Grantee Research Project Results

2001 Progress Report: Formation and Stability of Ozonation By-Products in Drinking Water

EPA Grant Number: R826833
Title: 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, 2000 through October 31, 2001
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 objective of the research project is to investigate new methodologies for targeting a series of new by-products. These methods, together with refined existing techniques, then will 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 byproduct formation in different waters, and a controlled study needs to be conducted in which the various contributory factors are investigated.

Progress Summary:

In Year 3 of the project, we further have developed the methods first evaluated in the previous year for organic peroxides and epoxides in drinking water analysis, and have studied approaches to minimize or remove matrix interferences specifically from natural organic matter.

The new procedure for peroxides adds a solid phase extraction (SPE) step prior to sample analysis, thus allowing for preconcentration of the target analytes. Once extracted, the peroxides are separated by reversed phase high performance liquid chromatography (RP-HPLC) and converted to radicals by horseradish peroxidase in the post column reaction. These radicals then react with p-hydroxyphenylacetic acid to form a fluorescent dimer, the signal of which is increased by the addition of sodium hydroxide. Ozonated water samples are quenched of residual ozone by the addition of glycine and analyzed within 48 hours of the time of collection. 100 mL of water is passed through an SPE cartridge, with about 1 mL kept aside for the analysis of hydrogen peroxide (H2O2) directly. The organic peroxides retained on the cartridge then are eluted with methanol and blown down to a final volume of 200 µL using ultrahigh purity nitrogen gas. 100-µL sample volumes are analyzed by RP-HPLC using a gradient mobile phase composed of deionized water and acetonitrile with a flow rate of 0.6 mL/minute. The detection limits of all the peroxides studied were lowered by application of this method. Theoretically, the SPE procedure offered a concentration factor of 500 times that in the original water sample, assuming 100 percent recovery. In actuality, SPE allowed detection of the organic peroxides to levels of approximately 5 µg/L, which is very close to the 1 µg/L goal set by this research.

Epoxides are another group of the targeted ozonation by-products for which no routine analytical method currently exists. An analytical method has been developed to quantify epoxides at low levels in drinking water. The method has been tested on three commercially available epoxides; 1,2-epoxybutane, epichlorohydrin, and -pinene oxide. The derivatization technique involves heating aqueous samples with a weak nucleophile, 2,5-difluoroaniline, in the presence of ferric chloride at 60°C for 1 hour. The reaction chemistry involves ring opening of the epoxide group through an SN1 mechanism with an initial attack of the ferric ions on the epoxide generating a carbocation. This then undergoes a rapid reaction with the weak nucleophile to give rise to a difluoroaniline adduct. The reaction mixture is cooled to room temperature and extracted with methyl tert-butyl ether-containing internal standard by either liquid-liquid extraction or SPE. The extract subsequently is analyzed by gas chromatography-electron capture detector, and structurally confirmed by gas chromatography-mass spectrometry. The chemical ionization (CI) mode of operation generated fingerprint fragment ions at m/z = 142 corresponding to the difluoroamino methane adduct. Moreover, the M⁺ and (M+1) ions can be observed in the CI mode, which further can aid in identifying the parent molecule.

We also expanded the suite of carbonyl compounds detected by the pentafluorobenyzlhydroxylamine (PFBHA) derivatization technique to include four new compounds: dimethylglyoxal (2,3-butanedione), trans-2-hexenal, 5-keto-1-hexanal, and 6-hydroxy-2-hexanone. Some of these were found in ozonated drinking waters at levels up to 4 µg/L, and the effects of different treatment plant operations on their stability and persistence in drinking water distribution was studied. In addition, halogenated acetaldehydes were identified as a result of chlorination alone and ozonation followed by chloramination. The by-products in this class included mixed chloro- and brominated species. PFBHA derivatization in the aqueous phase generated a consistent 85 percent conversion of chloro- and dichloroacetaldehyde to the corresponding oximes in a variety of matrices. For the measurement of bromochloroacetaldehyde, dichloroacetaldehyde was found to be a major contaminant in the synthesized product. The product generated by PFBHA derivatization, therefore, contained a mixture of 35 percent bromochloroacetaldehyde and 38 percent dichloroacetaldehyde. These "standards" were used to quantify the conversion of the aldehyde to the oxime during in situ derivatizations in water. Derivatizations showed a consistent 75 percent conversion. The sum of the syn and anti isomers were used for the quantitation of bromochloroacetaldehyde in water. Methods for haloacetamides also were investigated because these were suspected as being by-products of ozonation followed by postdisinfection.

Future Activities:

We will begin to deploy these methods next year in a water treatment plant survey, and will continue to develop analytical methods for additional potential by-products of ozonation, including those formed by a combination of ozone with postdisinfection.

Journal Articles:

No journal articles submitted with this report: View all 18 publications for this project

Supplemental Keywords:

disinfection, exposure, organics, analytical methods, ozonation, by-products, solid phase extraction, SPE, chemical ionization, CI, analytical method, organic matter, peroxide, epoxide., RFA, Scientific Discipline, Water, Chemistry, Environmental Chemistry, Analytical Chemistry, Drinking Water, chlorine-based disinfection, community water system, ozonation, treatment, water quality, water quality parameters, chloramines, drinking water system, drinking water contaminants, water treatment, exposure, formation, stability, disinfection byproducts (DPBs), public water systems, alternative disinfection methods, exposure and effects

Relevant Websites:

http://www.unc.edu/~weinberg Exit
http://www.unc.edu/~weinberg/Discussion-Forum/WelcomePage.html Exit

Progress and Final Reports:

Original Abstract

1999 Progress Report

2000 Progress Report

Final Report