Valuation of Biomaterial: Phragmites australis in the Retention of Metal-Complexed Dyes

Corresponding Author: Aida Kesraoui Laboratory of Energy and Materials (LABEM). High School of Sciences and Technology of Hammam Sousse, Tunisia Email: aida.kesraoui@gmail.com Abstract: The purpose of this research was to estimate the potential of cellulosic fibers of highly available and renewable Tunisian biomass Phragmites australis for the biosorption of an anionic metal complexed dye: Alpacide blue. The present study shows that the Phragmite australis were used successfully for the adsorption of Alpcide blue from aqueous solution. Equilibrium was reached after 5 h at 20°C and at pH 2. Optimal adsorption parameters for adsorption of dye onto fibers extract of upper rods were accomplished after 5 h of biosorption using an initial dye concentration of 50 mg L −1 , biosorbent amount of 0.5 g of Phragmites australis, pH 2 and a granulometry size between 250 and 500 μm. In these conditions, the adsorbed amount of Alpacide blue is 6.11 mg g −1


Introduction
The effluents from different industries like textile industries are in general very colored and can constitute a high source of water pollution (Ben Hamissa et al., 2013). Colorants are very stable, resistant to light, water, soaps etc. and relatively non-biodegradable. This is due to their synthetic origin and complex aromatic molecular structures (Maurya and Mittal, 2011;Won et al., 2006). Consequently, remove of textile colorant effluent has become a necessity both environmentally and for water reuse. There are several techniques for water treatment whatsoever biological wastewater treatment processes (Abidin and Rahmat, 2010) or different physico-chemical techniques such as: Adsorption on activated carbon (Mahmoudi et al., 2015), coagulation (Rodrigues et al., 2013), ultrafiltration (Căilean et al., 2009), reverse osmosis (Vijayageetha et al., 2014), techniques etc. Generally, these treatments have a major drawback common is the operating cost .
In this present study, we were interested particularly by the valorization of highly available and renewable Tunisian lignocellulosic biomass Phragmites australis for the depollution of industrial wastewater and retention of pollutants considered toxic (Mahmoudi et al., 2015) including metal complex dyes (Ben Hamissa et al., 2013). This process involving adsorption of organic compounds has been called biosorption. This process is defined as the accumulation and concentration of pollutants contained on aqueous solutions by the employment of biological materials (Aksu, 2002). The evaluation of potential use of these materials is important to propose as an alternative or complement to conventional and generally expensive methods used for remove metal ions and dyes. Indeed, these materials are very abundant in nature and are low cost.
However, the resulting wastes from the transformation of raw materials generally have little or no value. Thus, the use of these by-products as biosorbent is very timely. For the biosorption of metal cations and dyes, the most sought materials are those having a large amount of cellulose, hemicellulose and lignin such as pine bark for the treatment of effluents loaded with heavy metals (Teles De Vasconcelos and Gonzalez Beca, 1994;Vazquez et al., 1994;Al-Asheh et al., 1997;, palm scheme for the elimination of basic colorants (Nassar and Magdy, 1997), the fern trunk (Ho et al., 2005), papaya (Saeed et al., 2005), the nuclei of dates (Mohamed, 2006), the Eucalyptus wood (Tancredi et al., 2004), the peels bananas and oranges (Annadurai et al., 2002), corn Rafles (Nigam et al., 2000), cereal straw (Robinson et al., 2002), the fibers of Posidonia oceanica for the elimination of heavy metals and dyes  and the Agave americana fibers for the elimination of colorants (Ben Hamissa et al., 2013).
The principal objective of this research is to investigate the biosorption capability of a new, little cost and renewable biomass, Phragmites australis fibers, extracted from its stems and roots, for the elimination of metalic dyes (Alpacide Blue (AB)). Several parameters such as: Contact time, initial concentration of Alpacide blue, pH, temperature, granulometry and biomass amount were studied. In addition, mathematical modeling of the kinetics and adsorption isotherms was investigated.

Materials
Phragmites australis plants have a Tunisian origin. They were taken from the "Oued el Kharroub" in Sousse. First, these plants were washed several time with water to eliminate impurities and soil, then dried in air for 24 h. The stems and roots of this plant have been sorted in order to study them separately. They were finely cut and dried in an oven at 70°C for 48 h until obtaining constant weight. Then the biomass was ground using an electric grinder. Finally, the biomass was sieved into different particle size using an electric sifter AB employed in this research is a metal complexed dye, got from textile industry (Chimitex-Tunisia). Chemical structure of AB is unknown. Stock solutions of concentration of 100 mg L −1 were prepared by dissolving equal quantities of AB in distilled water. Every working solution was prepared by dilution the stock solution with distilled water to achieve the needed concentrations.

Methods
So as to determine the chemical composition of stems and roots of Phragmites australis, a series of extractions were achieved to isolate different substances contained in the material (fats and waxes, pectin, lignin, hemicellulose and cellulose). The protocols are described in the literature (Sedan, 2007;Garcia-Jaldon, 1992). The milled fibers (10 g dry material) is extracted with 400 mL at 80% ethanol in a flask under stirring at 80°C by reflux for 20 min in order to remove fats and waxes. The degreased material is then extracted with water at 100°C (200 mL, 1 h), then with an aqueous solution of ammonium oxalate (1% by mass) heated by reflux at 85°C (300 mL, 2 h) to remove pectins. Lignins are then extracted by two extractions in a mixture (400 mL) of sodium chlorite and glacial acetic acid (80°C, 1 h) with stirring. Lignin is totally degraded by this treatment, it cannot be recovered. Hemicelluloses are solubilized by a solution of potassium hydroxide (24% by mass) at 25°C (400 mL, 24 h) followed by a solution of sodium hydroxide (4.3% by mass) at 25°C (400 mL, 24 h) with stirring.
The biosorption experiences were realized in batch reactor. Stems or roots of fibers were added in 75 mL of dye solution with the desired concentration (10-100 mg L −1 ), pH (2-10), biomass amount (0.1-0.5 g), granulometry (1.25-5 mm) and temperature (20-60°C). All experiences were carried out at 20°C, apart from the experience realized to study the effect of temperature on biosorption. Temperature was monitored by a thermo-regulated water bath, model Memmert BME1420. The initial pH was adjusted by dilute solutions of HCl or NaOH. The residual concentrations of AB were measured by a double beam spectrophotometer analysis (FT-IR) (Camspec M550) at wavelength λ max of 616 nm. The tests were carried out in triplicate. The negative test (without biomass) was conducted to ensure that the retention capacity was only due to the Phragmites australis fibers. The adsorption capacity at equilibrium, Q (mg/g), was calculated by Equation 1. The evaluation of dye removal was determined according to the following Equation 2: Where: C 0 = The initial AB concentration (mg/L) C i = The residual AB concentration at any time (mg/L) V = The volume of solution (L) M = The mass of the biosorbent (g) At equilibrium, C i is equal to C e and Q is equal to Q e .

Error Estimation
Nonlinear chi-square (χ 2 ) test is a statistical tool necessary for the best fit of an biosorption process, obtained by judging the sum squares differences between the experimental and the calculated data, with each squared difference is divided by its corresponding value (calculated from the models). Small value indicates its similarities while a larger value represents the variation of the experimental data (Boulinguiez et al., 2008;Foo and Hameed, 2010

Chemical Composition of Phragmites australis
The Phragmites australis are composed of two parts: Stems and roots. As shown in Table 1, the two parts of Phragmites australis are composed by: Wax and grease, pectine, lignin, hemicellulose and cellulose.

Influence of Initial AB Concentration
Dye solutions with initial concentrations from 10 to 100 mg L −1 were investigated to examine the ability of the stems and roots of Phragmites australis to eliminate different quantities of AB from aqueous solutions and the corresponding times necessary to reach equilibrium. Fig. 1a and 1b show that the biosorption capacity of AB increased proportionally as a function of contact time at all initial dye concentrations. In addition, the biosorption capacity of AB function of time is composed of two parts. In the first part, biosorption capacity increases rapidly but, in the second part, the biosorption becomes very slow and attains equilibrium after 300 min for concentration of 100 mg L −1 with adsorption capacities for stems and roots of 12.83 and 14.03 mg g −1 , respectively.

Influence of pH
The effect of pH on AB biosorption onto Phragmites australis fibers (stems and roots), has been studied in the pH range between 2 and 10, at an initial concentration 20 mg L −1 . Figure 2 show that the AB biosorption by the stems and roots presents a similar variation with pH. The maximum biosorption is obtained in the vicinity of pH = 2. The maximum retention rate is around 72 and 94% respectively for the stems and roots. Then, the biosorption capacity of the two parts of the plant decreases with increasing pH, which can reach for the stems and roots 35 and 54%, respectively. Figure 3 represents the influence of the variation of the mass of fibers on biosorption capacity. It is noted that greater the quantity of fibers in the solution increases, greater the quantity of AB retention raises. Indeed, the augmentation of mass from 0.1 to 0.5 g is followed by an increase of retention rate from 59.48 to 85.93% for the stems and from 59.60 to 92.58% for roots.

Influence of Temperature
The biosorption capacity of the Phragmite australis (stems and roots) was also studied at various temperatures (20, 40 and 60°C). The investigation of the effect of temperature on the remove of AB onto Phragmite australis fibers was realized for initial concentrations of 20, 50 and 80 mg L −1 and a pH = 2 is represented in Fig. 4. When the temperature is augmented from 20 to 60°C, the biosorption capacity of AB augments for the two parts of plant. Indeed, it was found that AB biosorption onto stems increase from 1.87 to 2.97 mg g −1 , 6.11 to 6.86 and 9.83 to 11.45 for initial concentrations of 20, 50 and 80 mg L −1 respectively with rising temperature from 20 to 60°C. Similar result was found for roots. Biosorption capacity increase from 3.11 to 3.52 mg g −1 , 7.02 to 7.41 and 10.94 to 11.64 for initial concentrations of 20, 50 and 80 mg L −1 respectively with increasing temperature from 20 to 60°C.

Influence of Granulometry
The effect of biomass granulometry (stems and roots) was investigated at various granulometry (from 500 µm to 125 µm) as shown in Fig. 5. The retention rate of AB on to Phragmites australis fibers increased from 82,25 to 87,50% for stems and from 91,78 to 94,11% for roots with decrease granulometry of (>500 µm) to (250-125 µm) respectively. In addition, roots present a biosorption capacity higher than stems.

Thermodynamic Analysis
To investigate the influence of temperature on the AB biosorption onto Phragmite australis (stems and roots) at different dye concentrations, the thermodynamic was studied at temperatures of 293, 313 and 333 K. The thermodynamic parameters like Gibbs free energy (∆G°), enthalpy (∆H°) and entropy (∆S°) were studied from the change of the thermodynamic equilibrium constant K c with the variation in temperature. The apparent equilibrium constant K c (Yurtsever et al., 2009) Where: C ad,eq and C r,eq = Respectively the concentration of adsorbed AB at equilibrium and residual concentration AB at equilibrium respectively (mg/L) K c = The distribution coefficient for the biosorption employed to calculate the Gibbs free energy of biosorption in the following Equation 5: Where: R = The gas constant (8.314 J mol −1 K −1 ) T = The absolute temperature (K) Thermodynamic parameters (∆G°, ∆H° and ∆S°) for the biosorption of AB by Phragmites australis was calculated by the following Equation 6 (Ucun et al., 2008): The thermodynamic was performed at 293, 313 and 333 K and the thermodynamic parameters were represented in Table 2.

Kinetic Data Analysis
To predict the mechanism of adsorption of AB during process, the pseudo-first-order and the pseudo-secondorder models were analyzed. Table 2. Thermodynamic parameters for the biosorption of AB into Phragmite australis (stems and roots) at initial concentrations (C 0 ) of 20, 50 and 80 mg L −1   The model of pseudo-first-order and the pseudosecond-order equation (Ho and McKay, 1999) were employed to fit the experimental data of the dye adsorption before reaching equilibrium. The linearized form of the pseudo-first-order model is given by expression 7: Where: t = The time (min) k 1 = The equilibrium rate constant of pseudo-first-order biosorption (min −1 ) By against, the pseudo-second-order model is employed to a wide interval of time (Ho and McKay, 1999). This model is based on the biosorption capacity of the solid phase; it is described by the Equation 8: Where, k 2 is the equilibrium rate constant of pseudosecond-order adsorption (g/mg min).
The best-fit model was chosen according to both linear regression correlation coefficient (R 2 ) and the calculated Qe values and listed in Table 3.

Adsorption Isotherm Modeling
In order to optimize adsorption system for dyes removal, it is important to establish the most appropriate correlation for the equilibrium curves. The isotherms data were analyzed using Langmuir, Freundlich, Temkin and Elovich isotherm models. Further information's on the theoretical background of the mathematical expressions of those models could be found in Vargas et al. (2011). The mathematical expressions represented in Table 4 and 5.

Desorption Study
Desorption study was performed at three pH (7, 9 and 12) to study the reversibility of biosorption process and the type of interaction between AB and the Phragmites australis and also the possibility of regenerating biomass. For such studies, AB biosorption onto Phragmites australis (stems and roots) was carried out at 20°C and over a range of pH (5,8,10) values. Table 6 show that the AB desorption is better at pH 12.

Chemical Composition of Phragmites australis
It is noted that the two parts of the plant have the same percentage of cellulose (21%) and hemicellulose (29%). While, the percentage of all other compounds is different. In fact, the stems consist essentially of hemicellulose (29%) while the roots are formed in large part by the pectin (31%).
When compared with data for grapevine stalks (Ping et al., 2011) or Posidonia oceanica (Khiari et al., 2010), it appears that cellulose and hemicellulose contents are close. The lignin content of the stems is relatively low. The comparison with vine stems (Mansouri et al., 2012) confirms that the quantities of extractives fractions in the Phragmites australis are elevated. Concerning structural components, the Phragmites australis stems and roots are characterized by low lignin content and great quantity of hemicellulose, while the content in cellulose is relatively comparable.

Influence of Initial AB Concentration
For both part of Phragmites australis, the great biosorption capacity during the first period is probably due to the great number of available biosorption site during the first stage of the process and no less than 90% of AB was eliminated. However, during the second period, the amount of sites available for biosorption diminished so that the colorant molecules require longer time to attain the least accessible sites. Similar behaviors were observed in the literature for the dye adsorption by Posidonia fibers (Ncibi et al., 2007) and fiber Agave america (Ben Hamissa et al., 2008;.

Influence of Initial pH
The pH of the solution presents both an important effect on the surface of dye retention sites and the chemical formula of the dye itself.
AB is a metalliferous classified among the anionic dyes. Indeed, at acidic pH, the surface of Phragmites fibers will be positively charged by protonation. Obtaining maximum biosorption at an acid pH is probably due to an electrostatic attraction between the charges of the anionic dye and the positive charges of the surface of the fiber (Mahmoudi et al., 2015). However, the interaction of the AB with all functional groups of Phragmite australis fibers is possible via several adsorption mechanisms such as ion exchange, Van Der Waals interaction, hydrogen bond (between cellulose-OH and the AB) and microprecipitation (Ben Douissa et al., 2013).
When the pH of the solution increases, the positive charges located on the surface decreasing, while the negative charges increases. In fact, these negative charges at the surface of the biosorbent don't promote the biosorption of anionic dyes. This is due to an anionic repulsion. Similar results are obtained for other biological matrices such as Posidonia fibers (Ncibi et al., 2009), Luffa cylindrica (Kesraoui et al., 2015) and Date palm leaf base (Alsenani, 2014).

Influence of Mass of Fibers
The increase of mass of fibers in the solution is accompanied by an increase number of active sites for retention of dye. Therefore, retention rate of dye increases. These results are alike to those got by Ben Hamissa et al. (2008).

Influence of Temperature
Increasing biosorption capacity was observed according to temperature increase. This observation may be due to the relative increase in the mobility of dyes in solution which improves their exposure to the biosorption active sites on the one step and sends them to difficult access sites on the other. These results suggest that the biosorption of AB is an endothermic phenomenon. The same results are found by other authors (Alsenani, 2014;Ncibi et al., 2007).

Influence of Granulometry
Granulometry is important in the biosorption process, especially for dye biosorption. The retention rate of AB is inversely proportional to the granulometry of the fibers. This phenomenon can be explained by the fact that more particle size is low, more active area is large. As the biosorption is a surface phenomenon, the retention of the dyes will therefore greater on the fibers of smaller size. The same trend has been obtained by other researchers (Wong et al., 2008;Osu and Odoemelam, 2010;Seolatto et al., 2012).

Thermodynamic Analysis
The negative free energy values at all temperatures show that the biosorption of AB by Phragmite australis (stems and roots) is spontaneous. ∆G° is varying from -2.74 to -1.13 kJ mol −1 and from -4.52 to -3.51 kJ mol −1 from stems and roots, respectively. Moreover, these values are ranged from -20 to 0 kJ mol −1 (Ben Hamissa et al., 2010), this process may be considered as physisorption (Atmani et al., 2009). The positive value of the enthalpy change ∆H° shows that the biosorption process was endothermic. The same result has been observed for the adsorption of Direct and Reactive dyes from Posidonia oceanic (Ncibi et al., 2006). Positive values of the entropy ∆S° indicate the good affinity of the biosorbent towards AB dye (Namasivayam and Kavitha, 2002;Alsenani, 2014).

Adsorption Kinetic Modeling
The correlation coefficients obtained by the pseudofirst-order model were found close to 0.82 for stems and of 0.77 for roots, while those obtained by the secondorder model were equal to 0.999 for the both parts of plant and the nonlinear chi-square test was lower (χ 2 = 0.018 for stems and 0.010 for roots). Furthermore, the calculated with the pseudo-first-order (Qe 1 ) did not present acceptable values when compared to the experimental ones, while, for the second order model (Qe 2 ) is close to the theoretical value. However, the pseudo-second-order model presents the best fit to the experimental data of the biosorption of AB by Phragmites Australis fibers. The same trend has been found by other researchers (Mahmoudi et al., 2015;Ben Hamissa et al., 2012;Ncibi et al., 2009).

Adsorption Isotherm Modeling
Freundlich isotherms represents very well the equilibrium biosorption data with the highest correlation coefficients of 0.99 for the both part of plant and the lowest nonlinear chi-square test test (χ 2 = 0.79 for stems and 0.28 for roots). The Freundlich isotherm can be employed for heterogeneous systems with interaction between the molecules adsorbed. Consequently, we can deduce the occurrence of multilayer coverage of AB onto Phragmite australis predicted by the Frendlich isotherm. The Freundlich exponent n was equal to 1.23 and 3.55 for the stems and roots, respectively. The n value between 1 and 10 indicates a beneficial biosorption of the dyes on Phragmites australis (Namasivayam et al., 1996;Ncibi et al., 2006).
The Freundlich isotherm supposes that the biosorption heat of all molecules diminishes linearly when the layer is covered. Also, the Freundlich isotherm assumes that the biosorption has a maximum energy distribution of uniform bond (Vargas et al., 2011).

Desorption Study
At pH 7, the desorbed quantity is 0.45 mg g −1 for the rods and 3.34 mg g −1 for the roots. This value is very low when compared to that of pH = 12, which is 11.15 mg g −1 for stems and 11.42 mg g −1 for the roots.
Generally desorption study of AB at basic pH can inform us that the sorption is by ion exchange (Ben Hamissa et al., 2013). The best biosorption was at acidic pH and the best desorption was at basic pH. This phenomenon can be assigned to electrostatic attraction/repulsion between the anionic dye and Phragmites australis. So the AB biosorption onto Phragmites australis (stems and roots) can be considered as a physico-chemical biosorption process. The same trend has been found by other researchers (Ben Hamissa et al., 2013;Namasivayam et al., 1996).

Conclusion
According the results described above, it may be concluded that Phragmites australis stems are composed of 20.78% of cellulose, 28.96% of hemicellulose, 13.50% of pectin, 13.02 of lignin and 23.74% of fats and waxes. While the roots are composed by 20.37% of cellulose, 29.04% of hemicellulose, 31.39% of pectin, 9.95% of lignin and 9.25 of fats and waxes.
On the other hand, the present study demonstrates that the Phragmites australis fibers were used successfully for removal of AB from aqueous solution. Biosorption tests of AB onto Phragmites australis fibers (stems and roots) were carried out in batch system and in different conditions of pH, temperature, amount of fibers, granulometry and concentration.
Equilibrium is reached after 5 h at a temperature of 20°C. The biosorption maximum is reached at an acidic pH (2). Moreover, the augmentation in the temperature and the mass of the biomaterial increases the adsorbed quantity. Whereas, granulometry does not seem to have a remarkable influence on the adsorption. Experimental data at equilibrium was modeled and the results showed that the Freundlich model is most suitable to describe biosorption of AB by the fibers of Phragmites australis with correlation coefficient R 2 = 0.995 for stems and R 2 = 0.991 for roots.
Modeling of kinetics adsorption revealed that the pseudo-second-order model is most appropriate to describe the biosorption with R 2 of about 0.999 for both types of fiber (stem and root).