EVALUATION OF BIOMASS, INDIAN JUJUBA SEED (IJS) FOR REMOVAL OF CONGO RED

The present investigation deals with the removal of C ngo Red (CR) from aqueous solution by using Indian Jujuba Seed (IJS) as low-cost biosorbent. The effect of pH and size experimental parameters has been investigated using a Batch adsorption techniqu e. Adsorption data were modeled using Langmuir and Freundlich adsorption isotherms. Adsorption kin etics was verified by pseudo-first order, pseudosecond order and intraparticle diffusion models. Th e kinetic adsorption data fitted the pseudo-second order kinetic model well and also followed the intr aparticle diffusion model. The results indicated th at IJS could be employed as low-cost biosorbent in was tewater treatment for the removal of CR.


INTRODUCTION
Dyes and pigments were used in several industries such as textile, leather tanning, food industries, cosmetics, electroplating, paper and pharmaceuticals. Several classes of synthetic dyes (over 7×10 5 metric tons) are produced worldwide every year for industrial purposes. Above industries generate enormous volumes of wastewater every year. Industries wastewater carrying nearly 5-10% of quantity is released into the ecosystem. The amount of dye in wastewater depends on the type of dye used in industry; it varies from 2% for basic dyes and 10 to 50% for reactive dyes. Dyes containing wastewater discharged into water streams not only contribute negatively to aesthetic value but also causes considerable resistance to biodegradation and may upset aquatic life. Therefore, there is a necessity to treat dyes containing wastewater before their discharge into ecosystem (Rehman et al., 2012). Now a day's numbers of method are in practice for the removal of dyes from wastewater. Those are solar photo-Fenton degradation, electrochemical degradation, photo catalytic degradation, sonochemical degradation, oxidation and ozonation, integrated chemical-biological degradation, biodegradation, coagulation and flocculation, membrane separation and adsorption. Among the techniques, adsorption is one of the most efficient methods because of its low cost and easy operational conditions (Sivaramakrishna et al., 2012;Yuvaraja et al., 2012;Chowdhury et al., 2011).
To date, in many developed countries, activated carbon is the most widely used adsorbent for dye removal, but it is too expensive. Hence, removal of pollutants from the wastewater remains a challenge to the researchers. The main aim of this study is, to introduce a viable alternative to the commercial activated carbons.
This study describes the feasibility of removal of a cationic dye-Congo red from aqueous solutions by using IJS as a new low-cost biosorbent. Batch adsorption experiments were achieved out as a function of biosorbent dosage, contact time, effect pH of dye solution and size effect of adsorbent. The Langmuir and Freundlich isotherms models, kinetics adsorption are also studied.

Preparation of Biosorbent and Adsorbate Solution
The biomass of Indian Jujuba seed were collected from somayajulapally one of the author native places, these seeds were washed with water and shade dried. The dried material was crushed, powdered and used as biosorbent. These biosorbent was shown in Fig. 1.
The solutions of Congo red were prepared by dissolving appropriate amounts of dry powdered dye stuff in distilled water. Stock solution of 1000 mg L −1 was prepared by dissolving accurate quantity of the dye in double distilled water. The working solution was obtained by dilution of a stock solution that was prepared earlier to desire concentration.

Experimental Section
The primary adsorption test was carried out, to calculate the percentage of CR dye removal. Batch adsorption experiments were carried out by adding a fixed amount of IJS (0.05 g) into 50 mL screw type Erlenmeyer flasks containing 25 mL of CR dye solution (50 mg L −1 ). The conical flasks then were placed in a shaking thermostatic Julabo water bath shaker at 180 rpm at 35°C. The initial and equilibrium dye concentrations were determined by absorbance measurement using a Chemito UV-Vis spectrophotometer at 497 nm. It was then computed into dye concentration using a standard calibration curve. The same procedure mentioned above was used to study the effect of different parameters.
The amount of sorption at time t and at equilibrium time and the percentage of dye removal were calculated following Equation 1 and 2: where, C 0 and C t (mg L −1 ) are concentrations of dye at initial and at any time t, respectively, V is the volume of the solution (L) and W is the mass of dry adsorbent used (g). The dye removal percentage is to be calculated as follows: where, C e is the equilibrium concentration in solution (mg L −1 ).

Point of Zero Charge (pH PZC )
The zero surface charge characteristics of the IJS were determined, using the solid addition method (Sivaramakrishna et al., 2012). Forty milliliters of 0.1M KNO 3 solution was transferred to a series of 100 mL Stoppard conical flasks. The pH i values of the solutions were roughly adjusted between 2 and 12 by adding either 0.1N HCl or NaOH and measured by using pH meter (Systronics pH system 361 Model, India). The total volume of the solution in each flask was exactly adjusted to 50 mL by adding the KNO 3 solution of the same strength. The pH i of the solutions were then accurately noted. 0.05 gm of IJS was added to each flask and the flask was securely capped immediately. The suspensions were then kept shaking for 24 h and allowed to equilibrate for 0.5 h. The final pH values of the supernatant liquid were noted. The difference between the initial and final pH (pH f ) values (∆pH) was plotted against the pH i . The point of intersection of the resulting curve with abscissa, at which pH = 0, gave the pH PZC . It is observed from

Batch Adsorption Studies
In the present study, batch adsorption experiments were carried out by agitating 50 mg of adsorbent, IJS with 25 mL of dye solutions of concentration is 50mg L −1 , in a 50 mL screw type Erlenmeyer flask at room temperature (30±1°C). A good contact is made between adsorbent and dye by agitating at 180 rpm in a Julabo shaking water bath. Dye concentration is determined spectrophotometrically by monitoring the absorbance at 497 nm using Chemito UV-VIS Spectrophotometer and two 1 cm cells. The wavelength of the maximum absorbance for dye was selected and λ max value is 497 nm. The pH of dye solutions was determined using pH meter (Systronics pH system 361 model, India). The samples were withdrawn from the shaker at predetermined time intervals and the dye solution was separated from the adsorbent by centrifugation at 10,000 rpm for 20 min. The absorbance of supernatant solution is measured to Equation 1 and 2.

Effect of pH
The effect of pH studied at three different pHs of 5, 6.95 and 9. The pH is adjusted by using NaOH and HCl solutions of different concentrations depending on the requirement. In this study, 25 ml of different pH adjusted dye solution of 50 mg L −1 is taken in a screw type Erlenmeyer flask and agitated at 180 rpm, with 0.05 g of <53 µm of IJS at temperature, 30±1°C. The samples are withdrawn from the shaker at pre-determined time intervals and the dye was separated from the adsorbent by centrifugation at 10,000 rpm for 20 min. The absorbance of supernatant solution is measured. The amount of CR adsorbed is calculated by using Equation 1.

Effect of size
The effect of size studied at different sizes of IJS like <53 µm, >53<75 µm, >75<90 µm and >90<150 µm. In this study, 25 mL of dye solution of 50 mg L −1 is taken in a screw type Erlenmeyer flask and agitated at 180 rpm, with different size of IJS at temperature, 30±1°C. The dye solution pH is maintained at 6.95 in this study. The samples are withdrawn from the shaker at predetermined time intervals and the dye solution is separated from the adsorbent by centrifugation at 10,000 rpm for 20 min. The absorbance of supernatant solution is measured. The amount of CR adsorbed is calculated by using Equation 1.

Kinetic models
The Lagergren's Pseudo-First-Order model (PFO) (Equation 3) and Pseudo-Second-Order (PSO) model (Equation 4) (Sivaramakrishna et al., 2012) have been widely used to predict sorption kinetics. The PFO equation is generally applicable over the initial stage of the adsorption processes whereas the PSO equation predicts the behavior over the whole range of adsorption. These two models are used in this study to fit the experimental data: where, k 1 (min −1 ) is the rate constant of PFO adsorption and k 2 (g mg −1 min −1 ) is the rate constant Science Publications AJES of PSO adsorption. q e , amount of dye adsorbed on adsorbent at equilibrium.

Intra-Particle Diffusion Model
In order to investigate the mechanism of the CR adsorption onto IJS, intra-particle diffusion based mechanism is studied. The most commonly used technique for identifying the mechanism involved in the adsorption process is by hitting an intra-particle diffusion plot. It is an empirically found functional relationship, common to the most adsorption processes, where uptake varies almost proportionally with t 0.5 rather than with the contact time t. According to the theory proposed by Weber and Morris (Sivaramakrishna et al., 2012): where, k pi (mg g −1 min −0.5 ), the rate parameter of stage i, is obtained from the slope of the straight line of q t versus t 0.5 where as C i is the intercept of the plot which gives an idea about the thickness of the boundary layer. Langmuir isotherm model was applied to describe the adsorption of CR. It represented by the following equation: where, Q max is the maximum adsorption capacity of IJS (mg g −1 ) and K L is the Langmuir constant related to the adsorption energy (L mg -1 ). Freundlich isotherm model is also applied to describe the adsorption of CR. Linearized in logarthemic form of where, K F is the Freundlich constant and '1/n' is the heterogeneity factor.

Effect of Contact Time
The adsorption of CR on IJS was studied at different CR pHs ranges (5, 6.95 and 9) and different sizes (<53 µm, >53<75 µm, >75<90 µm and >90<150 µm) Fig. 2  and 3 shows the result for effect of pH and sizes on adsorption of CR onto IJS at 30±1°C.

Effect of pH
The effect of pH on the amount of dye removal is kinetically studied at three different pHs of 5, 6.95 and 9.
For understanding the effect of pH on the adsorption of CR on IJS, the PFO and PSO kinetic models were used to fit the experimental data obtained in these experiments. Using Equation 3 and 4, a log (q e -q t ) versus t is plotted at different pH of CR solutions (Fig. 5). The PFO model data do not fall on straight lines indicating that this model is less appropriate. The Lagergren firstorder rate constant (k 1 ) and calculated from the model are presented in Table 1 along with the corresponding with correlation coefficients.
The experimental kinetic data is further analyzed using the pseudo-second-order model. By plotting t/q t against t for different initial CR concentrations (Fig. 6), a straight line is obtained in all cases and using Equation (4), the PSO constant (k 2 ) and qe values were determined from the plots. The values of correlation coefficient are very high (R 2 >0.999) and the theoretical q e cal values obtained from this model are closer to the experimental qe exp values at different pHs ( Table 1). It is important to note that for the PFO model, the correlation coefficient obtained in this study, R 2 < 0.93 at different pHs of CR solution, is lower as compared to the correlation coefficient obtained from the pseudo-second order model. Moreover, from Table 1.

Effect of Size
The adsorption kinetic studies are also performed at three different particle sizes at adsorption dose of 2.0 g L −1 of IJS. For understanding the effect of size of IJS on the adsorption of CR on IJS, the PFO and PSO kinetic models are used to fit the experimental data obtained in these experiments. Using Equation 3 and 4, a log (q e -q t ) versus t is plotted at different size of adsorbent (Fig. 7). The PFO model data do not fall on straight lines indicating that this model is less appropriate. The Lagergren first-order rate constant (k 1 ) was calculated from the model and the results are presented in Table 3 along with corresponding correlation coefficients.

Kinetic Study
The kinetic results are analyzed by using the intraparticle diffusion model also. Weber and Moris model (Sivaramakrishna et al., 2012) was used through Equation 5 to investigate intra-particle diffusion mechanism by plotting a graph between q t versus t 0.5 (Fig. 8). At least three regions observed that represent boundary layer diffusion, followed by intra-particle diffusion in macro, meso and micro pores. These three regions are followed by a horizontal line representing the system at equilibrium. Table 1. Pseudo-first-order and pseudo-second-order rate constants at 30°C and different pH of CR solutions Pseudo-first-order model Pseudo-second-order model

AJES
(mg g -1 ) K 1 (min -1 ) q e cal (mg g -1 ) R 2 K 2 (min -1 ) q e cal ( Table 3. Pseudo-first-order and pseudo-second-order rate constants at 30 º C and different sizes of IJS Pseudo-first-order model Pseudo-second-order model At the beginning of adsorption, there is a linear region representing the rapid surface loading, followed by the second linear region representing pore diffusion and finally a horizontal linear region representing the equilibrium. The Microsoft Excel 2003 software package is used to analyze various regions available in the graph and results of linear regression are shown in Table 2 and 4 for various sizes of IJS and different pH of solutions. The intraparticle diffusion parameter, k pi , is determined from the slope of each region while the intercept of each region is proportional to the boundary-layer thickness.
The calculated values of k pi and the intercept, C, for all the linear regions are shown in Table 2

DISCUSSION
In this study dye uptake was rapid for the first 60 minutes and thereafter proceeds at a slower rate and finally attains saturation. Figure 3 and 4 indicates that an increase in CR pH leads to decrease in the adsorption of CR on IJS. The equilibrium adsorption decreases from 20.8804 to 20.8242 mg g −1 and 19.9197 to 8.2022 mg g −1 for pH and size respectively. However, the experimental data is measured at 300 min to be sure that full equilibrium is attained. Data on the adsorption kinetics of CR by various biosorbent have shown similar range of adsorption rates. Hu et al. (2010) and Sivaramakrishna et al. (2012) studied the adsorption of CR on cattail root (Hu et al., 2010) and Jujuba seeds (Sivaramakrishna et al., 2012) and both studies reported that the equilibrium was reached in 3 h.
The values of correlation coefficient are very high (R 2 >0.999) and the theoretical q e cal values obtained from this model are closer to the experimental qe exp values at different pHs ( Table 1). It is important to note that for the PFO model, the correlation coefficient obtained in this study, R 2 <0.93 at different pHs of CR solution, is lower as compared to the correlation coefficient obtained from the PSO model. Moreover, from Table 1, it can be seen that the experimental values of q e exp are not in good agreement with theoretical values calculated (q e cal ) from the PFO equation. Therefore, it can be concluded that the PSO kinetic model provides a better correlation for the adsorption of CR on IJS at different pHs of CR solution compared to the PFO model. The effect of pH of acid brown dye solution on the activated carbon (solid waste generated in leather industry) is studied (Sekaran et al., 1995) it is similar to this studies.
The experimental kinetic data are further analyzed using the PSO model. By plotting t/q t against t for different initial CR concentrations (Fig. 8), a straight line is obtained in all cases and using Equation 4, the PSO rate constant (k 2 ) and q e values are determined from the plots. The values of correlation coefficient are very high (R 2 >0.998) and the theoretical q e cal values obtained from this model were closer to the experimental q e exp values at different sizes of IJS (Table 3). It is important to note that for the PFO model, the correlation coefficient obtained in this study, R 2 <0.843 at different sizes of IJS, which is lower as compared to the correlation coefficient obtained from the PSO model. Moreover, from The effect of size of activated carbon on the removal of acid brown dye on activated carbon (solid waste generated in leather industry) was studied (Sekaran et al., 1995) and size of activated clay on the removal of basic blue 18, basic red 46 and basic yellow 28 by activated clay (Hsu et al., 1997) similar to this study.

Equilibrium Modeling
The adsorption of CR on IJS was modeled with the Langmuir and Freundlich adsorption isotherms. The details of the Langmuir and Feundlich isotherms are given in Equation 6 and 7 and their respective plots are shown in Fig. 9 to 12, respectively. The values of the Langmuir and Freundlich constants obtained in this study are presented in Table 5. Both, Langmuir and Freundlich models are well suited for the experimental data of CR on IJS, as per the coefficients of correlation. Negative values for the Langmuir and Freundlich isotherm constants in Table 5 indicate the inadequacy of the isotherm model to explain the sorption process. These kind of negative values are available in the literature (Rabinson et al., 2012).  Q max (mg g -1 ) K L (L mg -1 ) R 2 K F n R 2 Size (µm) 5.6497 -0.4854 0.9820 29.8000 -1.0050 0.9990 pH 16.6670 -9.9010 1.0000 33.6000 -4.4444 1.0000

CONCLUSION
The present study focuses on the biosorption of CR dye from aqueous solution using IJS. The adsorption characteristics have been examined by contact time, pH effect and effect of biosorbent size. The maximum removal of CR was observed at pH 5.0. The biosorption of CR onto IJS was found to increase with decrease in biosorbent size. Based on correlation coefficient (r 2 value), the experimental data was best fitted with Langmuir model than Freundlich isotherm model. The suitability of PFO, PSO and intraparticle diffusion kinetic models for the biosorption of CR onto IJS was also discussed. Kinetic data follows the PSO kinetic model. Intraparticle diffusion model proves that pore diffusion plays major role in the dye biosorption. The results showed the possibility of IJS for dye removal from aqueous solution as an alternative for most costly used biosorbent.