1648
Ind. Eng. Chem. Res. 2003, 42, 1648-1653
KINETICS, CATALYSIS, AND REACTION ENGINEERING Ozonation of Phenolic Wastewater in a Gas-Induced Reactor with a Fixed Granular Activated Carbon Bed Sheng H. Lin* and Ching H. Wang Department of Chemical Engineering, Yuan Ze University, Chungli 320, Taiwan, Republic of China
Treatment of phenolic wastewater by ozonation in a new gas-induced reactor was investigated. The reactor was designed in such a fashion that gas induction was created on the liquid surface by the high-speed action of an impeller turbine inside a draft tube to maximize the ozone usage. Another important feature of the present reactor design was the granular activated carbon (GAC) bed packed in a circular compartment between the reactor wall and the shaft tube. Because of the adsorption and possible catalytic reaction by GAC, enhanced phenol decomposition and chemical oxygen demand (COD) were observed in the experimental tests, providing the evidences of the synergistic effects of adsorption, catalytic reaction, and ozonation. In addition to enhanced phenol and COD removal, ozonation was found to provide in situ GAC regeneration, which was considered highly beneficial in the industrial GAC adsorption process. Introduction Many hazardous organic compounds frequently occur in various industrial wastewaters. The appearance of phenol and various phenolic derivatives in the chemical and petrochemical wastewaters is a typical example. Because of their strong toxicity to human and marine life, stringent regulations have been imposed on these organic concentration levels in the wastewater. These phenolic compounds have been designated by the U.S. EPA as the priority chemicals that need to be reduced to a very low level in the wastewaters for safe discharge. Treatment of the wastewater containing these organic compounds thus has become an integral part of wastewater treatment of the chemical and petrochemical industries. Traditionally, activated sludge treatment has been the most widely used method to treat industrial wastewaters containing phenols. This method is convenient and relatively inexpensive to operate under most circumstances.1,2 However, the microorganisms in an activated sludge system, even well acclimatized, still can only deal with chemical wastewater containing relatively low phenolic concentrations, usually much less than 100 mg/L, primarily because of the low biodegradability and/or inhibitory effects to microorganisms of these compounds.3 Unfortunately, there are various kinds of chemical and petrochemical wastewaters that contain phenolic compounds far exceeding this concentration level. For those instances, chemical or physical treatment methods can offer good alternatives. Incineration is one of the chemical methods. It is good for dealing with waste solvents but is considered * To whom correspondence should be addressed. Tel.: +886-3-463-8910. Fax: +886-3-455-9373. E-mail: ceshlin@ saturn.yzu.edu.tw.
too costly for other practical applications. In the past 2 decades, other physical and chemical methods have emerged as better alternatives for dealing with the phenolic wastewater. These methods include wet air oxidation,4-10 extraction by an emulsion liquid membrane,11-13 adsorption by activated carbon or activated carbon fiber,14-16 macroreticular resin,17-19 or organoclays,20-22 chemical decomposition by Fenton’s reagent,23 chemical precipitation,24 or ozonation.25-30 Among these methods noted above, ozonation was found by many investigators to be effective in rapidly decomposing phenolic compounds in aqueous solution. In this process, ozone needs to be dissolved in aqueous solution to be effective. Hence, ozone dissolution in aqueous solution is an important issue to be addressed. The previous investigations of phenol ozonation were primarily conducted in a conventional reactor.25-30 Ozone dissolution in aqueous solution in a conventional reactor was known to be inefficient because of solubility limitations. To remedy this drawback, a gas-induced reactor was conceived as an alternative.31-37 In this reactor, a vortex was created on the liquid surface by the high-speed impeller turbines and the gas in the headspace of the reactor was drawn into the aqueous solution by such a strong action. This gas-induction action was reported to considerably improve the ozone utilization.35,36 The objective of this study was to further improve the previous design of the gas-induced reactor by incorporating a fixed granular activated carbon (GAC) bed for enhanced oxidation of phenol. The fixed GAC bed was situated between the draft tube and the reactor wall. In the present design, the advantages of gas induction were retained while the GAC bed provided additional benefits of solid-phase adsorption and catalytic reaction. The combined effects of ozonation and GAC adsorption
10.1021/ie020545x CCC: $25.00 © 2003 American Chemical Society Published on Web 03/25/2003
Ind. Eng. Chem. Res., Vol. 42, No. 8, 2003 1649
Figure 1. Schematic of the gas-induced ozonation reaction system.
led to a significantly improved efficiency of phenol decomposition. Experiments were conducted to examine the operating characteristics of the new reactor design, and the test results can be conducive to optimal reactor design of the gas-induced reactor system.
Sumitomo SP-PSA-01A (Sumitomo Electric Co., Tokyo, Japan) that was equipped with a pressure swing adsorption unit for air processing. The ozone generator had a maximum capacity of 30 g of ozone/h. The actual ozone production rate was controlled by the current input and air flow rate and was measured by the standard potassium iodide (KI) absorption method.37 The ozone gas inlet was located just above the bottom impeller turbine. A stock solution was prepared using GR-grade phenol, as obtained from E. Merck GmbH, Darmstadt, Germany, with a maximum phenol concentration of 2000 mg/L. At the beginning of a test run, 7 L of the phenol solution was placed in the ozone reactor. The wastewater reached approximately a height of 34 cm in the reactor, about half of the reactor height. A constant reaction temperature of 30 ( 1 °C was maintained, and a GAC amount of 300 g was chosen for most of the test runs except for those conducted specifically to test the effect of the GAC amount on the ozone decomposition of phenol. The impeller motor was turned on and kept at a desired constant speed of 1500 ( 10 rpm, which was sufficient to maintain a steady vortex at the liquid surface, with the vortex center occurring right at the impeller shaft. The ozone gas generated at a fixed air flow rate of 1 L/min and a current input between 0.2 and 1 A was let in to start the ozone oxidation reaction. Small samples (20 mL each) were taken periodically from the reactor for measurements of phenol and chemical oxygen demand (COD) concentrations. The COD concentration was determined by the standard method,37 and the phenol concentration was measured using a HP gas chromatograph (model 5890 II, Hewlett Packard Instrument Co., Denver, CO) with a flame ionization detector and a 80/100 Carbopack SP-1000 packed column. A test run usually lasted no more than 2 h. Results and Discussion
Experimental Studies The experimental apparatus of the gas-induced ozone reactor is shown in Figure 1. The ozone reactor was a Pyrex glass tube of 180 mm i.d. and 700 mm height (5 mm wall thickness). It was equipped with a water jacket for temperature control. The draft tube was a Pyrex glass cylinder of 80 mm i.d. and 128 mm height (3 mm wall thickness) and was situated 75 mm above the reactor bottom. Two identical impeller turbines of 72 mm diameter were centrally located and were one diameter apart from each other. The impeller turbine had six 45° downward-facing blades, each to facilitate rapid downward movement of the aqueous solution in the draft tube. A 1/4 hp high-speed ac motor was employed to drive the impeller turbines, permitting a maximum speed of 4000 rpm. The draft tube was connected to the reactor wall by a circular compartment that held the GAC pellets. For the experimental tests, up to 500 g of GAC was randomly packed in the circular compartment. The GAC was made from bituminous coal, as obtained from Norit Ltd. of The Netherlands. According to the manufacturer, the extruded GAC pellet had a dimension of 3.6 mm (diameter) × 6.2 mm (length) and a density of 0.41 g/cm3. The Brunauer-EmmettTeller surface area and the average pore size were measured by a porosimeter (model ASAP 2000, Micrometric Instrument Corp., Norcross, GA) to be 1.147 m2/g and 24 Å, respectively. The ozone generator was a
Performance of the Gas-Induced Ozone Reactor. As would be elaborated later, the GAC amount had a strong influence on both the phenol and COD removal. Cooney and Xi15 reported that GAC is capable of adsorption and catalytic oxidation toward phenolic compounds in aqueous solution. To ascertain these two GAC functions in the present system, experimental tests were conducted separately for GAC adsorption, ozonation, and combined GAC adsorption/ozonation of phenol. The test results are shown in parts a and be of Figure 2 in terms of phenol and COD removal, respectively. By ozonation alone without GAC, the phenol removal increased steadily in Figure 2a and reached 75.5% in 120 min. The phenol removal was very rapid with GAC adsorption alone at the early stage of the process, and it tended to level off after 40 min, reaching a maximum phenol removal of 69.7%. With combined GAC adsorption and ozonation, the phenol removal was essentially the same as that of GAC adsorption within a short time period. This implied that GAC adsorption is a predominating factor and ozonation plays a very minor role within this period. However, after that, ozonation started to exert a strong influence on the liquid- and solid-phase phenol oxidation. The homogeneous and heterogeneous oxidation by ozonation, coupled with GAC adsorption and potential catalytic oxidation on the GAC surface, attributed to the rapid phenol removal, which reached a maximum of 99.2% at 120 min. Similar
1650
Ind. Eng. Chem. Res., Vol. 42, No. 8, 2003
Figure 2. Phenol (a) and COD (b) removal for ozonation, GAC adsorption, and combined GAC adsorption and ozonation with a 2000 mg/L initial phenol concentration, 4962 mg/L initial COD, 1500 rpm impeller speed, 79.6 mg/min ozone mass flow rate, 1 L/min air flow rate, and 30 °C.
Figure 3. Phenol (a) and COD removal as a function of the GAC amount and the reaction time with a 2000 mg/L initial phenol concentration, 4962 mg/L initial COD, 1,500 rpm impeller speed, 79.6 mg/min ozone mass flow rate, 1 L/min air flow rate, and 30 °C.
phenomena were observed in Figure 2b for COD removal. The COD removal for ozonation, GAC adsorption, and combined GAC adsorption and ozonation at 120 min were 50, 59.6, and 86.8%, respectively. With extended ozonation, the COD removal would be further improved. In the phenol decomposition, a number of small-molecule organics, such acetic acid, aldehyde, acetone, etc., were invariably generated, as reported by many previous investigators.6-8,27 These small-molecule organics were more resistant to ozone oxidation than phenol, and this accounts for lower COD removal than phenol by ozonation. It is further noted in Figure 2a,b that the phenol and COD removal efficiencies by combined GAC adsorption and ozonation are not simply equal to the sum of the individual removal efficiencies by ozonation and by GAC adsorption. This is due to the fact that the combined GAC adsorption and ozonation are more complex processes than the individual ones and hence the additive law of the individual system performances would be invalid. In addition, a constant initial phenol of 2000 mg/L was commonly employed for all experimental tests shown in Figure 2a,b. Hence, the amount of phenol available for each of GAC adsorption and ozonation would be less than 2000 mg/L because of their competition for the same phenol in the aqueous phase. A lower amount of phenol would negatively affect the phenol removal efficiency of either GAC adsorption or ozonation. This fact also partially accounts for the lower phenol removal efficiency of the combined process than the sum of the two individual ones. The effect of the GAC amount packed in the circular compartment of the reactor on the phenol and COD
removal was demonstrated in parts a and b of Figure 3, respectively, as a function of the ozonation time. The effect of the GAC amount on the phenol and COD removal is quite pronounced in both parts, and such an influence is particularly strong for a short ozonation time of 30 min. For this ozonation time, the phenol removal was drastically elevated from 20% without GAC to 95.9% with 500 g of GAC, while for 120 min of ozonation, the corresponding removal was much less drastic, but still very pronounced, at 75.5% and 99.7%, respectively. A similar strong influence pattern of the GAC amount was observed on the COD removal in Figure 3b. For this instance, the COD removal was elevated from 17.2% without GAC to 90.2% with 500 g of GAC for 30 min of ozonation. For a long ozonation of 120 min, the corresponding figures were 50% and 95.5%. Provision of the fixed GAC bed brings a highly beneficial advantage to the gas-induced ozonation system. On the basis of the above observations, an amount of 500 g of GAC and an ozonation time of 120 min would be needed for effective phenol and COD removal. Parts a and b of Figure 4 demonstrate the phenol and COD removal as a function of the initial phenol concentration and ozonation time, respectively. Figure 4a clearly reveals excellent phenol removal in the present treatment. For instance, at the end of 1 h, over 95% of phenol removal was achieved for an initial phenol concentration of 2000 mg/L, while by the end of 2 h, the phenol removal exceeded 99%. For a lower initial phenol concentration, the phenol removal was better than 99% in just 1 h of ozonation. However, this will not be the case for COD removal, as shown in Figure 4b. For the
Ind. Eng. Chem. Res., Vol. 42, No. 8, 2003 1651
Figure 4. Effect of the initial phenol concentration on the phenol (a) and COD (b) removal with 300 g of GAC, 1500 rpm impeller speed, 79.6 mg/min ozone mass flow rate, 1 L/min air flow rate, and 30 °C.
case of 2000 mg/L the initial phenol concentration or 4960 mg/L initial COD concentration, the COD removal efficiencies were 80% and 87% at the end of 1 and 2 h, respectively. To achieve 95% COD removal in 1 h, the initial phenol concentration must be lower than 1000 mg/L by extrapolation. The lower COD removal was anticipated primarily because small-molecule organic compounds were produced during ozonation,6-8,27 as noted earlier. These small-molecule organic acids were known to be more resistant to chemical oxidation than phenol but were significantly more biodegradable than the latter. Parts a and b of Figure 4, in general, indicate that the speed and extent of both phenol and COD removal were satisfactory. Hsu and Huang35,36 defined the ozone utilization efficiency in a gas-induced ozone reactor as
Uozone )
Cin - Cout × 100% Cin
where Cin and Cout are the inlet and outlet ozone concentrations of the reactor, respectively. For the test runs shown in Figure 4a, the inlet and outlet ozone concentrations were measured to be 141.6 and 12.3 mg/ L, respectively, for 99% phenol removal. This is equivalent to a 91.3% ozone utilization efficiency and is in line with those of Hsu and Huang,35,36 who reported an ozone utilization efficiency between 90% and 97% depending on the operating conditions. Gould and Weber25 found that the ozone dose required for complete phenol removal was between 4 and 6 mol of ozone/mol of phenol
present in the original wastewater. For the present tests in Figure 4a, the ozone dose for complete phenol removal was calculated to be 1.11 g of O3/g of phenol or 2.18 mol of O3/mol of phenol. This figure is 45.5-63.7% lower that the lower ozone dose reported by Gould and Weber,25 indicating a higher ozone utilization efficiency of the gas-induced ozonation system. Certainly, a simple comparison of the ozone utilization efficiencies of the present system and that of Gould and Weber25 may not be totally appropriate because of the possible differences of the water pH and other experimental conditions and the presence of scavengers and ozone-consuming solutes in the aqueous solution. However, it is reasonable to expect an improvement in the ozone utilization in the present gas-induced reaction system. Effect of GAC Reuse on Phenol Degradation. In a GAC adsorption process, the GAC will become saturated after all active adsorption sites are occupied by the pollutant molecules. High-temperature steam is generally employed in industrial practice for regenerating the exhausted GAC. Although reasonably effective, this process can lead to a significant weight loss of GAC (up to 20%) and is costly. This partially negates the advantages of the GAC adsorption process. Hence, the search for an effective and inexpensive GAC regeneration method is an important issue confronting the GAC adsorption process. In the present study, it was observed that the GAC regeneration occurred in situ during the ozonation period. To ascertain the GAC regeneration efficiency by ozonation, experimental tests were conducted by starting with a fresh batch of GAC to treat the phenolcontaining wastewater. The phenol and COD concentrations were determined for various reaction times up to 420 min. The treated wastewater was drained, and the GAC bed was washed twice with deionized water to get rid of the residual pollutants. The test was repeated with a new batch of phenolic wastewater. The same test process was repeated three times, and the test results are shown in parts a and b of Figure 5 in terms of phenol and COD removal, respectively. Both figures reveal that the ozonation time plays a crucial role in the GAC regeneration efficiency. In terms of phenol removal, the GAC regeneration efficiency exceeded 95 and 99% with 120 and 180 min of ozonation, respectively, as shown in Figure 5a. However, in terms of COD removal, the GAC regeneration efficiency with 180 min of ozonation decreased from 92.6% for the first repeated run to 79.3% for the third one. When ozonation was extended to 420 min, the GAC regeneration efficiency in terms of COD removal was increased to 99.8% for the first repeated test and 93.2% for the third one. The lower GAC regeneration efficiency in terms of COD removal was apparently caused by incomplete removal of small-molecule organic compounds from the GAC pore surface. In view of the fact that phenol and COD could be completely removed in less than half of the time (210 min), 420 min required for GAC regeneration may be too long to be practical. However, the present gasinduced ozonation does provide a rare method for in situ GAC regeneration. Conclusions Phenol oxidation in a new gas-induced ozonation reactor was investigated. A fixed GAC bed was incorporated into the present reaction system, and this incorporation represents a major departure from the
1652
Ind. Eng. Chem. Res., Vol. 42, No. 8, 2003
Figure 5. Effect of the reaction time on the regeneration efficiency in terms of phenol (a) and COD (b) removal for three repeated test runs with 300 g of GAC, 1500 rpm impeller speed, 79.6 mg/ min ozone mass flow rate, 1 L/min air flow rate, and 30 °C.
previous one. Experimental tests were conducted to ascertain the important role played by the GAC bed. On the basis of the results of experimental and theoretical investigations, the following conclusions can be drawn: (1) The GAC was found to considerably enhance ozonation oxidation of phenol. The test results reveal that the gas-induced ozonation oxidation can achieve a 99% phenol removal for an initial phenol concentration of 2000 mg/L in less than 120 min. However, only 87% COD removal can be realized under the same operating conditions, implying a more difficult decomposition of small-molecule organic compounds. The ozone utilization efficiency was found to exceed 90% based on 99% phenol removal. An ozone dose of 2.18 mol/mol of phenol was obtained, and this figure was higher than that reported in the literature. (2). In situ regeneration of an exhausted GAC was observed in the experimental tests that were considered crucial to the present GAC/ozonation system. Repeated experimental runs were performed to test the exhausted GAC regeneration efficiency. In terms of phenol removal, over 99% regeneration can be achieved in about 180 min of ozonation for three repeated runs, while in terms of COD removal, 93% regeneration efficiency was attained in about 420 min, which was deemed good. For 99% exhausted GAC regeneration in terms of COD removal, longer ozonation would be necessary. Literature Cited (1) Metcalf & Eddy, Inc. Wastewater Engineering: Treatment, Disposal and Reuse, 3rd ed.; McGraw-Hill: New York, 1991.
(2) Reynolds, T. D.; Richards, P. A. Unit Operations and Processes in Evironmental Engineering, 2rd ed.; PWS Publishing Co.: Boston, MA, 1996. (3) Bielefeldt, A. R.; Stensel, H. D. Modeling competitive inhibition effects during biodegradation of BTEX mixtures. Water Res. 1999, 33, 707. (4) Teletzke, G. H. Wet air oxidation. Chem. Eng. Prog. 1964, 60, 33. (5) Peoples, R. F.; Krishman, P.; Simonsen, R. N. Nonbiological treatment of refinery wastewaters. J. Water Pollut. Control Fed. 1972, 44, 2120. (6) Devlin, H. R.; Harris, I. J. Mechanism of the oxidation of aqueous phenol with dissolved oxygen. Ind. Eng. Chem. Fundam. 1984, 23, 387. (7) Foussard, J. N.; Debelfontaine, H.; Besombes-Vailhe, J. Efficient elimination of organic liquid wastes: Wet air oxidation. J. Environ. Eng. (N.Y.) 1989, 115, 367. (8) Joglekar, H. S.; Samant, S. D.; Joshi, J. B. Kinetics of wet air oxidation of phenol and substituted phenol. Water Res. 1991, 25, 145. (9) Lin, S. H.; Chuang, T. S. Wet air oxidation and activated sludge treatment of phenolic wastewater. J. Environ. Sci. Health 1994, A29, 547. (10) Lin, S. H.; Wu, Y. F. Catalytic wet air oxidation of phenolic wastewater. Environ. Technol. 1996, 17, 175. (11) Cahn, R. P.; Li, N. N. Separation of phenol from wastewater by the liquid membrane. Sep. Sci. Technol. 1974, 9, 505. (12) Kim, K. S.; Choi, S. J.; Ihm, S. K. Simulation of phenol removal from wastewater by liquid membrane emulsion. Ind. Eng. Chem. Fundam. 1983, 22, 167. (13) Teramoto, M.; Sakai, T.; Yamagawa, K.; Ohsuga, M.; Miyake, Y. Extraction of phenol and cresol by liquid surfactant membrane. Sep. Sci. Technol. 1983, 18, 397. (14) Noll, K. E.; Gounaris, V.; Hou, W. S. Adsorption Technology for Air and Water Pollution Control; Lewis Publishing Co.: Ann Arbor, MI, 1992. (15) Cooney, D. C.; Xi, Z. Activated carbon catalyzes reactions of phenolics during liquid-phase adsorption. AIChE J. 1994, 40, 361. (16) Lin, S. H.; Hsu, F. M. Liquid-phase adsorption of organic compounds by granular activated carbon and activated carbon fiber. Ind. Eng. Chem. Res. 1995, 34, 2110. (17) Fox, C. R. Remove and recover phenol. Hydrocarbon Process. 1975, 54 (7), 109. (18) Fox, C. R. Plant uses prove phenol recovery with resins. Hydrocarbon Process. 1978, 57 (11), 269. (19) Crook, E. H.; McDonnell, R. P.; McNulty, J. I. Removal and recovery of phenols from industrial waste effluents with Amberlite XAD polymer. Ind. Eng. Chem. Prod. Res. Des. 1978, 14, 113. (20) Boyd, S. A.; Shaobai, S.; Mortland, M. M. Pentachlorophenol adsorption by organoclays. Clays Clay Miner. 1988, 36, 126. (21) Dental, S. K.; Bottero, J. Y.; Khatib, K.; Demougeot, H.; Doguet, J. P.; Anselme, C. Sorption of tannic acid, phenol and 2,4,5-trichlorophenol on organoclays. Water Res. 1995, 29, 1273. (22) Lin, S. H.; Cheng, M. J. Phenol and chlorophenol removal from aqueous solution by organobentonites. Environ. Technol. 2001, 21, 475. (23) Huang, C. P.; Dong, C.; Tang, Z. Advanced chemical oxidation: Its present role and potential future in hazardous waste treatment. Waste Manage. 1993, 13, 361. (24) Lin, S. H.; Wang, C. S. Treatment of high-strength phenolic wastewater by a new two-step method. J. Hazard. Mater. 2002, B90, 206. (25) Gould, J. P.; Weber, W. J., Jr. Oxidation of phenols by ozone. J. Water Pollut. Control Fed. 1976, 48, 47. (26) Li, K. Y.; Kuo, C. H.; Weeks, J. L., Jr. A kinetic study of ozone- phenol reaction in aqueous phase. AIChE J. 1997, 25, 5583. (27) Yamamoto, Y.; Niki, E.; Shiokawa, H.; Kamiya, Y. Ozonation of organic compounds. 2. Ozonation of phenol in water. J. Org. Chem. 1979, 44, 2137. (28) Gurol, M. D.; Singer, P. C. Dynamics of the ozonation of phenols1. Experimental observation. Water Res. 1983, 17, 1163. (29) Gurol, M. D.; Vatistas, R. Oxidation of phenolic compounds by ozone and ozone + UV radiation. Water Res. 1987, 21, 895. (30) Ku, Y.; Su, W. J.; Shen, Y. S. Decomposition of phenols in aqueous solution by a UV/O3 process. Ozone Sci. Eng. 1996, 18, 443.
Ind. Eng. Chem. Res., Vol. 42, No. 8, 2003 1653 (31) Litz, L. M. A novel gas-induced stirred tank reactor. Chem. Eng. Prog. 1985, 81 (11), 36. (32) Saravanan, K.; Mundale, V. D.; Joshi, J. S. Gas inducing type mechanically agitated contactors. Ind. Eng. Chem. Res. 1994, 33, 2226. (33) Saravanan, K.; Joshi, J. S. Gas inducing type mechanically agitated contactors: Hydrodynamic characteristics of dual impeller system. Ind. Eng. Chem. Res. 1995, 34, 2499. (34) Hsu, Y. C.; Huang, C. J. Characteristics of a new gasinduced reactor. AIChE J. 1996, 42, 3146. (35) Hsu, Y. C., Huang, C. J. Ozone transfer with optimal design of a new gas-indudced reactor. AIChE J. 1997, 43, 2336. (36) Patwardhan, A. W.; Joshi, J. S. Design of gas-inducing reactor. Ind. Eng. Chem. Res. 1999, 38, 49. (37) APHA. Standard Methods for the Examination of Water and Wastewater, 17th ed.; American Public Health Association: Washington, DC, 1992.
(38) Joshi, M. G.; Shambaugh, R. L. The kinetics of ozonephenol reaction in aqueous solution. Water Res. 1982, 16, 933. (39) Li, L.; Chen, P.; Gloyna, E. F. Generalized kinetic model for wet oxidation of organic compounds. AIChE J. 1991, 37, 1687. (40) Lin, S. H.; Ho, H. J. Kinetics of wet air oxidation of highstrength industrial wastewater. J. Environ. Eng. (N.Y.) 1995, 123, 852. (41) Mishra, V. S.; Mahajani, V. V.; Joshi, J. B. Wet air oxidation. Ind. Eng. Chem. Res. 1995, 34, 2. (42) Zhang, Q.; Chuang, K. T. Lumped linetic model for catalytic wet oxidation of organic compounds in industrial wastewater. AIChE J. 1999, 45, 145.
Received for review July 23, 2002 Revised manuscript received December 16, 2002 Accepted February 20, 2003 IE020545X
