Chemical Product and ProcessModeling

Volume 4, Issue 4 2009 Article 8

CHEMPOR 2008

Application of Coagulation Systems Coupledwith Adsorption on Powdered ActivatedCarbon to Textile Wastewater Treatment

Franciele Regina Furlan∗ Laıs Graziela de Melo da Silva† Ayres Ferreira Morgado‡

Antonio Augusto Ulson de Souza∗∗ Selene Maria Arruda Guelli Ulson de Souza††

∗Federal University of Santa Catarina, franciele.furlan@karsten.com.br†Federal University of Santa Catarina, lais silva@msn.com‡Federal University of Santa Catarina, ayres@enq.ufsc.br

∗∗Federal University of Santa Catarina, augusto@enq.ufsc.br††Federal University of Santa Catarina, selene@enq.ufsc.br

Copyright c©2009 The Berkeley Electronic Press. All rights reserved.

Application of Coagulation Systems Coupledwith Adsorption on Powdered ActivatedCarbon to Textile Wastewater Treatment∗

Franciele Regina Furlan, Laıs Graziela de Melo da Silva, Ayres FerreiraMorgado, Antonio Augusto Ulson de Souza, and Selene Maria Arruda Guelli

Ulson de Souza

Abstract

The aim of the present study was to investigate the removal of reactive dyes, Black 5 andOrange 16, through a combined coagulation/adsorption process on activated carbon. A coconut-based powdered activated carbon was used as an adsorbent and aluminum chloride was chosenas the coagulant. In order to obtain the best removal conditions for these dyes, the influence ofthe following parameters were investigated: coagulant dosage, aqueous solution pH, addition ofsodium chloride and the application of increased temperature plus sodium chloride. Adsorptionresults for the reactive dyes were analyzed by Langmuir and Freundlich isotherm models andshowed good correlation. The presence of sodium chloride in the mixture resulted in significantadsorption improvement. The influence of increased temperature plus sodium chloride on the dyeremoval from aqueous solution showed the feasibility of adsorption and its endothermic nature.Through the reactivation experiments it was verified that the adsorbent can be reused three times,consecutively, after the first adsorption with the virgin carbon. For the final evaluation of theeffluent, obtained after the coagulation and adsorption process, acute toxicity tests were carriedout with Daphnia magna, and the results obtained showed that the final effluent was not toxic.The combined coagulation/adsorption process was found to be an excellent option for the removalof reactive dyes.

KEYWORDS: coagulation, adsorption, reactive dyes, aluminum chloride, reactivation

∗The authors are grateful to CAPES for the financial support given by way of the scholarship and toFINEP for financing the project INOTEXTIL, in partnership with the Brazilian textile companies:Buettner, Coteminas, Brandili and Tapajos.

1 Introduction The removal of dyes from industrial effluents is an extremely complex problem due to the different dye structures and properties and, more importantly, to the majority having a non biodegradable nature (Jain et al., 2002). However, many physical, chemical and biological treatment processes have been used for dye removal in order to achieve a better quality effluent. The choice of one or the combination of two or more techniques is dependent on the potential of each technique and on the mechanisms involved in the reduction of the contaminant of interest (Papic et al., 2004, Chakraborty et al., 2005, Solmaz et al., 2007). The adsorption of organic compounds on activated carbon is one of the most important technologies used for the treatment of industrial effluents. This adsorbent has a high surface area and a variety of functional groups at its surface (Duan et al., 2002, Guilarduci et al., 2006). Many of the materials present in a textile effluent cannot be removed by simple physical separation. In these cases, when the treatment is unsatisfactory, other processes are necessary (Tomaszewska et al., 2004). 2 Materials In this study, a synthetic wastewater was prepared to simulate the characteristics found in textile effluents, with the objective of controlling the effluent composition during the experimental investigation. Initially, a concentrated solution (2000 mg/L) was prepared from the mixture of the quantities of dyes established and distilled water. All the other solutions used experimentally were obtained through careful dilution of this solution. Next, the pH of the diluted solutions was adjusted with a pH meter to the levels selected with addition of NaOH and 0.1 M HCl. The experiments were carried out with two non-hydrolyzed reactive dyes, Black 5 (λ =598 nm) and Orange 16 (λ =491 nm). A coconut-based powdered activated carbon with a surface area of 734 m2/g was used as the adsorbent. Aluminum chloride (AlCl3.6H2O – 99.5 % purity) was used as the coagulant having a molecular mass of 241.43 g/mol. The dye concentration was evaluated using spectrophotometry (Shimadzu Model: UV-1240) at the wave of maximum absorbance.

3 Methods The chemical coagulation experiments were carried out in static reactors (Jar test) using 1 L of solution in each reactor at a temperature of 25 ± 1ºC. The samples were allowed to settle for a period of 1h after 1 min 40 s of rapid mixing (175

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Furlan et al.: Treatment of Textiles for Wastewater System Coupled

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rpm) and 10 min of slow mixing (15 rpm). At the end of the sedimentation period aliquots were removed at 2 cm below the surface of the effluent for the determination of the residual color. The optimum dosage of coagulant and pH of the mixture in the coagulation process were determined. The experimental adsorption tests were carried out with the pre-treated synthetic effluent using the activated carbon adsorbent. Kinetic and equilibrium data were determined and the influence of pH, salt addition (NaCl) and increased temperature plus salt addition on the dye removal using the adsorption process was investigated. In the preparation of the reactivated carbon, the material precursors of successive adsorptions were dried in an oven for 4 hours and then prepared for carbonization before subsequent chemical activation with acetic acid 1M. After the pore activation stage, the activated carbon was dried in an oven at 110ºC for a period of 4 hours. The experimental data on the variation of the solute concentration adsorbed in the solid phase (adsorbent) as a function of the equilibrium concentration in the fluid phase were adjusted using the Langmuir and Freundlich models. The tests with the bioindicator Daphnia magna were carried out according to the ABNT standard (1993), and results were expressed as the Factor of Dilution (FD). The FD represents the first of a series of sample dilutions at which acute toxic effects to the test organism are no longer observed (FATMA, 2002). The time for which the test organism was exposed to the effluent was 48 hours, after which the number of immobile organisms was observed and recorded. According to the legislation (article n°017/02 of FATMA), the maximum dilution factor for an effluent of textile origin is two (FATMA, 2002).

4 Results 4.1 Coagulation Tests: Optimum pH and Coagulant Dosage In the Jar Test experiments the pH values were varied from 4 to 12 in order to obtain the most favorable pH for the color removal. The best results were obtained in the acid region of pH 4 to 7, the greatest removal percentage being obtained at pH 6 for the two dyes under study, as shown in Figure 1a. Similar results were reported by Kim et al. (2004) for a chemical treatment by coagulation with removals of 71.7% at pH 6 and 93.9% at pH 5, for dyes Blue 106 and Yellow 54, respectively. The subsequent experiments were thus carried out at the pre-determined pH value of 6, varying the coagulant dosage from 150 mg/L to 750 mg/L. The dye removal as a function of the coagulant concentration is shown in Figure 1b. The removal efficiency for both dyes increased with an increase in the

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coagulant dosage up to a certain dosage and then remained constant for the dye Black 5 and reduced gradually for Orange 16. The maximum efficiency of color removal was for a coagulant dosage of 200 mg/L, for Black 5 and for Orange 16 the maximum removal was obtained with 250 mg/L of coagulant.

(a)

(b)

Figure 1: Optimization of the parameters in the pre-treatment stage for

reactive dye removal: (a) pH (b) coagulant concentration 4.2 Influence of pH on the adsorption process

The influence of pH on the dye adsorption on activated carbon was analyzed through data on the adsorption kinetics and isotherms, in order to select the most

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Furlan et al.: Treatment of Textiles for Wastewater System Coupled

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favorable pH for the adsorption of the dye by the carbon. Through the kinetic experiments it was verified that the time to reach equilibrium was approximately 380 minutes, for all the pH values investigated. The kinetics data allowed the construction of the adsorption isotherms, shown in Figure 2, for the pH values of 2, 3, 4 and 7, respectively. The maximum adsorption capacity, as shown in Figure 2, increased from 16.6 to 19 mg/g with an increase in the pH from 2 to 3. However, it decreased to 5.8 mg/g with a pH of pH 7. Thus, it can be concluded that pH 3 is the optimum pH for the color removal process.

Figure 2: Langmuir isotherms for the different pH values.

4.3 Influence of the Addition of Sodium Chloride Identical solutions were used for the kinetic experiments, varying only the values of sodium chloride between 0, 1, 3, 6 and 10% (by mass). Equilibrium was reached in approximately 340 minutes for solutions containing salt. In the case of solutions without salt, the adsorption was a little slower and equilibrium was reached in 380 minutes for both dyes. The values for the Langmuir parameters (qmáx) were calculated from the isotherms for addition of different quantities of sodium chloride to Black 5 and Orange 16. It was found that the maximum adsorption capacity increased from 19 to 87.7 mg/g with an increase in the quantity of sodium chloride from 0% to 6%. However, it decreased to 43.7 mg/g with an increase in the quantity of sodium chloride to 10%. In relation to the dye Orange 16, it was verified that the adsorption capacity increases from 27.5 to 74.1 mg/g with an increase in the quantity of sodium chloride from 0% to 1%.

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Chemical Product and Process Modeling, Vol. 4 [2009], Iss. 4, Art. 8

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Thus, 6 and 1% of sodium chloride appear to be the optimum quantities to improve the color removal process for the dyes Black 5 and Orange 16, respectively. According to Guelli U. Souza et al. (2008), the presence of salt promotes the adsorption of positive charges when compared with experiments in its absence. This may indicate that the salt cations neutralize the negative charge on the surface of the carbon, increasing the adsorption of molecules. 4.4 Influence of increased temperature plus Salt Addition

Increased temperature combined with sodium chloride addition (6% of the aqueous solution mass for the dye Black 5 and 1% for Orange 16) was found to improve the adsorption process. The time required for equilibrium to be reached was approximately 300 minutes, for the two dyes under study. On analyzing the Langmuir parameters, it was verified that the maximum adsorption capacity increased with the increase in the temperature from 87.7 mg/g at 25ºC to 95 mg/g at 70°C for the dye Black 5, and from 73.5 mg/g at 25ºC to 99.7 mg/g at 70°C, for Orange 16. These results indicate the endothermic behavior of this adsorption process. This result is consistent with that reported by Senthilkumaar et al. (2006), where the capacity for adsorption of the dye Crystal Violet increased by 40% when the temperature was increased from 28 to 48 °C. 4.5 Reactivated Carbon Tests Through the reactivation experiments, it was found that the adsorbent can be reused three times, consecutively, after the first adsorption with the virgin carbon. The time for the solutions with reactivated adsorbent to reach equilibrium was approximately 340 min; in the case of the solution with the virgin carbon, the equilibrium adsorption was reached in 300 min. Figure 3 shows the Langmuir isotherms obtained for the cases of adsorption with the virgin carbon and its respective reactivations. It is possible to verify in Figure 3 that the values for the maximum adsorption capacity, qm, were 95, 80, 44.4 and 28 mg/g for the virgin carbon and the first, second and third reactivations, respectively. For the four pH values studied, RL varies between 0.206 and 0.976 (0 < RL <1), and the Freundlich coefficient, n, varies between 0.671 and 0.939 (0 < n <1), confirming conditions favorable for adsorption. For the cases of sodium chloride addition, RL varied between 0.283 and 0.976 (0 < RL <1), and the Freundlich coefficient, n, between 0.756 and 0.918 (0 <n <1).

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Furlan et al.: Treatment of Textiles for Wastewater System Coupled

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For the three reactivation cases, RL varied between 0.292 and 0.940 (0 < RL <1), and the Freundlich coefficient, n, between 0.836 and 0.867, confirming conditions favorable for adsorption (0 <n <1).

Figure 3: Langmuir isotherms for the adsorption with the virgin carbon and three reactivations. 4.6 Acute Toxicity Tests The results with the bioindicator Daphnia magna showed that the dilution factor for the untreated effluent was 256, which is still higher than the maximum value allowed for textile industry effluent, indicating that it is necessary to carry out treatment before the effluent can be discarded to water bodies in compliance with the legislation in force. The toxicity of the solution reduced considerably after pre-treatment with coagulation/flocculation, with a dilution factor of 16. It is evident that the dye under study (Reactive Black 5) has a toxic effect on the test organism. After the complete treatment process it was verified that the effluent was not toxic (dilution factor = 1), indicating that, in achieving the complete removal of color, the chemical products used during the pre-treatment stage do not increase the effluent toxicity at the end of the process.

5 Conclusions The aluminum chloride coagulant demonstrated good results, and is suitable for the treatment of aqueous solutions containing reactive dyes. The best dosage found was 200 mg/L for Black 5 and 250 mg/L for Orange 16.

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The pH had a strong influence on the medium under study; the color removal process was favored in the acid region, pH 6 and 3 showing high efficiency for coagulation and adsorption, respectively. The use of this adsorbent in final wastewater treatment processes is not recommended in cases where it is necessary to neutralize the effluent to comply with environmental legislation, considering that for the best adsorbent performance acid solutions are required. The addition of sodium chloride to the synthetic wastewater favored the adsorption process, and the influence of increased temperature plus salt addition had an endothermic nature. The reactivation experiments revealed that the adsorbent could be reused three times, consecutively, after the first adsorption with the virgin carbon. In the evaluation of the acute toxicity with the bioindicator Daphnia magna as the test organism, the complete treatment process, besides having a good dye removal efficiency, reduces the toxicity of the final effluent. 6 References Associação Brasileira de Normas Técnicas (ABNT) (1993). NBR 12713: Água–

ensaio de toxicidade aguda com Daphnia sp. (Crustacea, Cladocera). Rio de Janeiro.

Chakraborty, S., De, S., Basu, J.K., Dasgupta, S. (2005). Treatment of a textile effluent: application of a combination method involving and nanofiltration. Desalination, 174, 73-85.

FATMA (2002). Limites máximos de toxicidade aguda para efluentes de diferentes origens. Portaria nº 017/02 – 18 abril.

Duan, J., Wilson, F., Graham, N., Tay, J.H. (2002). Adsorption of humic acid by powdered activated carbon in saline water conditions. Desalination, 151, 53–66.

Guelli U. Souza, S.M.A., Peruzzo, L.C., Souza, A.A.U. (2008). Numerical study of the adsorption of dyes from textile effluents. Applied Mathematical Modelling, 32, 1711-1718.

Guilarduci, V.V.S., Mesquita, J.P., Martelli, P.B., Gorgulho, H.F. (2006). Adsorção de fenol sobre carvão ativado em meio alcalino. Revista Química Nova, 29, 1226-1232.

Jain, A. K., Suhas, Bhatnagar, A. (2002). Methylphenols removal from water by low-cost adsorbents. Journal of Colloid and Interface Science, 251, 39–45.

Kim, T., Park, C., Shinb, E., Kim, S. (2004). Decolorization of disperse and reactive dye solutions using ferric chloride. Desalination, 161, 49-58.

Papic, S., Koprivanac, N., Bozic, A.L., Metes, A. (2004). Removal of some reactive dyes from synthetic wastewater by combined Al(III) coagulation/carbon adsorption process. Dyes and Pigments, 62, 291-298.

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Senthilkumaar, S., Kalaamani, P., Subburaam, C.V. (2006). Liquid phase adsorption of Crystal violet onto activated carbons derived from male flowers of coconut tree. Journal of Hazardous Materials, B136, 800-808.

Solmaz, S.K.A., Üstün, G.E., Birgül, A., Tasdemir Y. (2007). Treatability studies with chemical precipitation and ion exchange for an organized industrial district (OID) effluent in Bursa, Turkey. Desalination, 217, 301-312.

Tomaszewska, M., Mozia, S., Morawski, A.W. (2004). Removal of organic matter by coagulation enhanced with adsorption on PAC. Desalination, 161, 79–87.

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