DECOMPOSITION OF WASTEWATER CONTAINING ISOPROPYL ALCOHOL USING THE GAMMA-RAY/HYDROGEN PEROXIDE PROCESS

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1 J. Environ. Eng. Manage., 20(3), (20) 151 DECOMPOSITION OF WASTEWATER CONTAINING ISOPROPYL ALCOHOL USING THE GAMMA-RAY/HYDROGEN PEROXIDE PROCESS Kai-Yuan Cheng 1, Ling-Ling Hsieh 1, Kuo-Shan Yao 2, Ching-Hsing Lin 3, En-Jung Chang 1 and Chen-Yu Chang 4, * 1 Department of Medical Imaging and Radiological Science Central Taiwan University of Science and Technology Taichung 406, Taiwan 2 Department of Horticulture National Taitung Junior College Taitung 950, Taiwan 3 Department of Safety Health and Environmental Engineering Tungnan University Taipei 222, Taiwan 4 Department of of Biotechnology Mingdao University Changhua 523, Taiwan Key Words: Isopropyl alcohol (IPA), gamma-ray (γ-ray), free radicals ABSTRACT Isopropyl alcohol (IPA) is the major organic ingredient in wastewater of semiconductor manufacturing industry. The efficiency of traditional wastewater treatment processes using physicalchemical or microorganism decomposition approaches is limited. Wastewater containing organic solvents that are not decomposed deteriorates the quality of water in the environment, while its volatile nature results in air pollution that affects the health of factory workers and residents in the neighborhood. Hence, it is of urgent need to develop more efficient pollution reduction technology. In this study, gamma-rays were induced using a Co-60 radiation source to treat IPA alone or in combination with hydrogen peroxide. Experimental results reveal that the combined γ-ray/h 2 process shows better decomposition efficiencies than the use of γ-ray or H 2 alone. INTRODUCTION Semiconductor manufacturing and other hightech electronic industries contribute greatly to Taiwan s economic development over the past 20 years. Numerous organic solvents are used in the semiconductor manufacturing process. The organic compounds present in wastewater of semiconductor manufacturing and other photo-electric industries have become more complicated due to the intricate manufacturing processes. Isopropyl alcohol (IPA), acetone, propylene glycol monomethyl ether acetate, ethyl lactate, phenol, benzene, toluene and xylene are the common organic reagents present at high concentrations in the wastewater [1] and most of them are volatile in nature. These organic compounds pose direct or indirect harm to the liver, kidney, central nervous system and skin, and some of them have already been verified as carcinogen, teratogenic agent and gene mutagen for humans. Traditional wastewater treatment approaches involving physical-chemical decomposition or microorganisms have shown only limited efficiencies [2]. Chemicals that are not removed enter the environment producing detrimental impact on soil and water resources, agriculture, animals, plants and the climate. For example, workers and local residents in areas with pesticide factories, chemical factories and high-tech industries suffer from cancer. It is therefore necessary and urgent to develop more efficient methods for eliminating harmful chemicals from wastewater. Many advanced oxidation processes have been developed to treat pollutants that are hard to decompose [3-]. This study proposes a new technique; the γ-ray/h 2 process, for treating IPA. The γ-ray generated using Co-60 is often employed to treat cancers, *Corresponding author cychang@mdu.edu.tw

2 152 J. Environ. Eng. Manage., 20(3), (20) disinfect and kill microorganisms in foods or agricultural products [11]. In recent years, it has been applied to treat environmental pollutants [6,12-19]. The γ-ray has stronger energy than UV and can produce more free radicals when they interact with water. This highenergy characteristic makes γ-ray a potential candidate for treating a large quantity of wastewater. Due to relatively low boiling point (82.4 C) of IPA, it can be separated from the waste water by distillation [20] or pervaporation [21,22]. For the past decade, pervaporation has been becoming a popular method; however, it is a complex process and is not easy to operate. The aim of this study was to investigate the possibility of using γ-ray to treat IPA wastewater in the presence and absence of H 2. The efficiency of γ-ray or H 2 alone and in combination (γ-ray/h 2 process) in decomposing IPA was examined and the effect of free radicals in the γ-ray/h 2 process was also explored. 1. Materials EXPERIMENTAL METHODS AND MATERIALS All chemicals were of analytical or reagent grade from several suppliers and were used as received. Hydrogen peroxide (30 wt%, Merck) was standardized using iodometric titration. IPA and sodium thiosulfate were all purchased from Aldrich. All reaction solutions were prepared using double deionized water ( 18 MΩ cm) with a Milli-ultrapure R/O system (Millipore). The γ-rays were generated using the Co-60 irradiator at National Tsing-Hua University, Taiwan. Irradiation dose rates were determined by comparison to Fricke ferrous sulfate dosimeter [23]. 2.Procedure This study comprised two parts. In the first part, the IPA analytic method, chromatography and calibration were conducted, and the detection limits were also determined. In the second part, radiolysis using γ- ray or H 2 alone, and in combination was carried out to treat IPA. In the IPA basic analysis method, two calibration lines, 0-50 and ppm, were constructed using low and high IPA concentrations with five different concentration points for each calibration line. Solid phase micro-extraction was employed in the subsequent analysis and chromatography, in which polydimethylsiloxane/divinylbenzene (Supelco) was used to perform headspace sampling. The protocol was modified from the methods described by the Taiwan EPA (NIEA W788.50B) [24]. The gas chromatography with flame ionization detector (Agilent 6280) and DB- WAX chromatography columns (30 m 0.53 mm 1.0 μm; Supelco) were used for the analysis. The maximum legal IPA concentration in wastewater effluent had not been established in Taiwan. To simulate the real situation in γ-ray/h 2 radiolysis experiments, the -0 ppm value range was used in the experiments based on the statistic data released by the Hsin-Chu Science Park Administration in Taiwan. Batch reactions were conducted in the following experiments. A background test H 2 oxidation reaction,, 0 and 200 ppm IPA were added into 2.5, and 20 ppm H 2 for different reaction times up to 3 h without any light source. Results in the H 2 oxidation tests on IPA were evaluated. The background test of radiation decomposition was utilized a Co-60 γ-source at National Tsing-Hua University, Taiwan. Irradiation dose rates of Gy h -1 were used. When the 200 ppm IPA concentration was selected to simulate the special condition in general effluent, an irradiation high dose rate of 472 Gy h -1 was used. The radiolysis effect of γ-rays combined with H 2 to degrade IPA was evaluated with the same irradiated dosage and experimental procedure. All of the above parameters and experimental conditions are listed in Table 1. The influences and differences among the oxidation reaction, radiolysis effect and free radical effect were compared and discussed. Table 1. The IPA residues after H 2 oxidation treatment IPA Concentration H 2 Concentration Irradiation time (min)/ipa Residual percentage (%)

3 Cheng et al.: Decomposition of Wastewater Using γ-ray/h Degradation efficiency (%) ppm IPA 0 ppm IPA ppm IPA Degradation efficiency (%) ppm IPA (69 Gy h -1 ) 0 ppm IPA (69 Gy h -1 ) ppm IPA (69 Gy h -1 ) 200 ppm IPA (222 Gy h -1 ) 0 ppm IPA (222 Gy h -1 ) ppm IPA (222 Gy h -1 ) Irradiation time (min) Fig. 1. Isopropyl alcohol and hydrogen peroxide (20 ppm) reaction. 3. Quality Control All samples were collected in duplicate with control samples included for all-target analyses. The analytical method incorporated internal standard and quantification was based on response factors established by multi-level calibration with enhancing samples analyzed under identical conditions. RESULTS AND DISCUSSION 1. H2O2 Background Test Three concentrations (, 0 and 200 ppm) of IPA were placed in a brown glass bottle, where 2.5, and 20 ppm of H 2 with the same volume as IPA were added to react with IPA in the dark for 180 min. This was followed with the addition of sodium thiosulfate to terminate the reaction. H 2 was not effective in IPA decomposition, as shown in Table 1. Regardless of the amount of H 2, the IPA decomposition for the three H 2 concentrations was similar. This means that the H 2 oxidation capacity in a certain concentration range was not great enough to destroy the IPA structure completely. For example, In the case of 200 ppm IPA, the decomposition ratio was only 11% at the highest concentration 20 ppm H 2 (Fig. 1). The lowest concentration ( ppm) of IPA had a better removal efficiency at 30% Irradiation time (min) Fig. 2. The Irradiation dose effect on IPA decomposition with γ-rays. 2. γ -ray Irradiation Background Test Three concentrations, 200, 0 and ppm, of IPA were placed in sample bottles and irradiated using 69, 111, 138 and 222 Gy h -1 of γ-rays generated using Co-60 without H 2. The unusual effluent concentration of 200 ppm IPA was irradiated using an additional dose rate of 472 Gy h -1 of γ-ray. The IPA removal efficiency was evaluated after the irradiations for 1 h under different doses of γ-rays (Table 2). It is shown that the γ-ray was more efficient in lowering the IPA concentration ( ppm). The γ-rays at 222 Gy h -1 could achieve 49% IPA removal after 1 h. There was less than 15% removal efficiency for the higher IPA concentrations (200 and 0 ppm). The results indicate that single γ-ray irradiation is also not suitable for IPA treatment. Figure 2 also shows the reaction time had no effect on IPA making it useless to extend the reaction time to treat IPA wastewater with γ- ray irradiation. 3. Radiolysis of γ -ray/h 2O2 Process The IPA with 200, 0 or ppm of was added to 20, or 2.5 ppm of H 2 respectively in equal volumes, followed by γ-ray irradiation generated using Co-60. The other conditions were identical to those in previous experiments. Sodium thiosulfate was added to terminate the reaction after the irradiation. Radiolysis of water results in the formation of Table 2. The IPA residues after 1 h γ-ray irradiation γ-ray irradiation dose rate (Gy h -1 )/Residual Percentage (%) IPA Concentration

4 154 J. Environ. Eng. Manage., 20(3), (20) Table 3. The IPA residues after 1 h γ-ray/h 2 radiolytic processes IPA Concentration H Irradiation dose rate (Gy h -1 2 Concentration )/Residual percentage (%) Degradation efficiency (%) Reaction time (min) 200 ppm IPA + 0 ppm H ppm IPA + 20 ppm H 2 0 ppm IPA + 0 ppm H 2 0 ppm IPA + 20 ppm H 2 ppm IPA + 0 ppm H 2 ppm IPA + 20 ppm H 2 Fig. 3. The degradation efficiency of IPA under the γ- ray/h 2 radiolytic process at 222 Gy h -1. the following species [25]: H 2 O [2.8] - OH + [2.7]e aq + [0.6]H + [0.7]H 2 + [2.6]H + + [0.45]H 2 where the numbers in brackets [G-values] indicate the relative number of each species formed per 0 ev absorbed energy. These reactive species/radicals then react among themselves and with other ions and solutes present in water. The combination of γ-ray and H 2 demonstrated great effects on IPA decomposition (Table 3). For the same IPA dosage the higher added H 2 concentration produced higher IPA removal efficiency. The H 2 absorbs higher energy γ- rays and produces OH and hydrated electrons (e aq - ) species through dissociation. Hydroxyl radicals are powerful oxidant that is more reactive [26] and less selective in abstraction reactions from C-H bonds. Hydrated electrons act as a nucleophile in its reactions with organic molecules with more positive reduction potential. For the above reasons, hydroxyl radicals additionally produced from H 2 decomposition play a dominant role in the synergistic effect of the combined γ-rays/h 2. The higher γ-ray irradiation dose has higher removal efficiency due to the fact that it induces more OH, e aq - and high energy species. As discussed before, the single H 2 oxidation process or γ-ray irradiation alone could not produce more efficient destruction. However, the combined radiolytic γ-ray/h 2 process could easily decompose IPA and the removal efficiency had positive relationship with the irradiation dose. Under 472 Gy h -1 γ-ray irradiation for 1 h and 20 ppm H 2 added, the residual percentage of 200 ppm IPA could further descend to 28%. The IPA concentration investigation results indicated that the lower IPA concentration could present a good treatment goal and overall, the γ-ray/h 2 radiolysis process effect was better than that from the other two methods (Fig. 3). Under the 222 Gy h -1 dose of γ- ray irradiation for 1 h and 20 ppm H 2, the residual percentage of 200 ppm IPA was about 45%, the residual percentage of 0 ppm IPA was about 23% and the residual percentage of ppm IPA was only about 5%. The time effect is also shown in Fig. 3 with 20 ppm H 2 and 222 Gy h -1 of γ-ray irradiation for 2 h. The result was more correlated to the γ-ray/h 2 radiolysis process than using only IPA without added H 2. The combination of γ-ray and H 2 demonstrated the less H 2 consumption, the reduction in treatment time and the higher capability of wastewater treatment and water recovery would help the cost of such technology to decline to a level that makes it affordable and economically attractive. The residual percentage of Irradiated IPA ( ppm) was near 5% before they are analyzed. The reaction tendency for different IPA concentrations was also similar. CONCLUSIONS Wastewater containing IPA is difficult to be decomposed using conventional treatment processes. Radiation technology, as an advanced oxidation process, has been recognized as a promising process for IPA and other hazardous organic wastewater treatment. This study used three methods, H 2 oxidation, γ-ray irradiation and combined γ-ray/h 2 radiolysis process, to decompose IPA. The result showed that the γ-ray/h 2 process was better than the others. This is because of the effect of free radicals and other high energy products. In the reaction parameter investigation, the lower IPA concentration exhibited significant removal efficiency with similar tendencies in all three tested processes. The higher H 2 dose, higher γ-ray irradiation and longer reaction time did not significantly increase the removal efficiency at higher IPA concentrations using the H 2 oxidation or γ-ray irradiation process alone. On the other hand, the com-

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