Factors influencing formation of trihalomethanes in drinking water with special reference to Swedish conditions

Chemosp~ere, Vol.lO, No.11/12, pp 1265 - 1273, 1 9 8 1 Printed in Great Britain

OO45-6535/81/121265-O9502.OO/O ~1981 Pergamon Press Ltd.

FACTORSINFLUENCINGFORMATIONOF TRIHALOMETHANES IN DRINKINGWATERWITH SPECIALREFERENCETO SWEDISHCONDITIONS Harald Norin 1} , Lars Renberg 2) , Jan Hjort 3) and Per-Ore Lundblad 3) l) National Institute of Environmental Medicine, S-I04 01 Stockholm, Sweden; 2) National Swedish Environment Protection Board, Special Analytical Laboratory, Wallenberg Laboratory, University of Stockholm, S-I06 91 Stockholm, Sweden; 3) Stockholm Water and Sewerage Works, S-I13 82 Stockholm

ABSTRACT The trihalomethane (THM) concentrations in drinking water are greatly affected by the disinfection methods as well as the organic content of the water. The THM formation was shown to increase considerable during 24 hours. This indicates a higher concentration of THM at the consumers' tap compared to the levels in the outgoing water from the water work. The dosage ratio between chlorine and ammonium sulphate can be used to regulate the THM concentrations. Disinfection with a relatively high dosage of chlorine dramatically increase the THM level while the equal amount of chlorine dioxide produces trace concentrations of THM only. The relatively low THM concentrations in Swedish drinking water as compared to levels found in water from for example the USA may probably depend on the low chlorine dosage practiced in Sweden. INTRODUCTION

In 1974, the presence of several volatile organic compounds An drinking water was reported, includlng trihalomethanes (1, 2). It was also found that chloroform was formed as a result of the chlorination processes and the US Environmental Protection Agency immediately started an investigation concerning the presence of trihalomethanes (THM) in US water. Raw water and chlorinated drinking water from a number of water treatment plants were analysed, and it was found that the chlorinated drinking water contained <0.i - 311 ~g/l chloroform. Also other trlhalomethanes (bromodlchloromethane, dlbromochloromethane and bromoform) were detected. High levels of trihalomethane was found in water from water treatment plants which used surface or shallow ground water with a large content of organic material and where the water was treated with high doses of chlorine. In the investigation, water from 80 water works were analysed, the mean levels of THM were found to be 21 ~g/1 chloroform, 6 ~g/l bromodlchloro-

1265

1266

methane and 1.2 ~g/l chlorodibromomethane. The nine highest chloroform levels found were in the range 103 - 311 ~g/1 (3). The formation of THM is most probably analogous tion and can be summarized as:

organic material

+

halogens (C12, Br2,

I2)

~

to the well known haloform reac-

halogenated precursors

D

trihalomethanes

It has been claimed that the organic substrate which takes part in the reaction, mainly consists of humic substances (4). Such substances have shown to be present at high concentrations in most surface waters (5). The importance of the chlorine/carbon ratio (Clg/TOC) for the yield of chloroform have been investigated (6). Humic and fulv~c acids, chlorinated at CI2/TOC ratios greater than five, result in free chlorine residuals (i.e. excess chlorine is available) while systems with CI2/TOC ratios less than one leave no residual chlorine (i.e. excess TOC is presentT. The presence of bromine containing trihalomethanes is most probably depending on the oxidation of bromide ions by chlorine, followed by bromination of the organic compounds. In their review of the current knowledge of THM formation, Trussell and Umphres (7) reported a relationship between increased bromide concentrations and an increased THM formation. The presence of bromide increases the yield of THM for a given chlorine dose. The ratio of bromide to total organic carbon also appears to be an important factor for the ultimate THM levels reached. In water containing higher concentrations of bromide, above 0.1 mg/1, bromoform is the predominant species formed following chlorinatlon. Ozonatlon, followed by chlorination, results in a modest reduction of chloroform and dichlorobromomethane, a modest increase in chlorodibromomethane and substantial increase in bromoform. Lange and Kawesynskl (8) have found that water quality was changed by sea water intrusion. Due to relatively high levels of bromide the distribution of the individual trihalomethanes species were dramatically shifted towards brominated species. The interest in the presence of THM in drinking water is connected to the question whether they may have harmful effects on man and environment at the levels ordinarily occurring in drinking water. Chloroform has been shown to be carcinogenic in mice and rats (9) and the interest has thus been focused upon possible carcinogenic effects of drinking water. Some epidemiological studies have shown a relationship between mortality caused by cancer in different organs and chlorination of water (I0, 11, 12). It has also been shown that bromodichloromethane, chlorodibromomethane and bromoform are mutagenlc in Ames' bacterial test system (13). There are different possibilities to minimize the exposure for trihalomethanes. Investigations have shown (14, 15) the possibilities to reduce the formation of trihalomethane by: i. Using other disinfection compounds such as ozone, chlorlne dioxide or chloramine. 2. Removal of precursors. 3. Removal of trihalomethanes. Ozone treatment may result in unknown oxidation products with unknown biological effects (14). Usually, the ozone is used in combination with a post chlorination procedure which also will result in a formation of THM (16, 17). Chloramine is judged not to give sufficient protection against microbiological growth. Chemical precipitations, sedimentation followed by fast filtration is one way to reduce the level of precursors. In February, 1978 the US Environment Protection Agency suggested a "Maximum Contamination Level of 0.i0 mg/l for total trihalomethanes" and that water works which supplied drinking water for more than 75 000 persons should filtrate the

1267

water through active carbon filters. This treatment will reduce the precursors and will also remove synthetic organic chemicals (18). The chlorination condition used in Sweden differ markedly from conditions used in USA. Therefore, results from the above mentioned investigations could not be extrapolated to Swedish conditions without any further investigations. The present paper summarizes the results from full-scale experiments in a Swedish Water works during which different parameters in the chlorination procedures were varied. EXPERIMENTAL The water treatment process The full scale experiments were carried out at Norsborg's water works (Stockholm) where water from Lake MAlaren is taken from a depth of ii meters. The raw water passes through screens to prevent the entry of fish and large objects such as leaves, water-weeds etc. As shown in figure i, the water treatment process comprises of the following steps: chemical precipitation and flocculation with alum and activated silica, sedimentation in Lov5 settling tanks, rapid sand filtration, prealkalization to pH 8.0 with lime water, slow sand filtration, final alkalizatlon to pH 8.5 and desinfection with chlorine and ammonium sulphate. Normal chemical doses are reported in Table 1. Some typical data for the raw water and the treated water are reported in Table 2. ~eml

~

~

~

w

N

dd~e

Figure I. The water treatment process at Norsborg's water works.

Table i. Normal chemical doses in Norsborg's water works. Gram per m 3 water Alum Activated silica (waterglass) Lime Chlorine Ammonium sulphate

27 0.5 12.4 0.5 0.15

The chlorine dosage is carried out by continously adding chlorine gas to water. This concentrated water solution is then added in suitable amounts to the water treated as above. To regulate the ratio between free and combined chlorine residual, it is necessary to add ammonium sulphate. Solid a~nonium sulphate is dissolved in water to suitable concentration. Normally the drinking water has a total chlorine residual of 0.30 mg/l. To keep the ammonia nitrification at a sufficiently low level in the distribution system experiences have shown that the difference between the chlorlne dosage and the total chlorine residual should be keept between 0 . 1 5 - 0.20 mg/l. The temperature and the chemical composition of the water also have some influence at the chlorine dosage.

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Table 2. Data for raw water and treated water at Norsborg's Raw water Colour Turbidity Conductivity Potassium permanganate demand, KMnO. Ammonia, NH44 Nitrate, NO 3 Nitrite, NO 2 Alkalinity, HCO~ Plate coun~ on ~utrient agar at 22 C MPN Coliforms at 35°C

Gas chromatographic

water works.

Treated water

Colour units FTU mS/m

14 1.5 19.9

5 0.10 23.4

mg/l mg/l mg/l mg/1 mg/l

19 <0.01 1.5 <0.01 40

9 0.05 1.5 <0.01 47

pr ml per i00 ml

determination

105 40


of THM in water samples

The water samples were immediately preserved with ascorbic acid. The samples (100 ml) were shaken with 1 ml hexane-isopropylether (1:1) in 100 ml volumetric flasks for two minutes. After separation of the phases, the organic phases were injected i ~ o a Varian 3700 gas chromatograph equipped with an electron capture detector ( ~ N i ) . The 170 x 0.2 (i.d.) cm glass column was filled with 10% 0V-225 on acid washed silinized Chromoso~b W 100/120 mesh and held at 95 C for i min and then programmed 3 /mln to 130 C. (Full details of the method are given in ref 19). RESULTS AND DISCUSSION The trihalomethane

concentration

as function of time during normal conditions

Investigations of disinfection with chlorine causing a chlorlne residual have demonstrated (19, 20) that the trihalomethane concentration increases with time. The aim of the present investigation was to investigate the THM formation when chlorine disinfection is used in combination with ammonium sulphate. Samples were taken at the water works and have been preserved immediately after fixed intervals.

i

i

o

2

4

Figure 2. Formation of THM as a function of time during normal conditions.

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At normal conditions (0.5 mg chlorine/l and 0.15 mg ammonium sulphate/l), the total THM concentration increases from 1.8 ug/l to 4.1 ~g/1 during 24 hours. This is an increase of more than 100%. As can be seen from Figure 2, the increase of the THM concentration reaches its maximum after 24 hours. This indicates that the consumer receive a drinking water with considerably higher trihalomethane concentration than in the w a t e r leavlng the water work. The influence of ammonium dosage during constant addition of chlorine Norsborg's water works produces drinking water using an average chlorine dosage of 0.5 mg/1 and an ammonium sulphate dosage of 0.15 mg/1. In order to investigate the influence of an~onium sulphate on the THM formation, an experiment was carried out as follows. The dosage of chlorine was kept constant (0.5 mg/l) while the ammonium sulphate concentration was varied (0 - 0.35 mg/1). Every step in the anlnonlum sulphate dosage was kept constant during at least 2 hours. When the equilibrium was achieved at the sample collection point (about 30 minutes after the dosage) the samples were collected for analysis of chlorine residual ammonium nitrogen and THM. The results are summerized in Figure 3. The THM determination shows that without any addition of ammonium sulphate, the THM concentration reached 5.1 ~g/1. At an ammonium sulphate dosage of 0.35 mg/1 the THM levels decrease to 1.7 ~g/1 (time dependence was in this particular experiment found to be negligible within a 24 h period). The conclusion was that the THM concentration can be conslderably reduced with a relatively moderate dosage of ammonium sulphate. THM/~iA

3 t

2.

I 0.1

I 02

I 03

O

I 0.4

b (N~4)~SO4 .eA

Figure 3. The THM concentration as a function of the ammonium sulphate dose. Variation of chlorlne dosage and ammonium sulphate dosage while keeping constant chlorine residual It has been suggested that the THM concentration is limited principally by two factors (14). With a high content of organic material in the water the THM concentration is limited by the free chlorine residual consumed. If the organic content in the water is low, the THM concentrations is limited by the concentration of organic precursors. By varying the ratio xmmonlum sulphate/chlorine it is possible to affect the concentration independently of the above mentioned limitations. Our experiments demonstrate that the THM concentration decreased from 5.1 to 0.9 ~g/l when the ratio ~---onium sulphate/chlorine was change from 0 to i.i, which correspond to very moderate changes of the dosage (see Figure 4).

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However, a decrease in the THM concentration is accompanied by a decrease in disinfection ability, measured as a decreased redox potential. Another effect of high dosages of am~nonlum sulphate is a bacterlal oxidation of anmlonla into nitrite during the water transport through the pipeline system. Probably, the ratio ammonium sulphate/chlorine can be opitmlzed in every single case, resultlng in an acceptable compromise between disinfection ability and the formation of nitrite and THM. The experiments have not shown any simple correlation between these parameters. ~TNM vivt,

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Figure

•

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SM

"~3

o4

o!s

os"

S20

0"7

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4. The THM concentration as a function sulphate and chlorine.

Experiments

with relatively

~,

I;o

44e

~'1 (M~,l,so,,:~ 440

REDOXmtV

of the ratio between ammonium

high dosage of chlorlne

In order to investigate the influence of relatively high levels of chlorine on the THM concentration, a laboratory experiment was carried out with water from the water works, sampled immediately before the usual chlorination step. A single r H M ~;/k.

3O

,

~

;

Figure 5. The effect of chlorine dosage (2 mg C12/I) (pure water from Norsborg's water works).

on THM formation with time

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dose of 2 mg chlorine/1 was added to the water sample, i.e. approximately four times the normal value of 0.5 mg chlorlne/1. No ammonium sulphate was added to the water. The results, summarized in Figure 5 show that after 6 days the THM concentration increased to 70 ~g/1. The pH value of the water sample was relatively low (7.4) compared to the outgoing water (pH-8.5) and it must be pointed out that even a slightly higher pH value will speed up the reaction velocity according to the haloform reaction. The experiment shows the potential risk for high THM concentrations at water works treating surface water with temporary high chlorine dosage. Disinfection with chlorine dioxide Earlier investigations concerning disinfection with chlorine dioxide have shown that there is no THM produced in such a process (14, 15). To confirm these results, laboratory experiments were carried out with unchlorinated water from the water works. The water was treated with 2.0 mg chlorine/l and 2.0 mg chlorine dioxide/i, respectively. Disinfection with chlorine resulted in 7 ~g THM/1 after a reaction time of 30 minutes and increased to 67 ~g THM/I after six days Disinfection with chlorine dioxide showed a low level of 1.2 ~g THM/I at 30 minutes which increased to 1.8 ~g THM/I after six days. The investigations of disinfection with chlorine dioxide show that there is llttle risk for the formation of trlhalomethanes when pure chlorine dioxide is used. The very low level of chloroform in our investigation may be dependent on impurities of chlorine in the chlorine dioxide. It has been shown that THM may be formed if chlorine dioxide is produced from chlorlne and sodium chlorite with unequal molar ratio (14, 15). The time dependence of the THM concentration differ in both cases. Disinfection with chlorine dioxide shows a low constant level of chloroform while THM concentration formed by chlorine treatment increase to about I0 - 40 times higher levels. A much higher THM level can be expected with a larger chlorine dose as many data indicate that the chlorine residual is the restricted factor. An investigation of this hypothesis showed that addition of i0 mg C12/I to unchlorihated water produced about 130 ~g THM/1. In a small community outside Stockholm, chlorine dioxide was temporarily used as the disinfection agent and compared to the use of chlorine. The conditions in both cases were chosen to be as similar as possible. The results of the THM analysis from four sampling locations (consumer's tap; showed that the THM level were strongly reduced when chlorine dioxide was used (see Table 3). Only bromodichloromethane, which was the dominating species during normal conditions, could be detected. Table 3. The THM formation after the use of chlorine and chlorine dioxide respectively.

Location

Chlorination agent

Chloroform ~g/l

Bromodichloromethane ~g/l

Dibromochloromethane ~g/l

Bromo. form ~g/1

I II III IV

chlorine chlorine chlorine chlorine

0.49 0.58 0.57 0.59

0.87 0.84 1.2 1.0

0.87 0.88 1.3 1.0

0.24 0.25 0.34 0.32

I II III IV

chlorine chlorlne chlorine chlorine

0.006

0.01

dioxide dioxide dioxide dioxide

Detection level

-

0.021 0.023 0.023 0.023

0.01

0.005

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The i n v e s t i g a t i o n shows that c h l o r i n e d i o x i d e can be a s u i t a b l e a l t e r n a t i v e to c h l o r i n e as a d i s i n f e c t a n t for d r i n k i n g w a t e r as the T H M f o r m a t i o n is a l m o s t entirely eliminated. However, it m u s t be p o i n t e d out that c h l o r i n e to o x i d i z e h e m o g l o b i n e to m e t h e m o g l o b i n e (14) c o u n t r i e s h a v e l i m i t a t i o n s for c h l o r i t e w h i c h c h l o r i n e d i o x i d e for d i s i n f e c t i o n of d r i n k i n g The T H M s i t u a t i o n

d i o x i d e and c h l o r i t e are r e p o r t e d and for that r e a s o n c e r t a i n reduces the p o s s i b i l i t i e s of using w a t e r (23).

in S w e d e n

An e x t e n s i v e i n v e s t i g a t i o n have b e e n c a r r i e d out in S w e d e n by the N a t i o n a l S w e d i s h E n v i r o n m e n t P r o t e c t i o n B o a r d to m o n i t o r THM levels in S w e d i s h d r i n k i n g w a t e r (24). The i n v e s t i g a t i o n i n c l u d e s at least one w a t e r w o r k s in e v e r y community. The c h o i c e of w a t e r w o r k s has b e e n done by the c o m m u n i t i e s t h e m s e l v e s or in c o n s u l t a t i o n w i t h the N a t i o n a l S w e d i s h E n v i r o n m e n t P r o t e c t i o n Board. According to the r e s u l t s shown in F i g u r e 2, it is r e a s o n a b l e to b e l i e v e that T H M levels i n c r e a s e s i g n i f i c a n t l y w i t h i n the d i s t r i b u t i o n s y s t e m w h e r e the treated w a t e r c o n t a i n s a c h l o r i n e residual, THM p r e c u r s o r s or both. In o r d e r to r e f l e c t the s i t u a t i o n for the consumers, d r i n k i n g w a t e r was s a m p l e d at the c o n s u m e r ' s tap. F r o m each l o c a t i o n two samples w e r e collected. One of the samples was i m m e d i a t e l y p r e s e r v e d w i t h a s c o r b i c acid. The other sample was stored in the l a b o r a t o r y for seven days b e f o r e analysis. By c o m p a r i n g the results from the u n p r e s e r v e d and p r e s e r v e d samples, r e s p e c t i v e l y , the instantaneous T H M and the t e r m i n a l THM c o u l d be calculated. The results from this investigation, in w h i c h 249 w a t e r w o r k s have b e e n included, are s u m m a r i z e d in F i g u r e 6. %WATER W O R K S 40

30"

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F i g u r e 6. The i n s t a n t a n e o u s THM c o n c e n t r a t i o n s of w a t e r w h i c h h a v e some form of d i s i n f e c t i o n .

Ioo'

~o'

.THM ~ ug/L

from 191 w a t e r w o r k s

The i n v e s t i g a t i o n shows that the inst. THM level in m o s t of the w a t e r w o r k s is quite low. It is o n l y a few w a t e r w o r k s w h i c h have T H M c o n c e n t r a t i o n s around or c o n s i d e r a b l y a b o v e the s u g g e s t e d " M a x i m u m C o n t a m i n a n t Levels" of 0.i0 m g / l for the total t r i h a l o m e t h a n e s .

1273

REFERENCES i. 2. 3. 4. 5. 6. 7. 8. 9. i0. Ii. 12. 13. 14.

15. 16. 17. 18. 19. 20. 21. 22. 23. 24.

Rook J J, Water Treatment Exam 23 (1974) 234. Bellar T A, Lichtenberg J J and Kroner R C, Journal of American Water Work Association 66 (1974) 703. Symons J M, Bellar T A, Carswell J K, DeMarco J, Kropp K L, Robeck G G, Seeger D R, Slocum C J, Smith B L and Stevens A A, Journal of American Water Work Association 67 (1975) 634. Rook J J, Journal of American Water Work Association 68 (1976) 168. Oliver B G and Lawrence J, Journal of American Water Work Association 71 (1979) 161. Babcook D B and Singer D C, Journal of American Water Work Association 71 (1979) 149. Trussell R R and Umphres M D, Journal of American Water Work Association 70 (1978) 604. L--ange A L and Kawczynski E, Journal of American Water Work Association 70 (1978) 653. National Cancer Institute, Report on Carcenogenesis Bioassay of Chloroform, US Department of Health Education and Welfare 1976. Cantor K P, Hoover R, Mason T J and McCabe L J, Journal of National Cancer Institute 61 (1978) 979. Hogan M D, Chi P Y, Hoel D G and Mitchell T J, Journal of Environmental Pathology and Toxicology 2 (1979) 873. Alavanja M, Goldstein I and Susser M, Water Chlorination, Environmental Impact and Health Effects, 2 (1978) 395. Ed Jolley R L, Ann Arbor Science. Simmon V F and Tardiff R G, Water Chlorination, Environmental Impact and Health Effects, 2 (1978) 417. Ed Jolley R L, Ann Arbor Science. Ozon, Chlorine d~oxide and chloramines as alternatives to chlorine for disinfection of drinking water. State-of-the-Art, Water supply research, Office of research and development, US Environmental Protection Agency, Cincinatti, Ohio 45268, November, 1977. Love O T. Carswell J K, Miltner R J and Symons J M, Appendix 3 to "Interim Treatment Guide for the Control of Chloroform and Other Trihalomethanes". Hart O O, Progresss in Water Technology i O (1978) 917. Dore'M, Melet N, Blanchard T, and Langlais B, Progress in Water Technology i0 (1978) 853. Interim Primary Drinking Water Regulation, Federal Register 4 3 (1978) 28. Norin H and Renberg L, Water Research 14 (1980) 1397. Brett R W and Calverley R A, Journal of American Water Work Association 71 (1979) 515. Stevens A A, Slocum C J, Seeger D R and Robeck G G, Journal of American Water Work Association 68 (1976) 615. Stevens A A and Symons J M, Journal of American Water Work Association 69 (1977) 546. Myhrstedt J A and Samdal J E, Journal of American Water Work Association 6 1 (1969) 205. Norin H, Gottling L and Linnman L, Report No. 1/81, National Institute of Environmental Medicine (In Swedish). [Received in The Netherlands 8 October 1981)