Relationship between Brominated THMs, HAAs, and Total Organic

Chapter 8

Relationship between Brominated THMs, HAAs, and Total Organic Bromine during Drinking Water Chlorination Downloaded by GEORGETOWN UNIV on August 24, 2015 | http://pubs.acs.org Publication Date: August 5, 2008 | doi: 10.1021/bk-2008-0995.ch008

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Guanghui Hua , and David A. Reckhow 1

Jones Edmunds and Associates, Inc., 730 NE Waldo Road, Gainesville, FL 32641 Department of Civil and Environmental Engineering, University of Massachusetts, Amherst, MA 01003

2

Naturally occurring bromide present in drinking water can be quickly oxidized by chlorine to bromine, which can react with natural organic matter to form brominated disinfection byproducts (DBPs). This study investigated the relationship between known specific brominated DBPs and total organic bromine (TOBr) formed during chlorination of NOM isolates and natural waters in the presence of various levels of bromide. Unknown TOBr (UTOBr) is determined as the difference between TOBr and bromine incorporated into measured specific DBPs. The unknown TOBr fraction, as represented by the ratio of UTOBr to TOBr increased with increasing initial bromide concentrations during chlorination. The majority of organic bromine was incorporated into known specific DBPs during chlorination of low bromide containing waters. Hydrophilic and low molecular weight (MW) NOM was more reactive with bromine as measured by the formation of trihalomethanes and haloacetic acids than corresponding hydrophobic and high MW ΝΟΜ. However, hydrophobic and high MW NOM formed more TOBr than hydrophilic and low MW ΝΟΜ. Water utilities should work to remove both hydrophobic and hydrophilic NOM in the water sources to reduce the formation of chlorinated and brominated DBPs.

© 2008 American Chemical Society

In Disinfection By-Products in Drinking Water; Karanfil, T., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2008.

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Downloaded by GEORGETOWN UNIV on August 24, 2015 | http://pubs.acs.org Publication Date: August 5, 2008 | doi: 10.1021/bk-2008-0995.ch008

Introduction Bromide ions are nearly ubiquitous in natural waters. During drinking water chlorination, bromide can be quickly oxidized to hypobromous acid (HOBr) by chlorine (/). Both hypochlorous acid (HOC1) and HOBr react readily with natural organic matter (NOM) to form a series of chlorinated and brominated disinfection byproducts (DBPs) (2, 3). Trihalomethanes (THMs) and haloacetic acids (HAAs) are the two most abundant known specific DBPs identified in chlorinated waters. It has been shown that the formation of THMs and HAAs shifts to more brominated species in the presence of increasing initial bromide concentrations (2-4). In addition to THMs and HAAs, many other halogenated DBPs have also been identified in chlorinated drinking waters, such as haloketones, haloacetonitriles, chloropicrin, cyanogen halide, and chloral hydrate (5). These specific DBPs are usually present at much lower concentrations than the THMs and HAAs. The known specific DBPs together account for roughly 50% of the total organic halogen (TOX) formed during drinking water chlorination (6, 7). Bromide concentrations can affect the formation and distribution of TOX during chlorination. It has been shown that the fraction of TOX that is attributed to THMs and HAAs increased substantially with increasing bromide concentrations {4, 8). Conventional TOX analysis is a non-specific measurement of the total amount of halogenated organic DBPs. A method that combines adsorption, combustion and ion chromatography detection has been developed to measure total organic chlorine (TOC1) and total organic bromine (TOBr) in drinking waters (9). Toxicological studies have shown that brominated DBPs may be more toxic than chlorinated analogues (10). Therefore, it is important to understand the impact of bromide on the formation and distribution of TOC1 and TOBr during chlorination. This work was designed to investigate the relationship between brominated THMs, HAAs, and TOBr during chlorination at various bromide levels. The relationship between chlorinated THMs, HAAs, and TOC1 was also examined.

Experimental Methods Three sets of experiments were conducted in this research. First, two natural waters were collected and chlorinated after being spiked with various levels of bromide. Secondly, NOM in two natural waters was isolated using XAD-8 resin and ultrafiltration membranes. Chlorination was conducted on each N O M fraction solutions after being spiked with various levels of bromide. Finally, six natural waters were collected and chlorinated at ambient bromide concentrations.


Ill Chlorination of Bromide Spiked Natural Waters Raw waters were collected from the drinking water treatment plant intakes at the city of Winnipeg, Manitoba, and Tulsa, OK. Table I presents the characteristics of these two waters. Specific ultraviolet absorbance (SUVA) was calculated from UV absorbance at 254 nm (UV ) divided by the dissolved organic carbon (DOC) concentration. 254

Table I. Characteristics of Winnipeg and Tulsa Waters Downloaded by GEORGETOWN UNIV on August 24, 2015 | http://pubs.acs.org Publication Date: August 5, 2008 | doi: 10.1021/bk-2008-0995.ch008

Sample Winnipeg Tulsa

DOC (mg/L) 8.5 5.1

(cm') 0.131 0.160

SUVA (Umg/m) 1.6 3.1

Br 9 63

These two waters were spiked with bromide ions at levels of 0,2, 10, and 30 μΜ (0, 160, 800, and 2400 μg/L, respectively). Chlorination was conducted in 1 L chlorine demand-free, glass bottles on each sample buffered with 1 mM phosphate at pH 7. The chlorine doses were determined by preliminary chlorine demand tests on raw waters. The targetfreechlorine residual was 0.5 mg/L after 48 h at 20 °C. The requisite doses were 6.2 and 5.0 mg/L for Winnipeg water and Tulsa water, respectively. A stock solution of sodium hypochlorite (Fisher Scientific, Fairlawn, NJ) was standardized by DPD ferrous titrimetric method according standard method 4500-C1 F (//). After being dosed with chlorine, samples were stored headspace-free at 20 °C in the dark for 48 h.

Chlorination of NOM Fractions Raw waters were collected from the drinking water treatment plant intakes at the city of Springfield, MA, and Tampa, FL. A portion of raw water was acidified to pH 2 using concentrated sulfuric acid and then passed through X A D 8 resin (Rohm and Haas, Philadelphia, PA). The column distribution coefficient was kept at 50 (12). Effluent from the XAD-8 resin was referred to as the hydrophilic fraction. The fraction referred to as the hydrophobic N O M was retained by XAD-8 resin and eluted with 0.1 Ν NaOH in the reverse direction. The pH of the two fractions was adjusted to 7 using sulfuric acid or sodium hydroxide immediately after extraction. The DOC concentration of the hydrophobic fraction was adjusted to the same level as the hydrophilic fraction using deionized water.



112 Another portion of raw water was fractionated using Millipore YM3 ultrafiltration (UF) membranes with a molecular weight (MW) cut-off 3 kDa (Amicon, Beverly, MA). UF was performed with stirred 200 mL Amicon cells. The nitrogen pressure was maintained at 50 psi. For an initial sample volume of 200 mL, filtration was stopped when the volume of retentate decreased to 50 mL. Permeate was referred to as the MW 3 kDa ΝΟΜ. The DOC of the MW>3 kDafractionwas adjusted to the same level as the MW3kDa(82%) MW3kDa(67%) MW3 kDa fractions formed more fully chlorinated species (chloroform, DCAA, and TCAA) than hydrophilic and MW3 kDa MW3 kDa MW 300 μΜ/mM). Because limited data were obtained from this study, more work needs to be done to confirm these observations.


122 80 • •

UTOCi/roci UTOBr/TOBr y «0.063x4-20.87

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y = -0.098x4-60.33 R = 0.87


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0 0

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200

300

400

500

Br/CI Consumption (μΜ/mM) 2

Figure 9. Correlation between Br/Cl and UTOCI/TOCI, UTOBr/TOBr ratios 2

Implications on Drinking Water Treatment The results of this study suggest that hydrophilic and low MW NOM is highly reactive with bromine as measured by THMs and HAAs. Hydrophilic NOM is generally far less amenable to removal by coagulation. Water utilities with high natural bromide levels should endeavor to improve the removal of both hydrophilic and hydrophobic NOM to minimize the formation of DBPs. The percentages of UTOCI and UTOBr formed during chlorination are related to the bromide to chlorine consumption ratios. Most TOBr was in the form of THMs and HAAs when the bromide level was low. The UTOBr to TOBr ratio increased as the bromide to chlorine consumption ratio increased. The reverse was true for the UTOCI to TOC1 ratio. These results can be used to help estimate the UTOCI and UTOBr levels in chlorinated drinking waters.

Conclusions The ratio of UTOBr to TOBr increased, and the ratio of UTOCI to TOC1 decreased with increasing bromide to chlorine ratios. Hydrophilic and low MW NOM formed more brominated THMs and HAAs than hydrophobic and high MW NOM when chlorinated in the presence of high levels of bromide. However, more TOBr was formed by hydrophobic and high MW ΝΟΜ. Most organic bromine was incorporated into THMs and HAAs during chlorination of low bromide containing waters. Most organic chlorine was incorporated into THMs and HAAs during chlorination of high bromide containing waters.


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Acknowledgments This research was funded by AwwaRF through Project No. 2755. The authors thank the assistance from participating water utilities.


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Relationship between Brominated THMs, HAAs, and Total Organic

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