Characterization and Comparison of Disinfection ... - ACS Publications

Chapter 19

Characterization and Comparison of Disinfection By-Products of Four Major Disinfectants Downloaded by UNIV OF ARIZONA on July 31, 2012 | http://pubs.acs.org Publication Date: August 15, 2000 | doi: 10.1021/bk-2000-0761.ch019

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Xiangru Zhang , Shinya Echigo , Roger A. Minear , and Michael J. Plewa 2

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Departments of Civil and Environmental Engineering and Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801

Disinfection by-products (DBPs) generated from chlorination, chloramination, ozonation, and chlorine dioxide treatment were characterized and compared. DBPs examined included four trihalomethanes, nine haloacetic acids, four haloacetonitriles, two haloketones, chloropicrin, total organic halogen (TOX), total organic bromine (TOBr), total organic chlorine (TOC1), thirteen aldehydes, and bromate. The contributions of known DBPs to TOX, TOC1 and TOBr formed from using different disinfectants were given. The reaction of humic substances with small amount of free chlorine in equilibrium with NH Cl constitutes an important pathway for the formation of TOC1 during chloramination. The yields of TOBr and total aldehydes produced from using each disinfectant were found to be related to the redox potential corresponding to each disinfectant. This work makes a step toward better decisions about which disinfectant poses the lowest risk to human health. 2

Many oxidants are being considered as alternatives to chlorine to reduce halogenated organic disinfection by-products (DBPs). The most popular of these alternative disinfectants are ozone, chlorine dioxide and chloramine. While the use of alternatives helps to minimize the trihalomethanes (THMs), other by-products will be produced. Singer et al. (J) and Richardson (2) have developed excellent summaries of DBPs in drinking water. There have been numerous publications on DBPs in drinking water since 1970s, however, most of the research focused on the characterization of one or two D B P groups resulting from using only one or two © 2000 American Chemical Society

In Natural Organic Matter and Disinfection By-Products; Barrett, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

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Downloaded by UNIV OF ARIZONA on July 31, 2012 | http://pubs.acs.org Publication Date: August 15, 2000 | doi: 10.1021/bk-2000-0761.ch019

300 disinfectants, which limited a comprehensive comparison of DBPs resulting from using different disinfectants. Only Lykins et al. (3) evaluated the DBPs resulting from use of several major disinfectants, but their attention was focused on a disinfectant contact time of 30 min, followed by the addition of chlorine. Maintenance of a disinfectant residual to control bacterial concentrations throughout the distribution system can cause both increase or decrease in D B P concentrations (4-6). Thus, one focus of this research is to examine the DBPs formed after extended contact time in order to simulate tap water. In this work, the DBPs resulting from a 5-day contact time with chlorination, chloramination, and chlorine dioxide treatment were characterized and compared. Ozone DBPs were also examined, but after a contact time of 30 min. DBPs examined included four THMs, nine haloacetic acids (HAAs), four haloacetonitriles (HANs), two haloketones (HKs), chloropicrin, total organic halogen (TOX), total organic bromine (TOBr), total organic chlorine (TOC1), 13 aldehydes, and bromate, which covers halogenated and nonhalogenated, organic and inorganic, specific and nonspecific parameters.

Experimental Methods Suwannee river fulvic acid (SRFA, International Humic Substances Society) was added to deionized, distilled water to simulate a water of 3.0 mg/L of total organic carbon. Two sets of samples were prepared, one containing 0.100 mg/L of NaBr as Br", one without Br". Chlorination was performed in the model water (with/without Br") which was buffered with 0.50 mL of 0.25 M phosphate and small amount of HC1 solution at pH 7.4. Stock solutions of sodium hypochlorite were prepared by the adsorption of high purity chlorine gas with 1 M NaOH solution, and standardized by the iodometric method (7). Sodium hypochlorite was added to the sample in 250-mL, glassstoppered bottles at a dose of 4.5 mg/L as C l . Chloramination was performed in the model water (with/without Br") which was buffered with 0.50 mL of 0.25 M phosphate at p H 7.5. Monochloramine solutions were prepared just before use by reacting of ammonium chloride and sodium hypochlorite solutions in a chlorine-to-ammonia ratio of 0.8 mol/mol (8) to eliminate free chlorine. Monochloramine was added to the sample in 250-mL, glass-stoppered bottles at a dose of 5.0 mg/L as C l . Chlorine dioxide treatment was performed in the model water (with/without Br") which was buffered with 0.50 mL of 0.25 M phosphate at p H 7.5. Stock chlorine dioxide solution was prepared from the reaction between H S 0 and NaC10 . C I 0 gas was purified by bubbling through a saturated solution of NaC10 prior to absorption in deionized, distilled water. The generated C 1 0 stock solution was found to be essentially free of chlorine (i.e., purity of 99% or greater). Concentration of C10 in stock solution was measured spectrophotometrically (9). Chlorine dioxide 2

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301 was added to the sample in 250-mL, glass-stoppered bottles at a dose of 6.0 mg/L as C10 . A l l the sample bottles were vigorously shaken for thorough mixing, then stored headspace-free at 25°C in the dark for 5 days. After 5 days, samples were collected headspace-free in 40- or 60-mL glass vials with polypropylene screw caps and Teflon-lined septa. The vials contained 0.2 or 0.3 mL of 0.2 Ν N a S 0 solution to quench disinfectant residuals. Samples were stored at 5°C for no more than 2 days prior to analysis. At the time of sample collection, each of the treated waters was analyzed for disinfectant residuals by the DPD method (7). The results showed that after 5 days of contact time, the presence of disinfectant residuals were ensured at the following levels: 0.29 and 0.58 mg/L as C l in the chlorinated, 3.1 and 3.2 mg/L as C l in the chloraminated samples, 0.12 and 0.18 mg/L as C 1 0 in the chlorine dioxide treated samples, with and without bromide, respectively. 2

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Ozonation was conducted in a batch reactor (a modified 500-mL graduated cylinder) containing the model water and 2 m M phosphate buffer at pH 7.5. The aqueous stock solution of ozone was injected rapidly below the water surface in the reactor at a dose of 6.0 mg/L. A time series of samples produced from the reactor were analyzed for ozone residual. The result shows that ozone disappeared in about 30 min. After 30 min, samples were collected headspace-free in 40- or 60-mL glass vials with polypropylene screw caps and Teflon-lined septa. Samples were stored at 5°C for no more than 2 days prior to analysis. Gas chromatography was used for determination of H A A s , T H M s , H A N s , H K s and chloropicrin by using and slightly modifying EPA Methods 552.2, 551.1 and 501 (10-12). With the modified procedures, more than three series of DBPs were well separated with the same DB-1701, fused silica capillary column (30 m χ 0.32 mm i.d., 0.25 μιη film thickness) under two different programs. The program for the analysis of H A A s was: solvent, methyl terr-butyl ether; carrier gas, nitrogen; inlet pressure, 0.75 kg/cm ; 35°C for 12 min, ramp to 135°C at 5°C/min, ramp to 220°C at 20°C/min. The program for the analysis of THMs, H A N s , H K s and chloropicrin was: solvent, pentane; carrier gas, nitrogen; inlet pressure, 0.30 kg/cm ; 35°C for 18 min, ramp to 145°C at 5°C/min, ramp to 220°C at 20°C/min. 2

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The procedure for the determination of aldehydes included derivatization of aldehydes with o-(2,3,4,5,6-pentafluorobenzyl)-hydroxylamine hydrochloride follow ed by extraction with hexane and analysis by gas chromatography with an electron capture detector using a DB-5, fused silica capillary column (75). A n ion chromatograph, coupled with an anion column (AS9-HC, Dionex) and a guard column (AG9-HC, Dionex), was used to determine bromate concentration; a carbonate eluent (9 m M N a C 0 ) and a 500 uL injection loop were used. T O X was analyzed according to Standard Methods 5320B (14). TOC1 and TOBr were measured by combining T O X analysis and ion chromatography (IC) protocols where the titration cell of the T O X analyzer is electrode-disabled and, instead of electrochemically titrating halide ions, is used as a collection reservoir for sample subsequently analyzed by IC for CI" and Br" (75). 2

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Results and Discussion


Disinfection By-Products Data Table I shows D B P data from the determination of treated samples. Bromide versus Non-Bromide Samples Compared with bromide-free samples, the concentrations of chlorinated DBPs in the bromide-containing samples decreased while the levels of mixed bromochloroand bromo- species increased. With bromide in the water treated with chlorine, chloramine or chlorine dioxide, for instance, bromodichloromethane, chlorodibromomethane and bromoform levels increased with concurrent decrease of the concentration of chloroform; bromoacetic acid, bromochloroacetic acid, tribromoacetic acid levels increased with concurrent decrease of the concentration of chloroacetic acid, dichloroacetic acid or trichloroacetic acid; bromochloroacetonitrile or dibromoacetonitrile increased with concurrent decrease of concentration of dichloroacetonitrile. Minear and Bird (16) found that increasing bromide concen tration, at a given chlorine dose increased the bromine-substituted THMs, particu larly bromoform. Cowman and Singer (17) pointed that increasing bromide concentration gradually shifted H A A speciation to the mixed bromochloro species to the brominated species. Other chlorination by-products like haloacetonitriles, halopicrins and halonitromethanes were also affected with the same trend (18, 19). According to our data, it seems that the findings from chlorination studies can be extended to other disinfection processes like chloramination or chlorine dioxide treatment. This is because bromine produced from oxidizing bromide by disinfect ants is much more reactive than chlorine in substitution reactions. Now that the presence of bromide represents a typical raw water condition, only the bromide-containing samples are discussed in the following unless specified. Trihalomethanes Figure 1 shows the total amount of THMs from using different disinfectants. No significant T H M levels were observed during the ozone and chlorine dioxide treatment. The only species detected in the ozonated sample was bromoform at a sub-ppb level of 0.17 pg/L. The concentrations of chloroform, bromodichlorometh ane, chlorodibromomethane and bromoform in the chlorine dioxide treated sample were 0.36, 0.76, 1.1, and 0.46 pg/L, respectively, which were so low and near the method detection limits that chlorine dioxide had been thought not to produce T H M s (20, 21). The highest T H M concentrations were present in the chlorinated sample with a total amount of 247 pg/L. The total T H M concentration in the chloraminated sample was only 7.6 pg/L. Compared to the chlorination, chloramination decreases T H M levels greatly; this was also observed by other researchers (22).


303 Table L D B P data from using different disinfectants with/without B r (p|^L) NH Cl NH Cl C10 C10 Cl CÎ w/o w w/o w w/o w Br Br Br Br" Br Br Bromate ion

Characterization and Comparison of Disinfection ... - ACS Publications

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