IOA Conference and Exhibition Valencia, Spain October 29 – 31, 2007 Effectiveness of Advanced Oxidation Processes with O 3 and O 3+H 2O2 in Pesticides Degradation Natividad Miguel , María P. Ormad, Munia Lanao, Cristina Ibarz, José L. Ovelleiro Department of Chemical Engineering and Environmental Technologies. University of Zaragoza. Pedro Cerbuna, 12. 50009 Zaragoza (Spain). Tel: +34 976761156 Fax: +34 976762142 email: [email protected] Abstract The aim of this research work is to study the degradation of 44 organic pesticides, which are systematically detected in the Ebro River Basin (Spain), by advanced oxidation processes with O3 and H2O2. The pesticides studied are: alachlor, aldrin, ametryn, atrazine, chlorfenvinfos, chlorpyrifos, pp’ DDD, op’ DDE, op’ DDT. pp’ DDT, desethylatrazine, 3,4 dichloroaniline, 4,4’ dichlorobenzophenone, dicofol, dieldrin, dimethoate, diuron, a endosulphan, endosulphan sulphate, endrin, α HCH, β HCH, γ HCH, δ HCH, heptachlor, heptachlor epoxide A, heptachlor epoxide B, hexachlorobenzene, isodrin, 4 isopropylaniline, isoproturon, metholachlor, methoxychlor, molinate, parathion methyl, parathion ethyl, prometon, prometryn, propazine, simazine, terbuthylazine, terbutryn, tetradifon and trifluralin. The techniques applied are combinations of ozone and hydrogen peroxide and dosages used are 1 1 3 mg O 3 L and weigh ratios H 2O2/O 3 (gg ) of 0.1, 0.5 y 2. The treatment with ozone removes 72% of the studied pesticides, whereas applying O 3+H 2O2 treatment, average degradation yields achieved are less. The maximum average degradation of the studied pesticides by O3+H 2O2 treatment is 51%, and it is achieved with the weight ratio 1 H2O2/O 3 (gg ) of.5. This indicates combined treatment don’t improve the degradation of studied pesticides. Key words : Ozone, hydrogen peroxide, pesticides. Introduction The industrial activity increase and economic and social develop resulting have generate the growth of bid areas. This entails and complicates the supply of one the most essential element to live, water. Moreover, components give for environment and their human use have produced water pollution. Therefore, some parameters of water must to be altered to use it. In the case of human consumption, drinking process is totally necessary, process carried out in drinking water plants. Surface water and groundwater have a natural chemical composition. This composition results of the dissolution of soluble minerals and organic compounds. This natural composition can be modified by four contamination points: domestic water, industrial processes water, uncontrolled wastewaters and diffuse contamination. The last point can be the origin of the presence of pesticides in natural water, substances considered Hazardous Contaminants in accordance with current legislation about water [10,11]. Pesticides are a group of artificially synthesized substances used to fight pests and improve agricultural production. They are, however, generally toxic for living organisms and are difficult to degrade, being toxic agents with persistent bioaccumulative effects [9]. The use of pesticides also constitutes a risk for water quality in agricultural areas due to the fact that these components may
2.4 1 pass through the soil and subsoil and pollute surface waters and groundwater. In the Ebro River Basin (Spain), these substances are controlled via a Pesticides Control Network, which systematically analyzes 44 organic pesticides in surface waters. These pesticides were selected in accordance with their appearance in lists of hazardous substances and/or their high level of use in Spanish agriculture. Although the concentration of these substances detected in natural waters is generally very low, the maximum permissible concentration in human drinking waters in Spain is often exceeded [29], which establishes a limit of 0.5 g/l as the total amount of pesticides and 0.1 g/l for any single pesticide. Consequently, the treatment used to produce drinking water must guarantee the removal of these types of substances or at least reduce their concentration below the limits established in current legislation. A drinking water process consists of a group of operations more or less complex in accordance with natural water quality. In general, these operations are: sieve and bar system, preoxidation, activated carbon adsorption, coagulation flocculation, intermediate oxidation, filtration through sand and final disinfection. Pesticides can be removed from water by oxidation and adsorption onto activated carbon steps. However, these techniques have some disadvantages. Activated carbon adsorption doesn’t destroy pesticides, but it a process that transfers contaminants from water to carbon, which generates a new problem of pollution. With respect to oxidation steps, they use to carry out with chlorine or sodium hypochlorite as oxidant agent. The fundamental problem associated with the use of these agents lies in the generation of by products such as trihalomethanes, substances with proven carcinogenic power [2,4,7,21,23,25]. Due to this problem, some large plants now apply ozone in oxidation steps instead of chlorine or sodium hypochlorite due to the numerous advantages that this presents, in spite of its higher economic cost. Ozone has a high oxidant power and, in principle, does not generate hazardous organohalogenated by products, such as trihalomethanes (THMs) [30,32]. Moreover, colour, smell, and dissolved iron and manganese can be removed via ozonation and coagulation may be improved [14,22]. The reactivity of organic compounds with ozone is a function of the functional groups present in each molecule. However, in presence of bromides, the ozonation of natural water produces brominated disinfection by products, which are potentially carcinogenic [20,27]. Ozone may react with the organic matter present in the water via two distinct mechanisms: a direct or molecular reaction (low pH), by which cycleaddiction reactions and eletrophylic and nucleophylic attacks can be produced, and an indirect or radicalary reaction (basic pH). The indirect reaction takes place via chain mechanism by radicals generated in the decomposition of ozone (hydroxyl, superoxide, ozonide and hydroperoxide radicals). It’s proven that a large number of chlorinated pesticides react via the radical pathway [3,15,16,17,18,19]. The chain mechanism is describing next [24]: Iniciation: O 3 + OH O 2 + HO 2 + HO 2 ↔ O 2 + H + Propagation: O 2 + O 3 + H 2O 2 + OH + OH + O 3 H + O 2 + O 2 Termination: combinations of O 2 , HO 2 y OH . The ozone decomposition increases with the presence of OH , hydrogen peroxide, photolysis by ultraviolet radiation and metallic catalysts. These techniques are called advanced oxidation processes, which are based generation of hydroxyl radicals, which are highly reacting, few selective and capable to mineralize contaminants without generate any by product [5,6].
2.4 2 The direct comparison of the efficiency of these processes is really complicated by their various of factors, such as pH, temperature, auxiliary oxidants or catalysts concentration, substrate nature, etc. [26]. The most of studied pesticides are organic chlorinated compounds, which reactivity with hydroxyl radicals (OH ) is low, due to C Cl bounds, on the contrary that C H bounds, are inert to these radicals attack. To degrade these compounds, reductive radicals ( HO 2 /O2 ) are needed. Intermediated compounds with more hydrogen are formed and these compounds react faster with hydroxyl radicals, achieving their total degradation [26]. In this particular study, the aim is compare and study the effectiveness of treatments with O 3 (ozonation) and O3/H 2O2 (peroxone) to degrade 44 studied pesticides, which are systematically detected in the Ebro River Basin (Spain). Studied pesticides are shown in table 1. Material and methods Sample The natural water under study comes from the River Ebro, upstream from Zaragoza (Spain). Sampling took place during February, a month in which large amounts of pesticides are not historically registered due to the fact that the periods in which pesticides are applied and the first rains occur is between May and September. Accordingly, the initial concentration of pesticides obtained is very low and uniform for each of these. The Total Organic Carbon (TOC) of water is 2.5 mg C L 1. A single sample of 10 L is divided among several one litre amber glass bottles which are kept under refrigeration at 4 ºC until their subsequent preparation and analysis. Each 1 L sample is fortified with 500 ng L 1 of each of the pesticides under study so as to ensure its presence and to study its possible removal. Thus, the concentration of each pesticide in each sample is the sum of what was artificially added and what the natural water actually contained. These concentrations are shown in Table 1. The pH of the water is 8.2 and the TOC is 37 mg C L 1. Table 1. Studied pesticides and concentration in the studied sample Concentration Concentration Pesticide Pesticide (ng L 1) (ng L 1) Alachlor 500 γ HCH 521 Aldrin 500 δ HCH 500 Ametryn 500 Heptachlor 500 Atrazine 551 Heptachlor epoxide A 500 Chlorfenvinfos 500 Heptachlor epoxide B 500 Chlorpyrifos 520 Hexachlorobenzene 500 pp’ DDD 500 Isodrin 516 op’ DDE 500 4 Isopropylaniline 500 op’ DDT 500 Isoproturon 500 pp’ DDT 500 Metholachlor 524 Desethylatrazine 593 Methoxychlor 519 3,4 Dichloroaniline 658 Molinate 551 4,4’ Dichlorobenzophenone 519 Parathion ethyl 500 Dicofol 568 Parathion methyl 500 Dieldrin 500 Prometon 500 Dimethoathe 608 Prometryn 500 Diuron 500 Propazine 500 a Endosulphan 500 Simazine 554 Endosulphan sulphate 500 Terbuthylazine 524 Endrin 500 Terbutryn 500 α HCH 500 Tetradifon 500 β HCH 500 Trifluralin 566
2.4 3 Analysis of pesticides Water samples undergo a solid liquid extraction prior to their analysis by GC/MS (Gas Chromatography/Mass Spectrometry). Solid liquid extraction consists of the retention of organic compounds in a solid phase and subsequent elution with an organic solvent [12]. This extraction is carried out using an AUTOTRACE WorkStation automatic extractor (Zymark). Before extraction, 100 ng L 1 of surrogate compounds used to control the extraction process (simazine D5, atrazine D5 and prometryn D6 (Dr. Erhernstofer) are added to the water sample. During solid liquid extraction, 900 mL of the sample is passed through cartridges containing a solid ENV+ filter (polystyrene divinyl benzene copolymer) (ISOLUTE cartridges, 200 mg 6 mL 1). The pesticides contained in the sample are retained in the solid phase and dried under N 2 for 10 minutes. They are then eluted by passing 10 mL of ethyl acetate (SDS, for pesticide analysis) through the cartridge, thus facilitating the passage of these compounds from the water phase to an organic phase. The extracts so obtained are concentrated under a N 2 flow until an approximate volume of 1 mL is obtained, after which 3 mL of isooctane is added (SDS, for pesticide analysis) in order to carry out a change of solvent. The extract is then concentrated until obtaining an approximate volume of 0.5 mL. Anthracene deuterate (D10) (SUPELCO) is added to each extract as an internal standard for subsequent quantification of the pesticides present in the samples. These extracts are analysed by GC/MS. The chromatographic conditions employed and results of the validation of pesticides analysis methodology are shown in table 2 and 3 respectively. Table 2. Conditions to analysis of pesticides Gas Chromatographer TRACE GC 2000 (TermoFinnigan) Column DB5 MS (J&W, 30 m, 0,25 mm, 0,25 m) 90 ºC(1 min) 20 ºC min 1 180 ºC(1 min) 2 ºC min 1 Program of temperature 240 ºC(1 min) 20 ºC min 1 310 ºC(10 min) Temperature of injector 250ºC Volume of injection 1 L, splitless 0,8 min Carrier gas He (N55), 1mL min 1 Mass Espectrometer POLARIS (ThermoFinnigan) Energy of ionization 70 eV Mode of acquisition Full scan Range of masses 50 450 amu Velocity of screened 1 scan s 1 Time of acquisition 32,5 min Library of reference Nist Applied treatments Various treatments with O 3 and H 2O2 are tested to study the behaviour of the pesticides subjected to these treatments. The various operations studied were carried out twice and as follows: Treatment by O 3: Ozonation is carried out using a corona discharge generator (Fisher 500). The generator produces 1 1 1195 mg O 3 h , which is moved through 1 L of sample for 13 sec. Therefore 4.3 mg O 3 L are applied. No consumed and removed in gas phase ozone (O 3g noconsumed ) is absorbed in two serial gas washing bottles which contain 2% KI. O 3g noconsumed is calculated by valuate of IK, resulting 1.3 1 ® mg O 3 L . The waste dissolved ozone is measured with a Test of Ozone Spectroquant (MERCK) 1 1 resulting 0.01 mg O 3 L . Therefore the consumed ozone is 3 mg O 3 L , dosage usually used in drinking water plants in Spain. This value is calculated according to the next formula: O3consumed = O 3applied – O 3g-noconsumed – O 3waste-dissolved
2.4 4 Table 3. Results of the validation of pesticides analysis methodology Cuantification limit ( g L 1) Calibration Validity Pesticide interval interval Instrumental step Full method 1 1 ( g L ) ( g L ) Isoproturon 20 0,030 20 500 0,030 300 Diuron 20 0,030 20 500 0,030 300 3,4 Dichloroaniline 20 0,030 20 500 0,030 300 4 Isopropylaniline 20 0,030 20 500 0,030 300 Desethylatrazine 20 0,030 20 500 0,030 300 Trifluralin 20 0,015 20 500 0,030 300 Dimethoate 20 0,030 50 500 0,030 300 Simazine 50 0,030 20 500 0,030 600 Prometon 20 0,030 20 500 0,030 300 Atrazine 200 0,100 200 5000 0,100 3000 Propazine 20 0,015 20 500 0,015 300 Terbuthylazine 20 0,015 20 500 0,015 300 Parathion methyl 50 0,030 50 500 0,030 300 Parathion ethyl 20 0,030 20 500 0,030 300 Alachlor 20 0,015 20 500 0,015 300 Ametryn 20 0,030 20 500 0,030 300 Prometryn 20 0,030 20 500 0,030 300 Terbutryn 20 0,030 20 500 0,030 300 Chlorpyrifos 20 0,015 20 500 0,015 300 Chlorfenvinfos 20 0,015 20 500 0,015 300 HCH’s 20 0,015 20 500 0,015 300 Hexachlorobenzene 20 0,030 20 500 0,030 300 Heptachlor 20 0,015 20 500 0,015 300 Heptachlor epoxide A 20 0,015 20 500 0,015 300 Heptachlor epoxide B 20 0,015 20 500 0,015 300 Aldrin 20 0,015 20 500 0,015 300 4,4’ Dichlorobenzophenone 20 0,015 20 500 0,015 300 Isodrin 20 0,015 20 500 0,015 300 α Endosulphan 20 0,015 20 500 0,015 300 pp’ DDE 20 0,015 20 500 0,015 300 Dieldrin 20 0,015 20 500 0,015 300 Endrin 20 0,015 20 500 0,015 300 pp’ DDD + op’ DDT 40 0,030 40 1000 0,030 600 Endosulphan sulphate 20 0,015 20 500 0,015 300 pp’ DDT 20 0,030 20 500 0,030 300 Dicofol 50 0,030 50 500 0,030 300 Metoxychlor 20 0,015 20 500 0,015 300 Metholachlor 20 0,015 20 500 0,015 – 300 Molinate 20 0,015 20 500 0,015 – 300 Tetradifon 20 0,015 20 500 0,015 300 Treatment by O 3+H 2O2: The treatment with ozone and hydrogen peroxide is carried out in the same way than ozonation, but adding dosages of hydrogen peroxide (Carlo Erba, quality for analysis) corresponding to weight 1 ratios H2O2/O 3 (gg ) of 0.1, 0.5 y 2, before to produce the reaction. Results and discussion Degradation yields achieved to each pesticide applying previous treatments and average degradation percentages are showed in table 4.
2.4 5 Table 4. Single and average pesticide degradation yields (%) after applying treatments
Treatment 1 1 1 Pesticide 3 mg 3 mg O 3 L + 0.1 3 mg O 3 L + 0.5 3 mg O 3 L + 2 1 1 1 1 1 1 1 O3 L (gg ) mg H 2O2 L (gg ) mg H 2O2 L (gg ) mg H 2O2 L Isoproturon 70 65 40 25 4 Isopropylaniline 90 100 90 95 Diuron 75 30 65 20 3,4 Dichloroaniline 85 100 70 95 Molinate 75 35 55 50 Trifluralyn 80 75 50 75 Alachlor 70 45 30 60 Metolachlor 70 40 40 60 Simazine 65 15 30 30 Atrazine 50 20 50 20 Propazine 50 15 50 20 Terbuthylazine 45 15 45 25 Prometon 45 50 50 55 Ametryn 45 45 45 55 Prometryn 45 40 45 30 Terbutryn 55 50 50 40 Desethylatrazine 55 15 35 10 Parathion methyl 75 30 40 40 Parathion ethyl 80 30 45 40 Chlorpiryfos 80 45 60 55 Chlorfenvinfos 70 15 40 30 Dimethoathe 75 40 40 60 α HCH 75 20 60 15 β HCH 65 15 55 10 γ HCH 55 15 55 10 δ HCH 70 20 55 20 Hexachlorobenzene 90 30 35 30 Heptachlor 90 70 40 70 Heptachlor epoxide (B) 80 30 60 25 Heptachlor epoxide (A) 75 35 60 30 α Endosulphan 80 30 35 25 Endosulphan sulphate 75 20 55 20 Methoxychlor 90 50 45 25 Tetradiphon 90 15 50 15 Aldrin 85 100 95 100 Isodrin 90 100 100 100 Dieldrin 90 15 60 55 Endrin 80 15 45 15 pp' DDE 75 80 55 20 pp' DDD+op’ DDT 70 60 70 55 pp' DDT 75 70 50 65 Dicofol 80 0 15 0 4,4' Dichlorobenzofenone 85 25 55 25 AVERAGE 72 40 51 40 Treatment by ozone Ozonation achieves an average removal yield of 72% for the studied pesticides. High removal percentages of above 50% in practically all cases are obtained by means of this treatment. The degradation of each compound by ozone depends on its chemical structure. This degradation can be carried out via two pathways: the direct or molecular pathway (low pH) and the indirect or radical pathway (basic pH). Via the direct pathway, molecular ozone reacts directly with the substrate giving rise to selective reactions, mainly with unsaturated and aromatic hydrocarbons
2.4 6 with OH, CH 3 and NH 2 groups. The radical pathway is constituted by reactions in which the reacting species are radicals generated in the decomposition of ozone (hydroxyl, superoxide, ozonide and hydroperoxide radicals) [26]. These reactions are very fast and non selective. Aliphatic hydrocarbons, chlorinated solvents and a large number of chlorinated pesticides react via the radical pathway [3,15,16,17,18,19]. The lowest removal percentages after ozonation, around 50%, were obtained for triazines (simazine, atrazine, propazine, terbuthylazine, prometon, ametryn, prometryn, terbutryn and desethylatrazine). This is due to the major stability of triazinic rings present in these substances. Removal yields of above 60% were obtained for the remaining pesticides. The highest yields were obtained for heptachlors, drins (isodrin, endrin, dieldrin, aldrin), DDTs and other pesticides, such as 4 isopropylaniline, 3,4 dichloroaniline, trifluralin, chlorpyrifos, methoxychlor and tetradifon, all of which are chlorinated compounds that react with ozone quickly via the radical pathway [28]. Removal percentages of around 80% are obtained for the organophosphorous pesticides that possess P=S bonds. The main reaction that takes place in their degradation is oxidation of the P=S bonds with the formation of P=O bonds. The molecule breaks via one of the bonds that involves the phosphorus atom, forming simple esters of phosphoric acid [31]. Treatment by ozone and hydrogen peroxide An overall average removal percentage between 40 and 51% is obtained by means of this treatment with different hydrogen peroxide dosages. As a whole, hydrogen peroxide reduces the ozone reactivity with studied pesticides regardless the applied concentration. This can be due to the addition of hydrogen peroxide, which is done to improve the ozone decomposition, increases the extinction speed of reductive radicals ( HO 2 /O 2 ) in the reaction place. Like this, taking place start reactions to degrade studied pesticides is more difficult. The most of studied pesticides are better degraded by O3+H 2O2 treatment with weight ratio 1 H2O2/O 3 (gg ) of 0.5. This is due to the fact that, in general, an increase of radicals produced to degrade the studied pesticide happens when the hydrogen peroxide concentration rises. However, if very high concentrations of hydrogen peroxide are used, an inhibitory effect happens [1,8,13]. On the other hand, pesticides such as isoproturon and pp’ DDE are degraded better with a weight 1 ratio H2O2/O 3 (gg ) of 0.1, and other pesticides like alachlor, metolachlor and dimethoate, with a 1 weight ratio H2O2/O 3 (gg ) of 2. Moreover, there are pesticides such as trifluralin and heptachlor, which are degraded more effectively with hydrogen peroxide dosages corresponding to weight ratios of 0.1 or 2. Similar degradation percentages are achieved with both concentrations, whereas 1 less percentages are achieved with a weight ratio H2O2/O 3 (gg ) of 0.5 The comparison of O 3 and O3+H 2O2 treatments shows that only 4 isopropylaniline, 3,4 dichloroaniline, prometon, ametryn, aldrin and isodrin are better degraded by O 3+H 2O2 treatment than by O 3 treatment.
2.4 7 Conclusions Among studied treatments, the highest pesticides degradation is achieved by the treatment with 3 mg L 1 of ozone, obtaining an overall average removal percentage of 72%. Triazines, by ozonation, are degraded 50% approximately. In general, their degradation doesn’t improve with the addition of hydrogen peroxide. Only prometon and ametryn show degradation 1 percentages higher with peroxone system (H2O2/O 3 (gg ) of 2) than with ozonation. For organic phosporous pesticides, high degradation yields are achieved, around 80% by treatment with ozone. The treatment with hydrogen peroxide is less effective than ozonation to these pesticides. In all cases, degradation percentages achieved with O3+H 2O2 treatment are less than with O3 treatment. In the case of hexachlorochiclohexanes, heptachlors, endosulphans and DDTs, degradation yields achieved with O 3+H 2O2 are less or similar than with O 3 only. Therefore, the addition of hydrogen peroxide and titanium dioxide decreases the effectiveness of ozone with these pesticides. To drins, an improvement of the aldrin and isodrin degradation is observed by O3+H 2O2 treatment, regardless hydrogen peroxide concentration applied. The degradation of the remaining pesticides doesn’t increase with the addition of hydrogen peroxide to ozone. Only 4 isopropylaniline and 3,4 dichloroaniline are completely degraded and 1 lightly better with O 3+H 2O2 (H2O2/O 3 (gg ) of 0.1). By O 3 and H 2O2 combination, the maximum average degradation of studied pesticides is achieved 1 with a dosage of hydrogen peroxide corresponding to weight ratio H2O2/O 3 (gg ) of 0.5. This is due to the fact than the radicals production increases when the hydrogen peroxide concentration rises. But when this concentration is too much high, an inhibitory effect happens. In conclusion, the addition of H 2O2 to O 3 reduces the reactivity of this agent with studied pesticides. This can be due to this compound, although improves the ozone decomposition, causes a radicals decrease into the reaction place and these radicals are necessary to begin the degradation mechanism which takes place with studied pesticides by means of these treatments. Acknowledgements Authors wish thank for financial support given for Education and Science Ministry (Project CTM 2005 04585). References 1. Alnaizy, R., Akgerman, A. “Advanced oxidation of phenolic compounds”. Advances in Environmental Research, 4(3), 233 244 (2000). 2. Alouini, Z., Seux, R. “Kinetics and mechanisms of the hypochlorite oxidative action over alpha amino acids in water disinfection”. Water Research, 21(3), 335 343 (1987). 3. Beltrán, F.J. “Aplicación del ozono en el tratamiento de contaminantes del agua”. Seminario sobre el ozono en el tratamiento del agua. Burgos (1997). 4. Booman, G., Dellarco, V. et al. “Drinking water disinfection by products: rewiew and approach to toxicity evaluation”. Environ Health Perspect., 107, 207 217 (1999). 5. Cortés S., Ormad P., Puig A., Ovelleiro J.L. “Study of the advanced oxidation processes of chlorobenzenes in water”. Ozone Science and Engineering, 118, 291 298 (1996). 6. Cortés S., Sarasa J., Ormad P., Gracia R., Ovelleiro J.L. “Comparative efficiency of the systems O 3/high pH and O 3/catalyst for the oxidation of chlorobenzenes in water”. Ozone Science and Engineering, 22, 415 426 (2000).
2.4 8 7. Clark, R., Sivaganesan, M. “Predicting chlorine residuals and formation of THMs in drinking water”. J Envir Engrg, 124, 1903 1910, (1998). 8. De, A.K., Chaudhuri, B., Bhattacharjee, S., Dutta, B. “Estimation of OH radical reaction rate constants for phenol and chlorinated phenols using UV/H2O2 photo oxidation”. Journal of Hazardaous Materials, 64(1), 91 104 (1999). 9. Díaz, M.C., Garrido, S., Hidalgo, R. “Contaminación agraria difusa”. MOPU (1988). 10. Directive 2000/60/CE of 23 of October of 2000, related to communal marc to actuation about water politic. Diary Official of European Communities (DOCE), nº L 321, 19 of December of 2000. 11. Directive 2006/11/CE of the European Parliament and Council of 15 of February of 2006, related to pollution caused by dangerous substances tipped in the aquatic environment of the Community. Diary Official of European Communities (DOCE), nº L 64, 4 of March f 2006. 12. EPA Method 525.2. “Determination of organic compounds in drinking water by liquid solid extraction and capillary column gas chromatography/mass spectrometry Revision 2.0”. 13. Ghaly, M.Y., Härtel, G., Mayer, R., Haseneder, R. “Photochemical oxidation of p chlorophenol by UV/H2O2 and photo Fenton process. A comparative study”. Waste Management, 21(1), 41 47 (2001). 14. Hart, J.; Walker, I.; Armstrong, D.C. “The use of high concentration ozone for water treatment”. Ozone Science & Technology, 17, 485 497, (1995). 15. Hoigné, J., Bader, H. “The role of hydroxil radical reactions in ozonation proceses in aqueous solutions”. Water Research, 10(5), 337 386, (1976). 16. Hoigné, J. “Mechanims, rates and selectivities of oxidations of organic compounds initiated by ozonation in water”. Handbook of Ozone Technology and Applications. Ann Arbor Science Publishers, Inc., Ann Arbor, MI, (1982). 17. Hoigné, J., Bader, H. “Rate constants of reactions of ozone with organic and inorganic compounds in water. I: Non dissociating organic compounds”. Water Research, 17(2), 173 183, (1983a). 18. Hoigné, J., Bader, H. “Rate constants of reactions of ozone with organic and inorganic compounds in water. II: Dissociating organic compounds”. Water Research, 17(2), 185 194, (1983b). 19. Hoigné, J., Bader, H., Haag, W.R., Staehelin, J. “Rate constants of reactions of ozone with organic and inorganic compounds in water. III: Inorganic compounds and radicals”. Water Research, 19(8), 993 1004, (1985). 20. Huang, W.J., Chen, L.Y., Peng, H.S. “Effect of NOM characteristics on brominated organics formation by ozonation”. Environmental International 29(8), 1049 1055, (2004). 21. Hureiki, L., Croué, J.P., Legube, B. “Chlorination studies of free and combined amino acids”. Water Research, 28(12), 2521 2531 (1994). 22. Koga, M., Kadokami, K., Shinohara, R. “Laboratory scale ozonation of water contaminated uit trace pesticides”. Water Science & Technology, 26, 2257 2260, (1992). 23. Kuivinen J, Johnson H. “Determination of trihalomethanes and some chlorinated solvents in drinking water by headspacetechnique with capillarity column gas chromatography”. Water Research, 33(5), 1201 1208, (1999). 24. Kuo, C.H., Zhong, L., Zappi, M.E., Hong, A.P. “Kinetics and mechanism of the reaction betseen ozone and hydrogen peroxide in aqueous solutions”. Can. Journal Chemistry Engineering 77, 473 482, (1999). 25. Merlet, N., Thibaud, H., Doré, M. “Chloropicrin formation during oxidative treatment in the preparation of drinking water”. Science of the Total Environment, 47, 223 228 (1985). 26. Oppenländer, T. “Photochemical Purification of Water and Air”. Wiley VCH. ISBN: 3 527 30563 7 (2003). 27. Richardson, S.D., Thruston, A.D., Caughran, T.V., Chen, P.H., Collette, T.W., Floyd, T.L. “Identification of new ozone disinfection by products in drinking water”. Environmental Science & Technology, 33, 3368 3377, (1999). 28. Rodríguez Rodríguez Vidal, F.J. “Procesos de potabilización del agua e influencia del tratamiento de ozonización”. Díaz de Santos (2003). 29. Royal Decree 140/2003 of 7 of February of 2003, laid down the sanitary criteria for the quality of water for human consumption. Bulletin Official of State (BOE), nº 45, 21 of February of 2003. 30. Sorlini, S., Collivignarelli, C. “Trihalomethane formation during chemical oxidation with chlorine, chlorine dioxide and ozone of ten Italian natural waters”. Desalination, 176(1 3), 103 111, (2005). 31. Urfer, D., Huck, P., Gagnon, G., Mutti, D., Smith, F. “Modeling enhanced coagulation to improve ozone desinfection”. Journal AWWA, 91, 59 72, (1999). 32. Von Gunten, U. “Ozonation in drinking water. Part I: Oxidation kinetics and product formation”. Water Research, 37(7), 1443 1467, (2003).
2.4 9