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2. Comparison of the disinfection by-product formation potentials between a wastewater effluent and surface waters
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Water Research 39 (2005) 1025–1036 www.elsevier.com/locate/watres
2. Comparison of the disinfection by-product formation potentials between a wastewater effluent and surface waters Tanita Sirivedhin, Kimberly A. Gray Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA Received 18 August 2003; received in revised form 21 April 2004; accepted 18 November 2004
Abstract In this study, the chemical reactivity with chlorine as measured by disinfection by-product formation potential (DBPFP) is compared among samples of a wastewater effluent and surface waters. Water samples that had higher anthropogenic impacts were found to have higher overall DBPFP due primarily to higher dissolve organic carbon (DOC) concentrations. Effluent-derived organic matter (EfOM), however, was found to be less reactive with chlorine on a per DOC concentration basis. Yet, EfOM had higher proportions of brominated DBP, which may be associated with greater health risks. In this research, pyrolysis-GC/MS was used to establish relationship between structural features of DOC and DBPFP. We show that there is a critical set of pyrolysis fragments that separates the waters based on the degree of anthropogenic influence. Even though no single chemical marker was found to be indicative of the formation potentials of different classes of DBP, combinations of chemical fragments were found to be associated with the formation potentials of total trihalomethane (THM), brominated THM, total haloacetic acid (HAA), and brominated HAA for this set of samples. In contrast to previous work, the phenolic signature of these samples was negatively correlated to DBPFP, whereas strong relationships were found between DBPFP and the organic nitrogen and halogenated signatures. r 2005 Elsevier Ltd. All rights reserved. Keywords: Pyrolysis-GC/MS; Disinfection by-products; Wastewater; Trihalomethane; Haloacetic acid
1. Introduction In the chlorination process, aquatic organic matter (AOM) serves as a precursor to the formation of potentially harmful disinfection by-products (DBP) such as trihalomethanes (THM), haloacetic acids (HAA), and total organic halides (TOX). In general, waters with higher total organic carbon (TOC) concentrations are found to produce more DBP in chlorination (Singer and DOI of original article: 10.1016/j.watres.2004.11.032 author. Tel.: +1 847 467 4252; fax: +1 847 491 4011. E-mail address: [email protected] (K.A. Gray). Corresponding
Chang, 1989). DBP in drinking water are considered to be carcinogenic, mutagenic, and teratogenic (Kanitz et al., 1996; Singer, 1999; Zavaleta et al., 1999; Black et al., 1996), and therefore, they pose adverse health effects in both human and animals (Bull and Kopfler, 1991; Morris et al., 1992). Historically, much of the study of health risks associated with DBP has been centered on THM; however, there is a growing concern about the health risks associated with HAA. Previous research has studied the influences of temperature, pH, reaction time, free and combined chlorine concentrations, as well as precursor type and precursor concentration on the formation of DBP (Stevens et al., 1976, 1989; Reckhow et al., 1990). The
0043-1354/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.11.031
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extent of chlorine consumption and by-product formation is thought to be influenced by the chemical characteristics of the AOM. The measurement of the extent to which the organic material in a water sample reacts with chlorine under a set of controlled conditions and in the presence of excess free chlorine to form a suite of chlorinated products is called the DBP formation potential (DBPFP). The aqueous chlorine species are electrophilic, and therefore, tend to react with electron-rich sites in the organic structures, such as activated aromatics and bdicarbonyl aliphatics (Harrington et al., 1995). Many researchers found the aromatic moieties of AOM to be responsible for a significant amount of chlorine consumption (Reckhow et al., 1990; Debroux, 1998; Wu et al., 2000). Specific sites of AOM molecules that are thought to be chlorine reactive include phenol, 2,4pentanedione, amino nitrogen, meta-dihydroxy benzene, and various acetyl moieties (Stevens et al., 1976; Harrington et al., 1995; Hanna et al., 1991; Pomes et al., 1999; Rook, 1977). Organic nitrogen content, which indicates the presence of proteins and/or elevated algal content, was also found to be responsible for a significant proportion of THM and TOX formation (Reckhow et al., 1990; Gehr et al., 1993; Scully et al., 1988; Young and Uden, 1994). The measurement of such specific reactive sites is quite cumbersome; thus, certain surrogate parameters have been adopted to predict DBPFP. Many researchers have found TOC content (Arora et al., 1997), ultraviolet absorbance at 254 nm (UVA254) (Debroux, 1998; Edzwald et al., 1985; Gallard and Gunten, 2002), ultraviolet absorbance at 272 nm (Li et al., 1998), specific ultraviolet absorbance at 254 nm (SUVA254) (Reckhow et al., 1990), the ratio of dissolved organic carbon (DOC) concentration to absorbance at 260 nm (Debroux, 1998), and fluorescence spectral data (Aoki and Kawakami, 1992) to be good surrogate parameters that are well correlated to DBPFP, especially total THM formation potential (TTHMFP). The correlation of UV absorbance at 272 nm and TOX formation potential (TOXFP) was found to be independent of the source water quality (Korshin et al., 1996). However, the correlation of TOC/DOC and TTHMFP was found to be source specific (Gehr et al., 1993; Reckhow and Singer, 1990). The DBPFP of effluent-derived organic matter (EfOM) has not been widely evaluated. Since EfOM does not tend to be highly aromatic, it is often regarded to be biostabilized and less reactive with chlorine than AOM derived from natural sources (Aieta, 1998). However, EfOM tends to have much higher DOC concentrations than most surface water used as drinking water supplies. A survey of five wastewater treatment plants in southern CA showed that DBP produced after treatment was higher than before treatment (National
Research Council, 1998). In addition, the increase appeared to be strongly associated with the incoming organic quality. Others found that EfOM tended to form more brominated (Br)THM than NOM in the presence of bromide (Debroux, 1998). In a previous paper, we showed that the structural characteristics of EfOM differed from the NOM found in surface water having negligible anthropogenic impacts (Sirivedhin and Gray, 2005). Furthermore, wastewater effluent discharge to a surface water controlled the quantity and quality of organic material at various downstream locations. The goal of the research presented in this second paper was to determine if the structural differences associated with EfOM correspond to differences in function as measured by reactivity with chlorine or DBPFP. There were three specific objectives to this research: (1) to measure and compare the formation potentials of THM, HAA, and TOX between water samples that had minimal and high anthropogenic impact, (2) to examine the correlations between the different classes of DBPFP and conventional surrogate parameters (e.g., DOC, UVA254, and fluorescence spectral data), and (3) to identify chemical markers as produced by pyrolysis-GC/ MS that may be related to the formation potential of different classes of DBP.
2. Materials and methods 2.1. Study site This study was a continuation of the study conducted in 1998 (Sirivedhin and Gray, 2005); therefore, the same study site was used. In this study, there were five main sampling sites along the South Platte River (SPR) shown in Fig. 1: (1) SPR above Strontia Spring Reservoir (SPSS), (2) SPR above Marcy Gulch (SPMG), (3) effluent from Bi-Cities Wastewater Treatment Plant (BC EFF), (4) SPR at Burlington Canal headgate (SPBC), and (5) Clear Creek at Croke (CROKE). SPSS, SPMG, and CROKE were categorized as water samples that had minimal anthropogenic (e.g., wastewater) impact. The majority of SPBC flow was made up of BC EFF; therefore, these samples were categorized as having significant anthropogenic impact. Two sets of experiments were performed on these samples taken on two dates: 8/14/2000 and 9/5/2000. 2.2. Water quality measurements Water samples (8 L) were collected at each sampling location in two 4-L acid-washed amber glass bottles. The pH was measured in the field during the collection by the City of Thornton. These samples were packed in
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APHA, 1995). The test was conducted by first estimating the chlorine demand of each sample. Then each sample was buffered at pH 7, chlorinated with an excess of free chlorine, and stored at 25 1C for 7 days. At the end of 7 days, the free chlorine residual was measured using N,Ndiethyl-p-phenylenediamine (DPD) colorimetric method (4500-Cl G.; APHA, 1995). The different DBP (four THM, nine HAA, and TOX) were measured before and after the 7-day chlorine incubation period by an EPA certified laboratory (Barringer Laboratories, Inc., CO). The formation potential of each class of DBP was calculated as the difference between the concentrations in the 7-day chlorine incubated sample and the initial concentrations.
3. Results and discussion 3.1. General water data
Fig. 1. Locations of the sampling points along the South Platte River and wastewater treatment plants (not drawn to scale).
coolers filled with icepacks and shipped overnight to Northwestern University (Evanston, IL). Once received, sub-samples (10 mL) were taken for turbidity measurements, which were made with a Hach 2100P Turbidimeter. The rest of the samples were immediately filtered with 0.45 mm glass-fiber filter. The following analyses were performed on the filtered allotments: (1) DOC concentration measurement (Dohrmann DC-180 Automated TOC Analyzer), (2) UVA measurement at 254 nm (Hitachi U-2000 Spectrophotometer; 5910 B.; APHA, 1995), (3) fluorescence spectral analysis (Hitachi F-2000 Fluorescence Spectrophotometer; Smart et al., 1976), (4) pyrolysis-GC/MS (Sirivedhin and Gray, 2005; Bruchet et al., 1990; Widrig et al., 1996), (5) alkalinity measurement (2320 B.; APHA, 1995), (6) amino acids (Roth, 1971), and (7) glucosidic fraction (Dubois et al., 1956).
2.3. Disinfection by-product formation potential Seven-day DBPFP measurement was determined in accordance with the protocol in the Standard Methods for the Examination of Water and Wastewater (5710 A.;
Table 1 presents the general water quality data for the five locations in August and September 2000. Similar trends to the 1998 data (Sirivedhin and Gray, 2005) were observed in the pH and turbidity data. The pH and turbidity generally increased with the distance downstream, and the values for BC EFF were lower than other SPR water samples. In general, alkalinity, amino acids, and glucosidic fraction were lower in water samples having minimal anthropogenic impact (SPSS, SPMG, and CROKE) than those having high anthropogenic impact (BC EFF and SPBC). BC EFF samples exhibited the highest protein and polysaccharide contents as measured by amino acids and the glucosidic fraction, respectively. Although lower quantities were observed in SPBC samples, the protein and polysaccharide contents at this location were many times the values observed at CROKE or upstream on the SPR. Finally, the higher pH, amino acids, and glucosidic fraction measured in the August samples compared to the September samples are suggestive of algal bloom conditions. Table 2 shows the results from the analysis of organic carbon. In general, DOC concentration, UVA254, and the peak intensities of excitation and emission spectra were determined to be lower in water samples that had minimal anthropogenic impact than the ones that had high anthropogenic impact. As is generally found (MacCraith et al., 1993), the UVA and fluorescence of the samples increased linearly with increasing DOC. However, SUVA254 values were found to be lower in the samples that had high anthropogenic impact compared to those with minimal anthropogenic impact. This is in good agreement with their high glucosidic content (Table 1) since polysaccharides do not absorb in the UV range.
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1028 Table 1 General water quality data Sample ID
pH
Turbidity (ntu)
Alkalinity (mg/L as CaCO3)
Amino acids (mM)
Glucosidic fraction (mM)
August 14, 2000 SPSS 7.78 SPMG 9.75 BC EFF 8.60 SPBC 9.16 CROKE 9.44
7.55 8.08 3.94 5.70 5.80
37.92 79.32 109.71 142.10 40.76
0.43 1.48 5.70 2.38 0.87
3.72 7.00 52.52 16.47 8.09
September 5, 2000 SPSS 7.73 SPMG 7.78 BC EFF 7.93 SPBC 8.21 CROKE 7.86
7.74 7.15 3.88 11.2 5.03
45.68 76.73 121.07 172.94 46.67
ND ND 1.62 0.54 ND
ND 1.78 19.10 6.61 ND
ND ¼ not detected. Table 2 Analysis of organic carbon Sample ID
DOC (ppm C)
Fluorescence
UV254 UVA (cm1)
SUVA (L/mg m)
EXI (cm1)
SIEX (L/mg cm)
EMI (cm1)
SIEM (L/mg cm)
August 14, 2000 SPSS 2.31 SPMG 3.51 BC EFF 11.57 SPBC 11.51 CROKE 1.42
0.068 0.101 0.198 0.271 0.086
2.94 2.88 1.71 2.35 6.06
34.85 41.72 243.6 189.5 31.99
15.09 11.89 21.05 16.46 22.53
28.60 36.15 229.5 183.4 49.12
12.38 10.30 19.84 15.93 34.59
September 5, 2000 SPSS 1.91 SPMG 2.95 BC EFF 8.69 SPBC 5.64 CROKE 1.05
0.041 0.069 0.143 0.102 0.044
2.15 2.34 1.65 1.81 4.19
43.22 68.28 248.0 134.0 36.25
22.63 23.15 28.54 23.76 34.52
37.04 46.06 278.2 100.0 32.64
19.39 15.61 32.01 17.73 31.09
3.2. Formation potentials of THM, HAA, and TOX Table 3 summarizes TTHMFP, total HAA formation potential (THAAFP), and TOXFP for both August and September 2000 samples. In general, the formation potentials of all three categories of DBP were two to three times higher in the water samples with significant anthropogenic impact than those with minimal anthropogenic impact. This is attributed primarily to the high DOC levels of those samples having significant anthropogenic impact. In order to consider the reactivity with chlorine on a per carbon basis, all the DBPFP data were normalized relative to the DOC concentrations to obtain the specific yields. In this comparison, the water samples that had high anthropogenic impact possessed lower specific DBPFP yields in all three DBP categories. These
lower values correspond to the higher glucosidic content (Table 1) since polysaccharides are very poor DBP precursors. The CROKE samples produced the greatest specific yields of both TTHMFP and THAAFP as expected based on their spectral properties (e.g., high SUVA), but the lowest absolute quantities, which was consistent with their low DOC levels. Another interesting trend observed in these data was that the DBPFP levels were greater in general among the September samples than August, although the DOC concentrations were lower in the September samples. This illustrates the seasonal influences on the chlorine reactivity of DOC and is likely associated with a shift away from the algal inputs that prevailed in August. These comparisons illustrate the distinctive quantitative and qualitative influences on DBPFP. In general, higher DOC
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Table 3 Summary of DBPFP data TTHMFP (mg/L)
Specific TTHMFP yield
THAAFP (mg/L)
August 14, 2000 SPSS 9.35 SPMG 8.90 BC EFF 27.05 SPBC 13.30 CROKE 8.90
111 158 265 291 100
48.1 45.0 22.9 25.3 70.4
128 176 242 231 120
55.4 50.1 20.9 20.1 84.5
September 5, 2000 SPSS 38.55 SPMG 40.77 BC EFF 54.06 SPBC 40.32 CROKE 23.49
146 203 398 285 100
76.4 68.8 45.8 50.5 95.2
167 217 426 286 124
87.4 73.6 49.0 50.7 118.1
Sample
Chlorine demand (mg Cl2/L)
Specific THAAFP yield
TOXFP (mg/L)
Specific TOX yield
n/a n/a n/a n/a n/a
n/a n/a n/a n/a n/a
819.2 781.7 1610 1505 630.2
428.9 265.0 185.3 266.8 600.2
n/a ¼ not available.
Table 4 Concentrations (in mg/L) of individual THM and HAA Sample
Individual HAA species BCAA
BDCAA
August 2000 SPSS 3.4 SPMG 12.15 BC EFF 22 SPBC 18 CROKE 3.4
5.3 18 46 32 6
September 2000 SPSS 3.25 SPMG 10.35 BC EFF 34 SPBC 31 CROKE 4.275
12.75 27.5 62 64 14.25
Individual THM species CAA
1.7 4.9 3.3 6.22 3.87 ND ND 14 ND ND
CDBAA
DBAA
DCAA
TCAA
BDCM
TCM
DBCM
ND 2.25 8.2 4.4 1.8
ND 1.6 3 2.3 ND
55 68.75 101 70.5 48.5
62.5 68 58.5 66.5 56
8.93 22.50 64 56 13.75
101.5 132.5 185 225 84.75
0.3 3.48 16.5 10.5 1.43
ND 2.73 9.93 20.5 ND
ND 0.77 3.3 5.25 ND
67.75 90.75 185 95.5 50
83.75 85 117.5 70 55.75
9 23.5 68 79.5 9.63
137.5 180 320 185 90.25
ND ND 10.25 20.25 0.5
BCAA ¼ bromochloroacetic acid, BDCAA ¼ bromodichloroacetic acid, CAA ¼ chloroacetic acid, CDBAA ¼ chlorodibromoacetic acid, DBAA ¼ dibromoacetic acid, DCAA ¼ dichloroacetic acid, TCAA ¼ trichloroacetic acid, BDCM ¼ bromodichloromethane, TCM ¼ chloroform, DBCM ¼ dibromochloromethane, ND ¼ not detected.
concentration produced higher absolute DBPFP, but the differences in organic quality accounted for the differences in the reactivity observed on a molecular basis. Table 4 shows the concentrations (in mg/L) for individually measured HAA and THM species. Of the four THM species measured, only bromoform (TBM) was below the detection limit of 2 mg/L. Chloroform (TCM) was the major chlorination by-product, followed by bromodichloromethane (BDCM) and dibromochloromethane (DBCM). This same distribution was also found in another study (Croue´ et al., 2000). BDCM, which ranged from 17 to 28% of TTHM in the water samples that had high anthropogenic impact compared to 6 to 14% of TTHM in water samples that had
minimal anthropogenic impact, was recently associated with reproductive effects (Health Canada Report, 2000). DBCM was detected in trace amounts, if at all, in the less anthropogenically impacted surface water samples; however, it was 3–7% of TTHM in BC EFF and SPBC. Finally, higher percentages of Br-THM, ranging from 20 to 35%, were measured in BC EFF and SPBC samples, with the highest percentage of 35% being observed in September at SPBC. Of the nine HAA species measured, two species were below the detection limit of 2 mg/L, namely bromoacetic acid (BAA) and tribromoacetic acid (TBAA). Overall, trichloroacetic acid (TCAA) was the major HAA chlorination product in the surface waters that had
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EFF and that the bromide level in SPBC samples may have been higher than that in BC EFF.
minimal anthropogenic impact; however, the dominant HAA was shifted to dichloroacetic acid (DCAA) for water samples that had high anthropogenic impact. Higher Br-HAA levels were measured for BC EFF sample and SPBC sample. The Br-HAA species were less than 10% of the total for the SPSS samples, less than 15% for CROKE, and less than 20% for SPMG. In contrast, the Br-HAA levels were typically greater than 25% for the BC EFF and SPBC, with a high of 42% for the September SPBC sample. Although individual components of the EfOM were less reactive with chlorine as illustrated by the normalized or specific DBP yields, the overall DBPFP levels of EfOM (BC EFF and SPBC) were much higher than the water samples that had minimal anthropogenic impact because EfOM tended to have much higher DOC concentrations. Furthermore, EfOM produced a greater proportion of Br-DBP, which is considered particularly deleterious to human health. Similar distributions were also observed in other studies (Debroux, 1998; National Research Council, 1998). Finally, the greatest proportion of Br-DBP was observed in SPBC (September 2000), which may be due to the combined effect that the organic quality at this location was controlled by BC
3.3. Comparison of organic quality of EfOM and NOM In our previous paper (Sirivedhin and Gray, 2005), we showed that the organic qualities of EfOM and NOM are quantitatively and qualitatively distinct. In addition, under the flow conditions of SPR, the organic signature of BC EFF persisted and controlled the quantity and quality at SPBC. Fig. 2 shows the organic fingerprints of SPSS, SPMG, BC EFF, SPBC, and CROKE on 8/14/ 2000 and 9/5/2000. The organic fingerprints of this set of samples differed from the fingerprints of the 1998 samples. Specifically, the wastewater markers generated by pyrolysis-GC/MS in BC EFF and SPBC in 1998 were benzaldehyde, benzonitrile, chlorobutanoic acid, furancarboxaldehyde, and methylfurancarboxaldehyde; however, in 2000, these markers were present at relatively low levels and certainly not at a noticeably higher level compared to the organic fingerprints of the samples that had minimal anthropogenic impact. Instead, the distinct trait of the samples that had high anthropogenic
9/5/00
SPSS SPMG
100 75 50 25 0
BC EFF
100 75 50 25 0
SPBC
% Full Scale
100 75 50 25 0
100 75 50 25 0
CROKE
8/14/00
100 75 50 25 0
1
100 75 50 25 0
4 3
6
2 5
6 1 2
5
5
3
6
6 3 2
1
2
3 4
20
40
60
5
6 1 2 3 5
5
100 75 50 25 0
6
80
100
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6
3
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7
100 75 50 25 0
5
7
5
100 75 50 25 0
2
1
6 2 3
100 75 50 25 0
3
1
1
1
5
2
6
6
3 2
7
1 5 40
60
80
100
120
Retention Time (minute) Fig. 2. Organic fingerprints of SPSS, SPMG, BC EFF, SPBC, and CROKE on 8/14/2000 and 9/5/2000 (1 ¼ acetic acid, 2 ¼ propanoic acid, 3 ¼ benzonitrile, 4 ¼ benzothiophene, 5 ¼ acetamide, 6 ¼ phenol, and 7 ¼ hexahydroazepinone).
ARTICLE IN PRESS T. Sirivedhin, K.A. Gray / Water Research 39 (2005) 1025–1036
SPSS SPMG BC EFF SPBC CROKE
6 September
PC2 (28.6%)
impact in 2000 was an intense acetamide peak, which is linked to N-acetylaminosugars from bacterial cell walls (Irwin, 1982). Based on qualitative comparison alone, the SPBC samples bear a chemical fingerprint that differs markedly from SPSS in terms of predominant chemical nature and proportions of pyrolysis fragments. Yet, using this simple qualitative method of comparing pyrolysis profiles, the chemical quality of SPBC among these 2000 samples does not appear as similar to BC EFF as it did in 1998. As discussed below, this observation illustrates the limitations of simply making qualitative interpretation of the pyrolysis data. The dissimilarity between the organic quality of the 1998 and 2000 samples was probably due mainly to the drought conditions that prevailed in the summer of 2000. Nonetheless, the possible anthropogenic marker for this set of samples (i.e., acetamide), which was not present at a high level in the organic fingerprints of the samples that had minimal anthropogenic impact, persisted and was measured to be relatively high in SPBC sample in August. In September, a very intense hexahydroazepinone peak was detected in the organic fingerprint of SPBC, which overwhelmed the acetamide peak as well as the other pyrolysis fragments produced in this sample. Hexahydroazepinone (or caprolactam) is typically found among the pyrolysis products of aliphatic polyamides (e.g., nylon); this peak is suspected to be sample contamination. Nevertheless, the intensity of acetamide in the September SPBC fingerprint was still large compared to other chemical fragments. Principal component analysis (PCA) was performed on the data generated by pyrolysis-GC/MS to reduce the large, highly correlated variables (i.e., chemical fragments) to a much smaller set of independent variables (i.e., groupings of critical chemical fragments) while preserving most of the variation in the data. The August and September 2000 samples and their duplicates generated a total of 489 chemical fragments. PCA was carried out to reduce it down to 27 critical chemical fragments while still maintaining 80% of the total variance. The score plot of PC1 versus PC2 clearly separated the water samples that had minimal anthropogenic impact from those that had high anthropogenic impact as illustrated in Fig. 3. These two principal components account for nearly 60% of the variance of this sample set. The separation was mainly controlled by PC1, which accounts for 30.1% of the total variance of the data. Samples with minimal anthropogenic impact had negative PC1 scores. Since PC1 is negatively influenced by acetic acid, propanoic acid, methylpropanoic acid, phenol, and methylphenol, these chemical fragments are ‘‘natural’’ markers for this set of samples. In contrast, samples with high anthropogenic impact had positive PC1 scores. Since PC1 is positively influenced by acetamide, benzaldehyde, chlorobutanoic
1031
4 August
August
2
August
September
0
August September
August
−2
September
−4
−3
−2
September
−1
0
1
2
3
4
PC1 (30.1%) Fig. 3. Score plot of PC1 versus PC2 for the organic quality of all samples collected on 8/14/2000 and 9/5/2000.
acid, benzenedicarbonitrile, undecanoic acid, these chemical fragments are ‘‘wastewater’’ markers for this set of samples. This analysis statistically established that, as seen in the 1998 samples (Sirivedhin and Gray, 2005), the organic quality of SPSS, SPMG, and CROKE as characterized by pyrolysis-GC/MS was different from that of BC EFF and SPBC. For the August and September 2000 samples, these differences were not apparent from simple qualitative comparison (Fig. 2); therefore, this result clearly illustrates that the full power of pyrolysis-GC/MS comes from the use of multivariate statistical techniques in interpreting data.
3.4. Chemical markers for the formation of different classes of DBP TTHMFP, THAAFP, Br-THMFP, and Br-HAAFP were found to be negatively correlated to the ratio of total aromatic to total aliphatic based on the pyrolysisGC/MS data (Fig. 4). Previous research in our group (Gray et al., 1996; Gray, 1997) as well as others (Hwang et al., 2001) have found that phenolic content, as measured by pyrolysis-GC/MS, is generally negatively correlated to THMFP. Some other research groups, however, have found the contrary. For instance, the percent aromatic content (Croue´ et al., 2000) or phenolic content as measured by pyrolysis-GC/MS (Harrington et al., 1996) of the sample was reported to be good indicator of chlorine consumption and the formation of certain classes of DBP. It is important to note, however, that in both these studies, the organic material was extracted from the whole water samples using XAD resins. The extraction technique tends to concentrate the aromatic fraction disproportionally (Maurice et al., 2002), which explains why the observed reactivity of chlorine is attributed to aromatic structures. For this
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1032 400
100
Br-THMFP, µg/L
T THMFP, µg/L
350 300 r 2 = − 0.618 p = 0.057
250 200 150 100 50
60
r 2 = − 0.689 p = 0.027
40 20 0 −20
0 0.0
0.5
1.0
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(A) 450 400 350 300 250 200 150 100 50 0
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(B) 120
Br-HAAFP, µg/L
THAAFP, µg/L
80
2 r = − 0.571 p = 0.084
100 80 2
r = − 0.621 p = 0.055
60 40 20 0 −20
0.0
0.5
1.0
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Total Aromatic : Total Aliphatic
(C)
0.0
0.5
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(D)
Fig. 4. Correlations of (A) TTHMFP, (B) Br-THMFP, (C) THAAFP, and (D) Br-HAAFP with total aromatic to aliphatic ratio as measured by pyrolysis-GC/MS.
100
Br-THMFP, µg/L
T THMFP, µg/L
400 350 300 2
r = 0.866 p = 0.001
250 200 150
80
40 20
100
0 0
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Br-HAAFP, µg/L
THAAFP, µg/L
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450 400 350 300 250 200 150 100
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r = 0.905 p < 0.001
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Fig. 5. Correlations of (A) TTHMFP, (B) Br-THMFP, (C) THAAFP, and (D) Br-HAAFP with total halogenated signature as measured by pyrolysis-GC/MS.
reason, we study structure/function relationships using whole waters. The difference in sample preparation (organic extract versus whole water concentrate), then, explains the differences observed in the relationship between aromatic moieties and DBPFP.
Relatively good linear correlations were found between the formation potentials of TTHMFP and THAAFP with the total halogenated content as measured by pyrolysis-GC/MS (Fig. 5). This finding implies that the sites that are chlorine reactive during the
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chlorination process in wastewater treatment remain reactive in the DBPFP test. In contrast, the correlations between formation potentials of the Br-DBP and the total halogenated content were poorer, indicating that the chlorine reactive sites are not necessarily the same as the sites that promote the formation of Br-DBP. No single chemical fragment generated by pyrolysis was shown to be a strong marker for DBPFP, which was also found to be the case elsewhere and is likely the result of the vast complexity of AOM (Reckhow et al., 1990). The normalized peak height intensities of the critical 27 chemical fragments that were found to produce good separation between samples that had minimal and high anthropogenic impact with PCA (Fig. 3) were correlated to TTHMFP, THAAFP, BrTHMFP, and Br-HAAFP using a simple correlation matrix. Considering only the chemical fragments that carried absolute values of correlation coefficients higher than 0.5 (i.e., 11 of the 27 chemical fragments), the sum of the product of the normalized peak height intensities of the highly correlated fragments and their respective correlation coefficients were found to be linearly correlated to the formation potentials of each of the four classes of DBP. These chemical fragments as well as their correlation coefficients are shown in Table 5. The signs of the correlation coefficients indicated their respective positive or negative effect on the formation potential of each class of DBP. In general, the chemical fragments that contributed to these correlations included some organic nitrogen (i.e., acetamide, benzenedicarbonitrile), halogenated (i.e., chlorobutanoic acid), long-chained aliphatic (i.e., undecanoic acid), and aromatic (i.e., benzaldehyde) structures. Evidence that nitrogen-containing compounds (e.g., protein and amino sugars) in the organic matrix (Scully et al., 1988; Croue´ et al., 2000; Harrington et al., 1996; Pomes et al., 2000) and general aliphatic features (Gray et al., 1996) were possible precursor sites was also found in other studies.
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Fig. 6A shows the correlation between TTHMFP and the linear combination of the peak height intensities of acetamide, benzaldehyde, chlorobutanoic acid, methylpropanoic acid, and propanoic acid. Fig. 6B shows the correlation between Br-THMFP and the linear combination of the peak height intensities of acetamide, acetic acid, benzenedicarbonitrile, chlorobutanoic acid, dimethylphenol, methylphenol, methylpropanoic acid, phenol, propanoic acid, and undecanoic acid. Fig. 6C shows the correlation between THAAFP and the linear combination of the peak height intensities of acetamide, benzaldehyde, chlorobutanoic acid, methylpropanoic acid, and phenol. And Fig. 6D shows the correlation between Br-HAAFP and the linear combination of the peak height intensities of benzaldehyde, benzenedicarbonitrile, chlorobutanoic acid, methylpropanoic acid, phenol, propanoic acid, and undecanoic acid. Student’s t-tests were performed between each linear combination of the peak height intensities and its respective DBPFP (a ¼ 0:05) showing that all four correlations were all statistically significant (po0:0001). The surprising finding in this analysis is that the phenolic signature was not significantly correlated with TTHMFP, but rather it was negatively correlated with THAAFP, Br-THMFP, and Br-HAAFP (Table 5). These results strongly suggest that the nature of AOM was a very important factor influencing the product distribution of THM and HAA. While the amount of DOC is a major determinant in the total amount of DBP formed, the chemical nature of the AOM determines the product distribution of DBP. For these samples, varying combinations of pyrolysis fragments were found to be associated with the formation potentials of four general classes of DBP. This analysis of whole waters reveals that while aromatic structures do play a positive role in reactivity with chlorine, phenolic structures, as characterized by pyrolysis-GC/ MS, appear to be negatively correlated, when found to have an influence at all. Among these waters, reactivity with chlorine was found to be related to a complex
Table 5 Correlation coefficients (only shown when the absolute value is greater than 0.5) Pyrolysis fragment Acetamide Acetic acid Benzaldehyde Benzenedicarbonitrile Chlorobutanoic acid Dimethylphenol Methylphenol Methylpropanoic acid Phenol Propanoic acid Undecanoic acid
[TTHM]
[THAA]
0.768827
0.573536
0.677007
0.782077
0.848341
0.69398 0.55146
0.629117
0.53822 0.51164
[Br-THM]
[Br-HAA]
0.714681 0.58877 0.77418 0.863202 0.51749 0.54306 0.75758 0.56906 0.71855 0.531877
0.551291 0.547801 0.574305
0.57955 0.59298 0.5446 0.624769
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1034
140
Br-THMFP, µg/L
T THMFP, µg/L
400 350 300 250 200
r 2 = 0.883 p < 0.0001
150 100 50 −1.0
−0.5
0.0
0.5
1.0
20 −4
350 300 250 2
r = 0.905 p < 0.0001
Br-HAAFP, µg/L
THAAFP, µg/L
r 2 = 0.786 p < 0.0001
40
−3
−2
−1
0
1
2
Combination Peaks
(B)
100
Combination Peaks
100 80 60 40
r 2 = 0.867 p < 0.0001
20 0 −20 −4
−1.5 −1.0 −0.5 0.0 0.5 1.0 1.5
(C)
60
120
400
150
80
1.5
450
200
100
0
Combination Peaks
(A)
120
(D)
−3
−2
−1
0
1
2
Combination Peaks
Fig. 6. Correlation of the combination of normalized peak height intensities to the formation potentials of (A) TTHM, (B) Br-THM, (C) THAA, and (D) Br-HAA.
function of aliphatic and aromatic structures substituted with nitrogen, oxygen (carboxylic acids), and chlorine.
4. Conclusions In our previous paper (Sirivedhin and Gray, 2005), we found that the EfOM and NOM were structurally different and that EfOM persisted in natural waters. In this study, we found that the structurally different organic matrices of EfOM and NOM also behaved differently in the chlorination process. Although EfOM was found to be less reactive with chlorine on a DOC concentration basis, water samples that had higher anthropogenic impact were found to have higher overall DBPFP due to their higher DOC concentrations. Furthermore, a shift in DBP proportions to brominated species was observed for EfOM. This shift to higher BrDBP was amplified in effluent-dominated streams possibly because higher bromide concentrations prevail in the river water than in the effluent. These results are significant for indirect potable water reuse in that effluent-dominated streams will not only show elevated DBPFP, but also higher yields of brominated species and elevated health risks associated with their presence. Finally, individual chemical markers produced by pyrolysis-GC/MS were not found to be indicative of the formation potentials of different classes of DBP; rather, combinations of chemical fragments were found to be well associated with the formation potentials of
TTHM, Br-THM, THAA, and Br-HAA for this set of samples. In contrast to the conventional notion that DBPFP is higher in waters that have higher aromatic carbon content, we found a combination of aromatic and aliphatic structures including some substituted with nitrogen and chlorine to show a linear relationship with DBPFP.
Acknowledgements This work was supported by the City of Thornton. The authors would like to thank Vic Lucero from the City of Thornton for sample collection, Dr. Deanna Hurum for analytical assistance, and Dr. Rapeepat Ratasuk for multivariate statistical analysis help.
References Aieta, M., 1998. The impacts of the Strontia Springs/Bi-City water exchange practice by Denver water on Thornton source water quality and the Columbine treatment plant performance. pp. 26+ Appendix D. Aoki, T., Kawakami, K., 1992. Continuous-flow method for the determination of total trihalomethane formation potential in waters. Anal. Chim. Acta 261, 335–338. APHA, 1995. Standard Methods for the Examination of Water and Wastewater. American Public Health Association, Washington.
ARTICLE IN PRESS T. Sirivedhin, K.A. Gray / Water Research 39 (2005) 1025–1036 Arora, H., LeChevallier, M.W., Dixon, K.L., 1997. DBP occurrence survey. J. Am. Water Works Assoc. 89, 60–68. Black, B.D., Harrington, G.W., Singer, P.C., 1996. Reducing cancer risks by improving organic carbon removal. J. Am. Water Works Assoc. 88, 40–52. Bruchet, A., Rousseau, C., Mallevialle, J., 1990. Pyrolysis-GC/ MS for investigating high-molecular weight THM precursors and other refractory organics. J. Am. Water Works Assoc. 82, 66–74. Bull, R.J., Kopfler, F.C., 1991. Health Effects of Disinfectants and Disinfection By-products. AWWARF and AWWA, Denver. Croue´, J.-P., Korshin, G.V., Leenheer, J.A., Benjamin, M.M., 2000. Isolation, Fractionation and Characterization of Natural Organic Matter in Drinking Water. AWWA Research Foundation and American Water Works Association, Denver, CO. Debroux, J.-F., 1998. The physical–chemical and oxidantreactive properties of effluent organic matter (EfOM) intended for potable reuse. Ph.D. Thesis, University of Colorado, Boulder, p. 227. Dubois, M., Gilles, K.A., Hamilton, J.K., Rebers, P.A., Smith, F., 1956. Colorimetric method for determination of sugars and related substances. Anal. Chem. 28, 350–355. Edzwald, J.K., Becker, W.C., Wattier, K.L., 1985. Surrogate measures for monitoring organic matter and THM precursors. J. Am. Water Works Assoc. 77, 122–132. Gallard, H., Gunten, U.V., 2002. Chlorination of natural organic matter: kinetics of chlorination and THM formation. Water Res. 36, 65–74. Gehr, R., Startz, C., Offringa, G., 1993. Removal of trihalomethanes precursors from eutrophic water by dissolved air floatation. Water Res. 27, 41–49. Gray, K.A., 1997. Characterization of NOM using Py/GC/MS and NMR. Sunday Seminar, Annual Meeting AWWA. Gray, K.A., Simpson, A.H., McAuliffe, K.S., 1996. Use of pyrolysis gas chromatography–mass spectrometry to study nature and behavior of natural organic matter in water treatment. In: Minear, R.A., Amy, G.L. (Eds.), Water Disinfection and Natural Organic Matter: Characterization and Control. American Chemical Society, Washington, DC. Hanna, H.V., Johnson, W.D., Quezada, R.A., Wilson, M.A., Xiao-Qiao, L., 1991. Characterization of aqueous humic substances before and after chlorination. Environ. Sci. Technol. 25, 1160–1164. Harrington, G.W., Bruchet, A., Rybacki, D., Singer, P.C., 1995. Comparison of Pyrolysis GC/MS and 13C NMR for Characterization of Natural Organic Matter and its Reactivity with Chlorine. American Chemical Society, Division of Environmental Chemistry, Chicago, IL. Harrington, G.W., Bruchet, A., Rybacki, D., Singer, P.C., 1996. Characterization of natural organic matter and its reactivity with chlorine. In: Minear, R.A., Amy, G.L. (Eds.), Water Disinfection and Natural Organic Matter: Characterization and Control. American Chemical Society, Washington, DC. Health Canada Report, 2000. Reproductive and developmental effects of disinfection by-products. Hwang, C.J., Amy, G.L., Bruchet, A., Croue´, J.-P., Krasner, S.W., Leenheer, J.A., 2001. Polar NOM: Characterization,
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DBPs, Treatment. American Water Works Association Research Foundation [AWWARF Project #451], pp. 4–45. Irwin, W.J., 1982. Analytical Pyrolysis: A Comprehensive Guide. Marcel Dekker, Inc., New York. Kanitz, S., Franco, Y., Patrone, V., Caltabellotta, M., Raffo, E., Riggi, C., Timitilli, D., Ravera, G., 1996. Association between drinking water disinfection and tomatic parameters at birth. Environ. Health Perspect. 104, 516–520. Korshin, G.V., Li, C.-W., Benjamin, M.M., 1996. Use of UV spectroscopy to study chlorination of natural organic matter. In: Minear, R.A., Amy, G.L. (Eds.), Water Disinfection and Natural Organic Matter: Characterization and Control. ACS, Washington, DC. Li, C.-W., Korshin, G.V., Benjamin, M.M., 1998. Monitoring DBP formation with differential UV spectroscopy. J. Am. Water Works Assoc. 90, 88–100. MacCraith, B., Grattan, K., Connolly, D., Briggs, R., Boyle, W., Avis, M., 1993. Cross comparison of techniques for the monitoring of total organic carbon (TOC) in water sources and supplies. Water Sci. Technol. 28, 457–463. Maurice, P.A., Pullin, M.J., Cabaniss, S.E., Zhou, Q., Namjesnik-Dejanovic, K., Aiken, G.R., 2002. A comparison of surface water natural organic matter in raw filtered water samples, XAD, and reverse osmosis isolates. Water Res. 36, 2357–2371. Morris, R.D., Andet, A.-M., Angelillo, I.F., Chalmers, T.C., Mosteller, F., 1992. Chlorination, chlorination by-products, and cancer: a meta-analysis. Am. J. Public Health 82, 955–963. National Research Council, 1998. Issues in Potable Reuse: The Viability of Augmenting Drinking Water Supplies with Reclaimed Water. National Academy Press, Washington, DC. Pomes, M.L., Green, W.R., Thurman, E.M., Orem, W.H., Lerch, H.E., 1999. DBP formation potential of aquatic humic substances. J. Am. Water Works Assoc. 91, 103–115. Pomes, M.L., Larive, C.K., Thurman, E.M., Green, W.R., Orem, W.H., Rostad, C.E., Coplen, T.B., Cutak, B.J., Dixon, A.M., 2000. Sources and haloacetic acid/trihalomethanes formation potentials of aquatic humic substances in the Wakarusa River and Clinton Lake near Lawrence. Kansas Environ. Sci. Technol. 34, 4278–4286. Reckhow, D.A., Singer, P.C., 1990. Chlorination byproducts in drinking waters: from formation potentials to finish water concentrations. J. Am. Water Works Assoc. 82, 173–180. Reckhow, D.A., Singer, P.C., Malcolm, R.L., 1990. Chlorination of humic materials: byproducts formation and chemical interpretations. Environ. Sci. Technol. 24, 1655–1664. Rook, J.J., 1977. Chlorination reactions of fulvic acids in natural waters. Environ. Sci. Technol. 11, 478–482. Roth, M., 1971. Fluorescence reaction for amino acid. Anal. Chem. 43, 880–882. Scully Jr., F.E., Howell, G.D., Kravitz, R., Jewell, J.T., 1988. Protein in natural waters and their relation to the formation of chlorinated organics during water disinfection. Environ. Sci. Technol. 22, 537–542. Singer, P.C., 1999. Formation and control of disinfection byproducts in drinking water. American Water Works Association, Denver, CO.
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Singer, P.C., Chang, S.D., 1989. Correlations between trihalomethanes and total organic halides formed during water treatment. J. Am. Water Works Assoc. 81, 61–65. Sirivedhin, T., Gray, K.A., 2005. Identifying anthropogenic markers in surface water influenced by treated effluents: a tool in potable water reuse. Water Res., accepted for publication, doi:10.1016/j.watres.2004.11.032. Smart, P.L., Finlayson, B.L., Rylands, W.D., Ball, C.M., 1976. The relation of fluorescence to dissolved organic carbon in surface waters. Water Res. 10, 805–811. Stevens, A.A., Slocum, C.J., Seeger, D.R., Robeck, G.G., 1976. Chlorination of organics in drinking water. J. Am. Water Works Assoc. 68, 615–620. Stevens, A.A., Moore, L.A., Miltner, R.S., 1989. Formation and control of nontrihalomethanes disinfection byproducts. J. Am. Water Works Assoc. 81, 54. Widrig, D.L., Gray, K.A., McAuliffe, K.S., 1996. Removal of algal-derived organic material by preozonation and coagu-
lation: monitoring changes in organic quality by pyrolysisGC–MS. Water Res. 30, 2621–2632. Wu, W.W., Chadik, P.A., Davis, W.M., Delfino, J.J., Powell, D.H., 2000. The effect of structural characteristics of humic substances on disinfection by-product formation in chlorination. In: Barrett, S.E., Krasner, S.W., Amy, G.L. (Eds.), Natural Organic Matter and Disinfection By-products: Characterization and Control in Drinking Water. American Chemical Society, Washington, DC. Young, M.S., Uden, P.C., 1994. Byproducts of aqueous chlorination of purines and pyrimidines. Environ. Sci. Technol. 28, 1755–1758. Zavaleta, J.O., Hauchman, F.S., Cox, M.W., 1999. Epidemiology and toxicology of disinfection by-products. In: Singer, P.C. (Ed.), Formation and Control of Disinfection Byproducts in Drinking Water. American Water Works Association, Denver.
Water Research 39 (2005) 1025–1036 www.elsevier.com/locate/watres
2. Comparison of the disinfection by-product formation potentials between a wastewater effluent and surface waters Tanita Sirivedhin, Kimberly A. Gray Department of Civil and Environmental Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA Received 18 August 2003; received in revised form 21 April 2004; accepted 18 November 2004
Abstract In this study, the chemical reactivity with chlorine as measured by disinfection by-product formation potential (DBPFP) is compared among samples of a wastewater effluent and surface waters. Water samples that had higher anthropogenic impacts were found to have higher overall DBPFP due primarily to higher dissolve organic carbon (DOC) concentrations. Effluent-derived organic matter (EfOM), however, was found to be less reactive with chlorine on a per DOC concentration basis. Yet, EfOM had higher proportions of brominated DBP, which may be associated with greater health risks. In this research, pyrolysis-GC/MS was used to establish relationship between structural features of DOC and DBPFP. We show that there is a critical set of pyrolysis fragments that separates the waters based on the degree of anthropogenic influence. Even though no single chemical marker was found to be indicative of the formation potentials of different classes of DBP, combinations of chemical fragments were found to be associated with the formation potentials of total trihalomethane (THM), brominated THM, total haloacetic acid (HAA), and brominated HAA for this set of samples. In contrast to previous work, the phenolic signature of these samples was negatively correlated to DBPFP, whereas strong relationships were found between DBPFP and the organic nitrogen and halogenated signatures. r 2005 Elsevier Ltd. All rights reserved. Keywords: Pyrolysis-GC/MS; Disinfection by-products; Wastewater; Trihalomethane; Haloacetic acid
1. Introduction In the chlorination process, aquatic organic matter (AOM) serves as a precursor to the formation of potentially harmful disinfection by-products (DBP) such as trihalomethanes (THM), haloacetic acids (HAA), and total organic halides (TOX). In general, waters with higher total organic carbon (TOC) concentrations are found to produce more DBP in chlorination (Singer and DOI of original article: 10.1016/j.watres.2004.11.032 author. Tel.: +1 847 467 4252; fax: +1 847 491 4011. E-mail address: [email protected] (K.A. Gray). Corresponding
Chang, 1989). DBP in drinking water are considered to be carcinogenic, mutagenic, and teratogenic (Kanitz et al., 1996; Singer, 1999; Zavaleta et al., 1999; Black et al., 1996), and therefore, they pose adverse health effects in both human and animals (Bull and Kopfler, 1991; Morris et al., 1992). Historically, much of the study of health risks associated with DBP has been centered on THM; however, there is a growing concern about the health risks associated with HAA. Previous research has studied the influences of temperature, pH, reaction time, free and combined chlorine concentrations, as well as precursor type and precursor concentration on the formation of DBP (Stevens et al., 1976, 1989; Reckhow et al., 1990). The
0043-1354/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.11.031
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extent of chlorine consumption and by-product formation is thought to be influenced by the chemical characteristics of the AOM. The measurement of the extent to which the organic material in a water sample reacts with chlorine under a set of controlled conditions and in the presence of excess free chlorine to form a suite of chlorinated products is called the DBP formation potential (DBPFP). The aqueous chlorine species are electrophilic, and therefore, tend to react with electron-rich sites in the organic structures, such as activated aromatics and bdicarbonyl aliphatics (Harrington et al., 1995). Many researchers found the aromatic moieties of AOM to be responsible for a significant amount of chlorine consumption (Reckhow et al., 1990; Debroux, 1998; Wu et al., 2000). Specific sites of AOM molecules that are thought to be chlorine reactive include phenol, 2,4pentanedione, amino nitrogen, meta-dihydroxy benzene, and various acetyl moieties (Stevens et al., 1976; Harrington et al., 1995; Hanna et al., 1991; Pomes et al., 1999; Rook, 1977). Organic nitrogen content, which indicates the presence of proteins and/or elevated algal content, was also found to be responsible for a significant proportion of THM and TOX formation (Reckhow et al., 1990; Gehr et al., 1993; Scully et al., 1988; Young and Uden, 1994). The measurement of such specific reactive sites is quite cumbersome; thus, certain surrogate parameters have been adopted to predict DBPFP. Many researchers have found TOC content (Arora et al., 1997), ultraviolet absorbance at 254 nm (UVA254) (Debroux, 1998; Edzwald et al., 1985; Gallard and Gunten, 2002), ultraviolet absorbance at 272 nm (Li et al., 1998), specific ultraviolet absorbance at 254 nm (SUVA254) (Reckhow et al., 1990), the ratio of dissolved organic carbon (DOC) concentration to absorbance at 260 nm (Debroux, 1998), and fluorescence spectral data (Aoki and Kawakami, 1992) to be good surrogate parameters that are well correlated to DBPFP, especially total THM formation potential (TTHMFP). The correlation of UV absorbance at 272 nm and TOX formation potential (TOXFP) was found to be independent of the source water quality (Korshin et al., 1996). However, the correlation of TOC/DOC and TTHMFP was found to be source specific (Gehr et al., 1993; Reckhow and Singer, 1990). The DBPFP of effluent-derived organic matter (EfOM) has not been widely evaluated. Since EfOM does not tend to be highly aromatic, it is often regarded to be biostabilized and less reactive with chlorine than AOM derived from natural sources (Aieta, 1998). However, EfOM tends to have much higher DOC concentrations than most surface water used as drinking water supplies. A survey of five wastewater treatment plants in southern CA showed that DBP produced after treatment was higher than before treatment (National
Research Council, 1998). In addition, the increase appeared to be strongly associated with the incoming organic quality. Others found that EfOM tended to form more brominated (Br)THM than NOM in the presence of bromide (Debroux, 1998). In a previous paper, we showed that the structural characteristics of EfOM differed from the NOM found in surface water having negligible anthropogenic impacts (Sirivedhin and Gray, 2005). Furthermore, wastewater effluent discharge to a surface water controlled the quantity and quality of organic material at various downstream locations. The goal of the research presented in this second paper was to determine if the structural differences associated with EfOM correspond to differences in function as measured by reactivity with chlorine or DBPFP. There were three specific objectives to this research: (1) to measure and compare the formation potentials of THM, HAA, and TOX between water samples that had minimal and high anthropogenic impact, (2) to examine the correlations between the different classes of DBPFP and conventional surrogate parameters (e.g., DOC, UVA254, and fluorescence spectral data), and (3) to identify chemical markers as produced by pyrolysis-GC/ MS that may be related to the formation potential of different classes of DBP.
2. Materials and methods 2.1. Study site This study was a continuation of the study conducted in 1998 (Sirivedhin and Gray, 2005); therefore, the same study site was used. In this study, there were five main sampling sites along the South Platte River (SPR) shown in Fig. 1: (1) SPR above Strontia Spring Reservoir (SPSS), (2) SPR above Marcy Gulch (SPMG), (3) effluent from Bi-Cities Wastewater Treatment Plant (BC EFF), (4) SPR at Burlington Canal headgate (SPBC), and (5) Clear Creek at Croke (CROKE). SPSS, SPMG, and CROKE were categorized as water samples that had minimal anthropogenic (e.g., wastewater) impact. The majority of SPBC flow was made up of BC EFF; therefore, these samples were categorized as having significant anthropogenic impact. Two sets of experiments were performed on these samples taken on two dates: 8/14/2000 and 9/5/2000. 2.2. Water quality measurements Water samples (8 L) were collected at each sampling location in two 4-L acid-washed amber glass bottles. The pH was measured in the field during the collection by the City of Thornton. These samples were packed in
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1027
APHA, 1995). The test was conducted by first estimating the chlorine demand of each sample. Then each sample was buffered at pH 7, chlorinated with an excess of free chlorine, and stored at 25 1C for 7 days. At the end of 7 days, the free chlorine residual was measured using N,Ndiethyl-p-phenylenediamine (DPD) colorimetric method (4500-Cl G.; APHA, 1995). The different DBP (four THM, nine HAA, and TOX) were measured before and after the 7-day chlorine incubation period by an EPA certified laboratory (Barringer Laboratories, Inc., CO). The formation potential of each class of DBP was calculated as the difference between the concentrations in the 7-day chlorine incubated sample and the initial concentrations.
3. Results and discussion 3.1. General water data
Fig. 1. Locations of the sampling points along the South Platte River and wastewater treatment plants (not drawn to scale).
coolers filled with icepacks and shipped overnight to Northwestern University (Evanston, IL). Once received, sub-samples (10 mL) were taken for turbidity measurements, which were made with a Hach 2100P Turbidimeter. The rest of the samples were immediately filtered with 0.45 mm glass-fiber filter. The following analyses were performed on the filtered allotments: (1) DOC concentration measurement (Dohrmann DC-180 Automated TOC Analyzer), (2) UVA measurement at 254 nm (Hitachi U-2000 Spectrophotometer; 5910 B.; APHA, 1995), (3) fluorescence spectral analysis (Hitachi F-2000 Fluorescence Spectrophotometer; Smart et al., 1976), (4) pyrolysis-GC/MS (Sirivedhin and Gray, 2005; Bruchet et al., 1990; Widrig et al., 1996), (5) alkalinity measurement (2320 B.; APHA, 1995), (6) amino acids (Roth, 1971), and (7) glucosidic fraction (Dubois et al., 1956).
2.3. Disinfection by-product formation potential Seven-day DBPFP measurement was determined in accordance with the protocol in the Standard Methods for the Examination of Water and Wastewater (5710 A.;
Table 1 presents the general water quality data for the five locations in August and September 2000. Similar trends to the 1998 data (Sirivedhin and Gray, 2005) were observed in the pH and turbidity data. The pH and turbidity generally increased with the distance downstream, and the values for BC EFF were lower than other SPR water samples. In general, alkalinity, amino acids, and glucosidic fraction were lower in water samples having minimal anthropogenic impact (SPSS, SPMG, and CROKE) than those having high anthropogenic impact (BC EFF and SPBC). BC EFF samples exhibited the highest protein and polysaccharide contents as measured by amino acids and the glucosidic fraction, respectively. Although lower quantities were observed in SPBC samples, the protein and polysaccharide contents at this location were many times the values observed at CROKE or upstream on the SPR. Finally, the higher pH, amino acids, and glucosidic fraction measured in the August samples compared to the September samples are suggestive of algal bloom conditions. Table 2 shows the results from the analysis of organic carbon. In general, DOC concentration, UVA254, and the peak intensities of excitation and emission spectra were determined to be lower in water samples that had minimal anthropogenic impact than the ones that had high anthropogenic impact. As is generally found (MacCraith et al., 1993), the UVA and fluorescence of the samples increased linearly with increasing DOC. However, SUVA254 values were found to be lower in the samples that had high anthropogenic impact compared to those with minimal anthropogenic impact. This is in good agreement with their high glucosidic content (Table 1) since polysaccharides do not absorb in the UV range.
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1028 Table 1 General water quality data Sample ID
pH
Turbidity (ntu)
Alkalinity (mg/L as CaCO3)
Amino acids (mM)
Glucosidic fraction (mM)
August 14, 2000 SPSS 7.78 SPMG 9.75 BC EFF 8.60 SPBC 9.16 CROKE 9.44
7.55 8.08 3.94 5.70 5.80
37.92 79.32 109.71 142.10 40.76
0.43 1.48 5.70 2.38 0.87
3.72 7.00 52.52 16.47 8.09
September 5, 2000 SPSS 7.73 SPMG 7.78 BC EFF 7.93 SPBC 8.21 CROKE 7.86
7.74 7.15 3.88 11.2 5.03
45.68 76.73 121.07 172.94 46.67
ND ND 1.62 0.54 ND
ND 1.78 19.10 6.61 ND
ND ¼ not detected. Table 2 Analysis of organic carbon Sample ID
DOC (ppm C)
Fluorescence
UV254 UVA (cm1)
SUVA (L/mg m)
EXI (cm1)
SIEX (L/mg cm)
EMI (cm1)
SIEM (L/mg cm)
August 14, 2000 SPSS 2.31 SPMG 3.51 BC EFF 11.57 SPBC 11.51 CROKE 1.42
0.068 0.101 0.198 0.271 0.086
2.94 2.88 1.71 2.35 6.06
34.85 41.72 243.6 189.5 31.99
15.09 11.89 21.05 16.46 22.53
28.60 36.15 229.5 183.4 49.12
12.38 10.30 19.84 15.93 34.59
September 5, 2000 SPSS 1.91 SPMG 2.95 BC EFF 8.69 SPBC 5.64 CROKE 1.05
0.041 0.069 0.143 0.102 0.044
2.15 2.34 1.65 1.81 4.19
43.22 68.28 248.0 134.0 36.25
22.63 23.15 28.54 23.76 34.52
37.04 46.06 278.2 100.0 32.64
19.39 15.61 32.01 17.73 31.09
3.2. Formation potentials of THM, HAA, and TOX Table 3 summarizes TTHMFP, total HAA formation potential (THAAFP), and TOXFP for both August and September 2000 samples. In general, the formation potentials of all three categories of DBP were two to three times higher in the water samples with significant anthropogenic impact than those with minimal anthropogenic impact. This is attributed primarily to the high DOC levels of those samples having significant anthropogenic impact. In order to consider the reactivity with chlorine on a per carbon basis, all the DBPFP data were normalized relative to the DOC concentrations to obtain the specific yields. In this comparison, the water samples that had high anthropogenic impact possessed lower specific DBPFP yields in all three DBP categories. These
lower values correspond to the higher glucosidic content (Table 1) since polysaccharides are very poor DBP precursors. The CROKE samples produced the greatest specific yields of both TTHMFP and THAAFP as expected based on their spectral properties (e.g., high SUVA), but the lowest absolute quantities, which was consistent with their low DOC levels. Another interesting trend observed in these data was that the DBPFP levels were greater in general among the September samples than August, although the DOC concentrations were lower in the September samples. This illustrates the seasonal influences on the chlorine reactivity of DOC and is likely associated with a shift away from the algal inputs that prevailed in August. These comparisons illustrate the distinctive quantitative and qualitative influences on DBPFP. In general, higher DOC
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Table 3 Summary of DBPFP data TTHMFP (mg/L)
Specific TTHMFP yield
THAAFP (mg/L)
August 14, 2000 SPSS 9.35 SPMG 8.90 BC EFF 27.05 SPBC 13.30 CROKE 8.90
111 158 265 291 100
48.1 45.0 22.9 25.3 70.4
128 176 242 231 120
55.4 50.1 20.9 20.1 84.5
September 5, 2000 SPSS 38.55 SPMG 40.77 BC EFF 54.06 SPBC 40.32 CROKE 23.49
146 203 398 285 100
76.4 68.8 45.8 50.5 95.2
167 217 426 286 124
87.4 73.6 49.0 50.7 118.1
Sample
Chlorine demand (mg Cl2/L)
Specific THAAFP yield
TOXFP (mg/L)
Specific TOX yield
n/a n/a n/a n/a n/a
n/a n/a n/a n/a n/a
819.2 781.7 1610 1505 630.2
428.9 265.0 185.3 266.8 600.2
n/a ¼ not available.
Table 4 Concentrations (in mg/L) of individual THM and HAA Sample
Individual HAA species BCAA
BDCAA
August 2000 SPSS 3.4 SPMG 12.15 BC EFF 22 SPBC 18 CROKE 3.4
5.3 18 46 32 6
September 2000 SPSS 3.25 SPMG 10.35 BC EFF 34 SPBC 31 CROKE 4.275
12.75 27.5 62 64 14.25
Individual THM species CAA
1.7 4.9 3.3 6.22 3.87 ND ND 14 ND ND
CDBAA
DBAA
DCAA
TCAA
BDCM
TCM
DBCM
ND 2.25 8.2 4.4 1.8
ND 1.6 3 2.3 ND
55 68.75 101 70.5 48.5
62.5 68 58.5 66.5 56
8.93 22.50 64 56 13.75
101.5 132.5 185 225 84.75
0.3 3.48 16.5 10.5 1.43
ND 2.73 9.93 20.5 ND
ND 0.77 3.3 5.25 ND
67.75 90.75 185 95.5 50
83.75 85 117.5 70 55.75
9 23.5 68 79.5 9.63
137.5 180 320 185 90.25
ND ND 10.25 20.25 0.5
BCAA ¼ bromochloroacetic acid, BDCAA ¼ bromodichloroacetic acid, CAA ¼ chloroacetic acid, CDBAA ¼ chlorodibromoacetic acid, DBAA ¼ dibromoacetic acid, DCAA ¼ dichloroacetic acid, TCAA ¼ trichloroacetic acid, BDCM ¼ bromodichloromethane, TCM ¼ chloroform, DBCM ¼ dibromochloromethane, ND ¼ not detected.
concentration produced higher absolute DBPFP, but the differences in organic quality accounted for the differences in the reactivity observed on a molecular basis. Table 4 shows the concentrations (in mg/L) for individually measured HAA and THM species. Of the four THM species measured, only bromoform (TBM) was below the detection limit of 2 mg/L. Chloroform (TCM) was the major chlorination by-product, followed by bromodichloromethane (BDCM) and dibromochloromethane (DBCM). This same distribution was also found in another study (Croue´ et al., 2000). BDCM, which ranged from 17 to 28% of TTHM in the water samples that had high anthropogenic impact compared to 6 to 14% of TTHM in water samples that had
minimal anthropogenic impact, was recently associated with reproductive effects (Health Canada Report, 2000). DBCM was detected in trace amounts, if at all, in the less anthropogenically impacted surface water samples; however, it was 3–7% of TTHM in BC EFF and SPBC. Finally, higher percentages of Br-THM, ranging from 20 to 35%, were measured in BC EFF and SPBC samples, with the highest percentage of 35% being observed in September at SPBC. Of the nine HAA species measured, two species were below the detection limit of 2 mg/L, namely bromoacetic acid (BAA) and tribromoacetic acid (TBAA). Overall, trichloroacetic acid (TCAA) was the major HAA chlorination product in the surface waters that had
ARTICLE IN PRESS T. Sirivedhin, K.A. Gray / Water Research 39 (2005) 1025–1036
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EFF and that the bromide level in SPBC samples may have been higher than that in BC EFF.
minimal anthropogenic impact; however, the dominant HAA was shifted to dichloroacetic acid (DCAA) for water samples that had high anthropogenic impact. Higher Br-HAA levels were measured for BC EFF sample and SPBC sample. The Br-HAA species were less than 10% of the total for the SPSS samples, less than 15% for CROKE, and less than 20% for SPMG. In contrast, the Br-HAA levels were typically greater than 25% for the BC EFF and SPBC, with a high of 42% for the September SPBC sample. Although individual components of the EfOM were less reactive with chlorine as illustrated by the normalized or specific DBP yields, the overall DBPFP levels of EfOM (BC EFF and SPBC) were much higher than the water samples that had minimal anthropogenic impact because EfOM tended to have much higher DOC concentrations. Furthermore, EfOM produced a greater proportion of Br-DBP, which is considered particularly deleterious to human health. Similar distributions were also observed in other studies (Debroux, 1998; National Research Council, 1998). Finally, the greatest proportion of Br-DBP was observed in SPBC (September 2000), which may be due to the combined effect that the organic quality at this location was controlled by BC
3.3. Comparison of organic quality of EfOM and NOM In our previous paper (Sirivedhin and Gray, 2005), we showed that the organic qualities of EfOM and NOM are quantitatively and qualitatively distinct. In addition, under the flow conditions of SPR, the organic signature of BC EFF persisted and controlled the quantity and quality at SPBC. Fig. 2 shows the organic fingerprints of SPSS, SPMG, BC EFF, SPBC, and CROKE on 8/14/ 2000 and 9/5/2000. The organic fingerprints of this set of samples differed from the fingerprints of the 1998 samples. Specifically, the wastewater markers generated by pyrolysis-GC/MS in BC EFF and SPBC in 1998 were benzaldehyde, benzonitrile, chlorobutanoic acid, furancarboxaldehyde, and methylfurancarboxaldehyde; however, in 2000, these markers were present at relatively low levels and certainly not at a noticeably higher level compared to the organic fingerprints of the samples that had minimal anthropogenic impact. Instead, the distinct trait of the samples that had high anthropogenic
9/5/00
SPSS SPMG
100 75 50 25 0
BC EFF
100 75 50 25 0
SPBC
% Full Scale
100 75 50 25 0
100 75 50 25 0
CROKE
8/14/00
100 75 50 25 0
1
100 75 50 25 0
4 3
6
2 5
6 1 2
5
5
3
6
6 3 2
1
2
3 4
20
40
60
5
6 1 2 3 5
5
100 75 50 25 0
6
80
100
120
20
6
3
1
7
100 75 50 25 0
5
7
5
100 75 50 25 0
2
1
6 2 3
100 75 50 25 0
3
1
1
1
5
2
6
6
3 2
7
1 5 40
60
80
100
120
Retention Time (minute) Fig. 2. Organic fingerprints of SPSS, SPMG, BC EFF, SPBC, and CROKE on 8/14/2000 and 9/5/2000 (1 ¼ acetic acid, 2 ¼ propanoic acid, 3 ¼ benzonitrile, 4 ¼ benzothiophene, 5 ¼ acetamide, 6 ¼ phenol, and 7 ¼ hexahydroazepinone).
ARTICLE IN PRESS T. Sirivedhin, K.A. Gray / Water Research 39 (2005) 1025–1036
SPSS SPMG BC EFF SPBC CROKE
6 September
PC2 (28.6%)
impact in 2000 was an intense acetamide peak, which is linked to N-acetylaminosugars from bacterial cell walls (Irwin, 1982). Based on qualitative comparison alone, the SPBC samples bear a chemical fingerprint that differs markedly from SPSS in terms of predominant chemical nature and proportions of pyrolysis fragments. Yet, using this simple qualitative method of comparing pyrolysis profiles, the chemical quality of SPBC among these 2000 samples does not appear as similar to BC EFF as it did in 1998. As discussed below, this observation illustrates the limitations of simply making qualitative interpretation of the pyrolysis data. The dissimilarity between the organic quality of the 1998 and 2000 samples was probably due mainly to the drought conditions that prevailed in the summer of 2000. Nonetheless, the possible anthropogenic marker for this set of samples (i.e., acetamide), which was not present at a high level in the organic fingerprints of the samples that had minimal anthropogenic impact, persisted and was measured to be relatively high in SPBC sample in August. In September, a very intense hexahydroazepinone peak was detected in the organic fingerprint of SPBC, which overwhelmed the acetamide peak as well as the other pyrolysis fragments produced in this sample. Hexahydroazepinone (or caprolactam) is typically found among the pyrolysis products of aliphatic polyamides (e.g., nylon); this peak is suspected to be sample contamination. Nevertheless, the intensity of acetamide in the September SPBC fingerprint was still large compared to other chemical fragments. Principal component analysis (PCA) was performed on the data generated by pyrolysis-GC/MS to reduce the large, highly correlated variables (i.e., chemical fragments) to a much smaller set of independent variables (i.e., groupings of critical chemical fragments) while preserving most of the variation in the data. The August and September 2000 samples and their duplicates generated a total of 489 chemical fragments. PCA was carried out to reduce it down to 27 critical chemical fragments while still maintaining 80% of the total variance. The score plot of PC1 versus PC2 clearly separated the water samples that had minimal anthropogenic impact from those that had high anthropogenic impact as illustrated in Fig. 3. These two principal components account for nearly 60% of the variance of this sample set. The separation was mainly controlled by PC1, which accounts for 30.1% of the total variance of the data. Samples with minimal anthropogenic impact had negative PC1 scores. Since PC1 is negatively influenced by acetic acid, propanoic acid, methylpropanoic acid, phenol, and methylphenol, these chemical fragments are ‘‘natural’’ markers for this set of samples. In contrast, samples with high anthropogenic impact had positive PC1 scores. Since PC1 is positively influenced by acetamide, benzaldehyde, chlorobutanoic
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4 August
August
2
August
September
0
August September
August
−2
September
−4
−3
−2
September
−1
0
1
2
3
4
PC1 (30.1%) Fig. 3. Score plot of PC1 versus PC2 for the organic quality of all samples collected on 8/14/2000 and 9/5/2000.
acid, benzenedicarbonitrile, undecanoic acid, these chemical fragments are ‘‘wastewater’’ markers for this set of samples. This analysis statistically established that, as seen in the 1998 samples (Sirivedhin and Gray, 2005), the organic quality of SPSS, SPMG, and CROKE as characterized by pyrolysis-GC/MS was different from that of BC EFF and SPBC. For the August and September 2000 samples, these differences were not apparent from simple qualitative comparison (Fig. 2); therefore, this result clearly illustrates that the full power of pyrolysis-GC/MS comes from the use of multivariate statistical techniques in interpreting data.
3.4. Chemical markers for the formation of different classes of DBP TTHMFP, THAAFP, Br-THMFP, and Br-HAAFP were found to be negatively correlated to the ratio of total aromatic to total aliphatic based on the pyrolysisGC/MS data (Fig. 4). Previous research in our group (Gray et al., 1996; Gray, 1997) as well as others (Hwang et al., 2001) have found that phenolic content, as measured by pyrolysis-GC/MS, is generally negatively correlated to THMFP. Some other research groups, however, have found the contrary. For instance, the percent aromatic content (Croue´ et al., 2000) or phenolic content as measured by pyrolysis-GC/MS (Harrington et al., 1996) of the sample was reported to be good indicator of chlorine consumption and the formation of certain classes of DBP. It is important to note, however, that in both these studies, the organic material was extracted from the whole water samples using XAD resins. The extraction technique tends to concentrate the aromatic fraction disproportionally (Maurice et al., 2002), which explains why the observed reactivity of chlorine is attributed to aromatic structures. For this
ARTICLE IN PRESS T. Sirivedhin, K.A. Gray / Water Research 39 (2005) 1025–1036
1032 400
100
Br-THMFP, µg/L
T THMFP, µg/L
350 300 r 2 = − 0.618 p = 0.057
250 200 150 100 50
60
r 2 = − 0.689 p = 0.027
40 20 0 −20
0 0.0
0.5
1.0
1.5
2.0
2.5
Total Aromatic : Total Aliphatic
(A) 450 400 350 300 250 200 150 100 50 0
0.0
0.5
1.0
1.5
2.0
2.5
Total Aromatic : Total Aliphatic
(B) 120
Br-HAAFP, µg/L
THAAFP, µg/L
80
2 r = − 0.571 p = 0.084
100 80 2
r = − 0.621 p = 0.055
60 40 20 0 −20
0.0
0.5
1.0
1.5
2.0
2.5
Total Aromatic : Total Aliphatic
(C)
0.0
0.5
1.0
1.5
2.0
2.5
Total Aromatic : Total Aliphatic
(D)
Fig. 4. Correlations of (A) TTHMFP, (B) Br-THMFP, (C) THAAFP, and (D) Br-HAAFP with total aromatic to aliphatic ratio as measured by pyrolysis-GC/MS.
100
Br-THMFP, µg/L
T THMFP, µg/L
400 350 300 2
r = 0.866 p = 0.001
250 200 150
80
40 20
100
0 0
6
8
10
0
2
4
6
8
10
Total Halogenated Signature
(B)
120
Br-HAAFP, µg/L
THAAFP, µg/L
4
450 400 350 300 250 200 150 100
2
r = 0.905 p < 0.001
100 80
2
r = 0.754 p = 0.012
60 40 20 0
0
(C)
2
Total Halogenated Signature
(A)
r 2 = 0.703 p = 0.023
60
2
4
6
8
10
Total Halogenated Signature
0
(D)
2
4
6
8
10
Total Halogenated Signature
Fig. 5. Correlations of (A) TTHMFP, (B) Br-THMFP, (C) THAAFP, and (D) Br-HAAFP with total halogenated signature as measured by pyrolysis-GC/MS.
reason, we study structure/function relationships using whole waters. The difference in sample preparation (organic extract versus whole water concentrate), then, explains the differences observed in the relationship between aromatic moieties and DBPFP.
Relatively good linear correlations were found between the formation potentials of TTHMFP and THAAFP with the total halogenated content as measured by pyrolysis-GC/MS (Fig. 5). This finding implies that the sites that are chlorine reactive during the
ARTICLE IN PRESS T. Sirivedhin, K.A. Gray / Water Research 39 (2005) 1025–1036
chlorination process in wastewater treatment remain reactive in the DBPFP test. In contrast, the correlations between formation potentials of the Br-DBP and the total halogenated content were poorer, indicating that the chlorine reactive sites are not necessarily the same as the sites that promote the formation of Br-DBP. No single chemical fragment generated by pyrolysis was shown to be a strong marker for DBPFP, which was also found to be the case elsewhere and is likely the result of the vast complexity of AOM (Reckhow et al., 1990). The normalized peak height intensities of the critical 27 chemical fragments that were found to produce good separation between samples that had minimal and high anthropogenic impact with PCA (Fig. 3) were correlated to TTHMFP, THAAFP, BrTHMFP, and Br-HAAFP using a simple correlation matrix. Considering only the chemical fragments that carried absolute values of correlation coefficients higher than 0.5 (i.e., 11 of the 27 chemical fragments), the sum of the product of the normalized peak height intensities of the highly correlated fragments and their respective correlation coefficients were found to be linearly correlated to the formation potentials of each of the four classes of DBP. These chemical fragments as well as their correlation coefficients are shown in Table 5. The signs of the correlation coefficients indicated their respective positive or negative effect on the formation potential of each class of DBP. In general, the chemical fragments that contributed to these correlations included some organic nitrogen (i.e., acetamide, benzenedicarbonitrile), halogenated (i.e., chlorobutanoic acid), long-chained aliphatic (i.e., undecanoic acid), and aromatic (i.e., benzaldehyde) structures. Evidence that nitrogen-containing compounds (e.g., protein and amino sugars) in the organic matrix (Scully et al., 1988; Croue´ et al., 2000; Harrington et al., 1996; Pomes et al., 2000) and general aliphatic features (Gray et al., 1996) were possible precursor sites was also found in other studies.
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Fig. 6A shows the correlation between TTHMFP and the linear combination of the peak height intensities of acetamide, benzaldehyde, chlorobutanoic acid, methylpropanoic acid, and propanoic acid. Fig. 6B shows the correlation between Br-THMFP and the linear combination of the peak height intensities of acetamide, acetic acid, benzenedicarbonitrile, chlorobutanoic acid, dimethylphenol, methylphenol, methylpropanoic acid, phenol, propanoic acid, and undecanoic acid. Fig. 6C shows the correlation between THAAFP and the linear combination of the peak height intensities of acetamide, benzaldehyde, chlorobutanoic acid, methylpropanoic acid, and phenol. And Fig. 6D shows the correlation between Br-HAAFP and the linear combination of the peak height intensities of benzaldehyde, benzenedicarbonitrile, chlorobutanoic acid, methylpropanoic acid, phenol, propanoic acid, and undecanoic acid. Student’s t-tests were performed between each linear combination of the peak height intensities and its respective DBPFP (a ¼ 0:05) showing that all four correlations were all statistically significant (po0:0001). The surprising finding in this analysis is that the phenolic signature was not significantly correlated with TTHMFP, but rather it was negatively correlated with THAAFP, Br-THMFP, and Br-HAAFP (Table 5). These results strongly suggest that the nature of AOM was a very important factor influencing the product distribution of THM and HAA. While the amount of DOC is a major determinant in the total amount of DBP formed, the chemical nature of the AOM determines the product distribution of DBP. For these samples, varying combinations of pyrolysis fragments were found to be associated with the formation potentials of four general classes of DBP. This analysis of whole waters reveals that while aromatic structures do play a positive role in reactivity with chlorine, phenolic structures, as characterized by pyrolysis-GC/ MS, appear to be negatively correlated, when found to have an influence at all. Among these waters, reactivity with chlorine was found to be related to a complex
Table 5 Correlation coefficients (only shown when the absolute value is greater than 0.5) Pyrolysis fragment Acetamide Acetic acid Benzaldehyde Benzenedicarbonitrile Chlorobutanoic acid Dimethylphenol Methylphenol Methylpropanoic acid Phenol Propanoic acid Undecanoic acid
[TTHM]
[THAA]
0.768827
0.573536
0.677007
0.782077
0.848341
0.69398 0.55146
0.629117
0.53822 0.51164
[Br-THM]
[Br-HAA]
0.714681 0.58877 0.77418 0.863202 0.51749 0.54306 0.75758 0.56906 0.71855 0.531877
0.551291 0.547801 0.574305
0.57955 0.59298 0.5446 0.624769
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140
Br-THMFP, µg/L
T THMFP, µg/L
400 350 300 250 200
r 2 = 0.883 p < 0.0001
150 100 50 −1.0
−0.5
0.0
0.5
1.0
20 −4
350 300 250 2
r = 0.905 p < 0.0001
Br-HAAFP, µg/L
THAAFP, µg/L
r 2 = 0.786 p < 0.0001
40
−3
−2
−1
0
1
2
Combination Peaks
(B)
100
Combination Peaks
100 80 60 40
r 2 = 0.867 p < 0.0001
20 0 −20 −4
−1.5 −1.0 −0.5 0.0 0.5 1.0 1.5
(C)
60
120
400
150
80
1.5
450
200
100
0
Combination Peaks
(A)
120
(D)
−3
−2
−1
0
1
2
Combination Peaks
Fig. 6. Correlation of the combination of normalized peak height intensities to the formation potentials of (A) TTHM, (B) Br-THM, (C) THAA, and (D) Br-HAA.
function of aliphatic and aromatic structures substituted with nitrogen, oxygen (carboxylic acids), and chlorine.
4. Conclusions In our previous paper (Sirivedhin and Gray, 2005), we found that the EfOM and NOM were structurally different and that EfOM persisted in natural waters. In this study, we found that the structurally different organic matrices of EfOM and NOM also behaved differently in the chlorination process. Although EfOM was found to be less reactive with chlorine on a DOC concentration basis, water samples that had higher anthropogenic impact were found to have higher overall DBPFP due to their higher DOC concentrations. Furthermore, a shift in DBP proportions to brominated species was observed for EfOM. This shift to higher BrDBP was amplified in effluent-dominated streams possibly because higher bromide concentrations prevail in the river water than in the effluent. These results are significant for indirect potable water reuse in that effluent-dominated streams will not only show elevated DBPFP, but also higher yields of brominated species and elevated health risks associated with their presence. Finally, individual chemical markers produced by pyrolysis-GC/MS were not found to be indicative of the formation potentials of different classes of DBP; rather, combinations of chemical fragments were found to be well associated with the formation potentials of
TTHM, Br-THM, THAA, and Br-HAA for this set of samples. In contrast to the conventional notion that DBPFP is higher in waters that have higher aromatic carbon content, we found a combination of aromatic and aliphatic structures including some substituted with nitrogen and chlorine to show a linear relationship with DBPFP.
Acknowledgements This work was supported by the City of Thornton. The authors would like to thank Vic Lucero from the City of Thornton for sample collection, Dr. Deanna Hurum for analytical assistance, and Dr. Rapeepat Ratasuk for multivariate statistical analysis help.
References Aieta, M., 1998. The impacts of the Strontia Springs/Bi-City water exchange practice by Denver water on Thornton source water quality and the Columbine treatment plant performance. pp. 26+ Appendix D. Aoki, T., Kawakami, K., 1992. Continuous-flow method for the determination of total trihalomethane formation potential in waters. Anal. Chim. Acta 261, 335–338. APHA, 1995. Standard Methods for the Examination of Water and Wastewater. American Public Health Association, Washington.
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