BROMINATED DISINFECTION BY-PRODUCTS: FORMATION AND CONTROL DURING DRINKING WATER DISINFECTION

Project leader: Terttu Vartiainen, National Public Health Institute (KTL) and University of Kuopio P.O.Box 95, FIN-70701 Kuopio, Finland, tel. +358-17-201 346, e-mail: Terttu.Vartiainen@ktl.fi
 
 

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TIIVISTELMÄ SUOMEKSI

Researchers:
Tarja Nissinen, Tiia Myllykangas and Panu Rantakokko
National Public Health Institute, tel. +358-17-201 211
e-mail: Tarja.Nissinen@ktl.fi, Tiia.Myllykangas@ktl.fi, Panu.Rantakokko@ktl.fi

Consortium: Drinking water and health
Financing SYTTY organisation: Tekes
Funding from SYTTY / Total funding of project (€): 122777 / 270519
Person-months of work funded by SYTTY / Total person-months of work: 56 / 47

KEY  WORDS: drinking water, bromide, disinfection, disinfection by-products, mutagenicity
 

EXTENDED ABSTRACT

1 Introduction

The formation of brominated disinfection by-products during drinking water disinfection is possible if raw water contains bromide. Bromide can enter water sources from dissolution of geologic source, from saltwater intrusion and by human activities (Cooper et al. 1985). Trihalomethanes (THMs) were first identified in drinking water in 1974 (Rook 1974). They are formed during the chlorination of waters containing humic substances. Chloroform is normally the predominant THM species; however, in the water containing bromide, brominated trihalomethanes, bromodichloromethane, dibromochloromethane and bromoform can be formed. Two trihalomethanes, chloroform and bromodichloromethane, are suspected carcinogens for human. The formation of brominated THMs involves the initial oxidation of bromide to hypobromite (OBr-) by hypochlorite (OCl-) (Farkas et al.1949). Hypobromous acid (HOBr) reacts further with humic substances to form brominated THMs (Rook 1974). Even at a considerably low concentration of bromide relative to chloride brominated THMs are produced (Cooper et al. 1985). The new limit-value for the total THMs (100 µg/l) became valid in May 2000 (Council Directive 98/83/EC). In Finland the limit value reduced to a half compared to earlier values.

Besides chlorination brominated disinfection by-products can be formed also during ozonation. The use of ozone is most complicated if raw water contains bromide, because ozone is able to oxidize bromide to bromate (BrO3-), which is found to be a carcinogen. The limit-value for bromate formation is 10 µg/l.

2 Methods

Water samples were collected from 24 Finnish waterworks in 1998 and again from 5 waterworks in 2000. Twenty waterworks used surface water, three groundwater and one a mixture of artificially recharged groundwater and groundwater as raw water. Chlorine or chloramine was used as a disinfectant. Ozonation was a part of water treatment processes in eight waterworks and they all disinfected with chloramine.

The formation of brominated disinfection by-products and mutagenicity in waters containing bromide has been studied with laboratory and pilot scale experiments. Chlorination and chloramination were used as the final disinfectant, while ozonation, hydrogen peroxide-ozonation, and KMnO4-oxidation were used as preoxidation methods. For the pilot scale experiments pilot-plant equipment was built. The pilot-plant consisted of the ozone generator (Pacific Technology mdl OI), the column, the pump (Sigma 07220 PVT membrane pump), and the analyzer (Orbisphere 3600 and Dasibi 1180-HC) for analyzing both the dissolved ozone from the water and the ozone concentration in the feed gas. The water used in experiments was from the Kuopio waterworks. Both artificially recharged groundwater and purified artificially recharged groundwater were used. In the Kuopio water either 50, 100 or 500 ?g/l bromide was added prior to ozonation. The effect of ozone dosage, bromide concentration, pH, alkalinity, hydrogen peroxide addition and temperature on the formation of the brominated by-products were studied. Other oxidation methods used were chlorination with preoxidation by ozone, hydrogen peroxide-ozone and potassium permanganate.

The concentration of bromide (Rantakokko et al. 1999), the total organic carbon (TOC), and size fractionation of humic matter were analyzed from water samples from waterworks as well as from pilot-plant experiments. Besides that THMs, halogenated acetic acids, bromate, adsorbable organic halogens (AOX), 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) and mutagenicity were analyzed from drinking waters and chlorinated pilot-plant samples.

3 Results and discussion

The concentration of bromide in raw waters varied from below the detection limit (15 µg/l) up to 517 µg/l. The highest concentrations were measured from surface waters from the west coast of Finland. Ground waters at the coastal area contained bromide less than surface waters. In inland the concentrations were usually below the detection limit. There was some fluctuation in bromide concentrations of raw waters during different seasons, and usually the highest concentrations were measured in winter.

The concentration of THMs in drinking waters varied between values below the detection limit to 160 µg/l. The highest concentration was measured from chlorinated drinking waters, which used surface water as raw water. The formation of THMs was 80% lower in the waterworks, which used chloramine as a disinfectant chemical as compared to the waterworks, which used free chlorine. The lowest concentrations were found when ozone was a part of the treatment processes and chloramine was used as a disinfecting chemical. THMs of chlorinated artificially recharged groundwaters and chlorinated groundwaters were low.

The raw water bromide concentration affected much the concentrations of individual THMs compounds. When the bromide concentration in raw water exceeded 100 µg/l, 83 % of the total THMs produced were brominated. When bromide concentration decreased, also the percentage of brominated THMs decreased, and when the bromide concentration was below 100 µg/l, the formation of chloroform was clearly the greatest. The molar ratio of [OBr-]/[OCl-] regulates the product distribution of THMs. As the concentration of OBr- increases CHCl3 decreases and brominated THMs, especially CHBr3 increases in spite of the presence of high concentration of OCl-. The oxidation ability of OCl- is two times greater than that of OBr-, but the rate of substitution by HOBr is 17 times higher than by HOCl (Ichihashi et al. 1999).

The limit value for the total THMs (100 µg/l) was exceeded at one chlorinated waterworks. One reason for that was surface water containing high concentration of bromide (up to 517 µg/l) and the high percentage of brominated THMs formed: bromoform accounted for the greatest part of the THMs. In that waterworks water treatment processes has been improved. The amount of chlorine has been reduced with changing the first chlorination to potassium permanganate oxidation for manganese precipitation. Also the removal of organic carbon has been enhanced with improved coagulation, flotation, and sand filtration. For those reasons the concentrations of THMs has lowered under the 100 µg/l. Also the addition of Na-sulfate to the samples just after the sampling has reduced concentrations. However we have measured >100 µg/l concentrations from the distribution system.

Bromate was detected from one ozonated drinking water. The concentration (4 µg/l) was under the EU-limit value (10 µg/l).

Bromide concentration as low as 50 µg/l was sufficient to promote the formation of bromate during ozonation experiments with coagulated and sand filtrated water. The EU limit value for bromate was exceeded with water containing bromide 100 or 500 µg/l at ozone concentrations used in this study. Only at an alkalinity as high as 1.4 mmol/l, even if the bromide concentration was 500 µg/l, the limit value was not exceeded. According to these results, less than 35 mole-% (except for pH 9.0 being 65 mole-%) of the bromide consumed during ozonation was converted to bromate ion, which indicates that other brominated organic compounds are formed as well.

The concentration and molecular size fractionation of the aquatic humus as well as the formation of small-molecular-weight organic acids were studied. Both the concentration of the organic carbon and the molecular size fractionation of the aquatic humus decreased clearly during the oxidation experiments. The greatest decrease in the reduction of the molecular size fractions was observed when advanced oxidation processes (AOPs) were used. The formation of the organic acids was the greatest after ozonation and hydrogen peroxide-ozonation. The TOC concentration decreased as much as 23 % during the oxidation experiments. It was clearly observed that the oxidation methods used decomposed strongly the aquatic humus. Increase in ozone dosage increased the decomposition, as well as an increase in pH and alkalinity. Bromide concentration did not affect the decomposition of the aquatic humus.

Different oxidation methods were used to study the mutagenicity of the treated waters. It was clearly seen that the mutagenicity of bromide containing was higher than without bromide. It was also observed that with preoxidation prior to chlorination the mutagenicity was strongly reduced.

4 Conclusions

The highest concentrations of bromide were found from surface waters from the west coast of Finland. Chlorinated drinking waters originated from surface waters contained the highest concentrations of THMs. Because of higher substitution ability of HOBr than HOCl the formation of brominated THMs can be considerably higher compared to chloroform if raw water contains high concentrations of bromide. The formation of brominated THMs caused problems in one waterworks where the concentrations of THMs exceeded the limit value at the distribution system. The formation of bromate is possible during ozonation of bromide containing waters, but according to our results the formation does not cause any significant problem in Finnish waterworks.

From the laboratory experiments it is seen that bromate formation occurs at very low bromide concentrations. The decomposition of the aquatic humus is enhanced greatly with different oxidation methods, and the greatest decrease was found when AOPs were used. Mutagenicity of drinking water is almost double when bromide is present as compared to the waters without bromide.

5 References

Cooper, W.J., Zika, R.G. and Steinhauer, M.S. 1985. Bromide-oxidant interactions and THM formation: A literature review. J. Am. Wat. Wks. Ass. 77:116-121.
Council Direktive 98/83/EC. Concerning the quality of water intended for human consumption. 3rd November 1998.
Farkas, L., Lewin, M. and Bloch, R. 1949. The reaction between hypochlorite and bromides. J. Am. Chem. Soc. 71:1988-1991.
Ichihashi, K., Teranishi, K. and Ichimura, A. 1999. Brominated trihalomethane formation in halogenation of humic acid in the coexistence of hypochlorite and hypobromite ions. Wat. Res. 33:477-483.
Rantakokko, P., Nissinen, T. and Vartiainen, T. 1999. Determination of bromide ion in raw and drinking waters by capillary zone electrophoresis. J. Chrom. (In press).
Rook, J.J. 1974. Formation of haloforms during chlorination of natural waters. Water Treatm. Exam. 23:234-243.
 

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