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Sono-sorption as a new method for the removal of methylene blue from aqueous solution
Ultrasonics Sonochemistry 14 (2007) 599–604 www.elsevier.com/locate/ultsonch
Sono-sorption as a new method for the removal of methylene blue from aqueous solution M.H. Entezari *, Z. Sharif Al-Hoseini Department of Chemistry, Ferdowsi University of Mashhad, 91775 Mashhad, Khorassan, Iran Received 28 June 2006; received in revised form 17 October 2006; accepted 22 October 2006 Available online 5 December 2006
Abstract The sorption of methylene blue as a basic dye onto cellulosic materials such as waste newspaper was examined kinetically in the presence of ultrasound (sono-sorption) and in its absence (conventional method). The effects of various experimental parameters such as the amount of sorbent, type of cellulosic sorbents, initial dye concentration, temperature, and contact time have been investigated using a batch sorption technique. The information obtained can be used for treating effluents from the dye industry which deals with this kind of dye. The results show that as the amount of sorbent is increased, the dye removal in conventional method increases accordingly. In case of sono-sorption, it was stopped at specific amount of sorbent. More than 98% removal of the dye could be achieved in a very short period of time of sonication with respect to the conventional method. This behavior is related to the cavitation process which facilitates the removal of dye from aqueous solution. The method mentioned could be employed as a low cost alternative to the commercial activated carbon currently used in wastewater treatment for the removal of dyes. 2006 Elsevier B.V. All rights reserved. Keywords: Sono-sorption; Methylene blue; Cellulosic materials; Cavitation
1. Introduction Dyes and pigments are one of the problematic groups of pollutants. They are discharged from various industries such as dyestuff manufacturing, dyeing, printing, and textile finishing. These waste materials usually require especial treatment before being released to the environment. Most of the dyes are stable against photo-degradation, bio-degradation, and oxidizing agents [1]. From an environmental point of view, the synthetic dyes are of great concern due to the toxic and carcinogenics properties of some of them. Therefore, their removal from the aquatic environment is crucial. Several methods have been used for the removal of dyes from effluents, including physical, chemical, and biological processes. These methods are based on the decolorization by oxidation processes [2], photo-decomposi-
*
Corresponding author. Tel.: +98 511 8795457; fax: +98 511 8795560. E-mail address: [email protected] (M.H. Entezari).
1350-4177/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2006.10.004
tion [2,3], microbiological [2,4,5] and electrochemical decomposition [5,6] and adsorption [7–16]. Some of these methods especially have been applied for the removal of methylene blue from aqueous solutions [17–32]. However, these processes are costly and cannot effectively be used to treat the wide range of dye wastewater. Activated carbon (powdered or granular) is the most widely used sorbent which was successfully tested for the removal of dye from water [33] but, high operating costs and problems with regeneration hamper its large scale application. The use of ultrasound in degradation of dyes and other pollutants has developed in recent decades [34–39]. Acoustic cavitation derived from ultrasonic irradiation of a liquid provides unusual and unique conditions which are different from those of conventional methods. Combination of different advanced oxidation processes have recently been exploited for environmental detoxification and especially for wastewater treatment. In this regard, ultrasonic waves in conjunction with other techniques such as UV irradiation, ozonation and chemical oxidation increase the
M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604
decomposition efficiency and reduce the time required for removing the pollutants [40]. Sonochemical engineering of solid–liquid processes is an emerging field in environmental processes for removing of different pollutants [41–45]. The solid phase as a sorbent used in this work was cellulosic materials such as newspaper, white cardboard (used for boxes), white notebook paper (used for writing), printing paper (used as rolled paper in printer) and copy paper (Copimax A4). Most experiments were carried out with newspaper as a waste material. The basic ingredients that make up the cellulosic materials are cellulose, hemi-cellulose, lignin, and additives. The percentage of components is different from one kind to another one. The chemical composition is related to the chemical treatment applied on the wood for preparation of paste. In the case of newspaper, the chemical treatment is negligible and therefore the composition of the newspaper is approximately the same as the wood. It means that it contains cellulose (39–41%), hemi-cellulose (30–37%), lignin (20–27%), and other chemicals (2–4%). In other kinds of cellulosic materials, by chemical treatment reduces the amount of lignin and therefore the percent of cellulose is increased and this lead to the higher quality of the product which is related to the amount of lignin reduction [46]. The purpose of this study is to investigate the combination of ultrasound and cellulosic sorbent as a new method for the removal of methylene blue from aqueous solution and compare it with the sorption process without ultrasound. 2. Experimental 2.1. Material Methylene blue was obtained from Merck and used without further purification. A stock solution of the dye was prepared by dissolving the dye in twice distilled water. The sorbent used in this work was a waste newspaper. It was cut to small pieces of about 4–5 mm diameter.
were made at a wavelength of 664 nm, which corresponds to the maximum absorbance. The calibration curve was linear in the range studied. 2.4. Procedure The ultrasonic intensity was measured by a calorimetric method and was 33 W/cm2. The experiments were carried out in a 50 ml aqueous solution containing 50 mg/l methylene blue and the temperature was controlled at 30 C by a circulating bath, except in experiments in which the effect of temperature was investigated. The sorbent was added to the solution (0.3 g) and simultaneously the ultrasonic power was turned on. At selected intervals, samples were withdrawn, filtered, and analyzed. De-colorization experiments were classically carried out under the same conditions and mixed by a stirrer at 700 rpm. 3. Results and discussion 3.1. Effects of amount of sorbent The sorption of methylene blue on waste newspaper was studied by changing the amount of sorbent in aqueous solution while the initial dye concentration (50 mg/l) and the other variables were kept constant. In the conventional method sorption increased with increasing the amount of sorbent, it was very fast in the range of 0.1–0.4 g/50 ml but above this range the increase of sorption was negligible (Fig. 1, part A). The enhancement of sorption with higher amount of sorbent can be attributed to the increased surface area of sorbent and availability of more sorption sites. In the case of sono-sorption as is shown in Fig. 1 (parts A&B), a suitable amount of sorbent under the same conditions of conventional method was 0.3 g/50 ml; beyond that, there was no more sorption which is due to the almost com25
20
Concen. of dye ( ppm )
2.2. Apparatus The ultrasonic irradiation was carried out with equipment operating at 20 kHz (Sonifier W-450D). Waves were emitted from the bottom of the standard tip which immersed into the solution. The cylindrical sonochemical reactor (volume = 125 ml) was temperature controlled by the use of a water jacket.
1.4 Concen. of dye ( ppm )
600
15
1.2 1.0 0.8 0.6 0.0
10
B 0.1 0.2 0.3 0.4 0.5 Amount of sorbent ( g/50 ml )
0.6
5
0
2.3. Analysis The concentration of the dye was measured using a double beam UV–vis spectrophotometer (Agilen 8453) through a 1 cm path length. The degree of de-colorization was assessed by relating the amount of absorption in time to the original absorption at time zero. The measurements
A 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Amount of sorbent ( g/50ml )
Fig. 1. Effect of amount of sorbent on the reduction of dye concentration. (A) C0 = 50 ppm, temp. = 30 C, time = 10 min; j, ultrasound; h, classic and (B) curve of sonication on an enlarged scale j, ultrasound.
M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604 51 50
Concen. of dye ( ppm )
plete removal of the dye from solution and the remaining dye concentration was negligible. This behavior could be related to the cavitation process. Microjets and shockwaves produced by the cavitation can disrupt the texture of the waste newspaper and lead to a higher surface area. Therefore, lower sorbent in the presence of ultrasound is required for almost complete removal of the dye and the rate of removal was also faster in sono-sorption. Therefore 0.3 g of waste newspaper was chosen as an optimum amount for the latter experiments.
601
49 48 47 46 45
3.2. Effects of contact time and temperature
44
Fig. 2 presents the removal of methylene blue as a function of time at different temperatures. The effect of temperature in the range studied was negligible in both methods. As it is known the rate of diffusion of the sorbate molecule is increased by increasing the temperature, owing to the decrease in the viscosity of the solution. The negligible effect of temperature could be attributed to the sorption itself which is a determining step than diffusion process. As it is shown in Fig. 2, the dye sorption in the conventional method reached equilibrium in about 30 min while, in the presence of ultrasound this time reduced to about 5 min. The rate of removal was also faster in the presence of ultrasound. The shorter time to reach equilibrium and the faster rate of removal in the presence of ultrasound was attributed to the higher mass transfer and higher surface area produced by the cavitation process. Fig. 3 presented the removal of methylene blue by ultrasound without sorbent. As it was shown, ultrasonic waves can reduce the concentration of methylene blue up to about 10% in 30 min. The phenomenon responsible for this reduction is the formation of hydroxyl radical during sonication of aqueous solution by the cavitation process. This process consists of the formation, growth and collapse by
0
5
10
15
20
25
30
35
Time ( min. )
Fig. 3. Effect of sonication time on the dye removal in absence of sorbent (C0 = 50 ppm, temp. = 30 C).
violent implosions to release extreme temperatures and pressures at local hot spots in the liquid. Under these critical conditions, the entrapped molecules of water in the bubble dissociate into very reactive hydroxyl and hydrogen radicals. Therefore, less than 2% was decomposed by ultrasound alone in 5 min of sonication while nearly 96% was removed by the combined sono-sorption method. 3.3. Effect of initial dye concentration Experiments were conducted for 10 min of sonication by varying the methylene blue concentration (25–100 ppm) with constant amount of sorbent (0.3 g/50 ml) at 30 C. Fig. 4 shows that the percent removal decreased with increase in dye concentration. This could be related to the ratio of sorbate to sorbent which is important in sonication. The sorbent used (0.3 g) was optimized for the concentration of 50 ppm of methylene blue. With constant the
60 100
98 40
Removal of dye ( % )
Concen. of dye ( ppm )
50
30
20
10
96
94
92
0 0
10
20
30
40
50
Time ( min. )
Fig. 2. Effect of temperature on the dye removal versus contact time (C0 = 50 ppm, amount of sorbent = 0.3 g). j, 30 C (ultrasound); h, 30 C (classic); d, 40 C (ultrasound); s, 40 C (classic); m, 55 C (ultrasound); n, 55 C (classic).
90 20
40
60
80
100
120
Concen. of dye ( ppm )
Fig. 4. Effect of initial concentration of methylene blue on its removal percent in the presence of ultrasound (sorbent = 0.3 g, temp. = 30 C, time = 10 min).
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M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604
amount of sorbent and increasing the amount of dye concentration, the ratio mentioned increased and therefore, the percent removal was reduced. In other words, when the amount of sorbent is constant it means that the number of sorption sites is constant. By increasing the amount of dye, the percent removal should decrease due to the limitation of the sorption sites. It should be mentioned that the actual amount of dye sorbed per unit mass of sorbent increased by the increase of dye concentration in the solution. According to the percent removal of Fig. 4, it is possible to calculate the amount of sorption per unit mass of sorbent in each concentration of dye. As the concentration of methylene blue in the solution was increased from 25 ppm to 100 ppm, the sorption was increased from 82.5 mg/g to 315 mg/g. This means that by increasing the concentration of pollutant to four fold, the amount of sorption was also increased to about 3.8 fold.
rials. The newspaper as a sorbent was better than the other kinds of cellulosic materials for the removal of methylene blue from aqueous solution in point of economic and efficiency of removal. Higher efficiency in this case may be related to the higher amount of lignin which facilitates more destruction of newspaper with respect to the other cellulosic materials and produces more surface area for sorption process.
3.4. Effect of type of sorbent
where qe is the amount of solute sorbed per unit weight of sorbate at equilibrium (mg/g), ce is the equilibrium concentration of the sorbate in solution (mg/l), qm and b are the Langmuir constants related to the maximum capacity of sorption corresponding to complete coverage of available sorption sites and energy of sorption, respectively. According to Fig. 6 when 1/qe is plotted against 1/ce, straight lines with the slope of 1/bqm are obtained, which showed that the sorption of methylene blue is consistent with the Langmuir isotherm. The Langmuir constants, b and qm, were derived from Fig. 6 and the values are given in Table 1. As shown in this table, the maximum capacity is higher in the presence of
The Langmuir isotherm as an important model has been used for the sorption of variety of compounds. The linear form of Langmuir model is presented by the following equation: 1 1 1 ¼ þ qe qm bqm ce
0.07
0.06
0.05
1/qe
There are different cellulosic paper materials. The composition and the additives during the production process are different in these kinds of cellulosic materials. Therefore, some experiments were designed to check the extent of affects on the rate of removal of methylene blue from aqueous solution by changing the type of cellulosic materials. Fig. 5 presents the effect mentioned in the presence of ultrasound and in its absence. As it was shown, the rate and the yield of removal were higher in the presence of ultrasound for all kinds of sorbents used in comparison with conventional method. This could be related to the destruction of sorbent texture and to the increase of mass transfer in the presence of ultrasound by asymmetric collapse of cavitation which led to shock waves and production of microjets in the solution. In addition, different cellulosic materials have different porosity which is important in sorption process. This is mostly due to the different composition and manufacture processes of cellulosic mate-
3.5. Sorption isotherm
0.04
60
0.03
50
0.02
40
0.01 0.00
0.05
0.10
0.15
0.20
1/ce 30
Fig. 6. Langmuir sorption isotherm of methylene blue (temp. = 30 C, sorbent = 0.3 g) j, ultrasound; h, classic.
20
10
Table 1 Constants of Langmuir sorption isotherm of methylene blue
0
Copy paper
Printing paper Cardboard Notebook paper News paper
Ultrasound qm (mg/g)
Fig. 5. Effect of type of sorbent on the dye removal (C0 = 50 ppm, sorbent = 0.3 g, temp. = 30 C, time = 5 min) j, ultrasound; h, classic.
611
Classic b (l/mg) 3
5.6 · 10
R2 0.99
qm (mg/g) 59
b (l/mg) 3.7 · 10
2
R2 0.97
M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604
ultrasound than in the conventional method. This indicated that under sonication, new sites of sorption were appeared by disruption of sorbent particles. 4. Conclusion The removal of methylene blue from synthetic wastewater by the batch system has been investigated under different experimental conditions in the presence and absence of ultrasound. Newspaper as a waste material could be appropriate sorbent for the fast and effective removal of methylene blue from aqueous solution in comparison to the other cellulosic sorbent materials. This removal was faster and more efficient in the presence of ultrasound due to the cavitation process which facilitated the mass transfer and increased the surface area of the sorbent. The sorption data was fitted properly to the Langmuir model and led to determine the maximum sorption capacity. The higher capacity of sorbent and faster removal of methylene blue in the presence of ultrasound indicated that such sorbent could be employed as low cost alternatives to commercial activated carbon in wastewater treatment for the removal of color and dyes. This is due to the use of an inexpensive sorbent and a short period of time of sonication. In addition, the sorbent does not require an additional pretreatment step such as activation before its application. References [1] K.R. Ramakrishna, T.V. Viraraghavan, Dye removal using low cost adsorbents, Water Science and Technology 36 (1997) 189–196. [2] E. Forgacs, T. Csehati, G. Oros, Removal of synthetic dyes from wastewaters: a review, Environment International 30 (2004) 953–971. [3] H. Chun, W. Yizhong, Decolorization and biodegradability of photocatalytic treated azo dyes and wool textile wastewater, Chemosphere 21 (1999) 2107–2115. [4] C.I. Pearce, J.R. Lloyd, J.T. Guthrie, The removal of colour from textile wastewater using whole bacterial cells: a review, Dyes and Pigments 58 (2003) 179–196. [5] C.C.I. Guarantini, M.V.B. Zanoni, Corantes Texteis, Quimica Nova 23 (2000) 71–78. [6] A.G. Vlyssides, M. Loizidou, P.K. Karlis, A.A. Zorpas, D. Papaioannou, Electrochemical oxidation of a textile dye wastewater using a Pt/Ti electrode, Journal of Hazardous Materials B70 (1999) 41–52. [7] Y. Al-Degs, M.A.M. Khraisheh, S.J. Allen, M.N. Ahmad, Effect of carbon surface chemistry on the removal of reactive dyes from textile effluent, Water Research 34 (2000) 927–935. [8] W. Chu, Dye removal from textile dye wastewater using recycled alum sludge, Water Research 35 (2001) 3147–3152. [9] S. Karcher, A. Kornmuller, M. Jekel, Screening of commercial sorbents for the removal of reactive dyes, Dyes and Pigments 51 (2001) 111–125. [10] S. Karcher, A. Kornmuller, M. Jekel, Anion exchange resins for removal of reactive dyes from textile wastewater, Water Research 36 (2002) 4717–4724. [11] M.A. Al-Ghouti, M.A.M. Kraisheh, S.J. Allen, M.N. Ahmad, The removal of dyes from textile wastewater: a study of physical characteristics and adsorption mechanisms of diatomaceous earth, Journal of Environmental Management 69 (2003) 229–238. [12] G. Atun, G. Hisarli, W.S. Sheldrich, M. Muhler, Adsorptive removal of methylene blue from colored effluents on fuller’s earth, Journal of Colloid and Interface Science 261 (2003) 32–39.
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Sono-sorption as a new method for the removal of methylene blue from aqueous solution M.H. Entezari *, Z. Sharif Al-Hoseini Department of Chemistry, Ferdowsi University of Mashhad, 91775 Mashhad, Khorassan, Iran Received 28 June 2006; received in revised form 17 October 2006; accepted 22 October 2006 Available online 5 December 2006
Abstract The sorption of methylene blue as a basic dye onto cellulosic materials such as waste newspaper was examined kinetically in the presence of ultrasound (sono-sorption) and in its absence (conventional method). The effects of various experimental parameters such as the amount of sorbent, type of cellulosic sorbents, initial dye concentration, temperature, and contact time have been investigated using a batch sorption technique. The information obtained can be used for treating effluents from the dye industry which deals with this kind of dye. The results show that as the amount of sorbent is increased, the dye removal in conventional method increases accordingly. In case of sono-sorption, it was stopped at specific amount of sorbent. More than 98% removal of the dye could be achieved in a very short period of time of sonication with respect to the conventional method. This behavior is related to the cavitation process which facilitates the removal of dye from aqueous solution. The method mentioned could be employed as a low cost alternative to the commercial activated carbon currently used in wastewater treatment for the removal of dyes. 2006 Elsevier B.V. All rights reserved. Keywords: Sono-sorption; Methylene blue; Cellulosic materials; Cavitation
1. Introduction Dyes and pigments are one of the problematic groups of pollutants. They are discharged from various industries such as dyestuff manufacturing, dyeing, printing, and textile finishing. These waste materials usually require especial treatment before being released to the environment. Most of the dyes are stable against photo-degradation, bio-degradation, and oxidizing agents [1]. From an environmental point of view, the synthetic dyes are of great concern due to the toxic and carcinogenics properties of some of them. Therefore, their removal from the aquatic environment is crucial. Several methods have been used for the removal of dyes from effluents, including physical, chemical, and biological processes. These methods are based on the decolorization by oxidation processes [2], photo-decomposi-
*
Corresponding author. Tel.: +98 511 8795457; fax: +98 511 8795560. E-mail address: [email protected] (M.H. Entezari).
1350-4177/$ - see front matter 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2006.10.004
tion [2,3], microbiological [2,4,5] and electrochemical decomposition [5,6] and adsorption [7–16]. Some of these methods especially have been applied for the removal of methylene blue from aqueous solutions [17–32]. However, these processes are costly and cannot effectively be used to treat the wide range of dye wastewater. Activated carbon (powdered or granular) is the most widely used sorbent which was successfully tested for the removal of dye from water [33] but, high operating costs and problems with regeneration hamper its large scale application. The use of ultrasound in degradation of dyes and other pollutants has developed in recent decades [34–39]. Acoustic cavitation derived from ultrasonic irradiation of a liquid provides unusual and unique conditions which are different from those of conventional methods. Combination of different advanced oxidation processes have recently been exploited for environmental detoxification and especially for wastewater treatment. In this regard, ultrasonic waves in conjunction with other techniques such as UV irradiation, ozonation and chemical oxidation increase the
M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604
decomposition efficiency and reduce the time required for removing the pollutants [40]. Sonochemical engineering of solid–liquid processes is an emerging field in environmental processes for removing of different pollutants [41–45]. The solid phase as a sorbent used in this work was cellulosic materials such as newspaper, white cardboard (used for boxes), white notebook paper (used for writing), printing paper (used as rolled paper in printer) and copy paper (Copimax A4). Most experiments were carried out with newspaper as a waste material. The basic ingredients that make up the cellulosic materials are cellulose, hemi-cellulose, lignin, and additives. The percentage of components is different from one kind to another one. The chemical composition is related to the chemical treatment applied on the wood for preparation of paste. In the case of newspaper, the chemical treatment is negligible and therefore the composition of the newspaper is approximately the same as the wood. It means that it contains cellulose (39–41%), hemi-cellulose (30–37%), lignin (20–27%), and other chemicals (2–4%). In other kinds of cellulosic materials, by chemical treatment reduces the amount of lignin and therefore the percent of cellulose is increased and this lead to the higher quality of the product which is related to the amount of lignin reduction [46]. The purpose of this study is to investigate the combination of ultrasound and cellulosic sorbent as a new method for the removal of methylene blue from aqueous solution and compare it with the sorption process without ultrasound. 2. Experimental 2.1. Material Methylene blue was obtained from Merck and used without further purification. A stock solution of the dye was prepared by dissolving the dye in twice distilled water. The sorbent used in this work was a waste newspaper. It was cut to small pieces of about 4–5 mm diameter.
were made at a wavelength of 664 nm, which corresponds to the maximum absorbance. The calibration curve was linear in the range studied. 2.4. Procedure The ultrasonic intensity was measured by a calorimetric method and was 33 W/cm2. The experiments were carried out in a 50 ml aqueous solution containing 50 mg/l methylene blue and the temperature was controlled at 30 C by a circulating bath, except in experiments in which the effect of temperature was investigated. The sorbent was added to the solution (0.3 g) and simultaneously the ultrasonic power was turned on. At selected intervals, samples were withdrawn, filtered, and analyzed. De-colorization experiments were classically carried out under the same conditions and mixed by a stirrer at 700 rpm. 3. Results and discussion 3.1. Effects of amount of sorbent The sorption of methylene blue on waste newspaper was studied by changing the amount of sorbent in aqueous solution while the initial dye concentration (50 mg/l) and the other variables were kept constant. In the conventional method sorption increased with increasing the amount of sorbent, it was very fast in the range of 0.1–0.4 g/50 ml but above this range the increase of sorption was negligible (Fig. 1, part A). The enhancement of sorption with higher amount of sorbent can be attributed to the increased surface area of sorbent and availability of more sorption sites. In the case of sono-sorption as is shown in Fig. 1 (parts A&B), a suitable amount of sorbent under the same conditions of conventional method was 0.3 g/50 ml; beyond that, there was no more sorption which is due to the almost com25
20
Concen. of dye ( ppm )
2.2. Apparatus The ultrasonic irradiation was carried out with equipment operating at 20 kHz (Sonifier W-450D). Waves were emitted from the bottom of the standard tip which immersed into the solution. The cylindrical sonochemical reactor (volume = 125 ml) was temperature controlled by the use of a water jacket.
1.4 Concen. of dye ( ppm )
600
15
1.2 1.0 0.8 0.6 0.0
10
B 0.1 0.2 0.3 0.4 0.5 Amount of sorbent ( g/50 ml )
0.6
5
0
2.3. Analysis The concentration of the dye was measured using a double beam UV–vis spectrophotometer (Agilen 8453) through a 1 cm path length. The degree of de-colorization was assessed by relating the amount of absorption in time to the original absorption at time zero. The measurements
A 0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Amount of sorbent ( g/50ml )
Fig. 1. Effect of amount of sorbent on the reduction of dye concentration. (A) C0 = 50 ppm, temp. = 30 C, time = 10 min; j, ultrasound; h, classic and (B) curve of sonication on an enlarged scale j, ultrasound.
M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604 51 50
Concen. of dye ( ppm )
plete removal of the dye from solution and the remaining dye concentration was negligible. This behavior could be related to the cavitation process. Microjets and shockwaves produced by the cavitation can disrupt the texture of the waste newspaper and lead to a higher surface area. Therefore, lower sorbent in the presence of ultrasound is required for almost complete removal of the dye and the rate of removal was also faster in sono-sorption. Therefore 0.3 g of waste newspaper was chosen as an optimum amount for the latter experiments.
601
49 48 47 46 45
3.2. Effects of contact time and temperature
44
Fig. 2 presents the removal of methylene blue as a function of time at different temperatures. The effect of temperature in the range studied was negligible in both methods. As it is known the rate of diffusion of the sorbate molecule is increased by increasing the temperature, owing to the decrease in the viscosity of the solution. The negligible effect of temperature could be attributed to the sorption itself which is a determining step than diffusion process. As it is shown in Fig. 2, the dye sorption in the conventional method reached equilibrium in about 30 min while, in the presence of ultrasound this time reduced to about 5 min. The rate of removal was also faster in the presence of ultrasound. The shorter time to reach equilibrium and the faster rate of removal in the presence of ultrasound was attributed to the higher mass transfer and higher surface area produced by the cavitation process. Fig. 3 presented the removal of methylene blue by ultrasound without sorbent. As it was shown, ultrasonic waves can reduce the concentration of methylene blue up to about 10% in 30 min. The phenomenon responsible for this reduction is the formation of hydroxyl radical during sonication of aqueous solution by the cavitation process. This process consists of the formation, growth and collapse by
0
5
10
15
20
25
30
35
Time ( min. )
Fig. 3. Effect of sonication time on the dye removal in absence of sorbent (C0 = 50 ppm, temp. = 30 C).
violent implosions to release extreme temperatures and pressures at local hot spots in the liquid. Under these critical conditions, the entrapped molecules of water in the bubble dissociate into very reactive hydroxyl and hydrogen radicals. Therefore, less than 2% was decomposed by ultrasound alone in 5 min of sonication while nearly 96% was removed by the combined sono-sorption method. 3.3. Effect of initial dye concentration Experiments were conducted for 10 min of sonication by varying the methylene blue concentration (25–100 ppm) with constant amount of sorbent (0.3 g/50 ml) at 30 C. Fig. 4 shows that the percent removal decreased with increase in dye concentration. This could be related to the ratio of sorbate to sorbent which is important in sonication. The sorbent used (0.3 g) was optimized for the concentration of 50 ppm of methylene blue. With constant the
60 100
98 40
Removal of dye ( % )
Concen. of dye ( ppm )
50
30
20
10
96
94
92
0 0
10
20
30
40
50
Time ( min. )
Fig. 2. Effect of temperature on the dye removal versus contact time (C0 = 50 ppm, amount of sorbent = 0.3 g). j, 30 C (ultrasound); h, 30 C (classic); d, 40 C (ultrasound); s, 40 C (classic); m, 55 C (ultrasound); n, 55 C (classic).
90 20
40
60
80
100
120
Concen. of dye ( ppm )
Fig. 4. Effect of initial concentration of methylene blue on its removal percent in the presence of ultrasound (sorbent = 0.3 g, temp. = 30 C, time = 10 min).
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amount of sorbent and increasing the amount of dye concentration, the ratio mentioned increased and therefore, the percent removal was reduced. In other words, when the amount of sorbent is constant it means that the number of sorption sites is constant. By increasing the amount of dye, the percent removal should decrease due to the limitation of the sorption sites. It should be mentioned that the actual amount of dye sorbed per unit mass of sorbent increased by the increase of dye concentration in the solution. According to the percent removal of Fig. 4, it is possible to calculate the amount of sorption per unit mass of sorbent in each concentration of dye. As the concentration of methylene blue in the solution was increased from 25 ppm to 100 ppm, the sorption was increased from 82.5 mg/g to 315 mg/g. This means that by increasing the concentration of pollutant to four fold, the amount of sorption was also increased to about 3.8 fold.
rials. The newspaper as a sorbent was better than the other kinds of cellulosic materials for the removal of methylene blue from aqueous solution in point of economic and efficiency of removal. Higher efficiency in this case may be related to the higher amount of lignin which facilitates more destruction of newspaper with respect to the other cellulosic materials and produces more surface area for sorption process.
3.4. Effect of type of sorbent
where qe is the amount of solute sorbed per unit weight of sorbate at equilibrium (mg/g), ce is the equilibrium concentration of the sorbate in solution (mg/l), qm and b are the Langmuir constants related to the maximum capacity of sorption corresponding to complete coverage of available sorption sites and energy of sorption, respectively. According to Fig. 6 when 1/qe is plotted against 1/ce, straight lines with the slope of 1/bqm are obtained, which showed that the sorption of methylene blue is consistent with the Langmuir isotherm. The Langmuir constants, b and qm, were derived from Fig. 6 and the values are given in Table 1. As shown in this table, the maximum capacity is higher in the presence of
The Langmuir isotherm as an important model has been used for the sorption of variety of compounds. The linear form of Langmuir model is presented by the following equation: 1 1 1 ¼ þ qe qm bqm ce
0.07
0.06
0.05
1/qe
There are different cellulosic paper materials. The composition and the additives during the production process are different in these kinds of cellulosic materials. Therefore, some experiments were designed to check the extent of affects on the rate of removal of methylene blue from aqueous solution by changing the type of cellulosic materials. Fig. 5 presents the effect mentioned in the presence of ultrasound and in its absence. As it was shown, the rate and the yield of removal were higher in the presence of ultrasound for all kinds of sorbents used in comparison with conventional method. This could be related to the destruction of sorbent texture and to the increase of mass transfer in the presence of ultrasound by asymmetric collapse of cavitation which led to shock waves and production of microjets in the solution. In addition, different cellulosic materials have different porosity which is important in sorption process. This is mostly due to the different composition and manufacture processes of cellulosic mate-
3.5. Sorption isotherm
0.04
60
0.03
50
0.02
40
0.01 0.00
0.05
0.10
0.15
0.20
1/ce 30
Fig. 6. Langmuir sorption isotherm of methylene blue (temp. = 30 C, sorbent = 0.3 g) j, ultrasound; h, classic.
20
10
Table 1 Constants of Langmuir sorption isotherm of methylene blue
0
Copy paper
Printing paper Cardboard Notebook paper News paper
Ultrasound qm (mg/g)
Fig. 5. Effect of type of sorbent on the dye removal (C0 = 50 ppm, sorbent = 0.3 g, temp. = 30 C, time = 5 min) j, ultrasound; h, classic.
611
Classic b (l/mg) 3
5.6 · 10
R2 0.99
qm (mg/g) 59
b (l/mg) 3.7 · 10
2
R2 0.97
M.H. Entezari, Z. Sharif Al-Hoseini / Ultrasonics Sonochemistry 14 (2007) 599–604
ultrasound than in the conventional method. This indicated that under sonication, new sites of sorption were appeared by disruption of sorbent particles. 4. Conclusion The removal of methylene blue from synthetic wastewater by the batch system has been investigated under different experimental conditions in the presence and absence of ultrasound. Newspaper as a waste material could be appropriate sorbent for the fast and effective removal of methylene blue from aqueous solution in comparison to the other cellulosic sorbent materials. This removal was faster and more efficient in the presence of ultrasound due to the cavitation process which facilitated the mass transfer and increased the surface area of the sorbent. The sorption data was fitted properly to the Langmuir model and led to determine the maximum sorption capacity. The higher capacity of sorbent and faster removal of methylene blue in the presence of ultrasound indicated that such sorbent could be employed as low cost alternatives to commercial activated carbon in wastewater treatment for the removal of color and dyes. This is due to the use of an inexpensive sorbent and a short period of time of sonication. In addition, the sorbent does not require an additional pretreatment step such as activation before its application. References [1] K.R. Ramakrishna, T.V. Viraraghavan, Dye removal using low cost adsorbents, Water Science and Technology 36 (1997) 189–196. [2] E. Forgacs, T. Csehati, G. Oros, Removal of synthetic dyes from wastewaters: a review, Environment International 30 (2004) 953–971. [3] H. Chun, W. Yizhong, Decolorization and biodegradability of photocatalytic treated azo dyes and wool textile wastewater, Chemosphere 21 (1999) 2107–2115. [4] C.I. Pearce, J.R. Lloyd, J.T. Guthrie, The removal of colour from textile wastewater using whole bacterial cells: a review, Dyes and Pigments 58 (2003) 179–196. [5] C.C.I. Guarantini, M.V.B. Zanoni, Corantes Texteis, Quimica Nova 23 (2000) 71–78. [6] A.G. Vlyssides, M. Loizidou, P.K. Karlis, A.A. Zorpas, D. Papaioannou, Electrochemical oxidation of a textile dye wastewater using a Pt/Ti electrode, Journal of Hazardous Materials B70 (1999) 41–52. [7] Y. Al-Degs, M.A.M. Khraisheh, S.J. Allen, M.N. Ahmad, Effect of carbon surface chemistry on the removal of reactive dyes from textile effluent, Water Research 34 (2000) 927–935. [8] W. Chu, Dye removal from textile dye wastewater using recycled alum sludge, Water Research 35 (2001) 3147–3152. [9] S. Karcher, A. Kornmuller, M. Jekel, Screening of commercial sorbents for the removal of reactive dyes, Dyes and Pigments 51 (2001) 111–125. [10] S. Karcher, A. Kornmuller, M. Jekel, Anion exchange resins for removal of reactive dyes from textile wastewater, Water Research 36 (2002) 4717–4724. [11] M.A. Al-Ghouti, M.A.M. Kraisheh, S.J. Allen, M.N. Ahmad, The removal of dyes from textile wastewater: a study of physical characteristics and adsorption mechanisms of diatomaceous earth, Journal of Environmental Management 69 (2003) 229–238. [12] G. Atun, G. Hisarli, W.S. Sheldrich, M. Muhler, Adsorptive removal of methylene blue from colored effluents on fuller’s earth, Journal of Colloid and Interface Science 261 (2003) 32–39.
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