An alternative, low-cost and efficient biosorbent, powdered grape seeds (PGS), was prepared from wastes of a wine industry, and used to remove brilliant blue (BB) and amaranth red (AR) dyes from aqueous solutions. The biosorbent was properly characterized before and after the biosorption operation. The potential of PGS to remove BB and AR dyes was investigated thought kinetic, isotherm and thermodynamic studies. The biosorption of BB and AR was favored at pH 1.0 using biosorbent dosage of 0.500 g L−1, being attained more than 85% of removal percentage. For BB and AR dyes, pseudo-second-order and Elovich models were able to explain the biosorption kinetic. The biosorption equilibrium of BB on PGS was well represented by the Langmuir model, while for AR, the Sips model was the most adequate. The maximum biosorption capacities were 599.5 and 94.2 mg g−1 for BB and AR, respectively. The biosorption of BB and AR on PGS was a spontaneous, favorable and endothermic process. These findings indicated that PGS is a low-cost and efficient biosorbent, which can be used to treat dye containing waters.

Dyes are commonly employed in pharmaceutical formulations to enhance the aesthetic appearance and reduce errors in medication (Pérez-Ibarbia et al. 2016). During the pharmaceutical manufacturing, some of these dyes are lost and, consequently, discarded in effluents (Fernández et al. 2010). The incorrect disposal of dye-containing effluents is a well known problem, which can cause several damages to the environment and human health (Gupta & Suhas 2009). In this way, some countries created severe restrictions for the discharge of colored effluents (Hessel et al. 2007) and, consequently, many studies have been focused to search for treatments able to remove dyes from aqueous effluents (Crini & Badot 2008; Álvarez et al. 2013; Yagub et al. 2014; Dotto et al. 2015a; Khandare & Govindwar 2015).

Several treatments are used to remove dyes from industrial effluents, including chemical precipitation, ion flotation, ion exchange, membrane filtration, AOPs, adsorption, biosorption and electrochemical methods (Yagub et al. 2014; Ahmed et al. 2017). Among these, biosorption, which is defined as ‘the removal of contaminants from aqueous media by inactive or non-living biomass’, has gained attention due to advantages such as low cost, ease of operation, fast kinetics and use of diverse types of biomasses as biosorbents (Dotto et al. 2015a). In this sense, several biosorbents have been used to remove dyes from aqueous media, for example, papaya seeds (Weber et al. 2014), lotus seedpod (He et al. 2016), spent bleaching earth (Belhaine et al. 2016) and oricuri fiber (Meili et al. 2017). The use of grape wastes has been studied in recent years. Torab-Mostaedi et al. (2013) verified the potential of grape peels to remove cadmium and nickel from aqueous media. Al Bsoul et al. (2014) studied the potential of grape seeds as biosorbent for cooper ions. In spite of these efforts, the use of grape seeds as biosorbent for dye removal is scarce.

Currently, there is a great interest in the exploitation of the residues generated by the wine industry (Spiridon et al. 2016; Al-Hamamre et al. 2017). During wine production, it is estimated that approximately 25% of the grape weight results in by-product/waste (termed ‘pomace’ which is comprised of skins and seeds) (Dwyer et al. 2014). Grape seeds contain oil, lignin, cellulose and hemicellulose (Yedro et al. 2015). These compounds, in turn, contain several functional groups that can act as biosorption sites. Based on this information, we believe that grape seeds can be an available, low cost and efficient material, that can be used as biosorbent to remove dyes from aqueous media.

In this research, an alternative low-cost and efficient biosorbent named powdered grape seeds (PGS) was prepared from wastes of a wine industry, and used to treat synthetic solutions containing the pharmaceutical dyes brilliant blue (BB) and amaranth red (AR). The biosorbent was characterized according to the point of zero charge (pHzpc), Boehm titration, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM) and energy X-ray dispersive spectroscopy (EDS). The effects of initial pH of the solution and biosorbent dosage on the biosorption were studied. The biosorption kinetic data were evaluated by the pseudo-first-order (PFO), pseudo-second-order (PSO) and Elovich models. Langmuir, Freundlich and Sips models were used to fit the biosorption equilibrium data. Thermodynamic parameters such as standard Gibbs free energy change (ΔG0), standard enthalpy change (ΔH0) and standard entropy change (ΔS0) were also estimated.

Preparation of PGS biosorbent

PGS biosorbent was prepared from wastes of a wine industry located in Mendoza, Argentina. Vitis vinifera L. grapes were collected from vineyards located in Mendoza province, Argentina (33°04′S, 68°19′W). The grapevine bunches (red cultivar of the Bonarda variety) were subjected to the wine processing. During the wine processing, a pomace containing husks, stems and seeds was generated. This pomace was refrigerated and carried to the laboratory. The grape seeds were manually separated from the pomace, washed with drinking water and then rinsed with Milli-Q water. The seeds were lyophilized for 48 h (Virtis freeze mobile, model 6, USA), pulverized with a mill (Ultracomb, MO-8100A, Argentina) and sieved until the discrete particle size ranging from 80 to 110 μm. The resulting material was named PGS biosorbent.

Characterization techniques

The PGS biosorbent was characterized according to several important aspects regarding biosorption. The point of zero charge (pHzpc) was determined using the 11 points experiment (Park & Regalbuto 1995) in order to assess the surface charge of the biosorbent as a function of the pH. The total acidity and basicity of the biosorbent was verified by the Boehm titration method (Goertzen et al. 2010). FT-IR (Shimadzu, Prestige 21, Japan) was used to identify the main functional groups of the biosorbent (Silverstein et al. 2007). The textural characteristics of the biosorbent and the main elements on the surface were visualized by SEM coupled to EDS (Jeol, JSM-6610LV, Japan) (Goldstein et al. 1992). FT-IR and SEM were also performed after the biosorption process (optimum condition) in order to verify possible modifications on the biosorbent surface.

Pharmaceutical dyes

Two dyes commonly found in pharmaceutical effluents were selected to perform the study: BB and AR, both with industrial grade and purity higher than 85%. BB (triphenylmethane dye, molecular weight 792.8 g mol−1; C.I. 42,090; λmax = 408 nm) and AR (azo dye, molecular weight 604.5 g mol−1; C.I. 16,185; λmax = 521 nm) were supplied by a local manufacturer (Duas Rodas Ind. Jaraguá do Sul, Brazil) and were used without further purification. The three dimensional structural formulae of the dyes are shown in Figure 1. The solutions were prepared with distilled water and the reagents were of analytical grade.
Figure 1

Three dimensional structural formulae of the dyes: (a) BB and (b) AR.

Figure 1

Three dimensional structural formulae of the dyes: (a) BB and (b) AR.

Close modal

Biosorption experiments

The biosorption experiments were realized in batch mode at 200 rpm using a thermostated agitator (Marconi, MA 093, Brazil) in order to verify the effects of initial pH, PGS dosage and also to obtain the kinetic and isotherm curves. Four experimental steps were performed:

  • (I) The effect of initial pH was studied (from 1.0 to 8.0) (adjusted with HNO3 and NaOH) under the following conditions: initial dye concentration of 50 mg L−1, contact time of 1 h, volume of solution of 25 mL, PGS dosage of 2.00 g L−1 and temperature of 25 °C (PGS was put directly in contact with the solutions).

  • (II) The effect of PGS dosage (from 0.25 to 5.00 g L−1) was investigated under the same conditions, using the optimum pH defined elsewhere.

  • (III) Kinetic experiments were performed using the optimum pH and PGS dosage defined above. The initial dye concentration was 50 mg L−1. The experiments were performed at 25 °C with contact time varying from 0 to 120 min and the volume of solution was 25 mL.

  • (IV) Isotherm curves were constructed at 25, 35, 45 and 55 °C, using the optimum pH and PGS dosage defined above. The initial dye concentration ranged from 25 to 300 mg L−1 and the volume of solution was 25 mL, with the aliquots stirred until the equilibrium (maximum 6 h).

After all the experiments, the solid phase was separated by centrifugation (Centribio, 80-2B, Brazil) at 4,000 rpm for 20 min (Dotto et al. 2017) and, the remaining dyes concentration in the liquid phase was measured by spectrophotometry at the maximum wavelength for each dye (Biospectro SP-22, Brazil). To guarantee the experimental accuracy, the experiments were realized in replicate (n = 3) using closed vessels and, blanks were performed. The dye removal percentage (R, %), mass of dye biosorbed per gram of biosorbent at any time (qt (mg g−1)) and at equilibrium (qe (mg g−1)) were calculated as follows (Crini & Badot 2008):
formula
1
formula
2
formula
3
where Co, Ct, Ce (mg L−1) are the dye concentrations at t = 0 at any time and at equilibrium, respectively, W (g) is the biosorbent amount and V (L) is the volume of the solution.

Biosorption kinetics, isotherms and thermodynamics

The biosorption kinetics, isotherms and thermodynamics are fundamental investigations which should be performed in order to evaluate an alternative biosorbent material (Liu & Liu 2008). From the kinetic viewpoint, the biosorption of BB and AR pharmaceutical dyes on PGS was evaluated by the pseudo-first-order (Lagergren 1898), pseudo-second-order (Ho & McKay 1998) and Elovich models (Zeldowitsch 1934), as follows:
formula
4
formula
5
formula
6
where k1 and k2 are the rate constants of pseudo-first-order and pseudo-second-order models, respectively, in (min−1) and (g mg−1 min−1), q1 and q2 are the theoretical values for the biosorption capacity (mg g−1), a is the initial velocity due to dq/dt with qt = 0 (mg g−1 min−1), b is the desorption constant of the Elovich model (g mg−1) and, t is the time (min).
From the equilibrium viewpoint, the BB and AR biosorption on PGS was studied using the Langmuir (Langmuir 1918), Freundlich (Freundlich 1906) and Sips (Sips 1948) isotherm models, as follows:
formula
7
formula
8
formula
9
where qm is the maximum biosorption capacity (mg g−1), KL is the Langmuir constant (L mg−1), KF is the Freundlich constant (mg g−1)(mg L−1)−1/nF, 1/nF is the heterogeneity factor, qS the maximum biosorption capacity from Sips model (mg g−1), KS the Sips constant (L mg−1) and m is the Sips exponent. Another important aspect of the Langmuir model is the equilibrium factor, RL:
formula
10

For RL = 1, the isotherm is linear, 0 < RL < 1 indicates a favorable process and, RL = 0 indicates an irreversible process (Hamdaoui & Naffrechoux 2007).

From the thermodynamic viewpoint, the biosorption of BB and AR was evaluated according to the standard values of Gibbs free energy change (ΔG0, kJ mol−1), enthalpy change (ΔH0, kJ mol−1) and entropy change (ΔS0, kJ mol−1 K−1), which were estimated by the combination of the following equations (Zhou et al. 2012; Anastopoulos & Kyzas 2016):
formula
11
formula
12
formula
13
where Ke is the equilibrium constant (L g−1) (based in the parameters of the best fit isotherm model), T is the temperature (K), R is 8.31 × 10−3 kJ mol −1 K−1 and is the solution density (g L−1).

Parameter estimation

The kinetic and equilibrium parameters were estimated through nonlinear regression, minimizing the least squares function and using the Quasi-Newton estimation method. The Statistic 9.1 software (Statsoft, USA) was used to perform the calculations (El-Khaiary & Malash 2011). The fit quality was measured through determination coefficient (R2), adjusted determination coefficient and average relative error (ARE) (Dotto et al. 2013), as follows:
formula
14
formula
15
formula
16
where qi,model is each value of q predicted by the fitted model, qi,exp is each value of q measured experimentally, is the average of q experimentally measured, n is the number of experimental points and p is the number of parameters.

Characteristics of PGS biosorbent

PGS biosorbent was characterized according to the point of zero charge (pHzpc), total acidity and basicity, FT-IR, SEM and EDS. The pHzpc of the biosorbent was 6.85 (see supplementary material, available with the online version of this paper). This shows that at pH values lower than 6.85 the biosorbent is positively charged, while at pH values higher than 6.85, PGS is negatively charged. The values of carboxylic, lactonic and phenolic groups were, respectively, 0.05, 0.28 and 2.98 meq g−1. Consequently, the total acidity on the PGS surface was 3.31 meq g−1. The total basicity was 0.01 meq g−1.

The FT-IR spectra of PGS biosorbent before (PGS) and after the biosorption process (PGS loaded BB and PGS loaded AR are depicted in Figure 2.
Figure 2

FT-IR spectra of PGS biosorbent before (PGS) and after the biosorption process (PGS loaded BB and PGS loaded AR).

Figure 2

FT-IR spectra of PGS biosorbent before (PGS) and after the biosorption process (PGS loaded BB and PGS loaded AR).

Close modal

The PGS spectrum (before biosorption) in Figure 2 shows the main intense bands around 3,400, 2,900, 2,800, 1,750, 1,650, 1,510, 1,400 and from 1,300 to 1,000 cm−1. The broad band centered at 3,400 cm−1 is the -OH stretching. The stretchings of C-H and CH2 can be visualized at 2,900 and 2,800 cm−1, respectively. The band at 1,750 cm−1 could be assigned to the carbonyl groups (C = O). The C = O link of the acetyl groups can be seen at 1,650 cm−1. The C = C link of aromatic ring is visualized at 1,510 cm−1. The CH deformation can be seen at 1,400 cm−1. The vibrational bands in the region 1,300–1,000 cm−1 can be assigned to -CO, C-O-C and carboxylic acids. These bands reveal that the PGS biosorbent is composed by several functional groups that are able to bind with the pharmaceutical dyes AR and BB. In the spectra after biosorption (PGS loaded BB and PGS loaded AR) (Figure 2), no significant changes were observed. This shows that no links were formed or broken during the biosorption process, indicating that a physical biosorption occurred.

The SEM images of PGS biosorbent are presented in Figure 3. It can be seen that PGS is composed by irregular particles with a rough surface (Figure 3(a)). Figure 3(a) also confirms the mean diameter of the particles obtained by sieving (from 80 to 110 μm). Several cavities and protuberances can be also visualized in the PGS surface (Figure 3(b)). These characteristics are favorable to accommodate the large dye molecules on the biosorbent surface.
Figure 3

SEM images of PGS biosorbent.

Figure 3

SEM images of PGS biosorbent.

Close modal
The EDS spectra of PGS biosorbent before (PGS) and after the biosorption process (PGS loaded BB and PGS loaded AR) are shown in Figure 4. It was found that the main elements on the PGS surface before the biosorption process were C, O, P and Mg. These elements are common for biosorbents. However, after the biosorption process, the element S appeared. This is indicative that BB and AR dyes (see Figure 1) were biosorbed on the PGS surface. To confirm the EDS results, PGS samples (before and after biosorption) were analyzed in an elemental analyzer (Vario E1-CHNS). The results showed that PGS before biosorption presented traces of S. However, after biosorption, the S percentage was increased. This also confirms the attachment of the dyes on the PGS surface.
Figure 4

EDS spectra of PGS biosorbent before (PGS) and after the biosorption process (PGS loaded BB and PGS loaded AR).

Figure 4

EDS spectra of PGS biosorbent before (PGS) and after the biosorption process (PGS loaded BB and PGS loaded AR).

Close modal

Effects of initial pH and biosorbent dosage

The effect of initial pH on the biosorption of BB and AR by PGS is presented in Figure 5.
Figure 5

Effect of initial pH on the biosorption of BB and AR dyes by PGS (Co = 50 mg L−1, T = 25 °C, t = 1 h, V = 25 mL, biosorbent dosage = 2.00 g L−1 and stirring rate = 200 rpm).

Figure 5

Effect of initial pH on the biosorption of BB and AR dyes by PGS (Co = 50 mg L−1, T = 25 °C, t = 1 h, V = 25 mL, biosorbent dosage = 2.00 g L−1 and stirring rate = 200 rpm).

Close modal

It can be seen clearly in Figure 5 that the dye removal percentage increased with the pH decrease from 8.0 to 1.0. For both dyes, no biosorption occurred from pH 8.0 to 6.0, while the dye removal percentage was higher than 80% at pH 1.0. This shows that the biosorption of BB and AR dyes by PGS is strongly pH dependent. This behavior can be explained on the basis in the characteristics of the PGS and dye molecules. BB and AR are anionic dyes (Figure 1) and its sulphonated groups are negatively charged independent of the pH (since the pKa of these groups are negative). In parallel, the PGS biosorbent is positively charged at pH values lower than 6.85 (pHzpc of the biosorbent is 6.85). In this way, at pH of 1.0, the negatively charged dye molecules are attracted by the positively charged surface of the PGS biosorbent, leading to high values of removal percentage. Similar trends were found using other materials to remove BB, like chitosan (Dotto & Pinto 2011), flower wastes (Echavarria-Alvarez & Hormaza-Anaguano 2014) and Hydrilla verticillata (Rajeshkannan et al. 2011). Also, for the removal of AR using chitosan films (Cadaval et al. 2015), water hyacinth leaves (Guerrero-Coronilla et al. 2015) and tamarind pod shells (Ahalya et al. 2012) were used. Based on these results, the subsequent biosorption tests were performed at pH of 1.0.

The effect of biosorbent dosage on the biosorption of (a) BB and (b) AR dyes by PGS is presented in Figure 6.
Figure 6

Effect of biosorbent dosage on the biosorption of (a) BB and (b) AR dyes by PGS (Co = 50 mg L−1, T = 25 °C, t = 1 h, V = 25 mL, pH = 1.0 and stirring rate = 200 rpm).

Figure 6

Effect of biosorbent dosage on the biosorption of (a) BB and (b) AR dyes by PGS (Co = 50 mg L−1, T = 25 °C, t = 1 h, V = 25 mL, pH = 1.0 and stirring rate = 200 rpm).

Close modal

For BB dye (Figure 6(a)), the increase in biosorbent dosage from 0.25 g L−1 to 1.00 g L−1 caused an increase from 56 to 87% in the dye removal percentage (R). However, the biosorption capacity (q) decreased from 120 to 40 mg g−1. A new increase from 1.00 g L−1 to 5.00 g L−1 caused no significant effect on the dye removal percentage but, the biosorption capacity continued to decrease. In the case of AR dye (Figure 6(b)), the increase in biosorbent dosage from 0.25 g L−1 to 1.50 g L−1 caused an increase from 32 to 85% in the dye removal percentage (R). However, the biosorption capacity (q) decreased from 58 to 18 mg g−1. A new increase from 1.50 g L−1 to 5.00 g L−1 caused no significant effect on the dye removal percentage but the biosorption capacity continued to decrease. This behavior is common, since the increase in biosorbent dosage provides more biosorption sites and, consequently, more dye is removed from the solution. On the other hand, the biosorption capacity decreases, since these additional sites can block one each other. Aiming to obtain suitable values of R and q for both dyes, 0.50 g L−1 was selected as the optimum biosorbent dosage to be used in further studies.

Biosorption kinetics

The kinetic curves for the biosorption of BB and AR dyes by PGS were constructed at pH = 1.0 with biosorbent dosage of 0.50 g L−1. These curves are depicted in Figure 7.
Figure 7

Kinetic curves for the biosorption of BB and AR dyes by PGS (Co = 50 mg L−1, T = 25 °C, V = 25 mL, pH = 1.0, biosorbent dosage = 0.50 g L−1 and stirring rate = 200 rpm).

Figure 7

Kinetic curves for the biosorption of BB and AR dyes by PGS (Co = 50 mg L−1, T = 25 °C, V = 25 mL, pH = 1.0, biosorbent dosage = 0.50 g L−1 and stirring rate = 200 rpm).

Close modal

A typical kinetic behavior was observed for both dyes, where the biosorption capacity presented a strong increase in the first 5 min, followed by a gradual increase until 90 min. After, the biosorption rate decreased strongly, and the equilibrium was attained within 6 h. Also, Figure 6 shows that the biosorption capacity was higher for BB than for AR dye. This can occur because the BB molecule is higher than the AR molecule (see Figure 1), increasing the probability of this molecule being docked in an active site. This behavior was proved in other work, using physical statistics approaches (Dotto et al. 2015b).

PFO, PSO and Elovich models were fitted with the experimental data, in order to find an adequate and mathematically easy model to represent the experimental kinetic data. The results are presented in Table 1. The high R2 and low ARE values presented in Table 1 show that the PSO and Elovich models were adequate to explain the experimental kinetic data. The q2 value for BB was higher than the q2 value for AR, confirming its higher biosorption capacity. This behavior is corroborated by the b parameter of the Elovich model, which was lower for BB. The k2 values were similar for both dyes, indicating that the biosorption rate was also similar, during the entire biosorption period. However, the h0 value was higher for BB, indicating that, at the initial stages, the BB biosorption was faster. Finally, Table 2 shows that for both dyes, q2 closely very well with the experimental value qe (exp) confirming that the PSO model can be used to predict the experimental values of biosorption capacity.

Table 1

Kinetic parameters for the biosorption of BB and AR dyes on PGS

ModelsDyes
BBAR
PFO model 
q1 (mg g−174.4 41.0 
k1 (min−10.207 0.113 
R2 0.9721 0.9092 
ARE (%) 4.37 8.62 
PSO model 
q2 (mg g−179.6 45.2 
k2 (g mg−1 min−10.0040 0.0038 
h0 (mg g−1 min−125.3 6.15 
R2 0.9959 0.9689 
ARE (%) 1.73 5.66 
Elovich model 
b (g mg−10.122 0.146 
a (mg g−1 min−11533.13 46.69 
R2 0.9959 0.9853 
ARE (%) 1.63 3.43 
qe (exp) (mg g−180.2 43.9 
ModelsDyes
BBAR
PFO model 
q1 (mg g−174.4 41.0 
k1 (min−10.207 0.113 
R2 0.9721 0.9092 
ARE (%) 4.37 8.62 
PSO model 
q2 (mg g−179.6 45.2 
k2 (g mg−1 min−10.0040 0.0038 
h0 (mg g−1 min−125.3 6.15 
R2 0.9959 0.9689 
ARE (%) 1.73 5.66 
Elovich model 
b (g mg−10.122 0.146 
a (mg g−1 min−11533.13 46.69 
R2 0.9959 0.9853 
ARE (%) 1.63 3.43 
qe (exp) (mg g−180.2 43.9 
Table 2

Isotherm parameters for BB biosorption onto PGS

ModelsTemperature (K)
298308318328
Langmuir 
qm (mg g−1324.4 381.6 537.3 599.5 
KL (L mg−10.020 0.021 0.022 0.038 
RL (C0= 300 mg L−10.131 0.142 0.136 0.080 
R2 0.9790 0.9979 0.9939 0.9985 
 0.9736 0.9967 0.9918 0.9888 
ARE (%) 5.91 4.18 5.76 5.54 
Freundlich 
KF ((mg g−1)(mg L−1)−1/nF28.1 26.2 30.1 50.9 
1/nF 2.26 2.03 1.83 1.94 
R2 0.9424 0.9717 0.9757 0.9868 
 0.9303 0.9656 0.9708 0.9834 
ARE (%) 16.15 16.15 16.69 13.77 
Sips 
qs (mg g−1311.8 353.1 515.11 830.1 
Ks (L mg−10.025 0.024 0.023 0.017 
M 1.066 1.111 1.044 0.776 
R2 0.9790 0.9970 0.9930 0.9925 
 0.9676 0.9950 0.9890 0.9885 
ARE (%) 7.42 5.11 5.40 6.96 
ModelsTemperature (K)
298308318328
Langmuir 
qm (mg g−1324.4 381.6 537.3 599.5 
KL (L mg−10.020 0.021 0.022 0.038 
RL (C0= 300 mg L−10.131 0.142 0.136 0.080 
R2 0.9790 0.9979 0.9939 0.9985 
 0.9736 0.9967 0.9918 0.9888 
ARE (%) 5.91 4.18 5.76 5.54 
Freundlich 
KF ((mg g−1)(mg L−1)−1/nF28.1 26.2 30.1 50.9 
1/nF 2.26 2.03 1.83 1.94 
R2 0.9424 0.9717 0.9757 0.9868 
 0.9303 0.9656 0.9708 0.9834 
ARE (%) 16.15 16.15 16.69 13.77 
Sips 
qs (mg g−1311.8 353.1 515.11 830.1 
Ks (L mg−10.025 0.024 0.023 0.017 
M 1.066 1.111 1.044 0.776 
R2 0.9790 0.9970 0.9930 0.9925 
 0.9676 0.9950 0.9890 0.9885 
ARE (%) 7.42 5.11 5.40 6.96 

Biosorption isotherms

Figure 8 presents the equilibrium isotherms for the biosorption of (a) BB and (b) AR dyes by PGS. For both dyes a type I isotherm (Thommes et al. 2015) was observed, with an initial curved portion at lower concentrations, tending to a plateau at higher concentrations. The plateau was most pronounced for AR dye. This behavior indicates a high affinity between the BB and AR molecules with the PGS surface. Furthermore, it can be seen for both dyes that the biosorption capacity increased with the temperature. This can have occurred because the temperature increase caused an expansion of the biopolymeric matrix of the biosorbent providing more available biosorption sites. Similar trend was found by Guerrero-Coronilla et al. (2015) in the AR adsorption onto water hyacinth leaves, using a temperature range from 18 to 50 °C.
Figure 8

Equilibrium isotherms for the biosorption of (a) BB and (b) AR dyes by PGS (pH = 1.0 and biosorbent dosage = 0.50 g L−1).

Figure 8

Equilibrium isotherms for the biosorption of (a) BB and (b) AR dyes by PGS (pH = 1.0 and biosorbent dosage = 0.50 g L−1).

Close modal

In order to find an adequate representation for the equilibrium experimental data, the models named Langmuir, Freundlich and Sips were used. The fitting results are presented in Table 2 (for BB) and Table 3 (for AR). The higher values of R2 and and the lower values of ARE (Table 2) indicate that the Langmuir model was the best to represent the biosorption equilibrium for the BB dye. However, for the AR dye, the Sips model was the more adequate.

Table 3

Isotherm parameters for AR biosorption onto PGS

ModelsTemperature (K)
298308318328
Langmuir 
qm (mg g−159.8 65.6 85.6 94.4 
KL (L mg−10.041 0.040 0.031 0.045 
RL (C0= 300 mg L−10.075 0.076 0.097 0.068 
R2 0.8687 0.9218 0.9681 0.9981 
 0.8415 0.9053 0.9613 0.9972 
ARE (%) 22.77 16.04 9.29 1.16 
Freundlich 
KF ((mg g−1)(mg L−1)−1/nF14.3 14.7 13.4 20.2 
1/nF 4.03 3.84 3.07 3.62 
R2 0.8100 0.8611 0.9493 0.9686 
 0.7720 0.8332 0.9384 0.9613 
ARE (%) 28.59 22.44 12.89 8.32 
Sips 
qs (mg g−150.9 55.4 83.9 94.2 
Ks (L mg−10.045 0.047 0.033 0.048 
m 7.994 4.686 1.047 1.006 
R2 0.9999 0.9957 0.9682 0.9989 
 0.9988 0.9922 0.9522 0.9975 
ARE (%) 0.69 1.68 9.24 1.12 
ModelsTemperature (K)
298308318328
Langmuir 
qm (mg g−159.8 65.6 85.6 94.4 
KL (L mg−10.041 0.040 0.031 0.045 
RL (C0= 300 mg L−10.075 0.076 0.097 0.068 
R2 0.8687 0.9218 0.9681 0.9981 
 0.8415 0.9053 0.9613 0.9972 
ARE (%) 22.77 16.04 9.29 1.16 
Freundlich 
KF ((mg g−1)(mg L−1)−1/nF14.3 14.7 13.4 20.2 
1/nF 4.03 3.84 3.07 3.62 
R2 0.8100 0.8611 0.9493 0.9686 
 0.7720 0.8332 0.9384 0.9613 
ARE (%) 28.59 22.44 12.89 8.32 
Sips 
qs (mg g−150.9 55.4 83.9 94.2 
Ks (L mg−10.045 0.047 0.033 0.048 
m 7.994 4.686 1.047 1.006 
R2 0.9999 0.9957 0.9682 0.9989 
 0.9988 0.9922 0.9522 0.9975 
ARE (%) 0.69 1.68 9.24 1.12 

The RL values of the Langmuir model (Table 2) ranged between 0 and 1, indicating that the BB biosorption was a favorable process. The KL (Table 2) increased with the temperature, suggesting that the biosorbent–BB affinity was higher at 328 K. The same trend was found for Ks (Table 3). The qm (BB dye in Table 2) and qs(AR dye in Table 3) parameters increased with the temperature, corroborating that the biosorption capacity is favored at 328 K.

The maximum biosorption capacities were found at 328 K (55 °C) and were 599.5 and 94.2 mg g−1 for BB and AR, respectively. A comparison between the maximum biosorption capacities (qmax) of several materials used to remove BB and AR dyes from aqueous solutions is presented in Table 4. Based on this table, it can be stated that PGS is an excellent biosorbent to remove BB, since presented a very high biosorption capacity. Also, PGS is a suitable biosorbent for AR, since its biosorption capacity was comparable with the other materials. Furthermore, PGS has low cost, since is obtained from wastes using a simple processing.

Table 4

Comparison between the maximum biosorption capacities (qmax) of several materials used to remove BB and AR dyes from aqueous solutions

BiosorbentDyepHT (°C)qmax (mg g−1)Reference
PGS BB 1.0 55 599.5 This work 
Chitosan BB 3.0 25 210.0 Dotto & Pinto (2011)  
Flower wastes BB 2.0 54 40.16 Echavarria-Alvarez & Hormaza-Anaguano (2014)  
Hydrilla verticillata BB 3.0 30 38.46 Rajeshkannan et al. (2011)  
Mixed sorbents BB 3.0 30 53.6 Ho & Chiang (2001)  
PGS AR 1.0 55 94.2 This work 
Chitosan films AR 2.0 25 494.13 Cadaval et al. (2015)  
Water hyacinth leaves AR 2.0 18 70.0 Guerrero-Coronilla et al. (2015)  
Tamarind pod shells AR 2.0 – 65.04 Ahalya et al. (2012)  
Alumina reinforced polystyrene AR 2.0 50 20.23 Ahmad & Kumar (2011)  
Activated carbon AR 1.0 30 166.67 Al-Aoh et al. (2013)  
BiosorbentDyepHT (°C)qmax (mg g−1)Reference
PGS BB 1.0 55 599.5 This work 
Chitosan BB 3.0 25 210.0 Dotto & Pinto (2011)  
Flower wastes BB 2.0 54 40.16 Echavarria-Alvarez & Hormaza-Anaguano (2014)  
Hydrilla verticillata BB 3.0 30 38.46 Rajeshkannan et al. (2011)  
Mixed sorbents BB 3.0 30 53.6 Ho & Chiang (2001)  
PGS AR 1.0 55 94.2 This work 
Chitosan films AR 2.0 25 494.13 Cadaval et al. (2015)  
Water hyacinth leaves AR 2.0 18 70.0 Guerrero-Coronilla et al. (2015)  
Tamarind pod shells AR 2.0 – 65.04 Ahalya et al. (2012)  
Alumina reinforced polystyrene AR 2.0 50 20.23 Ahmad & Kumar (2011)  
Activated carbon AR 1.0 30 166.67 Al-Aoh et al. (2013)  

Biosorption thermodynamics and interaction mechanism

The biosorption thermodynamic of BB and AR was evaluated according to the standard values of Gibbs free energy change (ΔG0, kJ mol−1), enthalpy change (ΔH0, kJ mol−1) and entropy change (ΔS0, kJ mol−1 K−1). The results are presented in Table 5.

Table 5

Thermodynamic parameters for the biosorption of BB and AR dyes on PGS

T (K)BB dyea
AR dyea
ΔG0 (kJ mol−1)ΔH0 (kJ mol−1)ΔS0 (kJ mol−1 K−1)ΔG0 (kJ mol−1)ΔH0 (kJ mol−1)ΔS0 (kJ mol−1 K−1)
298 −22.0 ± 0.1 30.2 ± 0.5 0.17 ± 0.02 −19.1 ± 0.1 15.0 ± 0.4 0.11 ± 0.01 
308 −22.9 ± 0.1 −20.1 ± 0.1 
318 −24.6 ± 0.2 −20.9 ± 0.1 
328 −27.3 ± 0.2 −22.7 ± 0.3 
T (K)BB dyea
AR dyea
ΔG0 (kJ mol−1)ΔH0 (kJ mol−1)ΔS0 (kJ mol−1 K−1)ΔG0 (kJ mol−1)ΔH0 (kJ mol−1)ΔS0 (kJ mol−1 K−1)
298 −22.0 ± 0.1 30.2 ± 0.5 0.17 ± 0.02 −19.1 ± 0.1 15.0 ± 0.4 0.11 ± 0.01 
308 −22.9 ± 0.1 −20.1 ± 0.1 
318 −24.6 ± 0.2 −20.9 ± 0.1 
328 −27.3 ± 0.2 −22.7 ± 0.3 

aMean ± standard error.

For both dyes, negative ΔG0 values were obtained, demonstrating that the BB and AR biosorption onto PGS was a spontaneous and favorable process. The temperature increase provided more negative ΔG0 values, corroborating that the biosorption was favored at 328 K. The positive ΔH0 values indicated that the biosorption was endothermic in nature. The endothermic nature was also observed in the malachite green adsorption by Moroccan clay (Elmoubarki et al. 2015) (ΔH0 = 14.7 kJ mol−1) and reactive blue 19 adsorption on coconut shell activated carbon (Isah et al. 2015) (ΔH0 = 7.771 kJ mol−1). For both dyes, the magnitude of ΔH0 values suggests that physical electrostatic interactions occurred. The positive ΔS0 values indicated some rearrangements on the biosorbent surface during the biosorption.

Based on the FT-IR, pHzpc, Boehm titration, pH studies, thermodynamic parameters and dye properties, a possible main biosorption mechanism was proposed: it is known that at pH lower than 6.85, the PGS surface is positively charged. At pH 1.0, the majority of the PGS groups are protonated (basic groups, carboxylic and hydroxyl groups). In parallel, the sulphonated groups of the dye molecules are negatively charged (negative pKa). Then a physical electrostatic interaction occurs between the dyes and the PGS biosorbent. This mechanism is corroborated by the FT-IR spectra, which were not modified after the biosorption and also by the magnitude of ΔH0 values.

In this work, PGS biosorbent was developed using wastes of a wine industry, and then, applied as an alternative, low cost and efficient material to remove BB and AR dyes from aqueous solutions. The material characterization revealed that PGS has potential features for biosorption, like functional groups on the surface, cavities and protuberances. The biosorption of BB and AR was favored at pH of 1.0 and biosorbent dosage of 0.50 g L−1, where the dye removal percentage was higher than 80%. PSO and Elovich models were adequate to represent the biosorption kinetic. The biosorption equilibrium of BB on PGS was well represented by the Langmuir model, while for AR, the Sips model was the most adequate. The maximum biosorption capacities were 599.5 and 94.2 mg g−1 for BB and AR, respectively, attained at 328 K. The biosorption was a spontaneous, favorable and endothermic process. The biosorption occurred by physical electrostatic interaction between the dyes and the PGS biosorbent. These findings show that PGS is a potential candidate for biosorption purposes, since has low cost, availability, high biosorption capacity and high efficiency.

Ahalya
N.
Chandraprabha
M. N.
Kanamadi
R. D.
Ramachandra
T. V.
2012
Adsorption of methylene blue and amaranth on to tamarind pod shells
.
Journal of Biochemical Technology
3
(
5
),
189
192
.
Ahmad
R.
Kumar
R.
2011
Adsorption of amaranth dye onto alumina reinforced polystyrene
.
Clean – Soil, Air, Water
39
(
1
),
74
82
.
Ahmed
M. B.
Zhou
J. L.
Ngo
H. H.
Guo
W.
Thomaidis
N. S.
Xu
J.
2017
Progress in the biological and chemical treatment technologies for emerging contaminant removal from wastewater: a critical review
.
Journal of Hazardous Materials
323
(
A
),
274
298
.
Al-Aoh
H. A.
Jamil Maah
M.
Yahya
R.
Radzi Bin Abas
M.
2013
A comparative investigation on adsorption performances of activated carbon prepared from coconut husk fiber and commercial activated carbon for acid red 27 dye
.
Asian Journal of Chemistry
25
(
17
),
9582
9590
.
Al Bsoul
A.
Zeatoun
L.
Abdelhay
A.
Chihad
M.
2014
Adsorption of copper ions from water by different types of natural seed materials
.
Desalination and Water Treatment
52
(
31–33
),
5876
5882
.
Al-Hamamre
Z.
Saidan
M.
Hararah
M.
Rawajfeh
K.
Alkhasawneh
H. E.
Al-Shannag
M.
2017
Wastes and biomass materials as sustainable-renewable energy resources for Jordan
.
Renewable and Sustainable Energy Reviews
67
(
1
),
295
314
.
Álvarez
M. S.
Moscoso
F.
Rodríguez
A.
Sanromán
M. A.
Deive
F. J.
2013
Novel physico biological treatment for the remediation of textile dyes-containing industrial effluents
.
Bioresource Technology
146
(
1
),
689
695
.
Anastopoulos
I.
Kyzas
G. Z.
2016
Are the thermodynamic parameters correctly estimated in liquid-phase adsorption phenomena?
Journal of Molecular Liquids
218
(
1
),
174
185
.
Belhaine
A.
Ghezzar
M. R.
Abdelmalek
F.
Tayebi
K.
Ghomari
A.
Addou
A.
2016
Removal of methylene blue dye from water by a spent bleaching earth biosorbent
.
Water Science & Technology
74
(
11
),
2534
2540
.
Cadaval
T. R. S.
Jr
Dotto
G. L.
Pinto
L. A. A.
2015
Equilibrium isotherms, thermodynamics, and kinetic studies for the adsorption of food azo dyes onto chitosan films
.
Chemical Engineering Communications
202
(
10
),
1316
1323
.
Dotto
G. L.
Pinto
L. A. A.
2011
Adsorption of food dyes onto chitosan: optimization process and kinetic
.
Carbohydrate Polymers
84
(
1
),
231
238
.
Dotto
G. L.
Costa
J. A. V.
Pinto
L. A. A.
2013
Kinetic studies on the biosorption of phenol by nanoparticles from Spirulina sp
.
LEB 18. Journal of Environmental Chemical Engineering
1
(
4
),
1137
1143
.
Dotto
G. L.
Sharma
S. K.
Pinto
L. A. A.
2015a
Biosorption of organic dyes: research opportunities and challenges
. In:
Green Chemistry for Dyes Removal From Waste Water: Research Trends and Applications
(
Sharma
S. K.
, ed.).
John Wiley & Sons
,
Hoboken, NJ, USA
.
Dotto
G. L.
Santos
J. M. N.
Tanabe
E. H.
Bertuol
D.
Foletto
E. L.
Lima
E. C.
Pavan
F. A.
2017
Chitosan/polyamide nanofibers prepared by Forcespinning® technology: a new adsorbent to remove anionic dyes from aqueous solutions
.
Journal of Cleaner Production
144
(
1
),
120
129
.
Dwyer
K.
Hosseinian
F.
Rod
M.
2014
The market potential of grape waste alternatives
.
Journal of Food Research
3
(
2
),
91
106
.
Echavarria-Alvarez
A. M.
Hormaza-Anaguano
A.
2014
Flower wastes as a low-cost adsorbent for the removal of acid blue 9
.
Dyna
81
(
185
),
132
138
.
El-Khaiary
M. I.
Malash
G. F.
2011
Common data analysis errors in batch adsorption studies
.
Hydrometallurgy
105
(
3–4
),
314
320
.
Elmoubarki
R.
Mahjoubi
F. Z.
Tounsadi
H.
Moustadraf
J.
Abdennouri
M.
Zouhri
A.
El-Albani
A.
Barka
N.
2015
Adsorption of textile dyes on raw and decanted Moroccan clays: kinetics, equilibrium and thermodynamics
.
Water Resources and Industry
9
(
1
),
16
29
.
Fernández
C.
Larrechi
M. S.
Callao
M. P.
2010
An analytical overview of processes for removing organic dyes from wastewater effluents
.
Trends in Analytical Chemistry
29
(
10
),
1202
1211
.
Freundlich
H.
1906
Uber die adsorption in losungen
.
Zeitschrift fur Physikalische Chemie
57
(
A
),
358
471
.
Goertzen
S. L.
Theriault
K.
Oickle
A. M.
Tarasuk
A. C.
Andreas
H. A.
2010
Standardization of the Boehm titration: Part I-CO2 expulsion and endpoint determination
.
Carbon
48
(
4
),
1252
1261
.
Goldstein
J. I.
Newbury
D. E.
Echil
P.
Joy
D. C.
Romig
A. D.
Jr
Lyman
C. E.
Fiori
C.
Lifshin
E.
1992
Scanning Electron Microscopy and X-ray Microanalysis
.
Plenum Press
,
New York, NY, USA
.
Guerrero-Coronilla
I.
Morales-Barrera
L.
Cristiani-Urbina
E.
2015
Kinetic, isotherm and thermodynamic studies of amaranth dye biosorption from aqueous solution onto water hyacinth leaves
.
Journal of Environmental Management
152
(
1
),
99
108
.
Gupta
V. K.
Suhas
I.
2009
Application of low-cost adsorbents for dye removal-a review
.
Journal of Environmental Management
90
(
8
),
2313
2342
.
He
Q.
Wang
H.
Zhang
J.
Zou
Z.
Zhou
J.
Yang
K.
Zheng
L.
2016
Lotus seedpod as a low-cost biomass for potential methylene blue adsorption
.
Water Science & Technology
74
(
11
),
2560
2568
.
Hessel
C.
Allegre
C.
Maisseu
M.
Charbit
F.
Moulin
P.
2007
Guidelines and legislation for dye house effluents
.
Journal of Environmental Management
83
(
2
),
171
180
.
Ho
Y. S.
Chiang
C. C.
2001
Sorption studies of acid dye by mixed sorbents
.
Adsorption
7
(
1
),
139
147
.
Ho
Y. S.
McKay
G.
1998
Kinetic models for the sorption of dye from aqueous solution by wood
.
Process Safety and Environmental Protection
76
(
B2
),
183
191
.
Isah
U.
Abdulraheem
G.
Bala
S.
Muhammad
S.
Abdullahi
M.
2015
Kinetics, equilibrium and thermodynamics studies of C.I. reactive blue 19 dye adsorption on coconut shell based activated carbon
.
International Biodeterioration & Biodegradation
102
(
1
),
265
273
.
Khandare
R. V.
Govindwar
S. P.
2015
Phytoremediation of textile dyes and effluents: current scenario and future prospects
.
Biotechnology Advances
33
(
8
),
1697
1714
.
Lagergren
S.
1898
About the theory of so-called adsorption of soluble substances
.
Kungliga Svenska Vetenskapsakademiens
24
(
4
),
1
39
.
Langmuir
I.
1918
The adsorption of gases on plane surfaces of glass, mica and platinum
.
Journal of the American Chemical Society
40
(
9
),
1361
1403
.
Liu
Y.
Liu
Y. J.
2008
Biosorption isotherms, kinetics and thermodynamics
.
Separation and Purification Technology
61
(
3
),
229
242
.
Meili
L.
da Silva
T. S.
Henrique
D. C.
Soletti
J. I.
de Carvalho
S. H. V.
da Silva Fonseca
E. J.
de Almeida
A. R. F.
Dotto
G. L.
2017
Ouricuri (Syagrus coronata) fiber: a novel biosorbent to remove methylene blue from aqueous solutions
.
Water Science & Technology
75
(
1
),
106
114
.
Pérez-Ibarbia
L.
Majdanski
T.
Schubert
S.
Windhab
N.
Schuber
U.
2016
Safety and regulatory review of dyes commonly used as excipients in pharmaceutical and nutraceutical applications
.
European Journal of Pharmaceutical Sciences
93
(
1
),
264
273
.
Silverstein
R. M.
Webster
F. X.
Kiemle
D. J.
2007
Spectrometric Identification of Organic Compounds
.
John Wiley & Sons
,
New York, NY, USA
.
Sips
R.
1948
On the structure of a catalyst surface
.
Journal of Chemical Physics
16
(
1
),
490
495
.
Spiridon
I.
Darie-Nita
R. N.
Hitruc
G. E.
Ludwiczak
J.
Spiridon
I. A. C.
Niculaua
M.
2016
New opportunities to valorize biomass wastes into green materials
.
Journal of Cleaner Production
133
(
1
),
235
242
.
Thommes
M.
Kaneko
K.
Neimark
A. V.
Olivier
J. P.
Rodriguez-Reinoso
F.
Rouquerol
J.
Sing
K. S. W.
2015
Physisorption of gases, with special reference to the evaluation of surface area and pore size distribution (IUPAC Technical Report)
.
Pure Applied Chemistry
87
(
1
),
1051
1069
.
Torab-Mostaedi
M.
Asadollahzadeh
M.
Hemmati
A.
Khosravi
A.
2013
Equilibrium, kinetic, and thermodynamic studies for biosorption of cadmium and nickel on grapefruit peel
.
Journal of the Taiwan Institute of Chemical Engineers
44
(
2
),
295
302
.
Weber
C. T.
Collazzo
G. C.
Mazutti
M. A.
Foletto
E. L.
Dotto
G. L.
2014
Removal of hazardous pharmaceutical dyes by adsorption onto papaya seeds
.
Water Science & Technology
70
(
1
),
102
107
.
Yagub
M. T.
Sen
T. K.
Afroze
S.
Ang
H. M.
2014
Dye and its removal from aqueous solution by adsorption: a review
.
Advances in Colloid and Interface Science
209
(
1
),
172
184
.
Yedro
F. M.
García-Serna
J.
Cantero
D. A.
Sobrón
F.
Cocero
M. J.
2015
Hydrothermal fractionation of grape seeds in subcritical water to produce oil extract, sugars and lignin
.
Catalysis Today
257
(
2
),
160
168
.
Zeldowitsch
J.
1934
Über den mechanismus der katalytischen oxydation von CO an MnO2
.
Acta Physicochemical URSS
1
(
3–4
),
449
464
.
Zhou
X.
Liu
H.
Hao
J.
2012
How to calculate the thermodynamic equilibrium constant using the Langmuir equation?
Adsorption Science & Technology
30
(
1
),
647
649
.

Supplementary data