Decomposition of 2-Mercaptothiazoline in an Aqueous Solution by

Department of Chemical Engineering, National Taiwan University of Science and Technology,. Taipei 106, Taiwan. This study investigates the enhanced ...
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Ind. Eng. Chem. Res. 2004, 43, 1932-1937

Decomposition of 2-Mercaptothiazoline in an Aqueous Solution by Ozonation with UV Radiation Y. H. Chen,† C. Y. Chang,*,† C. C. Chen,† C. Y. Chiu,‡ Y. H. Yu,† P. C. Chiang,† C. F. Chang,† and Y. Ku§ Graduate Institute of Environmental Engineering, National Taiwan University, Taipei 106, Taiwan, Department of Environmental Engineering, Lan-Yang Institute of Technology, I-Lan 261, Taiwan, and Department of Chemical Engineering, National Taiwan University of Science and Technology, Taipei 106, Taiwan

This study investigates the enhanced ozonation of 2-mercaptothiazoline (2-MT), which is a pollutant of concern in the water environments, with ultraviolet (UV) radiation. Semibatch ozonation experiments are proceeded under various reaction conditions to examine the effects of ozone dosage and UV radiation on the decomposition of 2-MT. The enhancement of UV radiation on the ozonation of 2-MT is significant for overcoming the reaction resistance of the heterocyclic structure of 2-MT, which exhibits high resistance to the attack of ozone alone according to our previous study, indicating a low mineralization extent. The nearly complete mineralization of 2-MT via O3/UV photolysis can be achieved, accompanied with the generation of sulfate, ammonium, and nitrate ions. Furthermore, distinct relationships between the formation of ions and the mineralization extent of 2-MT during O3/UV photolysis are obtained. In addition, ozone consumption per mole of 2-MT, which increases significantly with the intensity of UV radiation, shows a high correlation with the treatment qualities of O3/UV photolysis of 2-MT. The results reveal that O3/UV photolysis is more feasible than pure ozonation and provide useful information for the proper application of an ozonation system for the removal of 2-MT. Introduction The chemical structure of 2-mercaptothiazoline (2MT) is composed of an exocyclic mercapto group and a heterocyclic molecule that contains sulfur, nitrogen, and carbon atoms. 2-MT has been used as a biocorrosion inhibitor, an antifungal reagent, and a brightening and stabilization agent in many industrial processes.1,2 Accordingly, 2-MT has been frequently detected in wastewater effluents as well as river water because of its high mobility in the aquatic system. 2-MT is harmful according to its Material Safe Data Sheet and exhibits persistence to microbial degradation. Therefore, 2-MT is an aqueous pollutant of concern in water and wastewater systems. Ozonation is an effective process to remove organic pollutants. The compounds would be attacked via two different reaction mechanisms: (1) direct ozonation by the ozone molecule and (2) radical oxidation by highly oxidative free radicals such as hydroxyl free radicals, which are formed by decomposition of ozone in the aqueous solution.3,4 Radical oxidation is nonselective and vigorous. The purpose of introducing ultraviolet (UV) radiation in the ozonation process is to enhance the ozone decomposition, yielding more free radicals for reaching a higher ozonation rate.5 The information about the ozonation of 2-MT is found to be scarce and desirable for evaluating the practicability of 2-MT removal via ozonation treatments. Recently, Chen et al.6 investigated decomposition of 2-MT via * To whom correspondence should be addressed. Tel./fax: +886-2-2363-8994. E-mail: [email protected]. † National Taiwan University. ‡ Lan-Yang Institute of Technology. § National Taiwan University of Science and Technology.

treatment using ozone only. Their results indicated that the heterocyclic structure of 2-MT has high resistance to ozone molecules for proceeding with further oxidation. In the present study, enhanced ozonation with UV radiation is employed to eliminate 2-MT. The results obtained can provide useful information about the proper application of the process for the removal of 2-MT via ozonation with UV radiation. Experimental Section Chemicals. 2-MT, with a chemical formula of C3H5NS2 purchased from Aldrich (Milwaukee, WI), has a molecular weight of 119.21, a melting point of 105-107 °C, and a CAS registry number of 96-53-7. All experimental solutions are prepared with deionized water without other buffers. The initial concentration of 2-MT (CBL0) in the aqueous solution is 100 mg/L. The initial pH value and concentration of total organic carbons (TOCs; CTOC0) are measured as about 5.50 and 29.1 mg/ L, respectively. The volatility of 2-MT in the aqueous solution is found to be negligible from the previous airstripping test. Instrumentation. The airtight reactor of 17.2 cm inside diameter is made of Pyrex glass with an effective volume of 5.5 L and equipped with a water jacket to maintain a constant solution temperature at 25 °C in all experiments. The design of the reactor is based on the criteria of the shape factors of a standard six-blade turbine.7 The gas diffuser in a cylindrical shape with a pore size of 10 µm is located at the bottom of the reactor. Two quartz tubes of 3.8 cm outside diameter symmetrically installed inside the reactor are used to house the UV lamps. The low-pressure mercury lamps, which emit principally at 254 nm, provide UV radiation. The intensity of the UV radiation (IUV) is measured by a

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Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 1933

digital radiometer (Ultra-Violet Products (UVP), Upland, CA) with a model UVP-25 radiation sensor. About 3.705 L of solution (VL) is used in each experiment, while the total sampling volume is within 5% of the solution. The stirring speed is 800 rpm to ensure the complete mixing of liquid and gas phases according to the previous study.8 The generation of ozone from pure oxygen is controlled by an ozone generator (model SG01A, Sumitomo, Tokyo, Japan) with a gas flow rate (QG) of 1.94 L/min. The fed (CAGi) and discharged (CAGe) concentrations of gaseous ozone are measured by an UV photometric analyzer (model SOZ-6004, Seki, Tokyo, Japan), which is calibrated by the KI titration method.9 A liquid ozone monitor (model 3600, Orbisphere, Neuchaˆtel, Switzerland) with a sensor of a membrane-containing cathode is used to measure the dissolved ozone concentration (CAL) in the aqueous solution. A circulation pump is used to transport the liquid from the reactor to the sensor and reflow it with a flow rate of 0.18 L/min during ozonation. A detailed experimental apparatus sketch may be referred to in the previous study.10 Samples are drawn out from the reactor at desired time intervals in the course of experiments. The residual dissolved ozone in the samples is removed immediately by stripping with nitrogen. The concentrations of 2-MT (CBL) are analyzed using a high-performance liquid chromatography (HPLC) system, with a 250 × 4.6 mm column (model BDS C18 (5 µm), Thermo Hypersilkeystone, Bellfonte, PA) and an UV/visible detector (model 1706, Bio-Rad, Hercules, CA) at 275 nm. The HPLC eluent with a flow rate of 1.0 mL/min has a composition of 73.5 mM [CH3(CH2)3]4N(HSO4)/CH3CN of 74:26. The injection volume of the analytical solution is 20 µL, and the detection limit of 2-MT analysis is 0.01 mg/L. Thus, the complete or nearly complete elimination of 2-MT simply denotes the reduction of 2-MT to below 0.01 mg/L. The anion ionic chromatography (IC) employed to analyze the concentrations of sulfate (CSO42-) and nitrate (CNO3-) is equipped with a 150 × 5.5 mm column (model AN300 column, MetaChem, Lake forest, CA) and a conductivity detector (model series IV, LabAlliance, Lemont, PA). The eluent with a flow rate of 2.0 mL/min has a composition of NaHCO3/Na2CO3 of 1.7 mM/1.8 mM. The cation IC employed to analyze the concentrations of ammonium (CNH4+) is equipped with a 250 × 4 mm column of model IonPac CS12A and a detector of model CSRS-II (both Dionex, Sunnyvale, CA). The eluent with a flow rate of 1.0 mL/min has a composition of 22 mM CH4O3S. The concentration of TOC (CTOC) is analyzed by the TOC analyzer (model 700, OI Corp., College Station, TX). During the experiments, several measurements are usually performed with relative standard deviations of about 1-3%. Experimental Procedures. The semibatch experiments of ozonation of 2-MT with UV radiation are performed to examine the concentration variations of 2-MT, ozone, TOC, and ions. Before ozonation experiments are started, the ozone-containing gas is bypassed to the photometric analyzer to ensure the stability and ozone concentration. Two different IUV of 35.96 and 69.30 W/m2 are employed to test the effect of the light intensity on ozonation. A portion of the gas stream at the preset flow rate is directed into the reactor when the ozonation system is ready to start.

Figure 1. Time (t) variations of normalized concentrations of 2-MT (CBL), sulfate (CSO42-), ammonium (CNH4+), nitrate (CNO3-), and TOCs (CTOC) for the ozonation of 2-MT with UV radiation in a semibatch system. Concentration of the feed ozone gas (CAGi) ) 40 mg/L with the intensity of UV radiation (IUV) ) 69.30 W/m2: (O, 4, 0, b, and 2) CBL/CBL0, YSO42- ) CSO42-/2CBL0 (MM-1), YNH4+ ) CNH4+/CBL0 (MM-1), YNO3- ) CNO3-/CBL0 (MM-1), and CTOC /CTOC0. CBL ) CBL0 and CTOC ) CTOC0 at t ) 0.

Results and Discussion Concentration Variations in Ozonation of 2-MT with UV Radiation. The concentration variations of 2-MT, sulfate, ammonium, nitrate, and TOCs with ozonation time (t) at CAGi ) 40 mg/L and IUV ) 69.30 W/m2 are shown in Figure 1. 2-MT can be rapidly decomposed in the early period of ozonation. The generations of sulfate, ammonium, and nitrate ions are found subsequently. As shown in Figure 1, the nearly complete mineralization can be gradually reached in about 180 min. Furthermore, an important characteristic time is that for achieving the reduction of 2-MT to below the detection limit (denoted as tf,MT). A comparison of the ozonation results at tf,MT for the four cases with various CAGi and IUV is given in Table 1. The values of tf,MT under various experimental conditions are between 4 and 15 min. At tf,MT, the yield of sulfate, YSO42- ) CSO42-/2CBL0 (MM-1), is found to be significant. However, the yields of ammonium and nitrate, YNH4+ ) CNH4+/CBL0 (MM-1) and YNO3- ) CNO3-/CBL0 (MM-1), as well as the removal efficiency of TOCs, ηTOC ) (CTOC0 - CTOC)/CTOC0, are relatively low. The intermediates produced from the destruction of 2-MT at tf,MT still contribute over 96% of TOCs relative to the initial value. Note that the mercapto substituent of 2-MT has high reactivity toward the electrophilic reaction.11 Therefore, the initial attack of oxidants on 2-MT during ozonation is mainly proceeded via the electrophilic substitution of ozone on the mercapto group. Nevertheless, comparing the results of ozonation of 2-MT with UV (present study) to those without UV, which showed smaller ηTOC values of 1.56-2.73% and undetectable YNH4+ and YNO3- at tf,MT, indicates that the heterocyclic ring can be attacked more vigorously because of the participation of nonselective hydroxyl free radicals generated from ozonation combined with UV radiation. The possible attacks by which the OH

1934 Ind. Eng. Chem. Res., Vol. 43, No. 9, 2004 Table 1. Comparison of the Ozonation Results at tf,MT under Various Experimental Conditions experimental conditiona case 1: case 2: case 3: case 4: a

tf,MT (min)

CAGi ) 10 mg/L, IUV ) 69.30 CAGi ) 20 mg/L, IUV ) 69.30 W/m2 CAGi ) 40 mg/L, IUV ) 69.30 W/m2 CAGi ) 40 mg/L, IUV ) 35.96 W/m2 W/m2

15 10 4 5

YSO42- (%) 31.1 21.5 23.7 NMc

YNH4+ (%)

YNO3- (%)

ηTOC (%)

2.42 NMc 1.19 NMc

NDb

3.91 3.29 2.66 3.35

1.83 1.83 NMc

CBL0 and CTOC0 are 100 and 29.1 mg/L, respectively. b ND: not detected. c NM: no measurement.

Figure 2. Simplified scheme of the decomposition pathways for ozonation of 2-MT with UV radiation.

Figure 4. Variation of YSO42- with time for ozonation of 2-MT with UV radiation in a semibatch system. YSO42- ) CSO42-/2CBL0 (MM-1). Notations are the same as those specified in Figure 3.

Figure 3. Variation of CBL/CBL0 with time for ozonation of 2-MT in a semibatch system under various experimental conditions: (O, 4, and 0) CAGi ) 10, 20, and 40 mg/L with IUV ) 69.30 W/m2; (9) CAGi ) 40 mg/L with IUV ) 35.96 W/m2; (3) UV alone with IUV ) 69.30 W/m2.

radicals react with 2-MT are to break the double bond of CdN and abstract the H atom of the mercapto group first.2 According to the concentration variations of the species and noting that the results of ozonation of 2-MT are significantly affected by the presence of UV radiation, one may propose a simplified scheme of the decomposition pathways for the O3/UV treatment of 2-MT as shown in Figure 2. The principal contribution of UV radiation is to promote the generation of OHnoted as reaction II.10 In addition, the pH value of the solution is found to decrease rapidly in the early time and then approach the constant value. In comparison with the final pH values in the sole ozone treatments (3.01-3.09),6 those in the O3/UV treatments of 3.693.96 are higher. This is caused by the different reaction pathways and products in these two processes. Decomposition of 2-MT and Formation of Sulfate. As shown in Figure 3, the effect of the ozone concentration of the feed gas (CAGi) on the destruction

rate of 2-MT is significant. However, comparing the results of CAGi ) 40 mg/L with IUV ) 69.30 and 35.96 W/m2 reveals that the intensity of UV radiation in the range of 35.96-69.30 W/m2 only slightly affects the destruction rate of 2-MT. This can be explained by the depiction of the decomposition pathways of 2-MT in Figure 2, showing that reaction II is enhanced by the high intensity of UV radiation, say 35.96-69.30 W/m2. The pathways via hydroxyl free radicals noted as reactions III and IV, would then be promoted. As the concentration of dissolved ozone decreases, the pathway via O3 of reaction I is weakened. Further, the pseudofirst-order kinetics for the elimination of 2-MT, CBL/CBL0 ) e-kBt, can be obtained from Figure 3 with kB (min-1) ) 0.0164CAGi, where CAGi is in milligrams per liter and IUV ) 35.96-69.30 W/m2. The obtained value of kB is close to that under the condition of sole ozonation with kB (min-1) ) 0.0167CAGi. As a result, the overall decomposition rate of 2-MT in ozonation is only slightly affected by the introduction of UV radiation, which strongly influences the mineralization of TOC. Moreover, the effect of direct UV photolysis on the removal of 2-MT is found to be relatively weak as shown in Figure 3, being compared with that of the O3/UV treatments. Figure 4 presents the variation of YSO42- with the ozonation time. The yield of sulfate reaches a constant value of 93.8 ( 0.2% in 180-240 min for the cases examined. It is obvious that the increases of CAGi and IUV accelerate the formation rate of sulfate. Furthermore, YSO42- increases consistently with ηTOC, as shown in Figure 5. The generation of sulfate from decomposition of 2-MT can be divided into two stages. The generation of sulfate in the first stage for YSO42- < 50%, which is attained accompanied with the small ηTOC

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Figure 5. YSO42- vs ηTOC for ozonation of 2-MT with UV radiation. ηTOC ) (CTOC0 - CTOC)/CTOC0: (]) sole O3 treatments of Chen et al.;6 other notations are the same as those specified in Figure 3; (s) average and smooth curve of experimental data of O3/UV treatments with R2 ) 0.966, where R2 (determination coefficient) ) 1 - [∑(Ce - Cp)2/∑(Ce - Ce)2]. Ce, Ce ) experimental data and the corresponding average value. Cp ) predicted values.

value, mainly comes from oxidation of the mercapto group of 2-MT. The second stage of sulfate generation for YSO42- > 50% is characterized by oxidation of the sulfur atom on the heterocyclic ring. Note that the value of YSO42- under the condition of sole O3 is smaller than 50%, as depicted in Figure 5.6 Also note that the variations of the sulfate generation with ηTOC during an early period of the reaction for the sole O3 and O3/ UV treatments are similar. However, further oxidation of the intermediates can be mainly proceeded via reaction VI, which is slight but vigorous under the conditions of sole O3 and O3/UV treatments, respectively. Consequently, overcoming the reaction resistance of the heterocyclic structure is critical for ozonation of 2-MT. The characteristic curve of the variation of YSO42with ηTOC in Figure 5 is useful to illustrate the distinct relationship between the sulfate generation and the mineralization extent of the heterocyclic molecule. Formation of Ammonium and Nitrate Associated with the Removal of TOC. During mineralization of 2-MT, ammonium is generated with the increase of ηTOC, as shown in Figure 6. Obviously, the ammonium yield (YNH4+) is smaller than ηTOC mainly because of the generation of other nitrogen-containing products such as nitrate. The final value of YNH4+ of about 67% indicates that ammonium is the major product of nitrogen species. Additionally, the case with higher CAGi ()40 mg/L) seems to have lower YNH4+ values than that with CAGi ) 10 mg/L at the same ηTOC. This phenomenon can be explained by noting the competitive mechanism of reactions V and VI, as depicted in Figure 2. Referring to the study of ozonation of glycine,12 reactions V and VI contribute to the generation of nitrate (or nitrite) and ammonium from the nitrogen-containing intermediates of 2-MT, respectively. Definitely, employing higher CAGi would be more favorable to the occurrence of reaction V than reaction VI. In addition, the relationship between YNO3- and ηTOC, as shown in Figure 7, reveals a proportion of the YNO3-/ηTOC ratio of about 0.26 during

Figure 6. YNH4+ vs ηTOC for ozonation of 2-MT with UV radiation. YNH4+ ) CNH4+/CBL0 (MM-1). Notations are the same as those specified in Figure 3.

Figure 7. YNO3- vs ηTOC for ozonation of 2-MT with UV radiation. YNO3- ) CNO3-/CBL0 (MM-1). Notations are the same as those specified in Figure 3: (s) average and smooth curve of experimental data with R2 ) 0.977.

the O3/UV treatments of 2-MT. Accordingly, the sum of ammonium (67%) and nitrate (26%) contributes to about 93% of nitrogen products from decomposition of 2-MT. For a further illustration of the effects of CAGi and IUV on the elimination of TOCs, Figure 8 shows the variation of the mean mineralization rate, rTOC,a ) (CTOC0 - CTOC)/t, with ηTOC under various experimental conditions. The nearly complete removal of TOCs requires about 180-240 min. Obviously, rTOC,a is accelerated with increases of CAGi and IUV. For comparison, the maximum value of ηTOC in the treatments of 2-MT with sole O3 is only 16%.6 Therefore, UV radiation in ozonation of 2-MT acts as a significant promoter for increasing the mineralization extent. Furthermore, the pseudofirst-order kinetics of mineralization of 2-MT, CTOC/ CTOC0 ) e-kTOCt, can be proposed to give kTOC (min-1) ) 6.72 × 10-5CAGi0.489IUV0.912 (with CAGi in milligrams per

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Figure 8. rTOC,a vs ηTOC for ozonation of 2-MT with UV radiation in a semibatch system. Notations are the same as those specified in Figure 3.

liter and IUV in watts per meter squared) from the experimental data with R2 ) 0.931. The value of rTOC,a increases with ηTOC in the regimes of low and high ηTOC, respectively. The lower value of rTOC,a in the early stage of ozonation is due to the fact that ozone is first consumed for oxidation of the mercapto group and the opening of the heterocyclic ring, thus accompanying the low diminution of TOCs. Moreover, comparing the variations of rTOC,a with ηTOC for the cases of CAGi ) 20 mg/L with IUV ) 69.30 W/m2 and CAGi ) 40 mg/L with IUV ) 35.96 W/m2, one notes that the effect of CAGi seems to be more significant on rTOC,a when the value of ηTOC is small. However, higher IUV enhances rTOC,a more significantly in the regime of higher ηTOC. This is due to the fact that the intermediates in the later stage of ozonation of 2-MT have a high reaction resistance toward ozone molecules. Therefore, the oxidation reaction via hydroxyl free radicals noted as reaction VI is predominant to proceed in this regime. In addition, the relation between YSO42- and the ozone consumption per mole of 2-MT, mO3R/CBL0VL (mol mol-1), is illustrated in Figure 9. Ozone consumption (mO3R) is calculated by eq 1, where VL and VF are the volumes of solution and free space in the reactor, respectively.

mO3R )

∫01QG(CAGi - CAGe) dt - CALVL - CAGeVF

Figure 10. mO3R/CBL0VL vs mO3A/CBL0VL for ozonation of 2-MT with UV radiation in a semibatch system. Notations are the same as those specified in Figure 3: (s) average and smooth curve of experimental data.

(1)

As a result, YSO4 increases with mO3R/CBL0VL apparently and agreeably in all cases examined, indicating a high correlation between decomposition of 2-MT and ozone consumption. YSO42- approaches the final constant value, which stands for the nearly complete mineralization of 2-MT because the value of mO3R /CBL0VL is greater than 16. Correspondingly, the relationships of YNH4+, YNO3-, and ηTOC with mO3R/CBL0VL can also be acquired according to Figures 5-7 and 9. It may be worth noting that the applications of the mass balance equation of eq 1 consider the ozone mass-transfer and chemical reactions simultaneously, which has been verified in the previous studies.6,10 Further, variation of mO3R /CBL0VL with the ozone applied per mole of 2-MT, mO3A/CBL0VL (mol mol-1), in 2-

Figure 9. YSO42- vs mO3R/CBL0VL (mol mol-1) for ozonation of 2-MT with UV radiation. Notations are the same as those specified in Figure 3: (s) average and smooth curve of experimental data with R2 ) 0.976.

the semibatch reactor is shown in Figure 10. The ozone applied (mO3A) is defined as follows.

mO3A ) QGCAGit

(2)

Obviously, the variations at various experimental conditions can be divided into three groups based on IUV and are almost independent of CAGi. The slopes of the curves in Figure 10 represent the utilization efficiencies of applied ozone. For instance, the utilization efficiencies of ozone at mO3A/CBL0VL ) 125 for the cases with IUV of 0, 35.96, and 69.30 W/m2 are 7, 26, and 47%, respectively. The differences of the utilization efficiencies of ozone among these groups are mainly due to the contribution of reaction II, of which the rate is significantly enhanced by higher IUV, especially in the later

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period of ozonation. Consequently, the introduction of UV radiation to the ozonation process can effectively increase the utilization efficiency of the applied ozone and accelerate decomposition of 2-MT. Conclusions (1) The results recommend employment of the ozonation process combined with UV radiation for the removal of 2-MT. The nearly complete mineralization of 2-MT can be achieved under the experimental conditions of this study. Mineralization is accompanied with the formation of sulfate, ammonium, and nitrate ions. (2) The use of UV radiation in ozonation of 2-MT significantly enhances decomposition of the heterocyclic structure, while the treatment using sole ozone is not effective. In addition, ozone consumption per mole of 2-MT, which is apparently promoted by UV radiation, can be introduced as a useful and easy index to assess the treatment qualities of 2-MT by ozonation. (3) Under the experimental conditions of this study, the destruction rate of 2-MT increases with the ozone concentration of the feed gas, while it is not significantly enhanced by UV radiation. However, both the ozone concentration of the feed gas and the intensity of UV radiation can significantly improve the oxidation rate of the intermediates. The explanation for these phenomena can be addressed with the mechanism of ozonation combined with UV radiation. (4) Furthermore, the clear-cut relationships between the formation of ions and the mineralization extent for the O3/UV photolysis of 2-MT are obtained in this study. Generation of sulfate, which can be divided into two stages, has a yield of 94%. The major product of nitrogen species is ammonium with a yield of about 67%, while the yield of nitrate is about 26%. Acknowledgment This study was supported by the National Science Council of Taiwan under Grant NSC 89-2211-E-002-107.

Literature Cited (1) Fang, C. L. General Concepts of Additives in the Electroplating Solution; Finishing Science Publisher Co.: Taipei, Taiwan, 1996. (2) Mahal, H. S.; Mukherjee, T. Kinetics and Spectroscopic Properties of Intermediates Formed by the Reaction of Some Oxidizing and Reducing Radicals with 2-mercaptothiazoline (2MT) in Aqueous Solutions. Radiat. Phys. Chem. 1999, 54, 29. (3) Gurol, M. D.; Singer, P. C. Kinetics of Ozone Decomposition: A Dynamic Approach. Environ. Sci. Technol. 1982, 16, 377. (4) Sotelo, J. L.; Beltra´n, F. J.; Benı´tez, F. J.; Beltra´n-Heredia J. Ozone Decomposition in Water: Kinetic Study. Ind. Eng. Chem. Res. 1987, 26, 39. (5) Prengle, H. W. Experimental Rate Constants and Reactor Considerations for the Destruction of Micropollutants and Trihalomethane Precursors by Ozone with Ultraviolet Radiation. Environ. Sci. Technol. 1983, 17, 743. (6) Chen, Y. H.; Chang, C. Y.; Chen, C. C.; Chiu, C. Y.; Yu, Y. H.; Chiang, P. C.; Ku, Y.; Chen, J. N.; Chang, C. F. Decomposition of 2-mercaptothiazoline in aqueous solution by ozonation. Chemosphere 2004, in press. (7) McCabe, W. L.; Smith, J. C.; Harriott, P. Unit Operations of Chemical Engineering; McGraw-Hill: New York, 1993. (8) Chang, C. Y.; Chen, Y. H.; Li, H.; Chiu, C. Y.; Yu, Y. H.; Chiang, P. C.; Ku, Y.; Chen, J. N. Kinetics of Decomposition of Polyethylene Glycol in Electroplating Solution by Ozonation with UV Radiation. J. Environ. Eng. 2001, 127, 908. (9) Rankness, K.; Gordon, G.; Langlais, B.; Masschelein, W.; Matsumoto, N.; Richard, Y.; Robson, C. M.; Somiya, I. Guideline for Measurement of Ozone Concentration in the Process Gas from an Ozone Generator. Ozone Sci. Eng. 1996, 18, 209. (10) Chen, Y. H.; Chang, C. Y.; Huang, S. F.; Chiu, C. Y.; Ji, D.; Shang, N. C.; Yu, Y. H.; Chiang, P. C.; Ku, Y.; Chen, J. N. Decomposition of 2-Naphthalenesulfonate in Aqueous Solution by Ozonation with UV Radiation. Water Res. 2002, 36, 4144. (11) Fiehn, O.; Wegener, G.; Jochimshn, J.; Jekel, M. Analysis of the Ozonation of 2-Mercaptobenzothiazole in Water and Tannery Wastewater Using Sum Parameters, Liquid and Gas Chromatography and Capillary Electrophoresis. Water Res. 1998, 32, 1075. (12) Berger, P.; Leitner, N. K. V.; Dore´, M.; Legube, B. Ozone and Hydroxyl Radicals Induced Oxidation of Glycine. Water Res. 1999, 33, 433.

Received for review August 14, 2003 Revised manuscript received January 27, 2004 Accepted January 27, 2004 IE0306729