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The application of textile sludge adsorbents for the removal of Reactive Red 2 dye
Journal of Environmental Management 168 (2016) 149e156
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
The application of textile sludge adsorbents for the removal of Reactive Red 2 dye bora de Oliveira*, Gabriela G. Sonai, Selene M.A. Guelli U. de Souza, De ^nio Augusto U. de Souza Anto polis, CEP 88040-900, SC, Brazil Laboratory of Mass Transfer, Chemical Engineering Department, PO Box 476, Federal University of Santa Catarina, Floriano
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 September 2015 Received in revised form 6 December 2015 Accepted 7 December 2015 Available online xxx
Sludge from the textile industry was used as a low-cost adsorbent to remove the dye Reactive Red 2 from an aqueous solution. Adsorbents were prepared through the thermal and chemical treatment of sludge originating from physicalechemical (PC) and biological (BIO) effluent treatment processes. The adsorbent characterization was carried out through physicalechemical analysis, X-ray fluorescence (XRF) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, pHPZC determination, Boehm titration method, BrunauereEmmetteTeller (BET) surface area analysis and scanning electron microscopy (SEM). Batch kinetic experiments and adsorption isotherm modeling were conducted under different pH and temperature conditions. The results for the kinetic studies indicate that the adsorption processes associated with these systems can be described by a pseudo-second-order model and for the equilibrium data the Langmuir model provided the best fit. The adsorption was strongly dependent on the pH but not on the temperature within the ranges studied. The maxima adsorption capacities were 159.3 mg g1 for the BIO adsorbent and 213.9 mg g1 for PC adsorbent at pH of 2 and 25 C. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Water reuse Adsorption Reactive dye Textile sludge Reactive Red 2
1. Introduction The textile industry generates large volumes of liquid effluents containing dyes, mostly as residues of textile fiber dyeing processes. Such effluents must be properly treated, as they can cause serious environmental problems. The presence of dyes reduces the water transparency, which interferes with photosynthesis and therefore ndez et al., 2010; Oliveira et al., harms aquatic plant life (Ferna 2007). Dyes are recalcitrant molecules, being resistant to aerobic digestion, light, heat, and oxidizing agents. Some studies also show that they may be carcinogenic or mutagenic, particularly in the case of azo dyes and their by-products (Gupta and Suhas, 2009; Carneiro et al., 2010; McKay, 1996). Adsorption is a separation and purification process that is broadly used to remove polluting substances which do not easily biodegrade. It is a promising technique and has received greater attention that other removal methods in recent decades (Jain et al., 2003; Ho and McKay, 2003).
* Corresponding author. E-mail address: [email protected] (D. de Oliveira). http://dx.doi.org/10.1016/j.jenvman.2015.12.003 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
Commercial-grade activated carbon is the most commonly used adsorbent for the removal of effluent color, due to its efficiency. However, its broader use is restricted due to its high cost. Moreover, the reuse or dispose of powdered activated carbons are difficult due to the very fine powder that can remain suspended in treated water during a long time. Thus, several alternative adsorbents have been studied in order to reduce the cost of this type of treatment (Crini, 2006; Bhatnagar and Jain, 2005; Gupta et al., 2003). An alternative adsorbent is considered to be of low-cost when minimal processing is required, it is abundant in nature, or it is derived from an industrial by-product (Gupta and Suhas, 2009; Bailey et al., 1999). Such adsorbents may be made of peat (Ho and McKay, 1998), seaweed (Vijayaraghavan and Yun, 2008), chitosan (Chang and Juang, 2004; Prado et al., 2004), leaves (Bhattacharyya et al., 2009), sawdust (Vijayaraghavan et al., 2009), agricultural industry waste (Mittal et al., 2010), peat (Allen et al., 2004) or sludge (Netpradit et al., 2004; Vasques et al., 2009), among others. Sludge can be defined as the residue generated from an effluent treatment process. In primary treatment, which is characterized by physicalechemical processes, the resulting residue contains a mixture of inorganic compounds. On the other hand, secondary treatment involving biological processes results in a residue containing a complex mixture of non-digested organic compounds and
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dead microorganisms (Aksu and Akin, 2010; Smith et al., 2009; Fonts et al., 2012). However, the final characteristics of such a residue may vary greatly depending on the sludge origin, treatments applied and even the coagulating agents used (Smith et al., 2009; Annadurai et al., 2003; Khursheed and Kazmi, 2011). Converting sludge into adsorbents may be of interest due to the potential value of the residue, and is of great significance considering the increasing amounts of sludge generated and the presence of more rigorous legislation that regulates its disposal and use (Smith et al., 2009). The conversion can be made through sludge pyrolysis. This process is characterized by decomposing organic matter in the absence of oxygen at between 300 and 900 C while generating gas, a carbonous residue, and oils. The resulting gas and oils can be used as fuels while the solid residue can be burned for energy or used to produce low-cost adsorbents (Vasques et al., 2009; Werther and Ogada, 1999; Inguanzo et al., 2001; Fonts et al., 2009). The removal of dyes from aqueous solution using alternative adsorbents has been extensively studied by several authors (Gupta and Suhas, 2009; Crini, 2006; Srinivasan and Viraraghavan, 2010). The removal of Reactive Red 2 (RR2) dye using sludge from several origins has been studied by Netpradit et al. (2003, 2004); Vasques et al. (2009); Babu et al. (2011); Geethakarthi and Phanikumar (2011). Taking into account the above presented statements, the aim of this study was to evaluate the thermal treatment (through pyrolysis) and chemical treatment (with 0.1 M H2SO4) of sludge samples generated during the physicalechemical or biological treatment of textile effluents, in order to obtain adsorbents for the removal of Reactive Red 2 dye from aqueous solution. The effects of solution pH and temperature were also investigated. The thermodynamic parameters Gibbs free energy (DG ), adsorption heat (DH ) and entropy (DS ) were determined.
2.2. Adsorbent characterization The physicalechemical properties of the adsorbents obtained were determined through X-ray fluorescence (XRF) spectroscopy (Shimadzu, EDX-700). The point of zero charge was estimated through an adapted version of the batch equilibrium method described by Babic et al. (1999). The adsorbents were analyzed by FTIR spectroscopy (Perkin Elmer, Spectrum 100) in order to determine the functional groups present. A scanning electron microscope (JEOL, JSM-6390LV) was used to observe the surface morphology of the material andBET surface area analysis (Autosorb 1C e Quantachrome)was performed in order to determine the textural properties. The acid properties of adsorbents surface were determined by the method ofBoehm (1994). First, 0.5 g of adsorbent were mixed with 100 mL of different bases (0.05 M NaHCO3, 0.05 M Na2CO3 or 0.05 M NaOH) in flasks of 250 mL. The Erlenmeyer flasks were sealed and kept under stirring during 24 h at25 C. The samples were filtered and aliquots of 10 mL were titrated with HCl 0.1 M. 2.3. Adsorbate solutions Dye solutions were prepared by diluting a stock solution with distilled water. The pH of each solution was adjusted to the desired value by adding diluted H2SO4 or NaOH, with the aid of a pHmeter (Quimis, Qe400M2). Details about the chemical structure of the dye Reactive Red 2 and its main physical and chemical properties are presented in the Supplementary Material 2. A UVevis spectrophotometer (Shimadzu, 1240) was used to determine the dissolved dye RR2 concentrations. Calibration curves were built in order to determine the final concentration in solution after the adsorption experiments, measured at the longest adsorption wavelength for this dye (lmax ¼ 538 nm).
2. Materials and methods
2.4. Equilibrium studies
2.1. Adsorbent preparation
2.4.1. Effect of initial pH The influence of solution pH was studied using 5 g L1 of adsorbent in solution. For each initial pH condition, this amount of adsorbent was placed in a 250 mL Erlenmeyer flask with 50 mL of 500 mg L1 dye RR2 solution. The system was stirred at 115 rpm in an orbital shaker at 25 C for 15 h. The resulting dye solutions were then collected and analyzed using a UVevis spectrophotometer and a pHmeter. The percentage of dye removed from the solution was calculated as follows:
Sludge generated by a Brazilian textile company was used to prepare the adsorbents. Sludge produced during physicalechemical (PC) or biological (BIO) effluent treatment were subjected to thermal and chemical treatment in order to obtain the adsorbents. The raw sludge samples were firstly sun-dried for three days and then dried in an oven (Tecnal, TE-393/1) at 80 C for approximately 4 h. Fractions with diameters of between 0.152 and 0.450 mm were selected for the experiments. Procedures for the thermal and chemical treatments were based on the work of Vasques et al. (2009). 2.1.1. Thermal treatment For the thermal treatment, approximately 40 g of raw sludge was placed in a stainless steel reactor attached to a muffle furnace (EDG, 3P-S 3000). The sample was heated in a closed system (Supplementary Material 1) at 500 C under low vacuum in the muffle furnace (1) for 70 min. The gases released were condensed (2) and collected in a flask (3). 2.1.2. Chemical treatment For the chemical treatment, 1g of pyrolyzed material was placed in a 250 mL Erlenmeyer flask with 50 mL of a 0.1 M solution of H2SO4. The system was stirred at 115 rpm in an orbital shaker (Tecnal, TE-424) at 25 C for 3 h. The resulting product was filtered through filter paper and left in the oven at 105 C until a constant weight was obtained.
%removal ¼
ðCo CÞ $100 Co
(1)
where C0 and C are the initial and final dye concentrations (mg L1), respectively. All adsorption experiments were performed in duplicate. 2.4.2. Adsorption isotherms In order to obtain the adsorption isotherms 50 mL of dye RR2 solutions in different concentrations (see Table 1) and 5 g L1 of adsorbent were placed in 250 mL Erlenmeyer flasks for equilibrium tests. Samples were placed under constant stirring at 115 rpm in an orbital shaker, under different pH (2 and 4) and temperature (25 and 45 C) conditions for 15 h, in order to guarantee the adsorption equilibrium. The samples were then decanted and aliquots of the supernatant solution were collected to obtain the final dye concentration. The quantity of adsorbed dye q (mg g1) was calculated through the mass balance relation:
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Table 1 Initial dye concentrations at each point on the adsorption isotherms for PC (a) and BIO (b) adsorbents under different pH and temperature conditions. CRR2 (mg L1)
Point
PC
BIO
1 2 3 4 5 6 7
q¼
pH ¼ 2 T ¼ 25 and 45 C
pH ¼ 4 T ¼ 25 C
pH ¼ 2 T ¼ 25 and 45 C
pH ¼ 4 T ¼ 25 C
400 500 600 700 800 900 1000
200 300 400 500 600 700 800
300 400 500 600 700 800 900
100 200 300 350 400 450 500
ðCo CÞV m
(2) 1
where C0 and C are the initial and final dye concentrations (mg L ), respectively, V is the solution volume (L) and m is adsorbent mass (g). 2.5. Effect of ionic strength Tests were carried out in order to study the behavior of dye RR2 adsorption in the presence of a salt (NaCl) broadly used in the textile industry for fabric dyeing and which is consequently present in the effluent at the treatment plants (Netpradit et al., 2004). To perform the tests, 5 g L1 of adsorbent and 800 mg L1 of dye RR2 solution were placed in 250 mL Erlenmeyer flasks at pH ¼ 2, with NaCl concentrations varying from 0.1 to 0.4 mol L1. Samples were stirred at 115 rpm in an orbital shaker for 15 h. In sequence, the resulting dye solutions were collected and analyzed on a UVevis spectrophotometer. The percentage of dye removed from the solution was calculated according to Equation (1). 2.6. Desorption Desorption tests were performed in order to investigate the dye RR2 adsorption process mechanism. Firstly, adsorbents were saturated with a 400 mg L1 dye RR2 solution. Saturation was achieved by leaving the samples in a shaker at 115 rpm and 25 C for 15 h. Dye-saturated adsorbents were filtered and dried in an oven. The amount of dye adsorbed was calculated through the difference between the initial and final concentrations of the 400 mg L1 dye solution. For the desorption tests, 0.5 g of saturated adsorbent was placed in a 250 mL Erlenmeyer flask with 100 mL of distilled water at alkaline pH (pH ¼ 11). Samples were stirred at 115 rpm and 25 C. Aliquots of the solution were collected at predetermined time intervals and analyzed on a UVevis spectrophotometer. The percentage of desorption was calculated according to Equation (3).
%Desorption ¼
! CRR2desorption $100 CRR2adsorption
Table 2 Experimental conditions applied in the adsorption kinetics tests. Run/Adsorbent
C0 (mg L1)
CAds (g L1)
pH
T ( C)
1 2 3 4 5 6 7 8
500 500 500 500 500 500 500 500
5 5 5 5 5 5 5 5
2 4 2 2 2 4 2 2
25 25 35 45 25 25 35 45
BIO BIO BIO BIO PC PC PC PC
orbital shaker at 115 rpm and aliquots of the solution were collected in regular time intervals, for analysis by UVevis spectroscopy, until equilibrium had been reached.
3. Results and discussion 3.1. Adsorbent characterization Table 3 shows the results for the chemical composition obtained by XRF spectroscopy. The main chemical elements are aluminum for the PC adsorbent (33.51% m/m) and silicon for the BIO adsorbent (12.59% m/m). The decrease in mass percentage for some elements may be due to erosion caused by the chemical treatment. The high values for the loss on ignition (LOI) of these materials indicate the presence of organic matter. The data on the physicalechemical properties, pHPZC, and BET surface area are presented in Table 4. The adsorbent obtained from the PC sludge (PC adsorbent) contained a greater amount of inorganic content than the adsorbent obtained from the BIO sludge (BIO adsorbent), which influenced the pH of the adsorbents and consequently, their pHPZC. The BET surface area values are low in relation to other adsorbents. According to Smith et al. (2009), one of the reasons for this is the high levels of inorganic, non-porous material present in these materials. The IR spectra of both adsorbents (Supplementary Material 3) present a broad absorption band at between 3000 cm1 and
(3)
where CRR2desorption is the concentration of dye released into the solution, and CRR2adsorption is the dye concentration in the saturated adsorbent (mg L1). 2.7. Kinetic studies The kinetics of batch adsorption experiments conducted under different pH and temperature conditions, according to Table 2, were investigated. Samples were kept under constant stirring on an
Table 3 XRF analyses results for thermally and chemically-treated sludges. Element
BIO (% m/m)
PC (% m/m)
Al Ca Si P Fe K S CO2
6.71 0.96 12.59 2.65 6.28 2.50 1.79 64.85
33.51 1.80 9.78 8.89 2.22 0.85 1.51 40.12
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Table 4 Results of physicalechemical characterization of adsorbents. Analysis
PC
BIO
Moisture (%)a Ash (%) Volatile materials (%) Fixed carbon (%) pH pHPZC BET (m2 g1) Volume of pores (cm3 g1) Average pore diameter (nm)
7.77 ± 0.01 59.88 ± 0.10 17.95 ± 0.03 22.17 ± 0.08 3.80 ± 0.03 4.5 50 0.15 12.20
7.91 ± 0.02 35.15 ± 0.08 20.39 ± 0.70 44.47 ± 0.78 3.01 ± 0.01 4.0 44 0.14 12.79
a
Dry basis.
3600 cm1. This band corresponds to OeH stretching of the hydroxyl groups in phenol, alcohol and carboxylic compounds. It is also associated with the NeH stretching of amine and amide groups (Silverstein et al., 2005; Gasco et al., 2007). According to Zhang et al. (2011), the strong bands observed at around 1085 cm1 and 1094 cm1 are attributable to the angular deformation of CeO groups. Among the compounds associated with this absorption ndez band are ethers, phenols, lactones, and carboxylic acids (Me et al., 2005). Absorption peaks on the spectra can be noted at around 1620 cm1, which correspond to C]O stretching. The broad brand in 500 cm1 refers to the angular deformation outside the plane of NeH bonding (Silverstein et al., 2005). By the method of Boehm (Supplementary Material 4) it was possible to quantify the presence of acid functional groups in the surface of the adsorbents. Both adsorbents have a high amount of carboxylic groups compared to phenolic and lactonic ones. The adsorbent PC presents higher content of carboxylic acids and acids groups compared to the BIO adsorbent. The SEM image of the raw BIO sludge shows no porous structures being evident on the surface. However, the BIO adsorbent shows porosity, due to the organic matter decomposed during the thermal and chemical treatments. The raw PC sludge shows no notable differences in comparison to the PC adsorbent (Supplementary Material 5). 3.2. Adsorption equilibrium studies 3.2.1. Effects of initial pH The results obtained indicate that the pH plays an important role in the dye RR2 adsorption for both the BIO and PC adsorbents. In Fig. 1a, it can be observed that the dye adsorption is favored at more acid pH values, for both adsorbents. Additionally, for pH value of 2 there was a greater percentage of removal. The dye used in this study, RR2, has sulfonate ions (ReSO 3 ) that enable adsorption onto positively-charged adsorbents (Netpradit et al., 2004). At pH < pHPZC, the adsorbent surface has positive charges, favoring the adsorption of anions. In contrast, for pH > pHPZC the adsorption of cations is favored due to the
negatively charged surface of the adsorbent (Geethakarthi and Phanikumar, 2011). The determination of the pHPZC was also found to be important in a study performed by Aldegs et al. (2008) in order to describe the adsorption behavior of reactive dyes with ReSO 3 groups in their structures. The pHPZC of BIO adsorbent and PC is 4.0 and 4.5, respectively. This indicates that, above these values of pHPZC, the adsorbents will be negatively charged and, then, the capacity of adsorption will be reduced, since there will be a repulsion of charges between the adsorbent and the dye. 3.2.2. Adsorption isotherms The adsorption isotherms for the two adsorbents related to the removal of dye RR2 from aqueous solutions under different pH (2 and 4) and temperature (25 and 45 C) conditions are presented in Figs. 2 and 3, respectively. Experimental data were fitted to the Langmuir and Freundlich models. The Langmuir isotherm (Langmuir (1918)) is represented as follows:
qe ¼
qm KL Ce 1 þ KL Ce
(4)
where qm is the maximum adsorption capacity, KL is the Langmuir adsorption constant, and Ce is the adsorbate equilibrium concentration in the liquid phase. The Freundlich isotherm (Freundlich (1907)) is represented as follows: ð1=nÞ
qe ¼ KF $Ce
(5)
where KF and n are constants in the Freundlich equation. The experimental data were fitted through non-linear regression, using the Fig. P software (Biosoft). Model variances were compared through the F-test. Fcalculated can be obtained as the ratio between the variances of the two models. When this value surpasses the Ftabulated value with 95% confidence the most appropriate model is that with the lowest variance. When Fcalculated is lower than Ftabulated, there is no significant difference between the models and therefore either can be used to describe the experimental data mathematically. Details are provided in Supplementary Material 6. Fig. 2 shows the effect of temperature on the dye adsorption at pH values of 2 and it is clear that the temperature does not significantly affect the final adsorption capacity for either adsorbent studied. In contrast, when the pH is increased there is a sharp decrease in the adsorption capacity for both adsorbents. The maximum adsorption capacities at pH values of 2 and 25 C were 213.9 mg g1 for the PC adsorbent and 159.3 mg g1 for the BIO adsorbent. Some studies have been performed on the dye RR2 using different adsorbent preparation techniques and different types of industrial sludge. Among these studies, relevant maximum adsorption capacities include 62.5 mg g1 obtained by Netpradit et al. (2003), while Vasques et al. (2009) reported 53.48 mg g1 and Geethakarthi and Phanikumar (2011) observed a value of
Table 5 Parameters and statistical data for dye RR2 adsorption isotherms (value ± deviation) for PC (a) and BIO (b) adsorbents, under different pH and temperature conditions. Ads.
T ( C)
pHi
Langmuir Model qm (mg g1)
BIO
PC
25 25 45 25 25 45
2 4 2 2 4 2
159.3 83.3 152.5 213.9 75.4 217.7
± ± ± ± ± ±
10.2 1.8 7.8 4.9 2.3 2.3
Freundlich Model KL (L mg1) 102 27.1 17.6 19.4 21.4 42.3 16.2
± ± ± ± ± ±
7.2 2.5 4.4 4.0 12.6 5.2
R2
KF (mg g1)
0.98 1.00 0.98 0.99 0.97 0.97
77.8 30.7 60.2 59.6 44.4 60.7
± ± ± ± ± ±
30.3 14.5 18.5 7.7 10.6 16.4
N 7.2 4.9 5.0 2.9 10.4 3.1
± ± ± ± ± ±
5.3 2.7 2.0 0.9 5.1 0.9
R2
Fcal
F0,05
0.71 0.86 0.90 0.91 0.87 0.94
15.19 65.75 7.07 13.70 4.41 2.10
4.28 4.28 4.28 4.28 4.28 4.28
G.G. Sonai et al. / Journal of Environmental Management 168 (2016) 149e156
Fig. 1. (a) Initial effect of pH on the removal of the dye RR2 at T ¼ 25 C, CRR2 ¼ 500 mg L1, using 5 g L1 of adsorbent; and (b) effect of adsorbent concentration on the final pH.
1
55.9 mg g . 3.3. Effect of ionic strength Fig. 4 shows the influence of NaCl on the removal of dye RR2 by adsorption. When the NaCl concentration is increased, the dye removal slightly decreases for both adsorbents. This is evident after the first addition of NaCl to the system. At the pH values studied, the adsorbent surface is positively charged, according to the pHPZC values. The adsorbate surface, on the other hand, is negatively charged, due to the ReSO 3 groups present in the dye RR2 structure. Cl ions may interfere with the electrostatic attraction between SO 3 and the adsorbent positive charges, hindering the effectiveness of the dye adsorption (Netpradit et al., 2004; Aldegs et al., 2008). On the other side, for values of pH > pHPZC it is expected that the system presents repulsion of charges between the dye and the adsorbents, both negatively charged. Consequently, with the addition of more negative charges (Cl) one could expect the occurrence of a decrease in the capacity of adsorption for both adsorbents, BIO and PC (Aldegs et al., 2008).
153
Fig. 2. Equilibrium isotherms for dye RR2 adsorption at 25 C with 5 g L1 BIO adsorbent (a) and PC adsorbent (b) for different pH values; experimental results and their fitting to the Freundlich (d) and Langmuir (d) models.
3.4. Desorption Fig. 5 presents the desorption results obtained. Approximately 45% of dye RR2 was desorbed in a strongly basic solution. This reveals that one of the main adsorption processes involved in this case is charge transfer. However, with 55% of the dye remaining adsorbed, chemical bonding may also be involved in the adsorption process (Mckay and Ireland, 1987; Santos et al., 2008). These results also show that, due to a relatively low desorption capacity, the adsorbents studied must be appropriately disposed of in a well-designed landfill site after their use. 3.5. Adsorption kinetics 3.5.1. Kinetic models Equations (6) and (7) describe the adsorption kinetics of the pseudo-first-order (Lagergren (1898)) and pseudo-second-order (Ho (1995)) models, respectively.
qt ¼ qeq 1 exp k1;ads $t qt ¼
k2;ads $q2eq $t 1 þ k2;ads $qeq $t
(6)
(7)
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Fig. 5. Desorption kinetics for dye RR2 adsorption onto BIO and PC adsorbents at 25 C and pH ¼ 11.
Fig. 3. Equilibrium isotherms for dye RR2 adsorption at pH ¼ 2 with 5 g L1 BIO adsorbent (a) and PC adsorbent (b) for different temperature values; experimental results and their fitting to the Freundlich (d) and Langmuir (d) models.
orders are, respectively, k1,ads and k2,ads. Fig. 6 presents the kinetics results. The experimental data were fitted to the pseudo-first-order and pseudo-second-order models, and the parameters found are presented in Supplementary Material 6. The results of the F-test indicate that the pseudo-second-order kinetic model provides the best fit for tests 1BIO, 2BIO, 4BIO, and 6PC. However, the pseudo-first-order model provides the best fit for the test 8PC. There was no significant difference between the models studied and therefore either can be used to describe tests 3BIO, 5PC, and 7PC mathematically. The studies on the effect of pH (Fig. 6) showed that in the case of the BIO adsorbent varying the solution pH from 2 to 4 lowers the adsorption capacity by approximately 15%, and by up to 31% for the PC adsorbent. On the other hand, the studies carried out varying the temperature of the dye RR2 solutions did not show significant differences in the final adsorption capacities. 3.6. Thermodynamic parameters The standard Gibbs free energy of adsorption (DG ) can be related to the Langmuir adsorption constant through Equation (8) (Ponnusami and Srivastava, 2009; Milonjic, 2007).
DG ¼ RT ln KL
(8)
where DG is the standard Gibbs free energy of adsorption, KL is the Langmuir adsorption constant, R is the gas constant (8314 kJ mol1 K1), and T is the temperature. The Langmuir equilibrium constants (KL1 and KL2) are related to two temperatures (T1 and T2) through the Van't Hoff equation, which was used to predict the values for the heat of adsorption (DH ) through Equation (9) (Doke and Khan, 2013).
ln
KL1 DH ¼ KL2 R
1 1 T1 T2
(9)
The standard entropy changes (DS ) for the adsorption process are determined through Equation (10). Fig. 4. Influence of ionic force on dye RR2 removal with BIO and PC adsorbents at 25 C and pH ¼ 2.
where qt and qeq are the solid-phase adsorbate concentrations per adsorbent mass unit at time t and at equilibrium, respectively. The adsorption kinetics constants of pseudo-first and pseudo-second
DG ¼ DН TDS
(10)
Negative enthalpy values indicate that the adsorption process is exothermic, which is characteristic of physical adsorption; additionally, the positive values for the entropy variation suggest that there is good affinity between the dye and the adsorbent. Values are presented in Supplementary Material 6. The negative values for
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155
Fig. 6. Adsorption kinetics for dye RR2 using PC (a) and BIO (b) adsorbents at different pH values; and different temperatures using PC (c) and BIO (d); experimental results and their fitting to the pseudo-first-order (d) and pseudo-second-order (d) models.
the Gibbs free energy indicate that the adsorption process occurs spontaneously (Jain et al., 2003; Dural et al., 2011).
4. Conclusions Most kinetic tests provided results which were best fitted to the pseudo-second-order model, while in the case of the equilibrium tests the results best fitted the Langmuir model, as determined through the F-test. On increasing the solution pH from 2 to 4 the adsorption capacity decreased. However, increasing the solution temperature from 25 to 45 C did not influence the dye adsorption capacity. The adsorption of the dye RR2 is less favored as the ionic force of the solution is increased. The PC adsorbent showed better adsorption capacity than the BIO adsorbent. This difference on performance between the catalysts can be associated with the higher amount of acid groups on the surface of PC than BIO surface, mainly carboxylic groups, which produce adsorbent positively charges, favoring the adsorption of anionic compounds. Therefore, the values of surface area, volume and pore diameter did not present high variation between the adsorbents, confirming the high influence of acid groups in the surface of PC and BIO on the removal of RR2 dye. . The thermodynamic parameters investigated indicated the occurrence of exothermic and spontaneous adsorption processes in which the adsorbate has an affinity for the adsorbents. The activation energy values determined indicate that the adsorption occurs through physical adsorption. Lastly, the results obtained indicate that the adsorption capacity of these textile industry residues in relation to the adsorption of dyes can be increased by applying thermal and chemical treatments, providing a low-cost alternative to the use of commercial-grade activated carbon.
Acknowledgments The authors are grateful to CNPq e National Counsel of Technological and Scientific Development, Brazil, for financial support and the Federal University of Santa Catarina. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2015.12.003. References Aksu, Z., Akin, A.B., 2010. Comparison of remazol black B biosorptive properties of live and treated activated sludge. Chem. Eng. J. 165, 184e193. Aldegs, Y., Elbarghouthi, M., Elsheikh, A., Walker, G., 2008. Effect of solution pH, ionic strength, and temperature on adsorption behavior of reactive dyes on activated carbon. Dyes Pigments 77, 16e23. Allen, S.J., McKay, G., Porter, J.F., 2004. Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems. J. Coll. Int. Sci. 280, 322e333. Annadurai, G., Juang, R.S., Yen, P.S., Lee, D.J., 2003. Use of thermally treated waste biological sludge as dye absorbent. Adv. Environ. Res. 7, 739e744. Babic, B.M., Milonjic, S.K., Polovina, M.J., Kaludierovic, B.V., 1999. Point of zero charge and intrinsic equilibrium constants of activated carbon cloth. Carbon 37, 477e481. Babu, C.S., Chakrapani, C., Rao, K.S., 2011. Equilibrium and kinetic studies of reactive Red 2 dye adsorption onto prepared activated carbons. J. Chem. Pharmac. Res. 3, 428e439. Bailey, S.E., Olin, T.J., Bricka, M., Adrian, D., 1999. A review of potentially low-cost sorbents for heavy metals. Water Res. 33, 2469e2479. Bhatnagar, A., Jain, A.K., 2005. A comparative adsorption study with different industrial wastes as adsorbents for the removal of cationic dyes from water. J. Coll. Int. Sci. 281, 49e55. Bhattacharyya, K.G., Sarma, J., Sarma, A., 2009. Azadirachta indica leaf powder as a biosorbent for Ni(II) in aqueous medium. J. Hazard. Mat. 165, 271e278.
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Boehm, H.P., 1994. Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 32, 759e769. Carneiro, G.A., Umbuzeiro, D.P., Oliveira, M.V.B., Zanoni, B., 2010. Assessment of water contamination caused by a mutagenic textile effluent/dyehouse effluent bearing disperse dyes. J. Hazard. Mat. 174, 694e699. Chang, M.Y., Juang, R.S., 2004. Adsorption of tannic acid, humic acid, and dyes from water using the composite of chitosan and activated clay. J. Coll. Int. Sci. 278, 18e25. Crini, G., 2006. Non-conventional low-cost adsorbents for dye removal: a review. Biores. Technol. 97, 1061e1085. Doke, K.M., Khan, E.M., 2013. Adsorption thermodynamics to clean up wastewater; critical review. Rev. Environ. Sci. Bio. Technol 12, 25e44. Dural, M.U., Cavas, L., Papageorgiou, S.K., Katsaros, F.K., 2011. Methylene blue adsorption on activated carbon prepared from Posidonia oceanica (L.) dead leaves: kinetics and equilibrium studies. Chem. Eng. J. 168, 77e85. ndez, C., Larrechi, M.S., Callao, M.P., 2010. An analytical overview of processes Ferna for removing organic dyes from wastewater effluents. Trends Anal. Chem. 29, 1202e1211. Fonts, I., Azuara, M., Gea, G., Murillo, M.B., 2009. Study of the pyrolysis liquids obtained from different sewage sludge. J. Anal. Appl. Pyrolysis 85, 184e191. Fonts, I., Gea, G., Azuara, M., Abrego, J., Arauzo, J., 2012. Sewage sludge pyrolysis for liquid production: a review. Renew. Sustain. Energy Rev. 16, 2781e2805. €esungen. J. Phys. Chem. 57, 385e470. Freundlich, H., 1907. Üeber die adsorption in lo ndez, A., 2007. The effect of acid treatment on the pyrolysis Gasco, G., Cueto, M.J., Me behavior of sewage sludges. J. Anal. Appl. Pyrolysis 80, 496e501. Geethakarthi, A., Phanikumar, B.R., 2011. Adsorption of reactive dyes from aqueous solutions by tannery sludge developed activated carbon: kinetic and equilibrium studies. Int. J. Environ. Sci. Technol. 8, 561e570. Gupta, V.K., Ali, I., Suhas, A., Mohan, D., 2003. Equilibrium uptake and sorption dynamics for the removal of a basic dye (basic red) using low-cost adsorbents. J. Coll. Int. Sci. 265, 257e264. Gupta, V.K., Suhas, A., 2009. Application of low-cost adsorbents for dye removal- a review. J. Environ. Manag. 90, 2313e2342. Ho, Y.S., 1995. Adsorption of Heavy Metals from Waste Streams by Peat. University of Birmingham, UK. Ho, Y., McKay, G., 1998. Sorption of dye from aqueous solution by peat. Chem. Eng. J. 70, 115e124. Ho, Y.S., McKay, G., 2003. Sorption of dyes and copper ions onto biosorbents. Process Biochem. 38, 1047e1061. ndez, J., Fuente, E., Pis, J., 2001. Reactivity of pyrolyzed sewage Inguanzo, M., Mene sludge in air and CO2. J. Anal. Appl. Pyrolysis 58e59, 943e954. Jain, A., Gupta, V., Bhatnagar, A., 2003. Utilization of industrial waste products as adsorbents for the removal of dyes. J. Hazard. Mat. 101, 31e42. Khursheed, A., Kazmi, A.A., 2011. Retrospective of ecological approaches to excess sludge reduction. Water Res. 45, 4287e4310. Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances. K. Sven. Vetensk. 24, 1e39. Langmuir, I., 1918. The adsorption of gases on plane surfaces of glass, mica and
platinum. J. Am. Chem. Soc. 40, 1361e1403. Mckay, G., Ireland, N., 1987. Desorption and regeneration of dye colours from lowcost materials. Water Res. 21, 375e377. McKay, G., 1996. Use of Adsorbents for the Removal of Pollutants from Wastewaters. CRC, New York. ndez, A., Gasco , G., Freitas, M.M.A., Siebielec, G., Stuczynski, T., Figueiredo, J.L., Me 2005. Preparation of carbon-based adsorbents from pyrolysis and air activation of sewage sludges. Chem. Eng. J. 108, 169e177. Milonjic, S., 2007. A consideration of the correct calculation of thermodynamic parameters of adsorption. J. Serbian Chem. Soc. 72, 1363e1367. Mittal, A., Mittal, J., Malviya, A., Kaur, D., Gupta, V.K., 2010. Decoloration treatment of a hazardous triarylmethane dye, Light Green SF (Yellowish) by waste material adsorbents. J. Coll. Int. Sci. 342, 518e527. Netpradit, S., Thiravetyan, P., Towprayoon, S., 2003. Application of “waste” metal hydroxide sludge for adsorption of azo reactive dyes. Water Res. 37, 763e772. Netpradit, A., Thiravetyan, S., Towprayoon, S., 2004. Adsorption of three azo reactive dyes by metal hydroxide sludge: effect of temperature, pH, and electrolytes. J. Coll. Int. Sci. 270, 255e261. Oliveira, D.P., Carneiro, P.A., Sakagami, M.K., Zanoni, M.V.B., Umbuzeiro, G.A., 2007. Chemical characterization of a dye processing plant effluent-identification of the mutagenic components. Mutat. Res. 626, 135e142. Ponnusami, V., Srivastava, S.N., 2009. Studies on application of teak leaf powders for the removal of color from synthetic and industrial effluents. J. Hazard. Mat. 169, 1159e1162. Prado, A.G.S., Torres, J.D., Faria, E.A., Dias, S.L.C.L., 2004. Comparative adsorption studies of indigo carmine dye on chitin and chitosan. J. Coll. Int. Sci. 277, 43e47. Santos, S.C.R., Vílar, V.J.P., Boaventura, R.A.R., 2008. Waste metal hydroxide sludge as adsorbent for a reactive dye. J. Hazard. Mat. 153, 999e1008. ~o espectrome trica de Silverstein, R.M., Webster, F.X., Kiemle, D.J., 2005. Identificaça ^nicos. LCT, Rio de Janeiro. compostos orga Smith, K.M., Fowler, G.D., Pullket, S., Graham, N.J.D., 2009. Sewage sludge-based adsorbents: a review of their production, properties and use in water treatment applications. Water Res. 43, 2569e2594. Srinivasan, A., Viraraghavan, T., 2010. Decolorization of dye wastewaters by biosorbents: a review. J. Environ. Manag. 91, 1915e1929. Vasques, A.R., Souza, S.M.G.U., Valle, J.A.B., Souza, A.A.U., 2009. Application of ecological adsorbent in the removal of reactive dyes from textile effluents. J. Chem. Technol. Biotechnol. 84, 1146e1155. Vijayaraghavan, K., Yun, Y.S., 2008. Biosorption of C.I. Reactive Black 5 from aqueous solution using acid-treated biomass of brown seaweed Laminaria sp. Dyes Pigments 76, 726e732. Vijayaraghavan, K., Won, S.W., Yun, Y.S., 2009. Treatment of complex. J. Hazard. Mat. 167, 790e796. Werther, J., Ogada, T., 1999. Sewage sludge combustion. Prog. Energy Combust. Sci. 25, 55e116. Zhang, B., Xiong, S., Xiao, B., Yu, D., Jia, X., 2011. Mechanism of wet sewage sludge pyrolysis in a tubular furnace. Int. J. Hydrogen Energy 36, 355e363.
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Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman
Research article
The application of textile sludge adsorbents for the removal of Reactive Red 2 dye bora de Oliveira*, Gabriela G. Sonai, Selene M.A. Guelli U. de Souza, De ^nio Augusto U. de Souza Anto polis, CEP 88040-900, SC, Brazil Laboratory of Mass Transfer, Chemical Engineering Department, PO Box 476, Federal University of Santa Catarina, Floriano
a r t i c l e i n f o
a b s t r a c t
Article history: Received 12 September 2015 Received in revised form 6 December 2015 Accepted 7 December 2015 Available online xxx
Sludge from the textile industry was used as a low-cost adsorbent to remove the dye Reactive Red 2 from an aqueous solution. Adsorbents were prepared through the thermal and chemical treatment of sludge originating from physicalechemical (PC) and biological (BIO) effluent treatment processes. The adsorbent characterization was carried out through physicalechemical analysis, X-ray fluorescence (XRF) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, pHPZC determination, Boehm titration method, BrunauereEmmetteTeller (BET) surface area analysis and scanning electron microscopy (SEM). Batch kinetic experiments and adsorption isotherm modeling were conducted under different pH and temperature conditions. The results for the kinetic studies indicate that the adsorption processes associated with these systems can be described by a pseudo-second-order model and for the equilibrium data the Langmuir model provided the best fit. The adsorption was strongly dependent on the pH but not on the temperature within the ranges studied. The maxima adsorption capacities were 159.3 mg g1 for the BIO adsorbent and 213.9 mg g1 for PC adsorbent at pH of 2 and 25 C. © 2015 Elsevier Ltd. All rights reserved.
Keywords: Water reuse Adsorption Reactive dye Textile sludge Reactive Red 2
1. Introduction The textile industry generates large volumes of liquid effluents containing dyes, mostly as residues of textile fiber dyeing processes. Such effluents must be properly treated, as they can cause serious environmental problems. The presence of dyes reduces the water transparency, which interferes with photosynthesis and therefore ndez et al., 2010; Oliveira et al., harms aquatic plant life (Ferna 2007). Dyes are recalcitrant molecules, being resistant to aerobic digestion, light, heat, and oxidizing agents. Some studies also show that they may be carcinogenic or mutagenic, particularly in the case of azo dyes and their by-products (Gupta and Suhas, 2009; Carneiro et al., 2010; McKay, 1996). Adsorption is a separation and purification process that is broadly used to remove polluting substances which do not easily biodegrade. It is a promising technique and has received greater attention that other removal methods in recent decades (Jain et al., 2003; Ho and McKay, 2003).
* Corresponding author. E-mail address: [email protected] (D. de Oliveira). http://dx.doi.org/10.1016/j.jenvman.2015.12.003 0301-4797/© 2015 Elsevier Ltd. All rights reserved.
Commercial-grade activated carbon is the most commonly used adsorbent for the removal of effluent color, due to its efficiency. However, its broader use is restricted due to its high cost. Moreover, the reuse or dispose of powdered activated carbons are difficult due to the very fine powder that can remain suspended in treated water during a long time. Thus, several alternative adsorbents have been studied in order to reduce the cost of this type of treatment (Crini, 2006; Bhatnagar and Jain, 2005; Gupta et al., 2003). An alternative adsorbent is considered to be of low-cost when minimal processing is required, it is abundant in nature, or it is derived from an industrial by-product (Gupta and Suhas, 2009; Bailey et al., 1999). Such adsorbents may be made of peat (Ho and McKay, 1998), seaweed (Vijayaraghavan and Yun, 2008), chitosan (Chang and Juang, 2004; Prado et al., 2004), leaves (Bhattacharyya et al., 2009), sawdust (Vijayaraghavan et al., 2009), agricultural industry waste (Mittal et al., 2010), peat (Allen et al., 2004) or sludge (Netpradit et al., 2004; Vasques et al., 2009), among others. Sludge can be defined as the residue generated from an effluent treatment process. In primary treatment, which is characterized by physicalechemical processes, the resulting residue contains a mixture of inorganic compounds. On the other hand, secondary treatment involving biological processes results in a residue containing a complex mixture of non-digested organic compounds and
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dead microorganisms (Aksu and Akin, 2010; Smith et al., 2009; Fonts et al., 2012). However, the final characteristics of such a residue may vary greatly depending on the sludge origin, treatments applied and even the coagulating agents used (Smith et al., 2009; Annadurai et al., 2003; Khursheed and Kazmi, 2011). Converting sludge into adsorbents may be of interest due to the potential value of the residue, and is of great significance considering the increasing amounts of sludge generated and the presence of more rigorous legislation that regulates its disposal and use (Smith et al., 2009). The conversion can be made through sludge pyrolysis. This process is characterized by decomposing organic matter in the absence of oxygen at between 300 and 900 C while generating gas, a carbonous residue, and oils. The resulting gas and oils can be used as fuels while the solid residue can be burned for energy or used to produce low-cost adsorbents (Vasques et al., 2009; Werther and Ogada, 1999; Inguanzo et al., 2001; Fonts et al., 2009). The removal of dyes from aqueous solution using alternative adsorbents has been extensively studied by several authors (Gupta and Suhas, 2009; Crini, 2006; Srinivasan and Viraraghavan, 2010). The removal of Reactive Red 2 (RR2) dye using sludge from several origins has been studied by Netpradit et al. (2003, 2004); Vasques et al. (2009); Babu et al. (2011); Geethakarthi and Phanikumar (2011). Taking into account the above presented statements, the aim of this study was to evaluate the thermal treatment (through pyrolysis) and chemical treatment (with 0.1 M H2SO4) of sludge samples generated during the physicalechemical or biological treatment of textile effluents, in order to obtain adsorbents for the removal of Reactive Red 2 dye from aqueous solution. The effects of solution pH and temperature were also investigated. The thermodynamic parameters Gibbs free energy (DG ), adsorption heat (DH ) and entropy (DS ) were determined.
2.2. Adsorbent characterization The physicalechemical properties of the adsorbents obtained were determined through X-ray fluorescence (XRF) spectroscopy (Shimadzu, EDX-700). The point of zero charge was estimated through an adapted version of the batch equilibrium method described by Babic et al. (1999). The adsorbents were analyzed by FTIR spectroscopy (Perkin Elmer, Spectrum 100) in order to determine the functional groups present. A scanning electron microscope (JEOL, JSM-6390LV) was used to observe the surface morphology of the material andBET surface area analysis (Autosorb 1C e Quantachrome)was performed in order to determine the textural properties. The acid properties of adsorbents surface were determined by the method ofBoehm (1994). First, 0.5 g of adsorbent were mixed with 100 mL of different bases (0.05 M NaHCO3, 0.05 M Na2CO3 or 0.05 M NaOH) in flasks of 250 mL. The Erlenmeyer flasks were sealed and kept under stirring during 24 h at25 C. The samples were filtered and aliquots of 10 mL were titrated with HCl 0.1 M. 2.3. Adsorbate solutions Dye solutions were prepared by diluting a stock solution with distilled water. The pH of each solution was adjusted to the desired value by adding diluted H2SO4 or NaOH, with the aid of a pHmeter (Quimis, Qe400M2). Details about the chemical structure of the dye Reactive Red 2 and its main physical and chemical properties are presented in the Supplementary Material 2. A UVevis spectrophotometer (Shimadzu, 1240) was used to determine the dissolved dye RR2 concentrations. Calibration curves were built in order to determine the final concentration in solution after the adsorption experiments, measured at the longest adsorption wavelength for this dye (lmax ¼ 538 nm).
2. Materials and methods
2.4. Equilibrium studies
2.1. Adsorbent preparation
2.4.1. Effect of initial pH The influence of solution pH was studied using 5 g L1 of adsorbent in solution. For each initial pH condition, this amount of adsorbent was placed in a 250 mL Erlenmeyer flask with 50 mL of 500 mg L1 dye RR2 solution. The system was stirred at 115 rpm in an orbital shaker at 25 C for 15 h. The resulting dye solutions were then collected and analyzed using a UVevis spectrophotometer and a pHmeter. The percentage of dye removed from the solution was calculated as follows:
Sludge generated by a Brazilian textile company was used to prepare the adsorbents. Sludge produced during physicalechemical (PC) or biological (BIO) effluent treatment were subjected to thermal and chemical treatment in order to obtain the adsorbents. The raw sludge samples were firstly sun-dried for three days and then dried in an oven (Tecnal, TE-393/1) at 80 C for approximately 4 h. Fractions with diameters of between 0.152 and 0.450 mm were selected for the experiments. Procedures for the thermal and chemical treatments were based on the work of Vasques et al. (2009). 2.1.1. Thermal treatment For the thermal treatment, approximately 40 g of raw sludge was placed in a stainless steel reactor attached to a muffle furnace (EDG, 3P-S 3000). The sample was heated in a closed system (Supplementary Material 1) at 500 C under low vacuum in the muffle furnace (1) for 70 min. The gases released were condensed (2) and collected in a flask (3). 2.1.2. Chemical treatment For the chemical treatment, 1g of pyrolyzed material was placed in a 250 mL Erlenmeyer flask with 50 mL of a 0.1 M solution of H2SO4. The system was stirred at 115 rpm in an orbital shaker (Tecnal, TE-424) at 25 C for 3 h. The resulting product was filtered through filter paper and left in the oven at 105 C until a constant weight was obtained.
%removal ¼
ðCo CÞ $100 Co
(1)
where C0 and C are the initial and final dye concentrations (mg L1), respectively. All adsorption experiments were performed in duplicate. 2.4.2. Adsorption isotherms In order to obtain the adsorption isotherms 50 mL of dye RR2 solutions in different concentrations (see Table 1) and 5 g L1 of adsorbent were placed in 250 mL Erlenmeyer flasks for equilibrium tests. Samples were placed under constant stirring at 115 rpm in an orbital shaker, under different pH (2 and 4) and temperature (25 and 45 C) conditions for 15 h, in order to guarantee the adsorption equilibrium. The samples were then decanted and aliquots of the supernatant solution were collected to obtain the final dye concentration. The quantity of adsorbed dye q (mg g1) was calculated through the mass balance relation:
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151
Table 1 Initial dye concentrations at each point on the adsorption isotherms for PC (a) and BIO (b) adsorbents under different pH and temperature conditions. CRR2 (mg L1)
Point
PC
BIO
1 2 3 4 5 6 7
q¼
pH ¼ 2 T ¼ 25 and 45 C
pH ¼ 4 T ¼ 25 C
pH ¼ 2 T ¼ 25 and 45 C
pH ¼ 4 T ¼ 25 C
400 500 600 700 800 900 1000
200 300 400 500 600 700 800
300 400 500 600 700 800 900
100 200 300 350 400 450 500
ðCo CÞV m
(2) 1
where C0 and C are the initial and final dye concentrations (mg L ), respectively, V is the solution volume (L) and m is adsorbent mass (g). 2.5. Effect of ionic strength Tests were carried out in order to study the behavior of dye RR2 adsorption in the presence of a salt (NaCl) broadly used in the textile industry for fabric dyeing and which is consequently present in the effluent at the treatment plants (Netpradit et al., 2004). To perform the tests, 5 g L1 of adsorbent and 800 mg L1 of dye RR2 solution were placed in 250 mL Erlenmeyer flasks at pH ¼ 2, with NaCl concentrations varying from 0.1 to 0.4 mol L1. Samples were stirred at 115 rpm in an orbital shaker for 15 h. In sequence, the resulting dye solutions were collected and analyzed on a UVevis spectrophotometer. The percentage of dye removed from the solution was calculated according to Equation (1). 2.6. Desorption Desorption tests were performed in order to investigate the dye RR2 adsorption process mechanism. Firstly, adsorbents were saturated with a 400 mg L1 dye RR2 solution. Saturation was achieved by leaving the samples in a shaker at 115 rpm and 25 C for 15 h. Dye-saturated adsorbents were filtered and dried in an oven. The amount of dye adsorbed was calculated through the difference between the initial and final concentrations of the 400 mg L1 dye solution. For the desorption tests, 0.5 g of saturated adsorbent was placed in a 250 mL Erlenmeyer flask with 100 mL of distilled water at alkaline pH (pH ¼ 11). Samples were stirred at 115 rpm and 25 C. Aliquots of the solution were collected at predetermined time intervals and analyzed on a UVevis spectrophotometer. The percentage of desorption was calculated according to Equation (3).
%Desorption ¼
! CRR2desorption $100 CRR2adsorption
Table 2 Experimental conditions applied in the adsorption kinetics tests. Run/Adsorbent
C0 (mg L1)
CAds (g L1)
pH
T ( C)
1 2 3 4 5 6 7 8
500 500 500 500 500 500 500 500
5 5 5 5 5 5 5 5
2 4 2 2 2 4 2 2
25 25 35 45 25 25 35 45
BIO BIO BIO BIO PC PC PC PC
orbital shaker at 115 rpm and aliquots of the solution were collected in regular time intervals, for analysis by UVevis spectroscopy, until equilibrium had been reached.
3. Results and discussion 3.1. Adsorbent characterization Table 3 shows the results for the chemical composition obtained by XRF spectroscopy. The main chemical elements are aluminum for the PC adsorbent (33.51% m/m) and silicon for the BIO adsorbent (12.59% m/m). The decrease in mass percentage for some elements may be due to erosion caused by the chemical treatment. The high values for the loss on ignition (LOI) of these materials indicate the presence of organic matter. The data on the physicalechemical properties, pHPZC, and BET surface area are presented in Table 4. The adsorbent obtained from the PC sludge (PC adsorbent) contained a greater amount of inorganic content than the adsorbent obtained from the BIO sludge (BIO adsorbent), which influenced the pH of the adsorbents and consequently, their pHPZC. The BET surface area values are low in relation to other adsorbents. According to Smith et al. (2009), one of the reasons for this is the high levels of inorganic, non-porous material present in these materials. The IR spectra of both adsorbents (Supplementary Material 3) present a broad absorption band at between 3000 cm1 and
(3)
where CRR2desorption is the concentration of dye released into the solution, and CRR2adsorption is the dye concentration in the saturated adsorbent (mg L1). 2.7. Kinetic studies The kinetics of batch adsorption experiments conducted under different pH and temperature conditions, according to Table 2, were investigated. Samples were kept under constant stirring on an
Table 3 XRF analyses results for thermally and chemically-treated sludges. Element
BIO (% m/m)
PC (% m/m)
Al Ca Si P Fe K S CO2
6.71 0.96 12.59 2.65 6.28 2.50 1.79 64.85
33.51 1.80 9.78 8.89 2.22 0.85 1.51 40.12
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Table 4 Results of physicalechemical characterization of adsorbents. Analysis
PC
BIO
Moisture (%)a Ash (%) Volatile materials (%) Fixed carbon (%) pH pHPZC BET (m2 g1) Volume of pores (cm3 g1) Average pore diameter (nm)
7.77 ± 0.01 59.88 ± 0.10 17.95 ± 0.03 22.17 ± 0.08 3.80 ± 0.03 4.5 50 0.15 12.20
7.91 ± 0.02 35.15 ± 0.08 20.39 ± 0.70 44.47 ± 0.78 3.01 ± 0.01 4.0 44 0.14 12.79
a
Dry basis.
3600 cm1. This band corresponds to OeH stretching of the hydroxyl groups in phenol, alcohol and carboxylic compounds. It is also associated with the NeH stretching of amine and amide groups (Silverstein et al., 2005; Gasco et al., 2007). According to Zhang et al. (2011), the strong bands observed at around 1085 cm1 and 1094 cm1 are attributable to the angular deformation of CeO groups. Among the compounds associated with this absorption ndez band are ethers, phenols, lactones, and carboxylic acids (Me et al., 2005). Absorption peaks on the spectra can be noted at around 1620 cm1, which correspond to C]O stretching. The broad brand in 500 cm1 refers to the angular deformation outside the plane of NeH bonding (Silverstein et al., 2005). By the method of Boehm (Supplementary Material 4) it was possible to quantify the presence of acid functional groups in the surface of the adsorbents. Both adsorbents have a high amount of carboxylic groups compared to phenolic and lactonic ones. The adsorbent PC presents higher content of carboxylic acids and acids groups compared to the BIO adsorbent. The SEM image of the raw BIO sludge shows no porous structures being evident on the surface. However, the BIO adsorbent shows porosity, due to the organic matter decomposed during the thermal and chemical treatments. The raw PC sludge shows no notable differences in comparison to the PC adsorbent (Supplementary Material 5). 3.2. Adsorption equilibrium studies 3.2.1. Effects of initial pH The results obtained indicate that the pH plays an important role in the dye RR2 adsorption for both the BIO and PC adsorbents. In Fig. 1a, it can be observed that the dye adsorption is favored at more acid pH values, for both adsorbents. Additionally, for pH value of 2 there was a greater percentage of removal. The dye used in this study, RR2, has sulfonate ions (ReSO 3 ) that enable adsorption onto positively-charged adsorbents (Netpradit et al., 2004). At pH < pHPZC, the adsorbent surface has positive charges, favoring the adsorption of anions. In contrast, for pH > pHPZC the adsorption of cations is favored due to the
negatively charged surface of the adsorbent (Geethakarthi and Phanikumar, 2011). The determination of the pHPZC was also found to be important in a study performed by Aldegs et al. (2008) in order to describe the adsorption behavior of reactive dyes with ReSO 3 groups in their structures. The pHPZC of BIO adsorbent and PC is 4.0 and 4.5, respectively. This indicates that, above these values of pHPZC, the adsorbents will be negatively charged and, then, the capacity of adsorption will be reduced, since there will be a repulsion of charges between the adsorbent and the dye. 3.2.2. Adsorption isotherms The adsorption isotherms for the two adsorbents related to the removal of dye RR2 from aqueous solutions under different pH (2 and 4) and temperature (25 and 45 C) conditions are presented in Figs. 2 and 3, respectively. Experimental data were fitted to the Langmuir and Freundlich models. The Langmuir isotherm (Langmuir (1918)) is represented as follows:
qe ¼
qm KL Ce 1 þ KL Ce
(4)
where qm is the maximum adsorption capacity, KL is the Langmuir adsorption constant, and Ce is the adsorbate equilibrium concentration in the liquid phase. The Freundlich isotherm (Freundlich (1907)) is represented as follows: ð1=nÞ
qe ¼ KF $Ce
(5)
where KF and n are constants in the Freundlich equation. The experimental data were fitted through non-linear regression, using the Fig. P software (Biosoft). Model variances were compared through the F-test. Fcalculated can be obtained as the ratio between the variances of the two models. When this value surpasses the Ftabulated value with 95% confidence the most appropriate model is that with the lowest variance. When Fcalculated is lower than Ftabulated, there is no significant difference between the models and therefore either can be used to describe the experimental data mathematically. Details are provided in Supplementary Material 6. Fig. 2 shows the effect of temperature on the dye adsorption at pH values of 2 and it is clear that the temperature does not significantly affect the final adsorption capacity for either adsorbent studied. In contrast, when the pH is increased there is a sharp decrease in the adsorption capacity for both adsorbents. The maximum adsorption capacities at pH values of 2 and 25 C were 213.9 mg g1 for the PC adsorbent and 159.3 mg g1 for the BIO adsorbent. Some studies have been performed on the dye RR2 using different adsorbent preparation techniques and different types of industrial sludge. Among these studies, relevant maximum adsorption capacities include 62.5 mg g1 obtained by Netpradit et al. (2003), while Vasques et al. (2009) reported 53.48 mg g1 and Geethakarthi and Phanikumar (2011) observed a value of
Table 5 Parameters and statistical data for dye RR2 adsorption isotherms (value ± deviation) for PC (a) and BIO (b) adsorbents, under different pH and temperature conditions. Ads.
T ( C)
pHi
Langmuir Model qm (mg g1)
BIO
PC
25 25 45 25 25 45
2 4 2 2 4 2
159.3 83.3 152.5 213.9 75.4 217.7
± ± ± ± ± ±
10.2 1.8 7.8 4.9 2.3 2.3
Freundlich Model KL (L mg1) 102 27.1 17.6 19.4 21.4 42.3 16.2
± ± ± ± ± ±
7.2 2.5 4.4 4.0 12.6 5.2
R2
KF (mg g1)
0.98 1.00 0.98 0.99 0.97 0.97
77.8 30.7 60.2 59.6 44.4 60.7
± ± ± ± ± ±
30.3 14.5 18.5 7.7 10.6 16.4
N 7.2 4.9 5.0 2.9 10.4 3.1
± ± ± ± ± ±
5.3 2.7 2.0 0.9 5.1 0.9
R2
Fcal
F0,05
0.71 0.86 0.90 0.91 0.87 0.94
15.19 65.75 7.07 13.70 4.41 2.10
4.28 4.28 4.28 4.28 4.28 4.28
G.G. Sonai et al. / Journal of Environmental Management 168 (2016) 149e156
Fig. 1. (a) Initial effect of pH on the removal of the dye RR2 at T ¼ 25 C, CRR2 ¼ 500 mg L1, using 5 g L1 of adsorbent; and (b) effect of adsorbent concentration on the final pH.
1
55.9 mg g . 3.3. Effect of ionic strength Fig. 4 shows the influence of NaCl on the removal of dye RR2 by adsorption. When the NaCl concentration is increased, the dye removal slightly decreases for both adsorbents. This is evident after the first addition of NaCl to the system. At the pH values studied, the adsorbent surface is positively charged, according to the pHPZC values. The adsorbate surface, on the other hand, is negatively charged, due to the ReSO 3 groups present in the dye RR2 structure. Cl ions may interfere with the electrostatic attraction between SO 3 and the adsorbent positive charges, hindering the effectiveness of the dye adsorption (Netpradit et al., 2004; Aldegs et al., 2008). On the other side, for values of pH > pHPZC it is expected that the system presents repulsion of charges between the dye and the adsorbents, both negatively charged. Consequently, with the addition of more negative charges (Cl) one could expect the occurrence of a decrease in the capacity of adsorption for both adsorbents, BIO and PC (Aldegs et al., 2008).
153
Fig. 2. Equilibrium isotherms for dye RR2 adsorption at 25 C with 5 g L1 BIO adsorbent (a) and PC adsorbent (b) for different pH values; experimental results and their fitting to the Freundlich (d) and Langmuir (d) models.
3.4. Desorption Fig. 5 presents the desorption results obtained. Approximately 45% of dye RR2 was desorbed in a strongly basic solution. This reveals that one of the main adsorption processes involved in this case is charge transfer. However, with 55% of the dye remaining adsorbed, chemical bonding may also be involved in the adsorption process (Mckay and Ireland, 1987; Santos et al., 2008). These results also show that, due to a relatively low desorption capacity, the adsorbents studied must be appropriately disposed of in a well-designed landfill site after their use. 3.5. Adsorption kinetics 3.5.1. Kinetic models Equations (6) and (7) describe the adsorption kinetics of the pseudo-first-order (Lagergren (1898)) and pseudo-second-order (Ho (1995)) models, respectively.
qt ¼ qeq 1 exp k1;ads $t qt ¼
k2;ads $q2eq $t 1 þ k2;ads $qeq $t
(6)
(7)
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Fig. 5. Desorption kinetics for dye RR2 adsorption onto BIO and PC adsorbents at 25 C and pH ¼ 11.
Fig. 3. Equilibrium isotherms for dye RR2 adsorption at pH ¼ 2 with 5 g L1 BIO adsorbent (a) and PC adsorbent (b) for different temperature values; experimental results and their fitting to the Freundlich (d) and Langmuir (d) models.
orders are, respectively, k1,ads and k2,ads. Fig. 6 presents the kinetics results. The experimental data were fitted to the pseudo-first-order and pseudo-second-order models, and the parameters found are presented in Supplementary Material 6. The results of the F-test indicate that the pseudo-second-order kinetic model provides the best fit for tests 1BIO, 2BIO, 4BIO, and 6PC. However, the pseudo-first-order model provides the best fit for the test 8PC. There was no significant difference between the models studied and therefore either can be used to describe tests 3BIO, 5PC, and 7PC mathematically. The studies on the effect of pH (Fig. 6) showed that in the case of the BIO adsorbent varying the solution pH from 2 to 4 lowers the adsorption capacity by approximately 15%, and by up to 31% for the PC adsorbent. On the other hand, the studies carried out varying the temperature of the dye RR2 solutions did not show significant differences in the final adsorption capacities. 3.6. Thermodynamic parameters The standard Gibbs free energy of adsorption (DG ) can be related to the Langmuir adsorption constant through Equation (8) (Ponnusami and Srivastava, 2009; Milonjic, 2007).
DG ¼ RT ln KL
(8)
where DG is the standard Gibbs free energy of adsorption, KL is the Langmuir adsorption constant, R is the gas constant (8314 kJ mol1 K1), and T is the temperature. The Langmuir equilibrium constants (KL1 and KL2) are related to two temperatures (T1 and T2) through the Van't Hoff equation, which was used to predict the values for the heat of adsorption (DH ) through Equation (9) (Doke and Khan, 2013).
ln
KL1 DH ¼ KL2 R
1 1 T1 T2
(9)
The standard entropy changes (DS ) for the adsorption process are determined through Equation (10). Fig. 4. Influence of ionic force on dye RR2 removal with BIO and PC adsorbents at 25 C and pH ¼ 2.
where qt and qeq are the solid-phase adsorbate concentrations per adsorbent mass unit at time t and at equilibrium, respectively. The adsorption kinetics constants of pseudo-first and pseudo-second
DG ¼ DН TDS
(10)
Negative enthalpy values indicate that the adsorption process is exothermic, which is characteristic of physical adsorption; additionally, the positive values for the entropy variation suggest that there is good affinity between the dye and the adsorbent. Values are presented in Supplementary Material 6. The negative values for
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Fig. 6. Adsorption kinetics for dye RR2 using PC (a) and BIO (b) adsorbents at different pH values; and different temperatures using PC (c) and BIO (d); experimental results and their fitting to the pseudo-first-order (d) and pseudo-second-order (d) models.
the Gibbs free energy indicate that the adsorption process occurs spontaneously (Jain et al., 2003; Dural et al., 2011).
4. Conclusions Most kinetic tests provided results which were best fitted to the pseudo-second-order model, while in the case of the equilibrium tests the results best fitted the Langmuir model, as determined through the F-test. On increasing the solution pH from 2 to 4 the adsorption capacity decreased. However, increasing the solution temperature from 25 to 45 C did not influence the dye adsorption capacity. The adsorption of the dye RR2 is less favored as the ionic force of the solution is increased. The PC adsorbent showed better adsorption capacity than the BIO adsorbent. This difference on performance between the catalysts can be associated with the higher amount of acid groups on the surface of PC than BIO surface, mainly carboxylic groups, which produce adsorbent positively charges, favoring the adsorption of anionic compounds. Therefore, the values of surface area, volume and pore diameter did not present high variation between the adsorbents, confirming the high influence of acid groups in the surface of PC and BIO on the removal of RR2 dye. . The thermodynamic parameters investigated indicated the occurrence of exothermic and spontaneous adsorption processes in which the adsorbate has an affinity for the adsorbents. The activation energy values determined indicate that the adsorption occurs through physical adsorption. Lastly, the results obtained indicate that the adsorption capacity of these textile industry residues in relation to the adsorption of dyes can be increased by applying thermal and chemical treatments, providing a low-cost alternative to the use of commercial-grade activated carbon.
Acknowledgments The authors are grateful to CNPq e National Counsel of Technological and Scientific Development, Brazil, for financial support and the Federal University of Santa Catarina. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jenvman.2015.12.003. References Aksu, Z., Akin, A.B., 2010. Comparison of remazol black B biosorptive properties of live and treated activated sludge. Chem. Eng. J. 165, 184e193. Aldegs, Y., Elbarghouthi, M., Elsheikh, A., Walker, G., 2008. Effect of solution pH, ionic strength, and temperature on adsorption behavior of reactive dyes on activated carbon. Dyes Pigments 77, 16e23. Allen, S.J., McKay, G., Porter, J.F., 2004. Adsorption isotherm models for basic dye adsorption by peat in single and binary component systems. J. Coll. Int. Sci. 280, 322e333. Annadurai, G., Juang, R.S., Yen, P.S., Lee, D.J., 2003. Use of thermally treated waste biological sludge as dye absorbent. Adv. Environ. Res. 7, 739e744. Babic, B.M., Milonjic, S.K., Polovina, M.J., Kaludierovic, B.V., 1999. Point of zero charge and intrinsic equilibrium constants of activated carbon cloth. Carbon 37, 477e481. Babu, C.S., Chakrapani, C., Rao, K.S., 2011. Equilibrium and kinetic studies of reactive Red 2 dye adsorption onto prepared activated carbons. J. Chem. Pharmac. Res. 3, 428e439. Bailey, S.E., Olin, T.J., Bricka, M., Adrian, D., 1999. A review of potentially low-cost sorbents for heavy metals. Water Res. 33, 2469e2479. Bhatnagar, A., Jain, A.K., 2005. A comparative adsorption study with different industrial wastes as adsorbents for the removal of cationic dyes from water. J. Coll. Int. Sci. 281, 49e55. Bhattacharyya, K.G., Sarma, J., Sarma, A., 2009. Azadirachta indica leaf powder as a biosorbent for Ni(II) in aqueous medium. J. Hazard. Mat. 165, 271e278.
156
G.G. Sonai et al. / Journal of Environmental Management 168 (2016) 149e156
Boehm, H.P., 1994. Some aspects of the surface chemistry of carbon blacks and other carbons. Carbon 32, 759e769. Carneiro, G.A., Umbuzeiro, D.P., Oliveira, M.V.B., Zanoni, B., 2010. Assessment of water contamination caused by a mutagenic textile effluent/dyehouse effluent bearing disperse dyes. J. Hazard. Mat. 174, 694e699. Chang, M.Y., Juang, R.S., 2004. Adsorption of tannic acid, humic acid, and dyes from water using the composite of chitosan and activated clay. J. Coll. Int. Sci. 278, 18e25. Crini, G., 2006. Non-conventional low-cost adsorbents for dye removal: a review. Biores. Technol. 97, 1061e1085. Doke, K.M., Khan, E.M., 2013. Adsorption thermodynamics to clean up wastewater; critical review. Rev. Environ. Sci. Bio. Technol 12, 25e44. Dural, M.U., Cavas, L., Papageorgiou, S.K., Katsaros, F.K., 2011. Methylene blue adsorption on activated carbon prepared from Posidonia oceanica (L.) dead leaves: kinetics and equilibrium studies. Chem. Eng. J. 168, 77e85. ndez, C., Larrechi, M.S., Callao, M.P., 2010. An analytical overview of processes Ferna for removing organic dyes from wastewater effluents. Trends Anal. Chem. 29, 1202e1211. Fonts, I., Azuara, M., Gea, G., Murillo, M.B., 2009. Study of the pyrolysis liquids obtained from different sewage sludge. J. Anal. Appl. Pyrolysis 85, 184e191. Fonts, I., Gea, G., Azuara, M., Abrego, J., Arauzo, J., 2012. Sewage sludge pyrolysis for liquid production: a review. Renew. Sustain. Energy Rev. 16, 2781e2805. €esungen. J. Phys. Chem. 57, 385e470. Freundlich, H., 1907. Üeber die adsorption in lo ndez, A., 2007. The effect of acid treatment on the pyrolysis Gasco, G., Cueto, M.J., Me behavior of sewage sludges. J. Anal. Appl. Pyrolysis 80, 496e501. Geethakarthi, A., Phanikumar, B.R., 2011. Adsorption of reactive dyes from aqueous solutions by tannery sludge developed activated carbon: kinetic and equilibrium studies. Int. J. Environ. Sci. Technol. 8, 561e570. Gupta, V.K., Ali, I., Suhas, A., Mohan, D., 2003. Equilibrium uptake and sorption dynamics for the removal of a basic dye (basic red) using low-cost adsorbents. J. Coll. Int. Sci. 265, 257e264. Gupta, V.K., Suhas, A., 2009. Application of low-cost adsorbents for dye removal- a review. J. Environ. Manag. 90, 2313e2342. Ho, Y.S., 1995. Adsorption of Heavy Metals from Waste Streams by Peat. University of Birmingham, UK. Ho, Y., McKay, G., 1998. Sorption of dye from aqueous solution by peat. Chem. Eng. J. 70, 115e124. Ho, Y.S., McKay, G., 2003. Sorption of dyes and copper ions onto biosorbents. Process Biochem. 38, 1047e1061. ndez, J., Fuente, E., Pis, J., 2001. Reactivity of pyrolyzed sewage Inguanzo, M., Mene sludge in air and CO2. J. Anal. Appl. Pyrolysis 58e59, 943e954. Jain, A., Gupta, V., Bhatnagar, A., 2003. Utilization of industrial waste products as adsorbents for the removal of dyes. J. Hazard. Mat. 101, 31e42. Khursheed, A., Kazmi, A.A., 2011. Retrospective of ecological approaches to excess sludge reduction. Water Res. 45, 4287e4310. Lagergren, S., 1898. About the theory of so-called adsorption of soluble substances. K. Sven. Vetensk. 24, 1e39. Langmuir, I., 1918. The adsorption of gases on plane surfaces of glass, mica and
platinum. J. Am. Chem. Soc. 40, 1361e1403. Mckay, G., Ireland, N., 1987. Desorption and regeneration of dye colours from lowcost materials. Water Res. 21, 375e377. McKay, G., 1996. Use of Adsorbents for the Removal of Pollutants from Wastewaters. CRC, New York. ndez, A., Gasco , G., Freitas, M.M.A., Siebielec, G., Stuczynski, T., Figueiredo, J.L., Me 2005. Preparation of carbon-based adsorbents from pyrolysis and air activation of sewage sludges. Chem. Eng. J. 108, 169e177. Milonjic, S., 2007. A consideration of the correct calculation of thermodynamic parameters of adsorption. J. Serbian Chem. Soc. 72, 1363e1367. Mittal, A., Mittal, J., Malviya, A., Kaur, D., Gupta, V.K., 2010. Decoloration treatment of a hazardous triarylmethane dye, Light Green SF (Yellowish) by waste material adsorbents. J. Coll. Int. Sci. 342, 518e527. Netpradit, S., Thiravetyan, P., Towprayoon, S., 2003. Application of “waste” metal hydroxide sludge for adsorption of azo reactive dyes. Water Res. 37, 763e772. Netpradit, A., Thiravetyan, S., Towprayoon, S., 2004. Adsorption of three azo reactive dyes by metal hydroxide sludge: effect of temperature, pH, and electrolytes. J. Coll. Int. Sci. 270, 255e261. Oliveira, D.P., Carneiro, P.A., Sakagami, M.K., Zanoni, M.V.B., Umbuzeiro, G.A., 2007. Chemical characterization of a dye processing plant effluent-identification of the mutagenic components. Mutat. Res. 626, 135e142. Ponnusami, V., Srivastava, S.N., 2009. Studies on application of teak leaf powders for the removal of color from synthetic and industrial effluents. J. Hazard. Mat. 169, 1159e1162. Prado, A.G.S., Torres, J.D., Faria, E.A., Dias, S.L.C.L., 2004. Comparative adsorption studies of indigo carmine dye on chitin and chitosan. J. Coll. Int. Sci. 277, 43e47. Santos, S.C.R., Vílar, V.J.P., Boaventura, R.A.R., 2008. Waste metal hydroxide sludge as adsorbent for a reactive dye. J. Hazard. Mat. 153, 999e1008. ~o espectrome trica de Silverstein, R.M., Webster, F.X., Kiemle, D.J., 2005. Identificaça ^nicos. LCT, Rio de Janeiro. compostos orga Smith, K.M., Fowler, G.D., Pullket, S., Graham, N.J.D., 2009. Sewage sludge-based adsorbents: a review of their production, properties and use in water treatment applications. Water Res. 43, 2569e2594. Srinivasan, A., Viraraghavan, T., 2010. Decolorization of dye wastewaters by biosorbents: a review. J. Environ. Manag. 91, 1915e1929. Vasques, A.R., Souza, S.M.G.U., Valle, J.A.B., Souza, A.A.U., 2009. Application of ecological adsorbent in the removal of reactive dyes from textile effluents. J. Chem. Technol. Biotechnol. 84, 1146e1155. Vijayaraghavan, K., Yun, Y.S., 2008. Biosorption of C.I. Reactive Black 5 from aqueous solution using acid-treated biomass of brown seaweed Laminaria sp. Dyes Pigments 76, 726e732. Vijayaraghavan, K., Won, S.W., Yun, Y.S., 2009. Treatment of complex. J. Hazard. Mat. 167, 790e796. Werther, J., Ogada, T., 1999. Sewage sludge combustion. Prog. Energy Combust. Sci. 25, 55e116. Zhang, B., Xiong, S., Xiao, B., Yu, D., Jia, X., 2011. Mechanism of wet sewage sludge pyrolysis in a tubular furnace. Int. J. Hydrogen Energy 36, 355e363.