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Ind. Eng. Chem. Res. 2011, 50, 866–870
Intensification of the Fenton Process by Increasing the Temperature Juan A. Zazo,* Gema Pliego, Sonia Blasco, Jose A. Casas, and Juan J. Rodriguez Ingenierı´a Quı´mica, Facultad de Ciencias, UniVersidad Auto´noma de Madrid, Cantoblanco, 28049 Madrid, Spain
The effect of temperature on the Fenton process has been studied within the range of 25-130 °C using phenol (100 mg/L) as target compound, 10 mg/L Fe2+, and a dose of H2O2 corresponding to the theoretical stoichiometric amount (500 mg/L) for mineralization. The TOC reduction was considerably improved as temperature increased. Whereas at 25 °C the TOC decreased less than 28%, a reduction of almost 80% was achieved at 90 °C. Beyond this temperature no significant improvement of mineralization was observed, although the rate of the process was considerably enhanced. Increasing the temperature leads to a more efficient consumption of H2O2 which indicates an enhanced iron-catalyzed H2O2 decomposition into radicals as temperature increases rather than the generally accepted thermal breakdown of H2O2 into O2 and H2O. Therefore, working at a temperature well above the ambient provides a way of intensifying the Fenton process since it allows a significant improvement of the oxidation rate and the mineralization percentage with reduced H2O2 and Fe2+ doses. Furthermore it would not represent a serious drawback in the case of many industrial wastewaters which may be already at that temperature. Besides, partial recovery of heat from the treated off-stream would always allow saving energy. The TOC time-evolution was well described by a kinetic model based on TOC lumps with apparent activation energy values in the range of 30-50 kJ/mol. 1. Introduction The need to develop technical solutions capable of fulfilling increasingly stringent discharge limits for industrial wastewaters or allowing water recycling or reuse promotes research efforts toward either the implementation of new treatments or the intensification of those already available. The Fenton process emerges as a suitable way of treating a wide variety of industrial effluents.1 This process implies the generation of · OH radicals (a strong and nonselective oxidant) from catalytic H2O2 decomposition by means of Fe2+ at acidic pH. The overall mechanism also includes several secondary reactions,2-5 among them the regeneration of Fe2+ by reaction between Fe3+ and H2O2 and competitive scavenging reactions involving Fe2+, H2O2, and · OH. This treatment has shown some significant advantages with respect to other processes, as the fact that iron is a widely available and nontoxic element and hydrogen peroxide is easy to handle and the excess decomposes to environmentally safe products.6 Besides, it requires relatively mild operating conditions and simple equipment.7,8 However its application to the treatment of real wastewaters has been so far limited mainly due to the high requirements of H2O2 and iron which results in high operational cost, and finally leads to the generation of high volumes of Fe(OH)3 in the neutralization step.9,10 Several alternatives have been proposed in order to overcome these drawbacks. On one hand, the combination of the Fenton process with biological treatment is one of the most developed.11-15 The effluent is first chemically oxidized for the sake of reducing the toxicity and increasing the biodegradability. Other possibilities such as semicontinuous H2O2 addition,16,17 or integrated Fenton-coagulation/flocculation18 have been proposed. On the other hand, heterogeneous Fenton,19-23 where iron is fixed on the surface of a support, is considered as a feasible solution for minimizing iron loss and the consequent generation of Fe(OH)3 sludge. * To whom correspondence should be addressed. E-mail: juan.zazo@ uam.es. Tel: +34 914978774. Fax: +34 914973516.
The possibility of increasing the operating temperature as a way of improving the efficiency of the Fenton process has been so far scarcely investigated, because the idea of thermal decomposition of H2O2 into O2 and H2O24,25 seems to be widely accepted as a serious drawback. However, higher temperatures could lead to a more efficient use of H2O2 (defined as the amount of TOC removed per unit weight of H2O2 decomposed) upon enhanced generation of · OH radicals at low Fe2+ concentration. A decrease of the iron dose is important since it reduces the amount of Fe(OH)3 sludge and also improves the efficiency of H2O2 by minimizing competitive scavenging reactions. Therefore, increasing the temperature can be considered as a way of intensification of the conventional Fenton process. On the other hand, working above ambient temperature would not represent any drawback in the case of many industrial wastewaters.26 Besides, partial recovery of heat from the treated off-stream would always allow saving energy. The aim of this work was to investigate in depth the effect of temperature on the performance of the Fenton process using phenol as target pollutant. The influence of this variable on the rate of mineralization as well as on the efficiency of H2O2 at low Fe2+ concentration was analyzed attempting to optimize this treatment. The results were compared to those obtained in previous works with higher H2O2 and Fe2+ doses at lower temperatures as commonly used in the conventional Fenton process. Finally, a kinetic lumped model was used, which described well the evolution of TOC thus providing a useful tool for design purposes. So far the effect of temperature on the performance of Fenton process has been scarcely investigated. Lopez et al.26 studied that effect at 25 and 70 °C on the evolution of TOC and the oxidation byproducts but these authors used H2O2 and Fe2+ doses substantially higher than ours as well as much longer reaction times. In the present work a wider temperature range (up to 130 °C) has been tested and the efficiency of H2O2 consumption is carefully considered given its critical importance on the economy of the Fenton process.
10.1021/ie101963k 2011 American Chemical Society Published on Web 12/16/2010
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2. Experimental The experiments were carried out in stoppered glass batch reactors (Bu¨chi, inertclave Type I) equipped with a backpressure controller. The reaction volume was 500 mL and the starting concentrations were 100 mg/L phenol, 10 mg/L Fe2+, and 500 mg/L H2O2 (which corresponds to the theoretical stoichiometric amount for complete oxidation of phenol up to CO2 and H2O, i.e., mineralization). Initially, an aqueous solution containing the aforementioned concentrations of phenol and Fe2+ was placed into the reactor. Once the desired temperature and pressure were achieved, 1.04 mL of a 30% w/v H2O2 solution was added, considered as the starting time for the reaction. The temperature effect was tested within the 25 to 130 °C range. Experiments at different pressures between atmospheric and 6 bar (achieved by pumping air into the reactor) were also carried out at 50 °C. The initial pH value was 3.0, which was not controlled along the process. Nevertheless, no significant changes in this value were observed during the experiments. Blank experiments with phenol in absence of H2O2 and Fe2+ were also performed. The progress of the reaction was followed by periodically taking samples from the reactor throughout 4 h. The samples were immediately analyzed. Phenol and aromatic byproducts were quantified by means of HPLC (Varian Pro-Star 240) using a diode array detector (330 PDA). A Microsorb C18 5 µm column (MV 100, 15 cm long, 4.6 mm diameter) was used as stationary phase and 1 mL/min of 4 mM aqueous sulfuric solution was used as mobile phase. Short-chain organic acids were analyzed by an ion chromatograph with chemical suppression (Metrohm 790 IC) using a conductivity detector. A Metrosep A supp 5-250 column (25 cm long, 4 mm diameter) was used as stationary phase and 0.7 mL/min of an aqueous solution 3.2 mM of Na2CO3 and 1 mM of NaHCO3 was used as mobile phase. Total organic carbon (TOC) was measured using a TOC analyzer (Shimadzu, model TOC VSCH) and hydrogen peroxide concentration was determined by colorimetric titration using the TiOSO4 method.27 All of the chemicals except H2O2 (Panreac, Hydrogen Peroxide 30% w/v PA) and formic acid (Fluka, puriss. p.a., w98%), were purchased from SigmaAldrich (>99% pure). 3. Results and Discussion Figure 1 shows the evolution of TOC and H2O2 concentration upon Fenton oxidation of phenol at different temperatures. Phenol and the aromatic byproducts were almost completely converted within the first 5 min of reaction time, even at the lowest temperature tested but a dramatic improvement of mineralization was observed as temperature increased, especially within the range of 25 to 100 °C. Short-chain organic acids (mainly formic and oxalic but also maleic and traces of acetic acid) were the only byproducts detected beyond the first 5 min of reaction. The differences between the measured TOC values and the amount of carbon in the identified compounds reveal the presence of unidentified byproducts, which are usually assessed to condensation species.28-30 Figure 2 shows the evolution of the estimated overall amount of those species as well as formic and oxalic acids, by far the two major identified byproducts. As can be seen in Figure 2 the amount of condensation byproducts formed decreases as the temperature increases, being almost negligible above 110 °C. The evolution of organic acids (Figure 2b and c) allows concluding that the condensation compounds are mostly mineralized rather than converted into
Figure 1. Influence of temperature on TOC (a) and H2O2 (b) conversion. ([phenol]0: 100 mg/L, [H2O2]0: 500 mg/L, [Fe2+]0: 10 mg/L, pH: 3).
organic acids. This behavior is different from that observed in a previous work29 at 25 °C using higher H2O2 and Fe2+ doses, where much higher concentrations of formic and oxalic acids were obtained. The amount of formic acid diminished monotonically as the temperature increased, and beyond 100 °C this compound disappeared almost completely after 2 h of reaction time. This systematic behavior with temperature was not observed in the case of oxalic acid. Within the range of 25-100 °C, this acid appeared quite resistant to Fenton oxidation as a significant remaining concentration was measured even after 4 h. At higher temperatures the concentration of oxalic acid clearly decreased upon reaction time and at 130 °C even completely disappear after 2 h. This fact might not be related with the oxidation of oxalic acid but is probably related with thermal decomposition of ferric oxalate.31 The thermal decomposition of ferric oxalate must be accompanied by ferric oxide precipitation as suggested by the slight development of turbidity in the reaction media. This solid was identified as Fe2O3 by means of polycrystal X-ray diffraction. The presence of remaining amounts of oxalic acid must be considered as recent works using respirometric techniques have pointed out the lower biodegradability of this compound by conventional wastewater activated sludge in spite of its very low ecotoxicity.32
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Figure 3. Evolution of TOC vs H2O2 conversion. ([phenol]0: 100 mg/L, [H2O2]0: 500 mg/L, pH: 3). Table 1. Values of η and ε at Different Temperatures Using the Stoichiometric H2O2 Dose (500 mg/L) and 10 mg/L Fe2+. ([Phenol]0: 100 mg/L, pH: 3, Reaction Time: 4h) 25 °C 50 °C 70 °C 90 °C 100 °C 110 °C 120 °C 130 °C XTOC ηa εb a
Figure 2. Evolution of reaction byproducts with temperature. ([phenol]0: 100 mg/L, [H2O2]0: 500 mg/L, [Fe2+]0: 10 mg/L, pH: 3).
Considering an increase of the temperature affects the pressure of the system it is necessary to learn more about the effect of this variable. Working at 50 °C and different pressures within the range of 1-6 bar we obtained fairly similar results so that we can conclude that pressure has no influence on the efficiency of the performance of the Fenton process within the range tested. Figure 1 shows a faster decomposition of H2O2 as temperature increases. Thermal instability of this reagent which provokes its decomposition into O2 and H2O has been claimed in the literature.6 However, a higher temperature could also enhance H2O2 decomposition toward · OH radicals. This last hypothesis is supported by the results gathered in Figure 3, which shows
0.28 64 43
0.54 103 83
0.58 113 89
0.77 118 118
0.79 121 121
0.80 122 122
0.81 124 124
0.81 124 124
mg TOC/g H2O2 converted. b mg TOC/g H2O2 fed.
the TOC vs H2O2 conversion values upon 4 h reaction time at different temperatures. For the sake of comparison, it also includes the results obtained at 25 °C in a previous work28 with different Fe2+ doses. As can be seen, the efficiency of H2O2 (η), defined as the amount of TOC converted per unit of H2O2 decomposed (w/w), does not decrease when increasing the temperature as should be expected if H2O2 would be decomposed into O2 and H2O due to thermal instability. On the contrary, a higher temperature implies a faster iron-catalyzed H2O2 conversion into radicals, which enhances mineralization. The TOC reduction reaches around 80% at 100 °C and almost 90% at 130 °C in 20 min. The consumption of H2O2 is a critical issue of Fenton process since it is by far the main component of the operating cost.33 For the assessment of reagent consumption we have considered the amount of TOC converted per unit weight of hydrogen peroxide decomposed (η) and fed (ε), respectively. The second variable is more representative as the residual H2O2 cannot be recovered and, moreover, needs to be eliminated before discharge due to its toxicity. Table 1 gathers the values obtained for both parameters after 4 h reaction time at different temperatures using the stoichiometric H2O2 dose and 10 mg/L Fe2+. The values of ε increase with temperature up to around 90 °C and at that temperature no residual H2O2 remained after 4 h reaction time so that it can be considered around the optimum from this point of view. The maximum values of ε at complete TOC conversion when using the stoichiometric H2O2 dose would be 153 mg TOC/g H2O2. Therefore, at 90 °C, 77% of that maximum value was achieved, almost 2.8 times the value observed at 25 °C. Beyond 90 °C, although this parameter hardly varied, the oxidation rate increased (Figure 1), thus allowing a
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Table 2. Values of η and ε at 90 °C and 10 mg/L Fe Using Substoichiometric H2O2 Dose ([Phenol]0: 100 mg/L, pH: 3, Reaction Time: 4h) 2+
a
H2O2 (mg/L)
XTOC
ηa
εb
250 375
0.40 0.55
122 112
122 112
mg TOC/g H2O2 converted. b mg TOC/g H2O2 fed.
Table 3. Values of η and ε at 25 °C Using Different H2O2 and Fe2+ Doses ([Phenol]0: 100 mg/L, pH: 3, Reaction Time: 4h) H2O2 (mg/L)
Fe2+ (mg/L)
XTOC
ηa
εb
500
1 5 10 100 100 100
0.08 0.20 0.28 0.28 0.37 0.55
38 66 64 43 11 8
12 31 43 43 11 8
2500 5000 a
mg TOC/g H2O2 converted. b mg TOC/g H2O2 fed.
Scheme 1. TOC Pathway Oxidation by Fenton Reagent Figure 4. Parity plot for TOC (mg/L). Table 4. Values of the Rate Constants (k1-k4: L2 · mg-2 · min-1; k5: min-1) and Activation Energies (kJ/mol)
lower reactor volume. Lowering the H2O2 dose up to one-half the stoichiometric hardly affected the values of ε, although the percentage of TOC removed decreased markedly (Table 2). The dose of Fe2+ can be also significantly lowered with increasing the temperature that would reduce the sludge volume resulting upon neutralization. Thus, increasing the temperature is a better strategy than stressing the H2O2 and Fe2+ doses beyond the stoichiometric amount and around 10 mg/L, respectively, as can be seen from the results of Table 3 obtained at 25 °C with different H2O2 and Fe2+ doses upon 4 h reaction time. 3.1. Kinetic Analysis. The evolution of TOC upon reaction time was adjusted to a simplified kinetic model described in a previous work.17 Briefly, TOC was lumped into three blocks depending on the degradability. Thus, TOCA which lumps the easily oxidizable compounds (phenol and aromatic intermediates), is converted to TOCB (which includes condensation byproducts and maleic and formic acid) and/or mineralized to CO2. Depending on the operating conditions TOCB can be oxidized up to TOCC (those compounds that are refractory to this treatment, mainly oxalic acid) and/or to CO2. Scheme 1 summarizes the TOC pathway. The model assumes second-order kinetics with respect to TOC and first-order kinetics with respect to H2O2, the evolution of which is directly related to the generation of · OH. Fitting of the experimental TOC vs time values to the proposed model can be seen in Figure 1 (lines). The model describes fairly well the time-evolution of TOC. Table 2 reports the values of the rate constants obtained by fitting the model to the experimental results using Scientist 3.0 software. The value of k5 corresponds to the first order rate constant of H2O2 decomposition into radicals. The correlation coefficients are also included. The increase of temperature favors TOCA oxidation up to CO2 rather than to TOCB, according to the values of k1 and k2. This fact significantly affects the distribution of byproducts. Thus, at temperatures below 90 °C, oxidation proceeds through the classical Fenton pathway, where direct mineralization of
T (°C)
k1 × 105
k2 × 105
k3 × 107
k4 × 107
k5
r2
25 50 70 90 100 110 120 130 Ea (kJ/mol)
0.18 0.14 0.71 1.59 0.70 1.80 4.00 11.97 31.8
0.04 0.07 0.28 0.81 2.34 5.92 13.54 34.62 43.2
0.02 0.08 0.55 0.55 7.47 12.2 37.09 158.5 53.4
0.03 0.11 0.50 0.82 1.53 8.87 23.13 130.3 47.4
0.04 0.12 0.13 0.23 0.47 0.58 0.67 0.74
0.99 0.99 0.99 0.99 0.99 0.99 0.99 0.99
aromatics hardly occurs, unlike what happens at higher temperatures. This justifies the lower concentration of condensation byproducts as well as the lower production of formic and oxalic acid as a consequence of the oxidation of TOCB up to TOCC. Figure 4 compares the experimental and predicted TOC values, confirming the validity of the model. In addition, the TOCi simulated profiles validate the nature of the lumping groups. The values of the kinetic constants obey the Arrhenius equation which allows obtaining the apparent activation energy for each step (Table 4). These values are comparable to those reported by Guedes et al.34 and Bautista et al.35 working with different industrial wastewaters. 4. Conclusions Increasing the temperature clearly improves both the oxidation rate and the degree of mineralization of phenol by Fenton oxidation allowing working with reduced amounts of H2O2 and Fe2+. Thus, it can be considered a way of intensification of the Fenton process. The temperature and the H2O2 dose can be conveniently adjusted for the sake of achieving a high mineralization (TOC reduction) at complete H2O2 conversion with a low Fe2+ concentration, which would reduce the amount of Fe(OH)3 sludge produced upon neutralization. Working above ambient temperature would not represent a serious drawback in the case of many industrial wastewaters which may be already at that temperature. Besides, partial recovery of heat from the treated off-stream would always allow saving energy. The TOC time-evolution was well described by a kinetic model based on TOC lumps with apparent activation energy values in the range of 30-50 kJ/mol.
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A lumped kinetic model has been used which describes well the time-evolution of TOC. The values of the kinetic constants show that phenol and aromatic intermediates are mainly transformed into organic acids at temperatures below 90 °C whereas they are mainly oxidized up to CO2 beyond that temperature. Acknowledgment We thank the financial support from the Spanish Plan Nacional I+D+i through the projects CTQ2007-61748/PPQ and CTQ2008-03988/PPQ and from the CAM through the project S2009/AMB-1588. Literature Cited (1) Bautista, P.; Mohedano, A. F.; Casas, J. A.; Zazo, J. A.; Rodriguez, J. J. An overview of the application of Fenton oxidation to industrial wastewaters treatment. J. Chem. Technol. Biotechnol. 2008, 83, 1323–1338. (2) Beltran De Heredia, J.; Torregrosa, J.; Dominguez, J. R.; Peres, J. A. Kinetic model for phenolic compound oxidation by Fenton’s reagent. Chemosphere 2001, 45, 85–90. (3) Kang, N.; Lee, D. S.; Yoon, J. Kinetic modeling of Fenton oxidation of phenol and monochlorophenols. Chemosphere 2002, 47, 915–924. (4) Mijangos, F.; Varona, F.; Villota, N. Changes in solution color during phenol oxidation by Fenton reagent. EnViron. Sci. Technol. 2006, 40, 5538– 5543. (5) Yavuz, Y.; Koparal, A. S.; Ogutveren, U. B. Phenol removal through chemical oxidation using Fenton reagent. Chem. Eng. Technol. 2007, 30, 583–586. (6) Jones, C. W. Applications of Hydrogen Peroxide and DeriVates; Royal Society of Chemistry: London, 1999. (7) Azbar, N.; Yonar, T.; Kestioglu, K. Comparison of various advanced oxidation processes and chemical treatment methods for COD and color removal from a polyester and acetate fiber dyeing effluent. Chemosphere 2004, 55, 35–43. (8) Esplugas, S.; Gime´nez, J.; Contreras, S.; Pascual, E.; Rodrı´guez, M. Comparison of different advanced oxidation processes for phenol degradation. Water Res. 2002, 36, 1034–1042. (9) Barrault, J.; Abdellaoui, M.; Bouchoule, C.; Majeste´, A.; Tatiboue¨t, J. M.; Louloudi, A.; Papayannakos, N.; Gangas, N. H. Catalytic wet peroxide oxidation over mixed (Al-Fe) pillared clays. Stud. Surf. Sci. Catal. 2000, 130, 749–754. (10) Can˜izares, P.; Paz, R.; Sa´ez, C.; Rodrigo, M. A. Costs of the electrochemical oxidation of wastewaters: A comparison with ozonation and Fenton oxidation processes. J. EnViron. Manage. 2009, 90, 410–420. (11) Mantzavinos, D.; Psillakis, E. Enhancement of biodegradability of industrial wastewaters by chemical oxidation pre-treatment. J. Chem. Technol. Biotechnol. 2004, 79, 431–454. (12) Oller, I.; Malato, S.; Sanchez-Perez, J. A.; Maldonado, M. I.; Gernjak, W.; Perez-Estrada, L. A. Advanced oxidation process-biological system for wastewater containing a recalcitrant pollutant. Water Sci. Technol. 2007, 55, 229–235. (13) Rodrigues, C. S. D.; Madeira, L. M.; Boaventura, R. A. R. Treatment of textile effluent by chemical (Fenton’s Reagent) and biological (sequencing batch reactor) oxidation. J. Hazard. Mater 2009, 172, 1551– 1559. (14) Tantak, N. P.; Chaudhari, S. Degradation of azo dyes by sequential Fenton’s oxidation and aerobic biological treatment. J. Hazard. Mater. 2006, 136, 698–705. (15) Oller, I.; Malato, S.; Sa´nchez-Pe´rez, J. A. Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination-A review. Sci. Total EnViron. 2010; DOI: 10.1016/j.scitotenv.2010.08.061.
(16) Mohanty, N. R.; Wei, I. W. Oxidation of 2,4-dinitrotoluene using Fenton’s reagent: Reaction mechanisms and their practical applications. Hazard. Waste Hazard. Mater. 1993, 10, 171–183. (17) Zazo, J. A.; Casas, J. A.; Mohedano, A. F.; Rodriguez, J. J. Semicontinuous Fenton oxidation of phenol in aqueous solution. A kinetic study. Water Res. 2009, 43, 4063–4069. (18) Du, Y.; Zhou, M.; Lei, L. Kinetic model of 4-CP degradation by Fenton/O2 system. Water Res. 2007, 41, 1121–1133. (19) Bautista, P.; Mohedano, A. F.; Casas, J. A.; Zazo, J. A.; Rodriguez, J. J. Oxidation of cosmetic wastewaters with H2O2 using a Fe/g-Al2O3 catalyst. Water Sci. Technol. 2010, 61, 1631–1636. (20) Carriazo, J.; Gue´lou, E.; Barrault, J.; Tatiboue¨t, J. M.; Molina, R.; Moreno, S. Catalytic wet peroxide oxidation of phenol by pillared clays containing Al-Ce-Fe. Water Res. 2005, 39, 3891–3899. (21) Melero, J. A.; Martı´nez, F.; Botas, J. A.; Molina, R.; Pariente, M. I. Heterogeneous catalytic wet peroxide oxidation systems for the treatment of an industrial pharmaceutical wastewater. Water Res. 2009, 43, 4010– 4018. (22) Molina, C. B.; Casas, J. A.; Zazo, J. A.; Rodrı´guez, J. J. A comparison of Al-Fe and Zr-Fe pillared clays for catalytic wet peroxide oxidation. Chem. Eng. J. 2006, 1-2, 29–35. (23) Zazo, J. A.; Casas, J. A.; Mohedano, A. F.; Rodrı´guez, J. J. Catalytic wet peroxide oxidation of phenol with a Fe/active carbon catalyst. Appl. Catal., B 2006, 65, 261–268. (24) Gogate, P. R.; Pandit, A. B. A review of imperative technologies for wastewater treatment I: Oxidation technologies at ambient conditions. AdV. EnViron. Res. 2004, 8, 501–551. (25) Rivas, F. J.; Navarrete, V.; Beltra´n, F. J.; Garcı´a-Araya, J. F. Simazine Fenton’s oxidation in a continuous reactor. Appl. Catal., B 2004, 48, 249–258. (26) Lopez, A.; Mascolo, G.; Detomaso, A.; Lovecchio, G.; Villani, G. Temperature activated degradation (mineralization) of 4-chloro-3-methyl phenol by Fenton’s reagent. Chemosphere 2005, 59, 397–403. (27) Eisenberg, G. M. Colorimetric determination of hydrogen peroxide. Ind. Eng. Chem. Anal. Ed. 1943, 327–328. (28) Zazo, J. A.; Casas, J. A.; Molina, C. B.; Quintanilla, A.; Rodriguez, J. J. Evolution of ecotoxicity upon Fenton’s oxidation of phenol in water. EnViron. Sci. Technol. 2007, 41, 7164–7170. (29) Zazo, J. A.; Casas, J. A.; Mohedano, A. F.; Gilarranz, M. A.; Rodriguez, J. J. Chemical Pathway and Kinetics of Phenol Oxidation by Fenton’s Reagent. EnViron. Sci. Technol. 2005, 39, 9295–9302. (30) Poerschmann, J.; Trommler, U. Pathways of advanced oxidation of phenol by Fenton’s reagent-Identification of oxidative coupling intermediates by extractive acetylation. J. Chromatogr. A 2009, 1216, 5570– 5579. (31) Riggs, W. M.; Bricker, C. E. Thermal decomposition of iron(III) oxalates. J. Inorg. Nucl. Chem. 1971, 33, 1635–1647. (32) Molina, C. B.; Pizarro, A. H.; Monsalvo, V. M.; Polo, A. M.; Mohedano, A. F.; Rodriguez, J. J. Integrated CWPO and biological treatment for the removal of 4-chlorophenol from water. Sep. Sci. Technol. 2010, 45, 1595–1602. (33) Andreozzi, R.; Caprio, V.; Insola, A.; Marotta, R. Advanced oxidation processes (AOP) for water purification and recovery. Catal. Today 1999, 53, 51–59. (34) Guedes, A. M. F. M.; Madeira, L. M. P.; Boaventura, R. A. R.; Costa, C. A. V. Fenton oxidation of cork cooking wastewatersoverall kinetic analysis. Water Res. 2003, 37, 3061–3069. (35) Bautista, P.; Mohedano, A. F.; Gilarranz, M. A.; Casas, J. A.; Rodriguez, J. J. Application of Fenton oxidation to cosmetic wastewaters treatment. J. Hazard. Mater. 2007, 142, 128–134.
ReceiVed for reView September 24, 2010 ReVised manuscript receiVed November 25, 2010 Accepted December 2, 2010 IE101963K
