Comparison of Different Advanced Oxidation Processes Involving Ozone to Eliminate Atrazine

Water Research 36 (2002) 1034–1042 Comparison of different advanced oxidation processes for phenol degradation Santiago Esplugas, Jaime Gime! nez*, Sandra Contreras, Esther Pascual, Miguel Rodrı́guez " 1, Departamento de Ingenierı´a Quı´mica y Metalurgia de la Universidad de Barcelona, Martı´ i Franques, 08028 Barcelona, Spain Received 7 July 2000; accepted 6 June 2001 Abstract Advanced Oxidation Processes (O3, O3/H2O2, UV, UV/O3, UV/H2O2, O3/UV/H2O2, Fe2+/H2O2 and photocatalysis) for degradation of phenol in aqueous solution have been studied in earlier works. In this paper, a comparison of these techniques is undertaken: pH influence, kinetic constants, stoichiometric coefficient and optimum oxidant/pollutant ratio. Of the tested processes, Fenton reagent was found to the fastest one for phenol degradation. However, lower costs were obtained with ozonation. In the ozone combinations, the best results were achieved with single ozonation. As for the UV processes, UV/H2O2 showed the highest degradation rate. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Phenol; Ozone; UV radiation; Hydrogen peroxide; Fenton; Photocatalysis 1. Introduction Most organic compounds are resistant to conventional chemical and biological treatments. For this reason, other methods are being studied as an alternative to biological and classical physico-chemical processes. Of these, Advanced Oxidation Processes (AOPs) will probably constitute the best option in the near future. AOPs have been defined broadly as those aqueous phase oxidation processes which are based primarily on the intermediacy of the hydroxyl radical in the mechanism(s) resulting in the destruction of the target pollutant or xenobiotic or contaminant compound [1]. The AOPs studied here are pollutant treatment processes, which use ozone, UV, ozone in combination with UV (O3/UV), ozone plus hydrogen peroxide (O3/H2O2), hydrogen peroxide and ultraviolet light (UV/H2O2), Fenton’s reagent and photocatalysis, which uses titanium dioxide (TiO2) in combination with light (UV) and oxygen. *Corresponding author. Tel.: +34-93-4021293; fax: +34-93402-1291. E-mail address: gimenez@angel.qui.ub.es (J. Gim!enez). The main problem of AOPs lies in the high cost of reagents such as ozone, hydrogen peroxide or energylight sources like ultraviolet light. However, the use of solar radiation as an energy source can reduce costs. Moreover, should be pointed out that AOPs lead normally to the best yields in pollutant destruction when biological treatments are unfeasible. 1.1. AOPs chemistry AOPs have considerable similarities due to the participation of hydroxyl radicals in most mechanisms that are operative during the reaction. Hydroxyl radicals are extremely unstable and reactive because of their high reactivity. The kinetics seem to be first order with respect to hydroxyl radical concentration and to the pollutant. Kinetic constants are in the range from 108 to 1010 M
1 s
1, whereas radical concentration, even in steady state, in these processes is between 10
10 and 10
12 M. Therefore, the pseudo first order constant is in the range of 1–10
4 s
1 [2]. Given that the hydroxyl radical is such an unstable and reactive species, it must be generated continuously 0043-1354/02/ -see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 3 - 1 3 5 4 ( 0 1 ) 0 0 3 0 1 - 3 S. Esplugas et al. / Water Research 36 (2002) 1034–1042 ‘‘in situ’’ through chemical or photochemical reactions. The main processes to obtain these radicals are described below. (a) O3: In an ozonation process two possible ways of oxidizing action may be considered: the direct way, because of the reaction between the ozone and the dissolved compounds, and the radical way owing to the reactions between the generated radicals produced in the ozone decomposition (hydroxyl radicals) and the dissolved compounds. Kinetic models for the reaction of ozone with different organic and inorganic compounds have been established by Hoign!e and Bader [3,4]. (b) O3/H2O2: In this system hydroxyl radicals are generated by a radical-chain mechanism by interaction between the ozone and the hydrogen peroxide [5–7]. The global reaction is as follows: H2 O2 þ 2O3 -2OHd þ 3O2 The efficiency of this process can be improved by adding UV radiation. (c) UV: This method is based on supplying energy to the chemical compounds as radiation, which is absorbed by reactant molecules that can pass to excited states and have sufficient time to promote reactions [8]. (d) UV/O3: The energy supplied by UV radiation interacts with O3 [9,10], the global reaction being: hn O3 þ H2 O - 2OHd þ O2 Glaze et al. [11] and Peyton and Glaze [12] studied the different steps involved in the mechanism of this process. In this system is also noted a high synergic effect between the ozone and the UV radiation separately. (e) UV/H2O2: Radiation with a wavelength lower than 400 nm is able to photolize H2O2 molecule. The mechanism accepted for the photolysis of hydrogen peroxide is the cleavage of the molecule into hydroxyl radicals with a quantum yield of two OH  radicals formed per quantum of radiation absorbed ([8] and references herein), according to the following reaction: The mechanism for the ferric ion catalyzed decomposition of hydrogen peroxide in acid solution has been widely described by Walling and Goosen [18]. (h) Photocatalysis: The interaction between a semiconductor and the UV radiation produces electron-hole pairs in the surface of the semiconductor. These charged points react both with organic compounds and water. In the first case, the redox reactions are responsible for the destruction of the organic compound, whereas in the latter hydroxyl radicals are generated and these radicals react with the organic compound [19]. The most common semiconductor used in photocatalysis is TiO2 (anatase). 2. Materials and methods 2.1. Experimental devices Installation A [20]. The experiments with ozone were done in a reactor designed to provide a good contact between the liquid and gas phase. Such a device offers the possibility of irradiating the reactant mixture with an UV radiation of 253.7 nm. The experimental device is shown in Fig. 1. It is a simple bubble reactor with a cocurrent circulation of gas and liquid, and an exterior cooling. A diffuser valve at the entrance produces good mixing between the liquid and the gas reactant. This essentially consists of a strong reduction in the diameter of the pipe through which the fluid passes. The reaction zone consists of a cylindrical quartz tube, 100 cm long, with an external diameter of 2.2 cm and an internal diameter of 1.85 cm. It is mounted into a quartz tube 48 cm in length, with an exterior diameter of 5.4 cm and an interior diameter of 5.0 cm. Air circulates through the tubular space between the two tubes. The outgoing zone was designed to maintain a constant level by means of a hn H2 O2 - 2OHd (f) O3/UV/H2O2: This is a very powerful method which allows the fast and complete mineralization of pollutants. It is considered to be the most effective treatment for high-polluted effluents [13,14]. The reaction pathways leading to the generation of OH  radicals have been summarized by Legrini et al. [8]. (g) Fenton’s reagent: This system consists in the generation of hydroxyl radicals by means of the reaction between hydrogen peroxide and iron(II) salts [15–17]. The global reaction for the production of OH  in acidic pH is: H2 O2 þ Fe2þ -Fe3þ þ OHd þ OH
1035 Fig. 1. Tubular photoreactor (installation A). 1036 S. Esplugas et al. / Water Research 36 (2002) 1034–1042 Fig. 2. Annular photoreactor (installation B). spillway, allowing also the gas to go out. It consists of a spherical vessel with a capacity of 4.54 L. The ozone used in the reaction is produced before it enters the reactor. Gas (air or oxygen) passes through a TDZ 11-20 TODOZONO ozonizer, with an ozone production of 0.2–0.3 g/h for a 100 L/h oxygen flow. The ozonizer is cooled with compressed air. Installation B [21]. The experiments with UV radiation were conducted in an experimental installation designed on the basis of a stirred annular photoreactor. Fig. 2 shows a detailed diagram of the experimental device. There are three distinguishable parts: the reactor, the source of radiation and the thermostatic circuit. In the stirred annular reactor used, it is possible to consider two parts: the circulation jacket of cooling fluid and the reaction chamber. The jacket is an annular quartz cylinder composed of two concentric tubes. The reaction chamber is also annular with a capacity of 1.5 dm3 and a height of 6.20 cm, with an inner and an outer radius of 9.65 and 9.85 cm, respectively. The internal part is made of quartz and the outer part is made of Pyrex. The system is also provided with two stirrers to achieve a perfect mixing flow into the reactor and four orifices to extract samples and to measure temperatures. In the axial center of the reaction chamber, there is the radiation source. It consists of a medium-pressure mercury vapour lamp (HPK 125) that emits radiation above 240 nm. The thermostatic circuit consists fundamentally of a storage tank equipped with a temperature control, a level control that regulates the volume of solution and also a thermometer, a reserve tank for the cooling fluid, a pump and a heat exchanger. Installation C [22]. The photocatalytic experiments were carried out by using discontinuous cylindrical microreactors placed in a Solar Simulator ‘‘Solarbox’’ (see Fig. 3) from CO.FO.ME.GRA (Milan, Italy). A fuller description of the experimental device has already been made in previous papers [22,19]. The radiation source was a Xe lamp (PHILIPS XOF-15-OF, 1500 W power) with a spectrum very similar to the solar Fig. 3. Solarbox scheme (installation C). Fig. 4. Fenton system (installation D). one, placed in the upper part of the Solarbox, in the axis of a parabolic mirror. The TiO2 was maintained in suspension in the phenol solution by magnetic stirring that ensured the perfect mixing flow. The oxygen was provided by means of a syringe and compressed air. Installation D. Fenton’s reagent experiments were performed in a 1 L discontinuous reactor with a cooling jacket (Fig. 4). The solution was mixed by means of a magnetic stirrer. The reactor was equipped with a pH and redox potential control. The thermostatic circuit is similar to the one described in installation B. 2.2. Analytical methods The phenol concentration in the photocatalytic experiments was determined by gas chromatography (HP 5890 series II) coupled to a flame ionization detector, controlled by a HP-3396 II terminal. The chromatographic column was a semicapillar SUPELCO SPB-1 (3 mm, 30 m  0.53 mm). The carrier gas was He, with a 6.6 mL/min flow. The phenol concentration of all the other experiments was determined by high performance liquid chromatography (HPLC) with an UV detector (WATERS, model S. Esplugas et al. / Water Research 36 (2002) 1034–1042 481) and an integrator (model SP 4270 of Spectra Physics). The column used was a SPHERISORB ODS 2.5 mm; 25 cm  0.46 cm. A mixture of 50% acetonitrile and 50% water was chosen as the optimal mobile phase for phenol. The wavelength of the UV absorbance detector was 270 nm. 1037 an initial concentration in the range of 95–100 ppm (1.01–1.06 mmol L
1). The refrigerant fluid flow was 60 L/h of water at 251C. The pH varied between 3 and 3.5. All the experiments were carried out in batch operation. The influence of hydrogen peroxide and iron(II) was studied. 2.3. Actinometric experiments 3. Results and discussion To determine the amount of radiation emitted by the lamp and transferred into the reactor, actinometric experiments were performed. The method is based on the photochemical decomposition of oxalic acid in the presence of uranyl [23,24]. Assuming the lineal spherical model for the radiation source [25], it was found that: * * * the Xe lamp of the photocatalytic reactor emits a flux of radiation of 2.04 meinstein s
1, in the annular reactor two lamps were used, and the flux of radiation is 91.72 and 72.84 meinstein s
1, respectively, the mercury vapour lamp of the tubular reactor emits a flux of radiation of 23.69 meinstein s
1. 2.4. Experimental methodology Ozonation processes (O3, O3/UV, O3/H2O2 and O3/UV/H2O2). The reactor was fed with 2.5 L of a phenol solution with an initial concentration in the range of 93–105 ppm (0.99–1.11 mmol L
1). The pH varied between 3 and 9. All the experiments were performed in batch operation, with a recirculation flow of 100 L/h. The experiments were carried out at 16– 201C. In the O3 and O3/UV processes the only studied variable was the pH, given the impossibility of changing the ozone flow. In O3/H2O2 and O3/UV/H2O2, the influence of pH and the amount of hydrogen peroxide were studied. UV processes (UV and UV/H2O2). The reactor was always charged with 1.5 L of an aqueous solution of phenol, with an initial concentration in the range of 93– 114 ppm (0.98–1.21 mmol L
1). The cooling fluid flowrate was 60 L/h of water at 251C. All experiments were carried out in batch operation. In the UV process the variable studied was pH and the influence of the amount of hydrogen peroxide was studied at free pH. Photocatalytic experiments. The reactor was always charged with 0.12 L of an aqueous solution of phenol, with an initial concentration in the range of 90–100 ppm (0.96–1.06 mmol L
1). The experiments were carried out at 85–901C and at free pH (6.7–2). The refrigerant fluid flow was 30–50 cm3 s
1 of air. All the experiments were carried out in batch operation. The effect of the catalyst concentration was studied. Fenton’s reagent experiments. The reactor was always charged with 1 L of an aqueous solution of phenol, with 3.1. Decrease in the pollutant concentration in the different processes Different variables (pH, oxidant and catalysts concentration) were studied in order to select the best conditions for each process, in accordance with the percentage of degraded phenol (Table 1). These results are summarized in Fig. 5. For comparison, the best experimental conditions were selected. It can be observed that in the ozone process the best results were obtained at basic pH because the contribution of the radical way increased with pH. In the O3/UV process, an improvement was not observed with regard to the earlier process. As regards the O3/H2O2, at neutral pH and at low H2O2 concentrations, this combination improved the ozonation slightly, but showed an inhibitory effect at concentrations higher than 6.2 mM. The same effect presented the combination O3/UV/H2O2 and the limiting H2O2 concentration was found to be 0.07 mM. As for the pH, the free pH was the most appropriate. Control of the process by the transfer of ozone into the liquid phase was only found in the ozonation carried out at basic pH [26]. That means that ozonation experiments could be expected to give even better results at higher ozone doses. In the UV process, the best conditions were found at free pH, when pH was increased quantum yield diminished because of secondary reactions. It can be observed that the degradation rate increased considerably when H2O2 was used. Nevertheless, the initial H2O2 concentration exerted little influence on the range used. In photocatalysis the degradation rate increased with the catalyst concentration up to a value of 0.5 g L
1 [19]. From this point, this rate was almost constant. In the Fenton system the limiting factor was the amount of hydrogen peroxide: the higher the amount, the faster the degradation. Also, as the concentration of Fe(II) ion is increased, the degradation rate is improved. TOC decrease was measured for some processes. In the experiment OP3, a 37% of TOC depletion was achieved after 90 min of treatment; 65% of TOC decrease in OR2 after 60 min and 45% in 120 min in the experiment ORP6. With the Fenton system, a 10% of TOC depletion was observed at 60 min with FP3 conditions. 1038 S. Esplugas et al. / Water Research 36 (2002) 1034–1042 Table 1 Experimental conditions for phenol degradation CTiO2 (g L
1) 0 0 0 0 0 0 0 0 0 80 80 80 85.4 90.0 100 free (5–3.4) free (5–3.4) 6.8 buffered 6.8 buffered 6.8 buffered 6.8 buffered 6.8 buffered 9.3 buffered 9.3 buffered 6.8 534 0.62 6.2 31 78 155 6.2 31 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 80 80 80 80 80 80 80 80 80.6 58.3 90.4 93.4 86.9 86.5 77.7 92.5 88.8 UV/O3 UV/O3 UV/O3 free (5.2–3.2) 6.9 buffered 9.4 buffered 0 0 0 0 0 0 0 0 0 80 80 80 80.9 92.6 91.9 R1 R2 R3 UV UV UV free (4.4–3.9) 6.8 buffered 11.5 buffered 0 0 0 0 0 0 0 0 0 30 30 30 24.2 14.0 5.0 RP1 RP2 RP3 RP4 UV/H2O2 UV/H2O2 UV/H2O2 UV/H2O2 free free free free 0 0 0 0 0 0 0 0 30 30 30 30 24.2 87.1 90.6 89.8 ORP1 ORP2 ORP3 ORP4 ORP5 ORP6 ORP7 ORP8 ORP9 ORP10 ORP11 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 O3/UV/H2O2 free (5–3) free (5–3) free (5–3) free (5–3) free (5–3) free (5–3) free (5–3) free (5–3) free (5–3) 7 buffered 9.3 buffered 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 60 60 60 60 60 60 60 60 60 60 60 77.5 89.2 92.6 94.5 98.0 99.4 95.1 96.8 93.2 70.5 70.9 FP1 FP2 FP3 FP4 FP5 FP6 Fe(II)/H2O2 Fe(II)/H2O2 Fe(II)/H2O2 Fe(II)/H2O2 Fe(II)/H2O2 Fe(II)/H2O2 free free free free free free (5–3) (5–3) (5–3) (5–3) (5–3) (5–3) 0.054 0.054 0.054 0.054 0.13 0.26 0 0 0 0 0 0 9 9 9 9 9 9 32.2 58.0 90.0 100 84.7 87.2 RT1 RT2 RT3 RT4 RT5 RT6 RT7 RT8 RT9 RT10 Photocatalysis Photocatalysis Photocatalysis Photocatalysis Photocatalysis Photocatalysis Photocatalysis Photocatalysis Photocatalysis Photocatalysis free free free free free free free free free free (init. (init. (init. (init. (init. (init. (init. (init. (init. (init. 0 0 0 0 0 0 0 0 0 0 0.05 0.1 0.2 0.3 0.5 0.6 0.7 0.8 2 5 150 150 150 150 150 150 150 150 150 150 42.2 52.2 58.6 56.8 77.7 74.4 60.8 73.1 73.4 74.6 Process pH CH2 O2 (mM) O1 O2 O3 O3 O3 O3 free (5.7–3) 7.2 buffered 9.4 buffered OP1 OP2 OP3 OP4 OP5 OP6 OP7 OP8 OP9 O3/H2O2 O3/H2O2 O3/H2O2 O3/H2O2 O3/H2O2 O3/H2O2 O3/H2O2 O3/H2O2 O3/H2O2 OR1 OR2 OR3 (4.9–3.8) (3.5–2.5) (3.2–2.3) (3.1–2.3) 0 3.19 7.41 12.7 0 0.0037 0.0082 0.014 0.035 0.070 0.11 0.14 0.18 0.007 0.007 1.07 2.45 5.34 10.7 2.45 2.45 6.8) 6.0) 6.2) 6.1) 6.4) 6.2) 6.0) 6.2) 6.2) 6.2) 0 0 0 0 0 0 0 0 0 0 Time of treatment (min) % of phenol degraded at this time CFe(II) (mM) Exp. no. S. Esplugas et al. / Water Research 36 (2002) 1034–1042 1039 Fig. 5. Comparison of the decrease of the pollutant concentration (Legend: see Table 1). Fig. 6. Neperian logarithm of the relative concentration vs. time. 3.2. Comparison of pseudo-first order kinetic constant Parameters chosen for comparison are the kinetic constants and t1=2 ; which are global parameters that include all the phenomena involved in the studied processes. This means that these parameters include kinetic and radiation influences, and also reactor design effects, on the global reaction rate. Thus, this allows the overall comparison between the different AOPs tested. The value of the pseudo-first order kinetic constant was obtained by fitting the experimental data shown in Fig. 5 to a straight line (see Fig. 6). These results are summarized in Table 2. In this table is also presented the value of half-life, that is, the time required to decrease 1040 S. Esplugas et al. / Water Research 36 (2002) 1034–1042 Table 2 Pseudo-first order kinetic and half-life for the different processes Process k (h
1) t1=2 (h) t3=4 (h) UV Photocatalysis O3/H2O2 O3/UV O3/UV/H2O2 O3 UV/H2O2 Fenton 0.528 0.582 2.13 3.14 4.17 4.42 6.26 22.2 1.31 1.19 0.325 0.221 0.166 0.157 0.111 0.0312 3.33 2.47 0.63 0.417 0.333 0.317 0.383 0.067 the concentration of the reactant to half the amount present before the reaction. As the values of t3=4 are equal to t1=2  2 in most of the cases, is possible to say that reactions obey a first order rate constants, in the experimental conditions tested. As can be observed, the process exhibiting the highest k is Fenton, 40 times higher than the UV and photocatalysis processes and five times higher than ozonation. 3.3. Influence of the amount of oxidant on the kinetic constant In this section the effect of the amount of hydrogen peroxide and the catalysts (Fe(II) and TiO2) on the kinetic constant (k) is presented. The influence of ozone cannot be included owing to the fact that the ozone production could not be changed. In Fig. 7 k vs. the amount of H2O2 and TiO2 is represented, and Fig. 8 shows k vs. H2O2 and Fe(II). 3.4. Cost estimation The evaluation of the treatment costs is today one of the most important aspects. The overall costs are represented by the sum of the capital costs, the operating costs and maintenance. For a full-scale system these costs strongly depend on the nature and the concentration of the pollutants, the flowrate of the effluent and the configuration of the reactor [28]. An estimation of costs has been made in this section (Table 4), regarding the operating costs for the processes plotted in Fig. 5, the costs of reagents and electricity being those shown in Table 3 (cost associated to the production of ozone is an average obtained from industrial references). However, it should be pointed out that costs can decrease considerably for photocatalytic treatments when solar light is used [19,22,27]. The cost per kg of degraded phenol was calculated for the degradation of 50% (half-life time) and for 75% of the initial phenol (see Table 4). As regards the operating costs, photocatalysis and UV are considerably more expensive than the others owing to the high nominal power of the lamp used in these experiments. Costs would be drastically reduced if solar light were used. O3 process appears to be the most attractive option for phenol degradation. Fig. 7. K vs. the amount of oxidant: H2O2 and TiO2 (For Fenton process [Fe(II)]=0.054 mM). 1041 S. Esplugas et al. / Water Research 36 (2002) 1034–1042 Fig. 8. K vs. the amount of oxidant: H2O2 and Fe(II) ((1) [Fe(II)]=0.054 mM; (2) [H2O2]=2.45 mM). Table 3 Cost of the reagents used in the studied processes Reagent Basis Cost ($) H2O2, 35% [29] FeSO4  7H2O [29] TiO2 [29] O3 [29] Electricity [29] lb. ton. lb. lb. kW.h 0.245 140.0 0.92 1.2 0.0765 Table 4 Kinetic constant, half-life and cost evaluation for all the processes Process k (h
1) t1=2 (h) Costs/kg ($) t3=4 (h) Costs/kg ($) UV O3/H2O2 O3/UV O3/UV/H2O2 O3 UV/H2O2 Fenton 0.528 2.13 3.14 4.17 4.42 6.26 22.2 1.31 172.2 0.325 2.71 0.221 9.28 0.166 7.12 0.157 0.81 0.111 13.1 0.0312 3.92 3.33 293.1 0.63 2.93 0.417 11.7 0.333 9.51 0.317 1.09 0.383 28.7 0.067 2.61 4. Conclusions Different AOPs (ozone and its combination, photolysis and UV/H2O2, Fenton and photocatalysis) have been studied and compared (with a view to the decrease in the pollutant concentration, the pseudo-first order kinetic constant and cost estimation) for the degradation of phenol in aqueous solution. It has been found that none of the ozone combinations (O3/H2O2, O3/UV and O3/UV/H2O2) improved the degradation rate of the ozone process, resulting even in an slightly inhibitory effect. With regard to the UV processes (UV, UV/H2O2 and photocatalysis), the degradation rate with the UV/ H2O2 process was almost five times higher than photocatalysis and UV alone, as evidenced by the kinetic constant values. Fenton’s reagent showed the fastest degradation rate, 40 times higher than UV process and photocatalysis and five times higher than ozonation. Nevertheless, degradation rate and the lower costs obtained with ozonation makes it the most appealing choice for phenol degradation. References [1] Ollis D. Comparative aspects of advanced oxidation processes. Emerging Technologies in Waste Management II, ACS Symposium Series 518. Washington, DC, 1993. p. 18–34. [2] Chamarro E, Marco A, Prado J, Esplugas S. Tratamiento ! de de aguas y aguas residuales mediante utilizacion procesos de oxidaci!on avanzada, Quı´mica & Industria. Sociedad Chilena de Qu!ımica, 1996;1/2:28–32. [3] Hoign!e J, Bader H. Rate constants of reaction of ozone with organic and inorganic compounds in water. Part I. 1042 [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] S. Esplugas et al. / Water Research 36 (2002) 1034–1042 Non-dissociating organic compounds. Water Res 1983;17:173–83. Hoign!e J, Bader H. Rate constants of reaction of ozone with organic and inorganic compounds in water. Part II. Dissociating organic compounds. Water Res 1983;17: 185–94. Staehelin S, Hoign!e J. Decomposition of ozone in water. Rate of initiation by hydroxide ions and hydrogen peroxide. Environ Sci Technol 1982;16:676–81. Glaze WH, Kang J-W. Advanced oxidation processes. Description of a kinetic model for the oxidation of hazardous materials in aqueous media with ozone and hydrogen peroxide in a semibatch reactor. Ind Eng Chem Res 1989;28:1573–80. Adams CD, Scanlan PA, Secrist NS. Oxidation and biodegradability enhancement of 1,4-dioxane using hydrogen peroxide and ozone. Environ Sci Technol 1994;28:1812–8. Legrini O, Oliveros E, Braun AM. Photochemical processes for water treatment. Chem Rev 1983;93: 671–98. Guittoneau S, De Laat J, Duguet JP, Bonnel C, Dor!e M. Oxidation of parachloronitrobenzene in dilute aqueous solution by O3+UV and H2O2+UV: a comparative study. Ozone Sci Eng 1990;12:73–94. Beltr!an FJ, Encinar JM, Alonso MA. Nitroaromatic hydrocarbon ozonation in water. 2. Combined ozonation with hydrogen peroxide or UV radiation. Ind Eng Chem Res 1998;37:32–40. Glaze WH, Kang JW, Chapin DH. The chemistry of water treatment processes involving ozone, hydrogen peroxide and ultraviolet radiation. Ozone Sci Eng 1987; 9:335–42. Peyton GR, Glaze WH. Destruction of pollutants in water with ozone in combination with ultraviolet radiation. 3. Photolysis of aqueous ozone. Environ Sci Technol 1988;22:761–7. Zeff JD, Barich JT. Symposium on Advanced Oxidation Processes and Treatment of Contaminated Water and Air: Wastewater Technologies. Center, Ontario (Canad!a), 1990. Mokrini A, Oussi D, Esplugas S. Oxidation of aromatic compounds with UV radiation/ozone/hydrogen peroxide. Water Sci Technol 1997;35(4):95–102. [15] Bigda RJ. Consider Fentons chemistry for wastewater treatment. Chem Eng Prog 1995;91(12):62–6. . S, Siegwart S, Dahlen EP, [16] Bossmann SH, Oliveros E, Gob . Payawan Jr L, Straub M, Worner M, Braun AM. New evidence against hydroxyl radicals as reactive intermediates in the thermal and photochemically enhanced Fenton reactions. J Phys Chem A 1998;102(28):5542–50. [17] Ben!ıtez FJ, Beltr!an-Heredia J, Acero JL, Rubio FJ. Chemical decomposition of 2,4,6-trichlorophenol by Ozone, Fenton’s reagent and UV radiation. Ind Eng Chem Res 1999;38(4):1341–9. [18] Walling C, Goosen A. Mechanism of ferric ion catalyzed decomposition of hydrogen peroxide. Effect of organic substrates. J Am Chem Soc 1973;95(9):2987–91. [19] Gim!enez J, Curco! D, Marco P. Reactor modelling in the photocatalytic oxidation of wastewater. Water Sci Tech 1997;35(4):207–13. [20] Prat C, Vicente M, Esplugas S. Ozonization of bleaching waters of the paper industry. Water Res 1989;23(1): 51–5. [21] Oussi D, Mokrini A, Esplugas S. Removal of aromatic compounds using UV/H2O2. Recent Res Dev Photochem Photobiol 1997;1:77–83. [22] Curc!o D, Malato S, Blanco J, Gim!enez J, Marco P. Photocatalytic degradation of phenol: comparison between pilot-plant scale and laboratory results. Sol Energy 1996;56(5):387–400. [23] Volman DH, Seed JR. The photochemistry of uranyl oxalate. J Am Chem Soc 1964;86:5095–8. [24] Heidt LJ, Tregay GW, Middleton FA. Influence of the pH upon the photolysis of the uranyl oxalate actinometer system. J Phys Chem 1979;74:1876–82. [25] Jacob SM, Dranoff JS. Light intensity profiles in a perfectly mixed photoreactor. AIChE J 1970;16:359. [26] Mokrini A. Degradaci!on de fenol mediante tratamientos de oxidaci!on avanzada. Ph.D. thesis, Universidad de Barcelona, Barcelona, Spain, 1998. [27] Gim!enez J, Curco! D, Queral MA. Photocatalytic treatment of phenol and 2,4-dichlorophenol in a solar plant in the way to scaling-up. Catal Today 1999;54:229–43. [28] Andreozzi R, Caprio V, Insola A and Marotta R. Advanced oxidation processes (AOP) for water purification and recovery. Catal Today 1999;53:51–9. [29] Chemical Market Reporter 2000;257(4):3 April.