Dye removal of tannery wastewater by adsorption in leather waste: the understanding of the phenomenon up optimization with real wastewater

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1 153 Dye removal of tannery wastewater by adsorption in leather waste: the understanding of the phenomenon up optimization with real wastewater Carolina S. Gomes 1, Jeferson S. Piccin 2* and Mariliz Gutterres 1 1 Federal University of Rio Grande dosul (UFRGS), Chemical Engineering Department, Laboratory for Leather and Environmental Studies (LACOURO). Luiz Englertstr., s/n, , Porto Alegre, RS, Brazil. * mariliz@enq.ufrgs.br 2 Passo Fundo University, Food Engineering Department, BR 285, km 171, Passo Fundo, RS, Brazil.Tel: * jefersonpiccin@upf. br Abstract For some time the LACOURO Research Team has been studying the leather dye adsorption by chromium-tanned leather waste (CTLW). In this context, this work aims to present the results of this research with the aim of using this process for the treatment of colorful dyeing process wastewater, for the water reuse or pretreatment of the wastewater. Thus, this work presents studies of ph, adsorbent dosage, and contact time on the adsorption of dyes AR 357 in aqueous solution. The results demonstrated that the electrostatic interactions of the dye with the leather amine groups is favored at ph between 2 and 3. Under this condition it was demonstrated that it is possible to remove close to 100% of dye in solution. Subsequently, the wastewater containing this dye was obtained through a dying in a wet end process in a pilot scale rotatory drum. It was observed that the dye effluent contains from 75 to almost 500 mg/l of dye, and several other substances that affect the water quality and toxicity. Using this wastewater and a response surface design, adsorption tests using CTLW in laboratory scale tannery rotatory drums were carried out. The optimum conditions of adsorption predicted was at ph 3.50 and adsorbent dosage of 15 g L -1. The model predicted a dye removal of approximately 90.25% under these conditions. 1 Introduction Many industries, such as leather, food, cosmetics, plastics, and textiles, use dyes to confer color or restore the color of their products. In these industries, during the processes involved in production dyes are usually dissolved in water. Despite being a contaminant that significantly contributes to the increase of chemical oxygen demand of wastewaters, even by low dye concentrations may significantly change the color of the water, causing aesthetic problems in water sources polluted with industrial effluents. In the leather production, dyes are added in the final stages to give leather the sensory characteristics of surface and interior coloration. This step is conducted in a liquid medium during the wet finishing process. This step is responsible for a significant volume of wastewater generation containing high concentrations of dyes. In addition to the undesirable visual pollution associated with the color in wastewater, the presence of dyes, especially azo and metal complexes, may result in reduced water reoxygenation capacity, acute and chronic toxicities and difficulties in water treatment by biological methods, furthermore preventing the reuse of the water in other process steps (Piccinet al., 2009; Gao et al. 2010). 1

2 Adsorption is one of the most effective methods used for removal of dyes and other soluble substances from wastewater. Activated carbon is a widely used adsorbent in various industrial sectors. However, especially due to its production and regeneration cost, the use of adsorption in industrial processes, as tanneries, is limited. Due to the low-cost adsorbents of natural materials or industrial wastes the interest of researchers for their use in dye removal is growing. Some examples are rice husk ash, palmfruit bunch, treated sawdust and chitosan (Mane et al., 2007; Nassar e Magdy, 1997; Garg et al., 2003; Piccinet al., 2011). Currently, there are studies investigating the use of adsorption for the treatment of contaminants in aqueous solutions, but only a few studies try to recreate industrial conditions by using effluents similar to those generated in industry (real wastewater) (Chong et al., 2009; Kyzas, 2012; Ozsoyand van Leeuwen, 2010; Tahir and Rauf, 2004). Studies on aqueous solutions are very important to understand the adsorption mechanisms of certain contaminants onto an adsorbent. However, these studies cannot be directly tested in industries because of the presence of numerous other chemicals, which will interfere with the process. Therefore treatment of real effluents under industrial conditions should be investigated. The LACOURO Research Team has been studying the leather dye adsorption of Acid Red 357 dye (AR357) by chromium-tanned leather waste (CTLW). In this context, the aim of this work is to present the results of this research starting from the investigation of the adsorption phenomenon until the optimization of the process with real wastewater and to demonstrate the feasibility of using this process for the treatment of colorful dyeing process wastewater, for the water reuse or pretreatment of the wastewater. 2 Experimental 2.1. Experiment with aqueous solutions Acid Red 357 dye (AR 357) adsorption in aqueous solution was carried out by batch operation system in laboratory. The adsorbent used was the chromium-tanned leather waste (CTLW) obtained from a local tannery (Porta o/rs, Brazil). The adsorbent wasdried, ground, and sieved according to Piccin et al. (2012). The ph adjustment was carried out adding 10 ml of McIlvaine buffer solution to 0.25 g (dry basis) of adsorbent and the suspension was stirred for 10 min. Then, 50 ml of dye aqueous solution was added to the system. The experiments were carried out under controlled temperature of 25 ºC and rotation speed (150 rpm). The ph effect was investigated in the range of 2.00 to Subsequently the effect of the adsorbent dosage was investigated until the value of almost 7 g.l -1, using the most favorable ph condition for adsorption. The adsorbate-adsorbent contact time was studied up to 120 minutes. The dye concentration in the liquid phase was analyzed using a UV-Visible spectrophotometer (PG Instruments T80 model) at λ máx 494 nm. The results were used to determine the percentage removal of the dye Wastewater characterization To characterize wastewater of the wet end stage in the tannery industry, the wet end process was carried out using a pilot-scale tannery drum (Master FLD-8 model). Chromium-tanned (wet-blue) leather from a half-bovine hide was used in atypical wet end process formulation (Piccin et al. 2012). 2

3 Two kinds of samples were collected; the first (CS1) was composed of all wastewater streams from the seven steps of the wet end process and was intended to characterize the pollution load as a whole. The second sample(cs1)was composed only of the last four steps, namely those with residual dye in the wastewater. Thus, it was possible to evaluate minimum and maximum contamination values of dyes from the process in pilot scale Experiment with real wastewater The adsorption trials using real wastewater and CLTW were performed in laboratory-scale tannery drums (Mathis LFA model). In each test 1 L of wastewater sample was used and its ph was adjusted using formic acid and sodium hydroxide. The ph of a known mass of adsorbent was also adjusted by adding 300 ml of McIlvaine buffer solution. After this, the wastewater and the adsorbent were placed in the tannery drum, set at a pre-determined temperature and rotation speed. Table 1: Factors and their levels in the experimental design Factor / Level -α α W (g L -1 ) ph C (mg L -1 ) Rot (rpm) A response surface methodology (RSM) based on a central composite rotatable design (CCRD) capable to analyze the curvature of the statistical model was used. The factors and levels used in the trials are adsorbent concentration (W), ph, dye concentration (C) and rotation speed (Rot) and they are shown in Table 1. 3 Results and Discussion 3.1. Experiment with aqueous solutions The ph effect on the adsorption The effect of ph is one of the most important process variables for the wastewater treatment. Figure 1 shows the results of dye removal (R) as a function of the ph for the dye AR 357 by CTLW. 3

4 Figure 1: ph effect on the adsorption of AR 357 dye in aqueous solution by CLTW From the Figure 1 it is shown that dye removal increased considerably by lowering the ph. The increase of ph from 2.00 to 7.00 caused dye removal reduction of almost 40%, showing that acid ph is more favorable for this adsorption process. This is due to the protonation of the amine groups of the leather when the ph is lowered, to generate the NH 3 + form. The AR 357 dye has an anionic character, so it is attracted to the surface of the adsorbent, resulting in adsorption (Fathima et al., 2009)and increasing the dye removal Adsorbent dosage The effect of using different adsorbent dosages was evaluated at ph 2.50 and 25 C. Figure 2 shows the obtained results. Figure 2: Adsorbent dosage effect on the adsorption of AR 357 dye in aqueous solution by CLTW The data show that it is possible to achieve an almost complete removal of the dye AR 357 using the CTLW adsorbent.as it is expected, the use of a higher adsorbent dosage increases the removal of dye, that is, the largerthe amount of adsorbent present in the medium, the larger the removal becomes, explained by the larger number of active sites available for adsorption. The use of higher dosage than 3 g.l -1 is sufficient to approach the complete removal. 4

5 Contact time The results obtained related to contact time effect between AR 357 dye and CLTW at ph 2.50 and 25 C is shown in Figure 3. Figure 3: Contact time effect on the adsorption of AR 357 dye in aqueous solution by CLTW The data evaluation indicates that is possible to reach 80% of color removal in only two hours of adsorbent-adsorbate contact. This relatively short time favors the industrial utilization of this proposed treatment. The data tendency also indicates that with a longer contact time would be possible to increase the dye removal Wastewater of wet end process Wastewater characterization The wet end process was carried out in a pilot scale rotatory drum in laboratory. The obtained wastewater showed a strong red coloration, visible presence of solid and foam and ph Table 2 Wet end effluents characterization CS1 CS2 Solids (%) 0,71 0,88 Cr(III) (mg L -1 ) 62,7 61,5 NTK (mg L -1 ) 48,21 68,03 TOC (mg L -1 ) C (mg L -1 ) 75,10 149,21 The characterizations results (Table 2) show that the dye concentration (C) can vary from 75 to almost 150 mg.g -1. The Brazilian legislation does not set emissions standards for color, but color cannot be attributed to water bodies. In addition, other pollutants are present as solid waste, residual chromium, organic and ammoniacal nitrogen (NTK) and total organic carbon (TOC). The presence of solids in the samples is due to the presence of fiber waste, soils and residual chemicals. Residual Cr(III) comes from the wet blue leather itself, as part of the chromium used in the tanning step is not well fixed in the leather and is eventually released into the baths. The total organic carbon values present in the baths are due to the presence of chemicals (oils, surfactants, dyes, and retanning agents) and the organic material of the leather. 5

6 NTK comes from the chemicals used in the formulation and also from the leather wastes. High NTK levels are especially problematic since these components are nutrients for photosynthetic organisms. Emission standards in Brazil vary from 10 to 20 mg.l -1, depending on the company daily flow rate (Resolution CONSEMA 128/2006). Thus, the values found (Table 2) show that the wet end step generates wastewater with nitrogen concentrations above those permitted by law, and that this must be taken into consideration in the wastewater treatment Experiment with wastewater Subsequent adsorption tests were made using the wastewater obtained in the wet end process and laboratory scale rotatory drums were used for the adsorption experiments in order to reach the optimum condition of adsorption. The response surface methodology (RSM) was used to determine the optimum conditions of adsorption. The standard Pareto chart allows analyzing, in a quick and clear way, the effects that are statistically significant (p < 0.15) for each response. The chartis represented in Figure 4, and the significant parameters are presented with asterisks in the charts legends. NS: non-significant effect, *: p < 0.01, **: p < 0.05, ***: p < 0.10, ****: p < 0.15 Figure 3: Pareto Chart of the standardized effects of removal of Acid Red 357 dye in dye-containing wastewater. The important factors for dye removal, in descending order, were adsorbent dosage (W), ph, and dye concentration (C). The rotation speed (Rot) was not important on the adsorption process. An increase in ph decreases the removal of dye. As mentioned before, the interactions between the leather s protonated surface and the anionic dye are favored. Oliveira et al. (2007) have observed a similar behavior in their study that tested the adsorption of two dyes, with anionic and cationic characters, respectively, onto chromium-tanned leather waste. While the anionic dye attained a maximum adsorption capacity of 163 mg g -1, the cationic dye only reached a value of 3 mg g -1, confirming that anionic dyes have greater interaction with the wet blue leather that cationic dyes. The effect of the adsorbent dosage and the dye concentration are related to the driving forces that cause mass transfer between the phases. The increase of adsorbent dosage has a positive effect for the dye removal. Many studies that reported high dye removal levels typically used high dosages of the adsorbent. Khosla et al. (2013) showed that the removal for Acid Orange 7 could be increased from 90% to 99% by increasing the adsorbent dosage. Garg et al. (2003) used the same strategy to increase the removal for Basic Green 4 from 59.6% to 99.8% by adsorbing the dye on sawdust. 6

7 A higher dye concentration has a negative effect on the dye removal, probably because a low dye concentration takes longer to saturate the available adsorbent, while being able to remove a higher percentage of the dye (Yagubet al., 2014). The response surface was generated using the results that were previously presented to verify the regions in which the best experimental conditions exist. Figure 5 shows the response surface for dye removal using a dye concentration and the rotation speed were at the -α level to evaluate the most important factors. Figure 5: Response surface graph for the effect of W and ph on R %, with Concentration of mg L -1 and Rotation of 27.5 rpm The response surface shows that the point where the removal of dye is optimized is approximately by the average ph value (ph 3.50) and adsorbent dosage (W of 15 g L -1 ). Evaluating the graphic visually it is possible to conclude that the optimal dye removal is of 90.25%. In the experiments previously made with aqueous solutions, under conditions of ph 2.50 and 25 ºC, very similar to the conditions used for real wastewater, the maximum dye removal was close to 100%. This value is higher than the value observed for real wastewater since the adsorption was studied using aqueous solutions and there are no other wet end chemicals present that may cause interference on the adsorption and take place in the active sites. 4 Conclusion This work presented the studies on adsorption of the dye AR357 by chromium-tanned leather waste (CTLW) and investigate its feasibility. Experiments with aqueous solutions were carried out in order to clarify the removal mechanisms and the interaction between AR357 and CLTW. These studies demonstrated that the removal is favored in ph between 2.00 and 3.00 and with an adsorption dosage higher 3 g.l -1. Under these conditions it was possible to remove most of the dye present in the aqueous solution. Leather dye concentration in tannery wastewater can vary in the range mg.g -1 in the effluent obtained in steps of wet finishing of leather. Other substances that affect the water quality and toxicity, as solid waste, residual chromium, NTK and TOC are also present in the wastewater. For the adsorption optimization, the studies were carried out with real wastewater generated in pilot scale. It was possible to reach the dye removal of approximately 90.25% under the conditions of ph 3.50 and adsorbent dosage of 15 g L -1. This high dye removal shows that this technic can be successfully used in tanneries as a pretreatment or to achieve the water reuse of these wastewaters. 7

8 5 Acknowledgments The authors would like to thank CAPES (Brazilian Agency for Improvement of Graduate Personnel) for the Master and the Ph.D. scholarship, to FINEP by Edict MCTI/FINEP CT-HIDRO 01/2013for the financial support and for the Business Leather Unit of Lanxess Company, for the technical support. 6 References 1. Alves, A., de Pinho, M., Ultrafiltration for colour removal of tannery dyeing wastewaters. Desalination, 130, , Chong, M. F., Lee, K. P., Chieng, H. J., Syazwani, I. I. S. B., Removal of boron from ceramic industry wastewater by adsorption flocculation mechanism using palm oil mill boiler (POMB) bottom ash and polymer, Water Res.,43, , Fathima, N.N., Aravindhan, R., Raghavarao, J., Nair, B.U., Utilization of organically stabilized proteinous solid waste for the treatment of coloured waste-water, J. Chem. Technol. Biot., 84, , Gao, J., Zhang, Q., Su, K., Chen, R., Peng, Y., Biosorption of Acid Yellow 17 from aqueous solution by non-living aerobic granular sludge, J. Hazard. Mater.,174, , Garg, V., Gupta, R., Yadav, A., Kumar, R., Dye removal from aqueous solution by adsorption on treated sawdust, Bioresource Technol., 89, , Gutterres, M., Passos, J., Aquim, P., Severo, L., Trierweiler, J., Reduction of water demand and treatment cost in tanneries through reuse technique, J. Am. Leather Chem. Assoc., 103, , Khosla, E., Kaur, S., Dave, P. N., Tea waste as adsorbent for ionic dyes, Desalination Water Treat., 51, , Kyzas, G., A Decolorization Technique with Spent "Greek Coffee" Grounds as Zero-Cost Adsorbents for Industrial Textile Wastewaters, Mater.,5, , Mane, V. S., Mall, I. D., Srivastava, V. C., Kinetic and equilibrium isotherm studies for the adsorptive removal of Brilliant Green dye from aqueous solution by rice husk ash, J. Environ. Manage.,84, , Martinez-Huitle, C., Brillas, E., Decontamination of wastewaters containing synthetic organic dyes by electrochemical methods: A general review, Appl. Catal. B: Environ.,87, , Nassar, M. M., Magdy, Y. H., Removal of different basic dyes from aqueous solutions by adsorption on palm-fruit bunch particles, Chem. Eng. J., 66, , Oliveira, L., Goncalves, M., Oliveira, D., Guerreiro, M., Guilherme, L., Dallago, R., Solid waste from leather industry as adsorbent of organic dyes in aqueous-medium, J. Hazard. Mater., 141, , Ozsoy, H. D., van Leeuwen, J. H., Removal of color from fruit candy waste by activated carbon adsorption, J. Food Eng., 101, , Piccin, J. S., Dotto, G., Vieira, M., Pinto, L., Kinetics and Mechanism of the Food Dye FD&C Red 40 Adsorption onto Chitosan. J. Chem. Eng. Data, 56, , Piccin, J. S., Gomes, C. S.,Feris, L. A.,Gutterres, M., Kinetics and isotherms of leather dye adsorption by tannery solid waste. Chem. Eng. J.183, 30-38, Piccin, J.S., Vieira, M.L.G., Gonçalves, J.O., Dotto, G.L., Pinto, L.A.A., Adsorption offd&c Red No. 40 by chitosan: isotherms analysis, J. Food Eng.,95, 16 20, Srinivasan, A., Viraraghavan, T., Decolorization of dye wastewaters by biosorbents: A review, J. Environ. Manage.,91, , Tahir, S. S., Rauf, N., Removal of Fe(II) from the wastewater of a galvanized pipe manufacturing industry by adsorption onto bentonite clay, J. Environ. Manage.,73, ,

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