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Desalination 176 (2005) 155-166 www.elsevier.com/locate/desal

Application of oxidative removal of NOM to drinking water and formation of disinfection by-products M. Bekbolet a*, C.S. Uyguner a, H. Selcuk b, L. Rizzo c, A.D. Nikolaou d, S. Meri9 c, V. B e l g i o m o c ~Institute of Environmental Sciences, Bogazici University, 34342, Bebek, Istanbul, Turkey Tel. +90 (212) 359-7012; Fax: +90 (212) 257-5033; email: [email protected] bEnvironmental Engineering Department, Pamukkale University, Kinikli-Pamukkale, Turkey CDepartment of Civil Engineering, University of Salerno, Faculty of Engineeering, 84084, Fisciano, Italy dWater and Air Quality Laboratory, University of the Aegean, University Hill, 8100 Mytilene, Greece Received 22 October 2004; accepted 3 November 2004

Abstract

Water samples of different origins (Buyukcekmece and Omerli, Istanbul, Turkey, and Alento, Salemo, Italy) were treated by coagulation, ozonation, and coagulation followedby ozonation and photocatalysis. Disinfection by-products (DBPs) formation potential of raw and treated water samples was compared in relation to removal efficiencies by the respective treatment methods. The major DBPs, namely trihalomethanes (THMs) and haloacetic acids (HAAs), and other DBPs were identified and quantified. Besides major THMs and HAAs, the presence of bromoform in high amounts was also detected due to the high levels of bromide ions in raw Buyukcekmece and Omerli water samples. Depending on the natural organic matter (NOM) removal efficiencies of each treatment process, the distribution of individual THMs and HAAs was found to be NOM-site specific. Other DBPs were also detected and chloral hydrate (C2H3C1302)was found in significant amounts. The responsible precursor sites could only be reduced by photocatalytic treatment of NOM.

Keywords:

Coagulation; Disinfection by-products; Drinking water; Haloacetic acids; Ozonation; Photocatalysis; Trihalomethanes

*Corresponding author.

Presented at the Seminar in Environmental Science and Technology: Evaluation of Alternative Water Treatment Systems for Obtaining Safe Water. Organized by the University of Salerno with support of NATO Science Programme. September 27, 2004, Fisciano (SA), Italy. 0011-9164/05/$- See front matter © 2005 Elsevier B.V. All rights reserved doi: 10.1016/j.desal,2004.11.011

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M. Bekbolet et aL / Desalination 176 (2005) 155-166

1. Introduction

While natural organic matter (NOM) itself is not of direct concern in drinking water, it affects water quality by increasing the disinfectant and coagulant demand, providing precursor material for disinfection by-products (DBPs) and enhancing regrowth in distribution systems. The dominant fraction of aquatic NOM is comprised of humic substances. Humic substances in natural waters have been shown to be especially reactive with a variety of oxidants and disinfectants that are used for the purification of drinking water, particularly chlorine. These substances react with chlorine species (OCI-/HOC1) to produce trihalomethanes (THMs), haloacetic acids (HAAs) and other halogenated DBPs [1]. Consumption of chlorinated drinking water has been linked through epidemiological studies to cancers of the urinary and digestive tracts and to a variety of adverse reproductive outcomes [2,3]. The US Environmental Protection Agency has established maximum contaminant levels for the sum of four THMs and five HAAs at 80 and 60 /~g L -1, respectively, in US drinking waters [4]. Humic substances also react with ozone to produce different DBPs such as aldehydes, aldo- and ketoacids and carboxylic acids [5]. The presence of these oxidation products may lead to the formation of problematic biofilms and microbial regrowth in distribution systems [6]. Generally, the reaction of chlorine species with humic substances in the presence of bromide ions can be expressed as follows: HOC1 + Br- + HS ~ - ~ THMs (CHC1 s + CHBrC12 + CHBr2C1 + CHBr3) + HAAs (C1AA + CI2AA+ CI3AA+ BrAA + Br2AA + Br3AA + BrC1AA+ BrClzAA+ Br2C1AA) + other chloro-, bromo- and bromochloro species (1) The treatment of water has traditionally focused on the removal of either color or

turbidity. However, due to the important role of humic substances, water treatment facilities have started to optimize the removal of natural organic matter. The USEPA regulations have led to the application of enhanced coagulation practices that are a treatment strategy for removing TOC, and thereby controlling formation of THMs and HAAs in drinking water systems [7]. Generally, oxidation processes are not used for the total oxidation of organic compounds to carbon dioxide. However, the efficiency of the following treatment steps was improved by preoxidation. Therefore, the effect of oxidation processes has to be examined in the context of other processes, usually following the oxidation step. The effects of ozonation on technology-related parameters, e.g., biodegradability and flocculation, have been examined extensively during the last 25 years, whereas little is known about the changes ofNOM effected by OH radicals. There is also a lack of information as to which structural changes induced by oxidation cause alterations in removal of the physicochemical character of NOM. Therefore, sophisticated examinations which combine the analysis of the technological behavior of NOM as well as the analysis of the structural changes are necessary. The purpose of this paper is to summarize the preliminary results related to DBP occurrence upon chlorination of three surface waters from different origins in relation to their oxidative and chemical-physical pretreatment scenarios. Daphnia magna was used to monitor the toxicity of raw and treated waters.

2. Materials and methods 2.1. Water samples

Water samples of different origins - - Buyukcekmece and Omerli (Istanbul, Turkey) and Alento (Salerno, Italy) - - were obtained. The Buyukcekmece water sample located on the European side was provided from the dammed

M. Bekbolet et al. / Desalination 176 (2005) 155-166

Buyukcekmece Lake that was created by constructing a separation between the lake and the Sea of Marmara in 1985. The largest stream feeding the lake is the Karasu. During treatment of drinking water by coagulation (60 mgL -1 alum) and flocculation, sedimentation and sand filtration, chlorine gas (3-3.5 mg L-~) is applied both for pre- and post-chlorination purposes. The Omerli water sample was taken from the Omerli Reservoir located in the Asian part of Istanbul. The reservoir serves as a domestic and industrial water supply and was constructed during 19681972. The main river feeding the reservoir is the Riva. Preozonation is applied before coagulation (40-60 m g L -~) and flocculation, sedimentation and sand filtration and, as a final step, postchlorination is employed to achieve disinfection efficiency. The Alento water sample was taken from the Alento constructed basin where C102 is applied for preoxidation followed by on-line coagulation with the addition of polyaluminum chloride (25 mg L-2) and final disinfection using

ClO2 [8]. 2.2. Treatment methods 2.2.1. Ozonation

A Corona discharge ozone generator (PCI Model GL-1 type) was used in the ozonation experiments. The ozone gas was transferred into a 10 L cylindrical reactor using a 10 cm ceramic porous tube type of commercial ozone diffuser. The system was operated in a semi-batch mode. Teflon tubing was used for the ozone gas lines. In this study 10.5 mg (L'min) -l ozone dose was applied for 5 min. The flow rate and the ozone concentration of the feed gas to the reactor were 1.9 L min -1 and 2.5 mg L -~, respectively. The system was described in detail by Kerc et al. [9]. 2.2.2. Photocatalysis

Photocatalytic (PC) oxidation experiments were carried out according to a previously out-

157

lined procedure [10]. A 125 W black light fluorescent lamp was used as the light source. The intensity of incident light as measured by a potassium ferrioxalate actinometer was 2.854× 1016 quanta s -~. After each run, TiO 2was removed by filtration through a 0.45 #m Millipore Millex-HA cellulose-based membrane filter. The absorption of the supernatant was determined using a Shimadzu UV 160A double beam spectrophotometer at 254 nm (UV254) and 280 nm (UV280) for evaluating the kinetics of the photocatalytic degradation of substances. 2.2.3. Coagulation

Coagulation experiments were performed at room temperature using aluminum sulfate A12(SO4)3.18H20 as the coagulant (60 mg L-~). Standard jar test experiments were made to achieve the coagulant dose by 1 min rapid mixing at 100 rpm, 30 min slow mixing at 30 rpm and 1 h settling. 2.2.4. Chlorination

Raw water samples and treated water samples were subjected to chlorination for 7 days to obtain DBPs according to the procedure outlined in Standard Methods [ 11].

2.3. Toxicity measurements

The toxicity test was conducted on raw, treated and treated-chlorinated water samples using 24 h newborn Daphnia magna according to the ISO-66431 method [12] and as explained else-where [ 13]. Experiments were carried out in quadruplicate without diluting the sample. Five daphnids were tested in each test beaker with 50 mL of effective volume. Before toxicity tests the residual chlorine was blocked by adding sodium thiosulphate penta-hydrate. The number of immobilized animals was divided by the total number of test animals to record the immobilisation percentage for each tested sample.

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Table 1 Disinfection by-products investigated during the present study THMs

HAAs

Other by-products

Chloroform Dibromochloroform Dichlorobromoform Bromoform

Monochloroacetic acid Monobromoacetic acid Dichloroacetic acid Bromochloroacetic acid Trichloroacetic acid Dibromoacetic acid Dichlorobromoacetic acid Dibrornochloroaceticacid Tribromoacetic acid

Monochloroacetonitrile Monobromoacetonitrile Dichloroacetonitrile Bromochloroacetonitrile Dibromoacetonitrile Trichloroacetonitrile Chloral hydrate Chloropicrin 1,1-Dichloropropanone 1,3-Dichloropropanone 1,1,1-Trichloropropanone

2.4. Analytical methodology

Molecular absorption spectra of the samples from 200 to 800 nm were recorded on a Shimadzu spectrophotometer with 1.0 cm quartz cells, and absorption values were recorded at 254 nm and 280 nm and expressed as UV254and UV280. Total organic carbon contents (TOC, mg L -~) of the samples were measured using a Shimadzu 5000A total carbon analyzer. The THM formation potential (THMFP), HAA formation potential (HAAFP) and other DBPs (chloral hydrate, haloacetonitriles, haloketones) formation potential measurements were performed according to standard procedure using a Hewlett Packard gas chromatograph (GC), 5890 Series II, with a 63Ni electron capture detector as explained elsewhere [8,14,15]. The measured DBPs are given in Table 1. Source water parameters as pH, alkalinity, bromide and chloride were also measured according to the Standard Methods [ 11 ].

3. Results and discussion 3.1. General

The general raw water characteristics in terms of parameters such as, pH, alkalinity, chloride concentration, bromide concentration, UV254and

TOC are presented in Table 2. Under similar pH conditions, the alkalinity o f the Omerli sample was quite low with respect to the other samples. On the other hand, the bromide level of the Buyukcekmece raw water sample was much higher (274 #g L -l) than the Omerli raw water while the Alento raw water did not contain bromide. TOC values of Buyukcekmece and Omerli water samples were similar, but the Alento sample had a lower TOC content although the UV254values of the samples were insignificantly different. The samples exhibited quite low color forming moieties as determined by the visible part of the spectra (data not shown). THMFP, HAAFP and other DBPs of the raw water samples were presented in detail elsewhere [8]. As seen in Table 3, the highest THMFP was obtained for Buyukcekmece followed by Omerli and Alento in decreasing order. Bromoform was only detected in the Buyukcekmece water sample as can be expected due to the high concentration of bromide ions (Table 2). All of the HAAs except tribromoacetic acid were detected in all of the samples in a decreasing order of HAAFP as Alento, Omerli and Buyukcekmece. No linear/ non-linear relationship between TTHMFP and HAAFP was obtained as reported for different water resources (>82% for 4 m g U l of chlorine

M. Bekbolet et aL ~Desalination 176 (2005) 155-166

Table 2 Source water characteristics Buyukcekmece Omerli Alento pH Alkalinity, mg CaCO3L- L Bromide, #g L-' Chloride, mgL -~ UV254,cm ~ TOC, mgL -I

7.65 150

7.18 70

7.97 170

274 98 0.100 3.61

95 45 0.097 3.05

-14 0.101 2.47

Table 3 Concentrations of DBPs detected in the water samples and specific TTHMFP and THAAFP values Conc. (#gL -1)

Buyukcekmece Omerli Alento

TTHMs Raw THAAs Other DBPs Monochloroacetonitrile Dichloroacetonitrile Chloral hydrate Monobromoacetonitrile Specific parameters:

159.4 89.9

128.5 117.1

75.6 243

2.4

2.0

2.0

3.5

3.4

3.9

69.2 1.6

78.1 0.6

61.3 2.6

2.77 (m-lL mg C-1) Specific TTHMFP 44.2 (/zgmg C-1) Specific THAAFP 24.9 (#gmg C 1)

3.18

4.08

42.1

30.6

38.4

98.4

SUVA254

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mouse liver tumors at a drinking water dose of 1 g L i, was quite high with respect to the other compounds in all o f the samples [17]. To investigate the correlations between treatability and reactivity of organic matter, specific parameters were calculated for TOC normalized UV254 as SUVA254and for THMFP and HAAFP values as specific TTHMFP and specific THAAFP, respectively, as shown in Table 3. The SUVA254 parameter can be used to describe the composition of the water in terms of hydrophobicity, hydrophilicity and aromaticity [18]. SUVA254 values greater than 4 indicate that the water sample is composed of mostly aquatic humics, expressing high hydrophobicity and high molecular weight [19]. SUVA254 values between 2 and 4 indicate that the sample is a mixture of aquatic humics and other NOM fractions possessing hydrophobic and hydrophilic fractions [19]. Since the SUVA254 value of Alento water is 4.08 >_4, this water sample can be considered to be composed ofpolydisperse moieties containing a mixture of diverse molecular weight fractions. Specific TTHMFP values were found to be in the order of 30.6, 42.1 and 44.2/xgmg C -1 for the Alento, Omerli and Buyukcekmece samples, respectively, due to increasing bromide concentrations. On the other hand, the Alento sample exhibited the highest specific THAAFP value (98.4 # g m g C -1) as compared to the lower specific THAAFP values for the Omerli and Buyukcekmece water samples.

3.2. Treatment o f water samples

applied) [16]. From the other DBPs, the compounds trichloroacetonitrile, 1,3-dichloropropanone and chtoropicrin were not detected in the samples. Bromochloroacetonitrile was only detected in the Alento sample whereas dichloroacetonitrile was not detected in the same sample. The concentration o f chloral hydrate, which was found to be a very weak mutagen and can cause

Photocatalytic treatment (PC) of raw water samples was performed, and the kinetics of degradation was followed by a pseudo-first-order reaction model. Samples were then partially oxidized to obtain a residual precursor for DBPs formation in terms of UV254, UVzs0 and TOC in water samples. The pseudo-first-order kinetic parameters are presented in Table 4.

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Table 4 Kinetic parameters of photocatalytic degradation of raw water samples

UV254 Buyukcekmece Omerli Alento

k, min-l,x 10-3 7.63 6.78 10.2

UV280

TOC

tin, min

k, min-~,x10-3

t~/2,min

k, rain-t,× 10 3

t~/2, rain

91 102 68

9.13 8.37 11.8

76 83 59

4.53 1.75 nd

153 396 nd

nd = not detected. The removal rate ofWV254 by PC oxidation for the Alento sample was higher than that of the Omerli and Buyukcekmece water samples. The removal rate constants for UV2s0 were found to be higher than the removal rate constants obtained for UV254. The UV254 and UV280 wavelengths could be used interchangeably to describe the removal of aromatic moieties in humic structure. On the other hand, quite slow TOC removal rate constants were calculated for the Buyukcekmece and Omerli water samples. Since ozonation is applied as a preoxidation step in the Omerli treatment plant, all samples were ozonated for 5 rain in order to achieve approximately 50% removal of UV254 for comparison purposes. Optimized coagulation experiments were applied to the raw water samples to observe the removal of UV254 and TOC parameters in a traditional manner. A combined system composed of ozonation followed by coagulation was also applied to the water samples. The related UVz54 removal percentages are presented in Table 5. The highest UV254 removal efficiencies by ozonation, coagulation and PC oxidation individually used were observed for the Alento sample. The decreasing removal trend ofAlento> Omerli >Buyukcekmece obtained for coagulation was consistent with the previous finding related to high SUVA value [20]. The effects of ozone on coagulation in drinking water treatment originate from the interactions between ozone and NOM that is known to be site specific. Preozonation

Table 5 Comparison of UV254removals by treatment methods applied

UV254removal, %

Buyukcekmece Omerli Alento

Ozonation Coagulation Combined" PCb

40 33 59 20

46 38 61 30

64 48.5 -48

aCombined systems: ozonation followed by coagulation (60 mgL -1 of alum). bphotocatalysis: TiO2:0.1 mg mL-~, 30 rain. leads to a splitting of NOM molecules, reduced molecular weight, reduced SUVA and oxidized organics with higher hydrophilic character. The effect o f preozonation on the removal efficiency was evident for the Buyukcekmece and Alento samples. UV254 removal efficiencies by PC oxidation followed the same trend for the samples, but the related percentages were quite low due to the low TiO2 loading (0.1 m g m L ~) and short reaction periods (30 min). 3.3. Effect o f t r e a t m e n t on D B P o c c u r r e n c e

Specific THMFP values are presented in Table 6 after each treatment procedure. Due to the lack o f representative data concerning specific HAAFP values for the Alento sample, comparisons were only based on specific THMFP values of raw and treated samples.

M. Bekbolet et aL /Desalination 176 (2005) 155-166

Table 6 Specific THMFP of the treated water samples" STHMFP

Buyukcekmece Omerli

Alento

Ozonation Coagulation Combined PC

45.6 54.2 22 31.9

nd 24.8 nd nd

39.7 65.7 55.2 28.4

aTreatmentmethods as described in Table 5. Ozonation slightly decreased the specific THMFP of the Omerli sample from 42.1 to 39.7 ~tgmg C -1 while a slight increase was observed in the Buyukcekmece sample (from 44.2 to 45.6 # g m g C-1). An increasing trend in specific TTHMFP was observed for the Buyukcekmece and Omerli samples due to coagulation, whereas it decreased the specific TTHMFP of the Alento water sample (from 30.6 to 24.8/Lgmg C-1) since waters with higher SUVA values were found to be more amenable to the removal of organic material by coagulation than waters having a low SUVA [21] and low molecular weight distribution [22]. TTHMFP was decreased at higher degrees by alum coagulation due to the origin of NOM for soil sourced NOM containing water than vegetation and reservoir sourced NOM containing water [23]. The coagulated water samples exhibited lower SUVA254 values as 2.22 and 2.53 for the Buyukcekmece and Omerli water samples (Tables 3 and 6). On the other hand, due to reduced SUVA254 conditions, the fractions of the humic substances in water samples are expected to display different specific TTHMFP (Table 6) and THAAFP values. Oxidized molecular fractions may acquire various NOM sites exhibiting different reactivities towards aqueous chlorine species. Upon application of the combined system, the specific THMFP of the Buyukcekmece water sample decreased. However, an increase was observed for the Omerli water sample. On the other hand, the oxidative

161

conditions of PC treatment resulted in a decrease in specific THMFP of the Buyukcekmece and Omerli reflected as a decreasing trend in all of the samples. Since the aim was to observe the formation of DBPs rather than achieving complete mineralization, the conditional comparative results are presented in Figs. 1-4. The effect of each treatment procedure could be observed in the formation potentials of individual THMs with respect to the TTHMs in water samples. The major DBPs produced by PC treatment of NOM were previously reported as three THMs, (chloroform, bromodichloromethane and dibromochloromethane) and four haloacetic acids (dichloroacetic acid, trichloroacetic acid, bromochloroacetic acid and dibromoacetic acid) [24]. The effect of each treatment procedure could be observed in the formation potentials of individual THMs with respect to the TTHMs in water samples. The presence of bromide ions in the raw sample of Buyukcekmece water resulted in a higher formation of brominated THMs as CHBr2C1 and CHBrC12 than the ones observed for the Omerli sample. In waters that contain low bromide concentrations, ozone is believed to react with NOM before it reacts with bromide. At high bromide concentrations some competition might exist between bromide and the organic matter. As bromide concentration increases, at constant ozone dose and organic matter concentration, the formation of bromo-substituted organic compounds also increases. It should also be noted that the diverse nature of organic matter displays a major role in the formation of by-products. The distribution of the DBPs species particularly depends on the ratio of bromide to TOC [25]. Considering comparable TOC and pH conditions and the Br-/TOC ratios of 0.076 and 0.031 for the Buyukcekmece and Omerli water samples, higher concentrations of the brominated DBPs are expected, as was actually found. On the other hand, treatment that lowers the TOC concentration, thus raising the initial Br/TOC ratio, causes

162

M. Bekbolet et al. / Desalination 176 (2005) 155-166 E~Ozone [3 Coag, i l Combined [3 PC A Raw

~Ozone [3Coag. ICombined DPC J, Raw

45

40

40

35

35

30

.~

30

25

"5 ~,

25

~

20

[]

15

t5

t0

10

5

5

0

CH2GICOOH

0

CHCI3

CHBr2CI

CHBrCl2

Fig. 1. Individual THM changes of the Buyukcekmece water sample with respect to treatment.

Fig. 3. Individual HAA changes of the Buyukcekmece water sample with respect to treatment. @Ozone E]Coag. RCombined DPC ARaw

6O 60

[]

50

50

g

CHCI2COOH CClaCOOH CBr#CICOOH

CHBr3

g

=

40

40

30

3oE

20

20

C3 t0 0 CHCla

CHBrzCt

CHBrCIz

CHBr3

0

CH2CtCOOH CHGI2COOH CCI3COOH

CBr2CICOOH

Fig. 2. Individual THM changes of the Omerli water sample with respect to treatment.

Fig. 4. Individual HAA changes of the Omerli water sample with respect to treatment.

the TTHM and HAAs formation reaction to be precursor limited. The compositional change observed by treatment methods of each individual THM could be considered as insignificant for the Buyukcekmece water sample (Fig. 1). On the other hand, the Omerli water sample displayed less CHC13 formation as a result of each treatment method (Fig. 2). A variable effect was observed on the distribution of individual THMs after a ozonation, coagulation and combined system. Due to the low degradation effect of PC oxidation, the recorded changes with respect to raw water sample could be considered as insignificant. The formations of mono- and dichloroacetic acids were favored by ozonation, coagulation and

combined systems (Figs. 3 and 4). A significant increase was observed on the formation of CC13COOH by photocatalysis although the effects of other treatment methods could be considered as minor for the Buyukcekmece water sample (Fig. 3) and considerably lower for the Omerli sample in accordance with the literature [24] (Fig. 4). The formation of dibromochloroacetic acid, which was found developmentally toxic in mouse whole embryo culture, was reduced by all o f the treatment methods for the Buyukcekmece water sample, but the effect could be considered as insignificant in the case of the Omerli water sample [26]. The treated water samples displayed diverse effects on the formation o f other DBPs (Tables 7


163

Table 7 Effect of treatment methods on the formation of other DBPs for the Buyukcekmece water sample Concentration,/~g L ]

Raw

Ozonation

Coagulation

Combined

PC

Monochloroacetnitrile Dichloroacetonitrile Trichloroaeetnitrile Chloral hydrate

1,1,1-trichloropropane

2.4 3.5 nd 69.2 0.6 nd 0.7

2.1 3.4 nd 56.9 0.8 nd 0.8

2.1 3.2 nd -1.4 nd 0.9

1.6 nd nd 19 nd nd 0.6

2.1 3.7 nd 24.5 1.1 nd 0.7

Monobromoacetonitrile Dibromoacetonitrile Bromochloroacetonitrile Chloropierin

1.6 1.1 nd nd

1.2 0.9 nd nd

3.5 0.9 nd 3.6

0.5 nd nd 3.5

0.8 1.0 3.3 nd

1,1-dichloropropane 1,3-dichloropropane

Table 8 Effect of treatment methods on the formation of other DBPs for the Omerli water sample Concentration,/zg L1

Raw

Ozonation

Coagulation

Combined

PC

Monochloroaeetnitrile Dichloroacetonitrile Trichloroacetnitrite Chloral hydrate 1,1-dichloropropane 1,3-dichloropropane

1,1,1-trichloropropane

2.0 3.4 nd 78.1 0.4 nd 0.7

2.3 3.5 nd 71.4 nd nd 0.8

1.5 nd nd 75.9 0.3 nd 1.0

1.6 nd nd 47.1 0.4 nd 0.9

1.5 3.6 nd 14.9 1.1 nd 0.8

Monobromoacetonitrile Dibromoacetonitrile Bromoehloroacetonitrile Chloropicrin

0.6 0.9 nd nd

0.5 nd nd nd

0.7 nd nd 3.6

0.6 nd nd 3.7

0.7 0.9. 3.5. nd

and 8). Except for chloral hydrate, the levels o f the other DBPs were too low to make a comparison between the B u y u k c e k m e c e and Omerli treated water samples. Chloral hydrate was removed more effectively b y the combined system in the B u y u k c e k m e c e sample while PC oxidation was the most effective treatment system in the Omerli water sample. Although chloropicrin was not detected in the raw water samples following coagulation and ozonation combined

b y coagulation treatment methods, comparatively higher concentration levels were observed for the B u y u k c e k m e c e (Table 7) and Omerli (Table 8) water samples while bromochloroacetonitrile was detected only after PC treatment.

3.4. Toxicity test results Daphnia magna was used to test the toxicity o f many chemicals and accurately simulated the

164


Table 9 Daphnia magna immobilization test results in raw and

treated" water samples (quadruplicateexperiments) Immobilization(%) Buyukcekmece Omerli Alento Raw water Ozonation Coagulation Combined Photocatalysis

70 20 15 35 35

20 40 60 25 60

30 40 Nd -40

aTreatmentmethods as described in Table 5.

effects of the mixture of the chemicals on mammals [27]. The immobilization o f D a p h n i a magna in raw and treated samples is given in Table 9. The immobiliation of raw water (70%) decreased significantly after treatment methods in the Buyukcekmece sample. The ozonated sample displayed 20% immbolization while the coagulated sample exhibited less toxicity (15%). However, immobilization increased (35%) due to the combined system treatment. This additive toxicity reflected disagreement with the UV254 removal (Table, 5) which was removed at the highest level (59%) by the combined system but supported formation of brominated species due to higher Br-/TOC. For instance, at 0.1 mg Br-/mg TOC ratio (around 200 #g L- 1of bromide and 2 mg L-1 of TOC were considered), brominated species (detected by a TOBr/TOX ratio) accounted for at least 29% of the activity inducing chromosomal aberrations of DBPs formed during chlorination [28]. The shift in specific TTHMFP (Table 3) and THMs distribution due to treatment systems (Fig. 1) confirmed this. However, the increase in CHBr2C1 and CHBr3 formations with respect to coagulation after a combined system was slight to prove this hypothesis concretely. On the contrary, HAAs distribution due to the treatment system reflected that the dibromoacetic acid level decreased due to treatment systems, particularly by the combined system with respect to raw water,

while trichloroacetic acid and dibromoacetic acid increased due to ozonation (Fig. 3). However, keeping in mind that there are still many unknowns about the complex mixture toxicity of DBPs [29], these results can be assumed as the preliminary evaluation without focusing on the individual speciation. It can also be evaluated that the by-products formed due to ozonation may cause toxicity by forming alum complexes [30]. PC-treated water displayed 35% immobilization. The impact of light on the properties of aquatic NOM resulting in toxicity was established [31]. UVA and UVB irradiated water samples were found non-toxic on Daphnia carinata; in contrast, acute toxicity was observed for UVC and UVC/ H202 treated samples [32] because the photoxidized water contained elevated free copper released from NOM-metal binding sites. However, the case of this study can be evaluated in relation to the low NOM removal (20%) as seen in Table 5. The distribution ofTHMs speciation reflected the same tendency with the coagulated water (Fig. 1) with the exception of the highest trichloroacetic acid formation (Fig. 3), which was reported as one of the least potent mutagens [17]. The ozonated and coagulated Omerli water samples displayed 40% and 60% immobilization, respectively, which indicated an increase with respect to raw water toxicity (20%). An ozone dose applied as the same for the Buyukcekmece sample must be optimized due to its different water characteristics (lower pH and alkalinity). Furthermore, the coagulation process must be well optimized to avoid high residual aluminum concentrations [33] and its organic complexes [30]. The combined system treated water sample exhibited 25% immobilization. This can be explained due to preozonation, which improved the removal of smaller colloids more effectively by sequential coagulation, resulting in 61% of NOM removal (Table 5). This was also in accordance with a specific TTHMFP tendency, although it was still higher than ozonation used alone

M. Bekbolet et al. /Desalination 176 (2005) 155-166

(Table 7). The PC treated Omerli water sample showed 60% immobilization similar to coagulation of that NOM removal was also at the same order, although specific TTHMP decreased due to PC oxidation to the lowest level. This can be attributed to the fact that photocatalysis did not decrease chloroform percentage of raw water (Fig. 2) while it increased trichloroacetic formation of raw water (Fig. 4) with respect to the other treatment methods. The lack of data for coagulation treatment did not allow us to compare its effectiveness on the immobilization for the Alento sample. However, ozone and PC treated water samples did display slightly higher immobilization (40%) than raw water sample (30%), although ozone gave a higher NOM removal (64%) than PC treatment (48%). This slight increase in immobilization might be due to the by-products formed during oxidation, which requires better optimization or the use combined with the other processes.

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enhanced by photocatalysis. Minor amounts of other DBPs were detected with the exception of chloral hydrate, which displayed significantly high levels but diminished after PC treatment. The immobilization test results were in accordance with the DBP distribution more than NOM removal efficiency. However, these findings, more than generalized, can be surrogates for further studies.

Acknowledgements The authors gratefully acknowledge the support provided by NATO through Grant EST.CLG 980506. The authors would like to express their specials thanks to Rosario Casale and Paolo Napodano for their technical assistance. The valuable contribution of Prof. Marc Anderson and Prof. Themistokles Lekkas is appreciated.

References 4. Conclusions An effective NOM control program relies upon a good understanding of the origin, occurrence, and fluctuation of the organic matter in surface water. The results presented here display the effects o f treatment methods on the removal of organic matter taken from different regions of Istanbul, Turkey, and Salerno, Italy. The effects ofozonation, coagulation, ozonation followed by coagulation and photocatalysis were investigated in terms of SUVAz54 and DBP formation potentials in relation to D. m a g n a immobilization. The related removal efficiencies were found to be site specific. All of the THMs were formed, and the presence of high levels o f bromide ions in the Buyukcekmece and Omerli water samples resulted in considerable amounts ofbromoform. The distribution of HAAs was not significantly affected by the treatment methods except for the fact that trichloroacetic acid formation was

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