TiO2-catalysed ozonation of raw Ebro river water

PII: S0043-1354(99)00297-3

Wat. Res. Vol. 34, No. 5, pp. 1525±1532, 2000 # 2000 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0043-1354/00/$ - see front matter

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TiO2-CATALYSED OZONATION OF RAW EBRO RIVER WATER R. GRACIA*, S. CORTES, J. SARASA, P. ORMAD and J. L. OVELLEIRO Department of Chemical Engineering and Environmental Technology, University of Zaragoza, Pedro Cerbuna 12-50009, Spain (First received 1 August 1998; accepted in revised form 1 July 1999) AbstractÐThis paper presents the results obtained with heterogeneous catalytic ozonation in which raw Ebro river (Spain) water is ozonated in the presence of titanium dioxide supported on alumina as a solid catalyst at two di€erent O3:C weight basis ratios. The in¯uence of catalytic ozonation on the trihalomethane (THM) formation during drinking-water treatment is also studied. It is shown that using this catalyst during ozonation of the natural water allowed reductions in THM formation. Characterization of the raw, ozonated and chlorinated water was made by concentrating the sample through liquid±liquid extraction, along with the gas chromatography/mass spectrometry (GC/MS). A total of 66 di€erent organic compounds were identi®ed, mainly carboxylic acids, aromatics, aldehydes, ketones and alcohols. The percentage of elimination or formation levels reached during ozonation and chlorination are discussed. # 2000 Elsevier Science Ltd. All rights reserved Key wordsÐozonation, drinking-water, by-products, catalyst, titanium dioxide, trihalomethanes

INTRODUCTION

Zaragoza, a town with 650,000 inhabitants, is supplied with water from the Ebro river. The drinkingwater treatment plant in the town comprises prechlorination, coagulation±¯occulation, clari®cation, sand ®ltration and ®nal chlorination. The authors are studying with pre-ozonation replacing prechlorination for improving the water treatment since the discovery of potentially harmful chlorination byproducts such as trihalomethanes (THM) and with the introduction of a new stage of heterogeneous catalytic ozonation between settling and ®ltration. The ozonation reduces the THM formation potential (Amy et al., 1991; Dore et al., 1988; Miltner et al., 1992; Singer, 1990). Heterogeneous catalytic ozonation is a novel type of advanced oxidation which combines ozone with the adsorptive and oxidative properties of solidphase metal oxide catalysts to achieve at room temperature mineralization of dissolved organics (Paillard et al., 1991). Titanium dioxide (TiO2) shows a high catalytic activity, and it is used as a heterogeneous catalyst (Allemane et al., 1993). TiO2 is a non-toxic, insoluble, comparatively cheap catalyst. Heterogeneous catalytic ozonation in which water is ozonated in the presence of a solid catalyst composed of TiO2 supported on alumina allows a *Author to whom all correspondence should be addressed. Tel.: +34-976761156; fax: +34-976762142

high oxidation level of organic matter (Gracia et al., 1997), besides not causing any dissolution of the titanium in the water treated by ozonation. Consequently, the potentially harmful chlorination by-products are reduced. The main advantage of supported catalysts is avoiding the separation of solid±liquid phase. Also other characteristics of the supported catalyst can increase the reaction rate. MATERIAL AND METHODS

Sampling and storage Water samples were collected from the Ebro river. The samples were placed in amber glass bottles and stored at 48C. Water samples were ®ltered through a prewashed 0.45 mm ®lter paper (Millipore) to eliminate the e€ect of suspended particles on the measurements. Table 1 shows the quality characteristics of the water that was used. Preparation and characterization of the catalyst TiO2 supported on alumina was prepared by adsorption in dissolution method. a-alumina (Probus, speci®c surface area Sp = 141.7322.59 m2/g area) was immersed in a suspension consisting of TiO2 anatase (Probus, Sp = 8.51 2 0.24 m2/g area) with constant shaking for 5 h for impregnation of TiO2 in the support pores. The pH of the solution was 5.5 (H2SO4 0.1 N). Then, the particles were washed by organic-free water until the e‚uent was clear in colour indicating that all TiO2 had been adsorbed. The water was removed by settling/®ltration. After being dried at ambient temperature (208C) in air, the catalyst was put in an oven for calcination for 24 h at 5008C. Finally, the catalyst was compacted to granular form (particle diam-

1525

1526

R. Gracia et al. Table 1. Water quality characteristics

Temperature (8C)

pH

Conductivity (mS/cm)

TOC (mg/L)

UV absorbance

11.0

7.94

1.24

4.46

0.067

eter about 2±4 mm). The catalyst contained about 2.5% (weight basis ratio) impregnated TiO2. Characterization of the catalyst was performed by means of X-ray power di€raction (XRD), speci®c surface area and mercury porosimetry. XRD was used to determine crystallinity and crystal phase with a Philips PW1825 apparatus. XRD spectra were obtained in a Rygaku/Max System, using Cuka radiation at a scanning rate of 0.028/s. It is shown that anatase was the only crystallographic phase in the utilized TiO2. The speci®c surface area was determined by the method of Brunauer, Emmett and Teller (BET) using low-temperature nitrogen adsorption. BET surface area was measured in a PulseChemisorb 2700 Micromeritics equipment. The surface area of TiO2 supported on alumina calcined at 5008C was 132.5020.8 m2/ g. Mercury intrusion porosimetry was determined by an AutoporeII 9215, Micromeritics equipment. For this catalyst, its pore volume was 0.33 cm3/g and its pore size distribution was around 4.4 nm (micropores, about 12%) and 20.56 mm (macropores, about 88%). All aluminium oxides have very few pores smaller than 6 nm in diameter, therefore, almost all pores are large enough to accommodate the organic compounds to be oxidised (Lei et al., 1997). For TiO2 anatase, its pore size distribution was signi®cantly di€erent from the supported catalyst, which was mainly macropores. Organic compound analysis Characterization of the samples was made following US EPA method 625 (EPA, 1984). This method is based on liquid±liquid extraction with methylene chloride, followed by a division of the extract into acid and bases plus neutral fractions. To 1 ml of both extracts were added 10 ml of anthracene D10 as an internal standard. The concentration factors obtained for extracts were between 200 and 300. Finally, the acid and bases plus neutral fractions were analysed by gas-chromatography/mass-spectrometry (GC/ MS). A Varian 3300 gas chromatograph connected to an ion trap detector (ITD, Finnigan Mass 800) mass spectrometer was used for identifying the organic compounds. The chromatography conditions were as follows: . column: DB-5 J&W Scienti®c, 5% diphenyl and 95% dimethylpolysiloxane; . injection: 2 ml. Splitless: 0.8 min; . injection temperature: 2508C. Detection temperature: 3508C; . carrier gas: helium (30 cm/s); . temperature programme: 378C (3 min)-68C/min-2808C (10 min).

Injection with a Head Space: . HSS Programmer DANI 3950. HSS Sampling unit Dani 3950; . bath temperature: 708C; manifold temperature: 908C; . press time: 19 s; vent time: 5 s; injection time: 30 s. Global parameters To study the behaviour of water samples when subjected to ozonation, the following global parameters were analysed. UV absorbance. The degradation of organic matter was measured with a Hitachi U-1100 spectrophotometer, by optical means at 254 nm, in a 1-cm quartz cell. pH. This was measured with a Crison 505 pHmeter. TOC. Total organic carbon was measured with a TOCTC Astro 1850 Analyser, following standard method 5310C (Clesceri et al., 1989). Chlorination Water samples were bu€ered at pH 7.0 using a phosphate bu€er, chlorinated with sodium hypochlorite (NaOCl), sealed with a TFE-lined screw cap and stored in the dark at room temperature (208C) for the selected time. At the end of the holding time analyses for residual chlorine and THMs were performed and the reaction was quenched with sodium sul®te to prevent further THM formation. Free residual chlorine and combined chlorine as chloramines were measured using DPD ferrous titrimetric method (Clesceri et al., 1989). The selected chlorine dosage was based on a free chlorine residual ranging between 0.1 and 1 mg/l after a reaction time of 24 h. Ozonation Ozone was generated from dry pre®ltered oxygen by using a Fischer Model 500 ozonizer. The ozonizer was connected to a glass closed reactor where is located the supported catalyst with simultaneous ozonation and catalyst e€ects. This reactor worked in semi-continuous mode: continuous to gas and discontinuous to liquid. The type of contact between water and catalyst is in ®xed bed. All experiments were conducted in the ozonation reactor described in Fig. 1. The surplus ozone was retained by two bubblers, containing 250 ml of a 2% KI solution. Through the titration

Trihalomethanes analysis Trihalomethanes were measured by a Head Space connected to an HP5890 gas chromatograph equipped with an electron capture detector (ECD). The chromatography conditions were as follows: . column: DB-624. (30 m0.23 mm d.i.); . injection temperature: 2508C; detection temperature: 3508C; . carrier gas: helium (30 cm/s); auxiliar gas: N2; . temperature programme: 508C (8 min)±128C/min±2508C (5 min).

Fig. 1. Experimental apparatus used for catalytic ozonation.

TiO2-catalysed ozonation

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Table 2. Ozone dosing Oxidizing system O3 alone O3 catalyst

O3 dosage gO3O/gTOC

O3 introduced (mg/l)

O3 in o€-gas (mg/l)

O3 residual (mg/l)

O3 consumed (mg/l)

O3 dosage gO3c/gTCO

1.5 3.0 1.5 3.0

6.69 13.38 6.69 13.38

3.0 6.01 3.0 6.01

0.05 0.05 0.05 0.05

3.64 7.32 3.64 7.32

0.82 1.64 0.82 1.64

of the solutions in the bubblers using sodium thiosulphate and starch as an indicator, the ozone in o€-gas was determined. The ozone in solution form (residual) was measured by a spectrophotometer using the Indigo method (Bader and HoigneÂ, 1981). The consumed ozone was obtained by the following calculation: ozone introduced ÿ …ozone in off-gas ‡ ozone residual †: RESULTS AND DISCUSSION

In each experiment was ozonated 2 l water from Ebro river, at two di€erent O3:C weight basis ratios and using a concentration of 2.5 g/l TiO2 supported on alumina as a catalyst. The amount of ozone generated in each experiment was 396.4 mgO3/h. The ozonation times were 2 and 4 min, respectively, according to ozone dosages used (1.5 and 3.0 g O3/ g initial TOC). Table 2 presents ozone dosing (g consumed O3/g initial TOC) and Table 3 presents the degradation of organic matter in optical units and also by measuring the TOC in relation to the raw water, comparing the presence of catalyst with ozone alone. It can be seen from Table 3 that the TOC removal obtained was greater in the presence of a catalyst in the ozonation system than with ozone alone, under the same operating conditions. The results obtained show that the adsorption phenomena on the catalyst are important, the initially adsorbed TOC is about 10%. It is necessary for the adsorption of organic matter from water to catalyze the oxidation. The best result is observed for an ozone dosage of 1.6 g O3 consumed/g TOC. The spectroscopic study of the samples showed the rapid disappearance of the aromatic ring absorption at 254 nm, specially with catalytic ozonation. The proposed heterogeneous catalytic ozonation mechanism consists in simultaneous adsorption of ozone and organic molecules on the catalyst surface, decomposition of ozone on the metallic sites, producing surface bound O
ÿ radicals more reactive

than ozone and oxidation of adsorbed organic molecules by adjacent O
ÿ radicals. Oxidation proceeds step wise through several oxidised intermediates whilst O
ÿ radicals are continuously generated by dissolved ozone that is transferred to the catalyst surface. The anity of the oxidation products to the catalyst decreases and ®nal oxidation products desorb from the catalyst surface (Logemann and Annee, 1997). Water from Ebro river was chlorinated with a dosage of 1.5 mg Cl2/l for 24 h as an oxidation treatment (pre-chlorination) and later was chlorinated with a dosage of 2.5 and 5 mg Cl2/l for 24 h as a disinfection treatment (®nal chlorination). The ozonated water was also chlorinated with a dosage of 2.5 and 5 mg Cl2/l for 24 h. Table 4 presents the degradation of organic matter in optical units and also by measuring the TOC in relation to the raw water, comparing the presence of catalyst with ozone alone. It can be seen from Table 4 that the TOC removal obtained was greater with chlorination after pre-ozonation than when chlorine was used as the sole oxidant. The more TOC abatement was obtained to increase the ozone dose and with catalytic ozonation. Tables 5 and 6 show the THM formation, quanti®ed by GC/ECD, for a ®nal chlorination of 2.5 and 5 mg Cl2/l, respectively. Also, residual free chlorine is quanti®ed for each selected chlorination time (2, 6 and 24 h). Chloramines have not been detected after a chlorination time of 24 h. In natural water and ozonated water have not been detected any trihalomethane. It can be seen from Tables 5 and 6 that after prechlorination did not remain any free chlorine and after ®nal chlorination the free residual chlorine decreased with time. A minimum free residual chlorine content of 0.1 mg/l remained after ®nal chlorination; under these conditions disinfection is guaranteed in most of waters (Wricke et al., 1993).

Table 3. Degradation of organic matter Oxidizing system O3 alone O3 catalyst Catalyst

O3 dosage gO3/gTOC

TOC ®nal (mg/l)

TOC reduction %

UV absorbance

UV absorb. reduction %

pH ®nal

0.8 1.6 0.8 1.6 0

3.96 3.85 3.86 3.73 4.03

11.2 13.7 13.4 16.4 9.6

0.048 0.032 0.043 0.022 0.060

28.4 52.2 35.8 67.2 10.4

7.92 7.91 7.90 7.89 7.88

UV absorbance

0.067 0.026 0.027 0.028 0.026 0.026 0.017 0.022 0.016 0.062 0.044 0.049

TOC reduction %

0 28.9 29.4 27.8 29.1 27.1 32.1 28.7 32.5 4.9 18.8 25.1 Prechlorination+Cl2 (2.5 mg/l)+Cl2 (5 mg/l)

O3/catalyst+Cl2 (5 mg/l)

O3/catalyst+Cl2 (2.5 mg/l)

O3+Cl2 (5 mg/l)

0 0.8 1.6 0.8 1.6 0.8 1.6 0.8 1.6 0 0 0 Natural water O3+Cl2 (2.5 mg/l)

4.46 3.17 3.15 3.22 3.16 3.25 3.03 3.18 3.01 4.24 3.62 3.34

Ozone dosage gO3/gTOC

TOC ®nal (mg/l)

As it could be expected the THM formation obtained with the chlorination after pre-ozonation was lower than with chlorine alone. Tables 5 and 6 show a decrease of the THM formation with catalytic ozonation (the higher ozone doses, the greater reduction) and an increase with increasing chlorination time. Catalytic ozonation allowed the greater reduction in the content of organic matter and therefore in the concentration of THMs. The concentration of CHCl2Br and CHClBr2 were greater than the CHCl3 concentration in ozonated water and later chlorinated for less than 6 h. It was due to the formation of intermediate brominated compounds in ozonated water. However, after chlorination at 5 mg Cl2/l for 24 h the CHCl3 was found to be the major THM compound and at 2.5 mg Cl2/l the CHCl2Br was found to be the major.

Qualitative analysis

Oxidizing system

Table 4. Degradation of organic matter

0 61.2 59.7 58.2 61.2 61.2 74.6 67.2 76.1 7.5 34.3 26.9

R. Gracia et al. UV absorb. reduction %

1528

The reduction of TOC obtained after ozonation showed that the organic matters have been degraded only partially to CO2. Many by-products have therefore been identi®ed by means of GC/MS analysis. In Table 7 are classi®ed the compounds identi®ed by GC/MS in the natural water and in the ozonated and chlorinated sample. Column 2 shows the concentration for each compound, in the natural water. Columns 3±7 show the percentage reduction or increase in concentration after ozonation at 3.0 g O3/g initial TOC, with addition of the catalyst and after chlorination at 2.5 mg Cl2/l for 24 h, the initial amount of natural water being the reference. The concentrations of the compounds were calculated on the basis of their peak area relative to the peak area of the anthracene D10 (semiquantitative estimation). This is based on a response factor of 1 for all compounds relative to the anthracene D10 internal standard. The concentration of the internal standard in the bases plus neutral and acid fractions represents 1 mg/l of the original raw water. In Table 7 is shown a decrease of aromatics, specially with catalytic ozonation. Also ozonation and chlorination cleaved double bonds, opened aromatic rings and removed or oxidized alkyl groups. Figure 2 shows the percentage of di€erent groups of substances in natural water, after ozonation at 3.0 g O3/g initial TOC, used a catalyst and after chlorination at 2.5 mg Cl2/l for 24 h. The compounds have been classi®ed according to their functional group in six di€erent groups. Phthalates and acids are the organic compounds found in the greatest abundance whereas aromatics, ketones and aldehydes are found in the least proportion. After ozonation and chlorination, a decrease is observed in the percentages of all the

TiO2-catalysed ozonation

1529

Table 5. Quanti®cation of trihalomethanes for a ®nal chlorination of 2.5 mg Cl2/l Oxidizing system O3 alone 0.8 gO3/gTOC O3 alone 1.6 gO3/gTOC O3/catalyst 0.8 gO3/gTOC O3/catalyst 1.6 gO3/gTOC Prechlorination Prechlorination and ®nal chlorination

Time (h)

Free chlorine

CHCl3 (mg/l)

CHCl2Br (mg/l)

CHClBr2 (mg/l)

CHBr3 (mg/l)

THMs (mg/l)

2 6 24 2 6 24 2 6 24 2 6 24 24 2 6 24

0.4 0.3 0.1 0.5 0.3 0.1 0.4 0.3 0.1 0.5 0.3 0.1 0 0.7 0.5 0.2

1 5 24 1 7 23 1 2 25 1 2 25 3 15 34 55

6 14 39 5 11 30 5 8 30 3 8 26 4 16 27 30

6 12 16 4 8 21 4 7 21 2 6 11 2 13 17 23

0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 0

13 31 80 10 26 75 10 17 77 6 16 62 9 44 78 108

Table 6. Quanti®cation of trihalomethanes for a ®nal chlorination of 5 mg Cl2/l Oxidizing system O3 alone 0.8 gO3/gTOC O3 alone 1.6 gO3/gTOC O3/catalyst 0.8 gO3/gTOC O3/catalyst 1.6 gO3/gTOC Prechlorination Prechlorination and ®nal chlorination

Time (h)

Free chlorine

CHCl3 (mg/l)

CHCl2Br (mg/l)

CHClBr2 (mg/l)

CHBr3 (mg/l)

THMs (mg/l)

2 6 24 2 6 24 2 6 24 2 6 24 24 2 6 24

0.5 0.4 0.3 0.7 0.6 0.3 0.8 0.5 0.3 0.6 0.6 0.3 0 0.9 0.5 0.5

4 14 49 8 18 45 6 11 37 3 10 37 3 23 36 64

10 25 36 12 20 38 9 20 38 6 16 36 4 24 29 43

7 16 24 6 15 26 6 14 22 3 10 16 2 15 20 23

0 0 1 0 0 1 0 0 1 0 0 0 0 0 0 1

21 55 110 26 53 110 21 45 98 12 36 89 9 62 85 131

groups or these remain practically unchanged, except for the phthalates. A greater decrease in the percentage of all the groups, except for the phthalates, is observed for the catalytic ozonation. CONCLUSIONS

1. The TOC and UV absorbance removals obtained were greater in the presence of a catalyst compared to these obtained with ozone alone, under the same operating conditions. As expected, the increase of ozone dose led to an increase of TOC level reduction. The best results for this natural water were obtained for an ozone dosage of 1.6 mg consumed O3/mg initial TOC. 2. The TOC removal obtained was greater with chlorination after pre-ozonation than when

chlorine was used as the sole oxidant. The more TOC abatement was obtained to increase the ozone dose and with catalytic ozonation. 3. Water samples were analysed by GC/MS during TiO2-catalysed ozonation and chlorination. These analyses have allowed us to identify a total of 66 di€erent organic compounds. Phthalates and acids are the organic compounds found in the greatest abundance, whereas aromatics, ketones and aldehydes are found in the least proportion. After ozonation and chlorination, the percentages of all the groups decreased or these remain practically unchanged, except for the phthalates. 4. Chlorination after pre-ozonation produced less THMs than chlorinated only. The least THM formation is obtained with catalytic ozonation. The THM concentration also diminished at high ozone doses.

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Table 7. Compounds identi®ed by GC/MS in the natural water, and the percentage variation in concentration after ozonation, used a catalyst and after chlorinationa Compounds (% variation) Oxidation treatment Disinfection (2.5 mg Cl2/l)

C (ppm) Ozone alone Ozone catalyst Ozone alone Ozone catalyst 0 0 Cl2 Cl2

Aromatic Benzene, (1-methylethyl)Benzene, methylBenzene, 1,n-dimethylBenzene, ethylBenzene, 1-ethyl-n-methylBenzene, 1,n,m-trimethylBenzene, (methoxymethyl)-

0.05 0.63 0.08 0.79 0.05 0.2 0.15

ÿ55.3 ÿ16.4 ÿ60 ÿ80 ÿ95 ÿ77 ÿ11

ÿ60.0 ÿ14.0 ÿ58 ÿ93.8 ÿ92 ÿ81 ÿ39

Acids and esters Propanoic acid, octyl ester Benzoic acid Octanoic acid Nonanoic acid 7-Nonenoic acid Undecanoic acid, 10-methylDodecanoic acid, 10-methylDodecanoic acid Tridecanoic acid Tridecanoic acid, 12-methylTetradecanoic acid Tetradecanoic acid, 12-methylPentadecanoic acid Pentadecanoic acid, 14-methylHexadecanoic acid 9-Hexadecenoic acid Heptadecanoic acid, 16-methyln-Octadecenoic acid Nonanedioic acid 9,12-Octadecadienoic acid

0 0 0.12 0 0.1 1.35 0 0.65 0 1.3 0.68 0 0.2 1.9 0 0.7 2.55 1.90 0.4 0.9

+100 ND +11 ND ÿ100 ÿ37.8 +100 ÿ87.7 ND ÿ91 +9.0 ND ÿ100 +12 ND ÿ100 +5 +12 ÿ93 ÿ100

Alcohols and phenols 2-Pentanol,2,4-dimethyl1,3-Pentanediol,2,4,4-trimethyl1-Hexanol,3,5,5-trimethyl1,2,6-Hexanetriol 1-Hepten-3-ol 1-Octanol 1-Tridecanol Phenol,2,6-bis(1,1-dimethylethyl)-4-methylPhenol,2,6-bis(1,1-dimethylethyl)-4-ethyl-

0 0 2.54 0.05 0 0.08 0.15 0.33 0

Ketones and aldehydes Bicyclo(3,2,1)octan-2-one,1-(1-propenyl)Benzaldehyde Hexadecanal,2-methyl10-Undecenal 9-Octadecenal Phthalates Dimethyl phthalate Diethyl phthalate Dibutyl phthalate 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic 1,2-Benzenedicarboxylic

acid, acid, acid, acid, acid, acid, acid, acid,

bis(2-methoxyethyl) ester butyl-2-methylpropyl ester bis(4-methylpentyl) ester butyl cyclohexyl ester mono(2-ethylhexyl) ester butyl methyl ester butyl octyl ester dipropyl ester

Miscellaneous Cyclohexane, (1,1-dimethylethyl)Pentane, 2,2,3,4-tetramethyl1-Hexene, 3,4-dimethyl Hexane, 1-(hexyloxy)-5-methylOctane, 2,5,6-trimethylDecane, n,m-dimethylDecane, 2,n,m-trimethyln-Decene, m-methylHeptadecane,2,6,10,15-tetramethyln-Octadecene Oxirane, decylOxirane, ((dodecyloxy)methyl)Oxirane, (((2-ethylhexyl)oxy)methyl)Oxirane, (((2-ethylhexyl)oxy)methyl)a

ND: not detected; +100: generated compound.

Prechl. Cl2

ÿ100 ÿ6.35 ÿ100 ÿ14.8 ÿ100 ÿ100 ÿ63

ÿ100 ÿ32 ÿ100 ÿ30.9 ÿ100 ÿ100 ÿ87

ÿ100 ÿ25 ÿ30 ÿ78.9 ÿ100 ÿ60 +8.5

ND ND +37 ND +110 ÿ65.2 +100 ÿ20.7 ND ÿ95.8 ÿ35.3 ND ÿ100 ÿ50.5 +100 ÿ100 ÿ70.2 ÿ78.9 ÿ80 ÿ100

+100 ND +80 +100 +24 +11.1 +100 ÿ92.9 ND ÿ98.8 +52.9 +100 ÿ100 +73.7 ND ÿ100 +9.4 +50 ÿ100 ÿ30

ND ND +85 +100 ÿ100 ÿ7.3 ND ÿ55.4 ND ÿ100 +25 +100 ÿ100 ÿ60.2 +100 ÿ100 ÿ80.0 ÿ100 ÿ100 ÿ100

ND +100 +16.6 +100 ÿ100 +26.7 ND ÿ100 +100 ÿ13.8 ÿ44.1 +100 ÿ90 ÿ23.1 ND ÿ42.9 ÿ65.5 ÿ58.4 ÿ22.5 ÿ100

ND ND ÿ100 +200 +100 ÿ100 ÿ100 ÿ60 ND

+100 ND ÿ100 +460 +100 ÿ100 +93.3 ÿ87.9 +100

ND +100 ÿ100 +720 ND +87.5 ÿ100 ÿ65.8 ND

+100 ND ÿ100 +106 ND ÿ100 ÿ48.7 ÿ100 ND

ND +100 ÿ100 ÿ46 ND ÿ100 +148 ÿ56.7 +100

1.7 0.1 0.21 0 0

ÿ96 ÿ100 ÿ100 ND ND

ÿ99 ÿ100 ÿ100 ND ND

ÿ100 ÿ100 ÿ100 +100 ND

ÿ100 ÿ100 ÿ100 +100 +100

ÿ92.9 ÿ94.0 ÿ100 ND +100

0.1 0.33 1.28 1.19 3.5 2.33 1.32 2.08 0 2.51 2.45

+2 ÿ6.1 ÿ11 +9.2 +8.6 +11.6 ÿ54.5 +77.9 ND ÿ28.3 ÿ55.1

ÿ80 ÿ77.9 ÿ2.3 ÿ42 +8.0 ÿ53.6 ÿ44.7 +73.1 +100 +56.6 ÿ8.2

+40.5 ÿ9.1 ÿ25 +47 +14.9 +63.1 ÿ43.9 ÿ13.0 +100 ÿ60.6 ÿ94.3

ÿ98 ÿ56.4 ÿ29.7 ÿ61.6 +17.4 +10.3 +28.8 +107 ND ÿ40.6 +6.1

+50 ÿ59.4 ÿ69.8 +118 +2.6 ÿ53.6 +201 ÿ77.4 +100 ÿ85.7 ÿ38.8

0.09 0.9 0 0.25 0.04 0 0.14 0 0 0.12 0 0 0.3 0.14

ÿ100 ÿ100 ND ÿ100 ÿ100 +100 +41.8 ND ND ÿ100 +100 ND ÿ100 ÿ64.5

+433 ÿ100 ND +0.8 ÿ100 ND ÿ22 ND ND ÿ100 ND +100 ÿ36.7 ÿ5.0

ÿ100 ÿ65.6 +100 ÿ100 ÿ100 +100 +170 ND +100 +208 ND +100 +90 +311

+287 ÿ23.3 +100 +60 ÿ100 ND +77.3 ND +100 +466 +100 ND ÿ100 ÿ90.8

ÿ100 ÿ100 +100 ÿ100 +495 ND +198 +100 ND +658 ND +100 ÿ93.3 ÿ64.5

TiO2-catalysed ozonation

Fig. 2. Distribution in groups of the compounds identi®ed in the natural water and in the ozonated and chlorinated sample.

1531

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AcknowledgementsÐThe authors thank the sta€ of ConfederacioÂn Hidrogra®ca del Ebro for their assistance. REFERENCES

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