38 Chlorinated Humic Acid Mixtures
Downloaded by UCSF LIB CKM RSCS MGMT on September 4, 2014 | http://pubs.acs.org Publication Date: December 15, 1988 | doi: 10.1021/ba-1988-0219.ch038
Criteria for Detection of Disinfection Byproducts in Drinking Water Alan A. Stevens, Leown A. Moore, Clois J. Slocum, Bradford L. Smith, Dennis R. Seeger , and John C. Ireland 1
Drinking Water Research Division, Water Engineering Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, OH 45268
This chapter reports on the feasibility of using a chlorinated humic acid byproduct data base, developed in-house, as a drinking water quality screening tool. Specifically, a gas chromatographic-mass spectral (GC-MS) data base of more than 780 compounds identified during experiments involving the reaction of humic acids with chlorine has been compiled and systematically compared to GC-MS profiles from extracts offinisheddrinking water sampled from 10 preselected operating utilities. A major goal of the research was to narrow this library down to a smaller, more significant target compound list that would be representative of the chlorination byproducts most frequently encountered in thefinisheddrinking water of utilities practicing chlorine disinfection. In addition, the study demonstrates the practicality of using the described methodology for concentrating and identifying specific compounds from water samples at low concentrations.
DRINKING WATER CHLORINATION FOR DISINFECTION PURPOSES
produces numerous organic byproducts other than trihalomethanes (THMs) (1-11). 1Current address: University Hygienic Laboratory, Oakdale Campus, University of Iowa, Iowa City, IA 52242 0065-2393/89/0219-0681$06.00/0 © 1989 American Chemical Society
In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.
Downloaded by UCSF LIB CKM RSCS MGMT on September 4, 2014 | http://pubs.acs.org Publication Date: December 15, 1988 | doi: 10.1021/ba-1988-0219.ch038
682
AQUATIC H U M I C SUBSTANCES
Naturally occurring humic substances in water serve as precursor material for reaction with chlorine to produce a variety of n o n - T H M compound classes, a large percentage of which are halogenated (1-13). The results of most available studies on this topic suggest that the number and identity of all possible chlorination byproducts have not yet been determined. Because a need exists to estimate the true extent of the chlorination byproduct prob lem in full-scale drinking-water-treatment systems, we set out to develop an experimental screening approach that would reveal the maximum possible number of such byproducts. A relatively large data base of compounds formed by the reaction of chlorine with humic acids had already been compiled in-house in previous studies. We attempted to use this data base (via computerized gas chromatographic-mass spectral ( G C - M S ) searching techniques) to screen for water chlorination byproducts in finished drinking water sample extracts obtained from 10 representative treatment facilities. Modifications to a pre viously reported sample concentration technique (11) were also tested for improved separation and recovery of trace organic materials from aqueous solution.
Experimental Procedures Materials. Commercial humic acid was obtainedfromFluka Chemicals (Ronkonkoma, NY). Household bleach (Clorox) was used as the chlorinating agent. Chlo rine content was determined by diluting 5 mL of Clorox to 1 L with demand-free water (Milli-Q) and titrating 50 m L of this solution to a KI-starch-iodine endpoint. Diazomethane gas was generated fresh from p-tolylsulfonylmethylnitrosamide (Diazald, Aldrich Chemical Co., Milwaukee, WI) and was stripped by nitrogen gas from the generation tube into sample vials. For the resin-granular-activated-carbon (XAD-GAC) extractions, dried, unpreserved, peroxide-free ether was prepared by treatment with acidified ferrous sulfate and sodium sulfate crystals. Buffer solutions were preparedfromreagent-grade potassium dihydrogen phosphate and adjusted to the required pH with HC1 or NaOH. All glassware (except volumetricflasks)was heated for 1 h at 400 °C in a muffle furnace to remove trace organic substances. Methods. Humic acid solutions at organic carbon concentrations representa tive of drinking water sources were chlorinated in the laboratory to produce chlorination-oxidation byproducts. Confidence in the use of the readily available commercial humic acid as a reaction-product model was based on the comparative studies reported previously by Seeger et al. (11). For typical experiments, concen trated humic acid (HA) solutions were made by mixing 800 mg of HA in 1 L of 0.02 Ν sodium hydroxide solution and stirring for 30 min. This mixture was neu tralized with sulfuric acid andfilteredthrough glassfiberfilters (Whatman 934 AH). ThefilteredHA concentrate was then split equally, and the 500-mL portions were each diluted to 20 L with demand-free water in separate glass containers. The solution in one container was used to produce a chlorinated sample, and the solution in the other container served as an unchlorinated control. The resulting total organic carbon (TOC) of these samples (both chlorinated and unchlorinated) was 5 to
In Aquatic Humic Substances; Suffet, I., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1988.
38.
Disinfection Byproducts in Drinking Water
STEVENS E T AL.
683
Downloaded by UCSF LIB CKM RSCS MGMT on September 4, 2014 | http://pubs.acs.org Publication Date: December 15, 1988 | doi: 10.1021/ba-1988-0219.ch038
7 mg/L, in the range of that found in drinking water sources. Experiments were performed in duplicate, starting with afreshconcentrate of HA each time. The chlorination of HA solutions was studied at three different pH levels, 5, 7, and 11. In addition, a separate experiment with bromide was performed at pH 7. A phosphate buffer was used to control pH. The chlorine was added in sufficient quantity to produce a free chlorine residual at the end of a 3-day reaction period. After the 3day period, the concentration of free (and total) chlorine residual was determined (14), and an excess of sodium sulfite was added to destroy that chlorine residual. The pH was then lowered to 2.0 with HC1 and the XAD-GAC extraction was initiated. X A D - G A C Adsorption Analysis. This analysis was a variation of the procedure reported by Seeger et al. (11) to concentrate products of reactions of chlorine with natural humic materialsfromlarge volumes (10-20 L) of dilute solution. Figure 1 presents a schematic diagram of the experimental apparatus. Briefly, the XAD-GAC adsorption analysis was carried out as follows: Three 1-galfinishedwater samples were combined in a 20-L glass carboy. Chlorine residual was then determined by N,N-diethyl-p-phenylenediamine (DPD) titrimetric analyses (14) for free and total CI. Anhydrous Na S0 (2 mg) was then added for each 1 mg of total CI residual and allowed to react for 30 min. An influent sample was taken for THM and total organic halogen analysis, and a check was made to be sure no chlorine remained. Phosphate buffer (100 mL) and 35 mL of 6 Ν HC1 were added to reduce the pH to the range of 2.0-2.2. After approximately 10 L had been passed through the columns in the adsorption mode (Figure 1A)—the XAD resin above the GAC—the columns, inverted so the GAC was above the XAD, were drained of water. Special fittings were then connected to the top and bottom of the connected columns so that ether could be distilled through a side arm leading to a condenser at the top. The condensed ether drained directly onto the GAC and eventuallyfloodedthe entire column length. In this way, ether was continuously refluxed (Figure IB) through the connected GAC and XAD columns, backwashing the previously adsorbed organic compounds. The extracted organic compounds were concentrated in the receivingflaskat the bottom. After 3 h of continuous extraction, the ether was cooled; 1 mL of 1 Ν HC1 was added (to ensure a pH
