ozonation?
(2) What are the products of interaction for chlorine or chloramines?
(3) What are their degradation products in distribution systems?
Because both ketoacids and hydroxyl carbonyls in their double derivatization mode generate product ions in a mass spectrum that are specific to each function in the original molecule, the analytical methods developed in this research project will be used to attempt the identification of new by-products in ozonated and distributed waters by recognition of the fragment ions in electron ionization, and in subsequent confirmation of the molecular ion and daughter ions in chemical ionization to assist in building a likely structure of the target compound.
Future Activities:
For the final year of the project, we will focus on completing the stability studies of the target by-products, identifying their products of interaction with terminal plant disinfectants, and collecting occurrence data for drinking water treatment plants with a variety of treatment processes and water quality. It also is anticipated that with the acquisition of a new liquid chromatograph with electrospray interface mass spectrometry, we will be able to gather some initial qualitative information about the identity of other ozonation by-products.
Journal Articles:
No journal articles submitted with this report: View all 18 publications for this projectSupplemental Keywords:
disinfection, exposure, organics, analytical methods, ozonation, methyl tert-butyl ether, MtBE, organic carbon, by-product, drinking water system, treatment., RFA, Scientific Discipline, Water, Environmental Chemistry, Chemistry, Analytical Chemistry, Drinking Water, alternative disinfection methods, public water systems, water quality parameters, exposure and effects, disinfection byproducts (DPBs), stability, exposure, community water system, treatment, chlorine-based disinfection, chloramines, DBP risk management, water quality, drinking water contaminants, water treatment, formation, drinking water systemRelevant Websites:
http://www.unc.edu/~weinberg Exit
http://www.unc.edu/~weinberg/Discussion-Forum/WelcomePage.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.