Adsorptive Removal of Synthetic Dye Effluent Using Sago Waste as Low Cost Adsorbent
Received Date: Jun 04, 2018 / Accepted Date: Jun 15, 2018 / Published Date: Jun 22, 2018
Agricultural waste (Sago waste) used as low-cost adsorbent for the removal of synthetic dye effluent from aqueous solution by batch adsorption technique. The various parameters that influence in this adsorption process such as contact time, initial dye concentration, adsorbent dosage, temperature, pH, agitation speed and desorption studies. The experimental data were analysed using Langmuir isotherm model. Kinetic data well fitted for pseudosecond order model. Thermodynamic parameters have also been calculated. The sago waste was characterized by SEM and FT-IR studies. The low-cost adsorbent was found to be efficient for the dye removal process.
Keywords: Sago waste; Synthetic dye effluent; Adsorption; Dye removal
In recent years, discharge of waste products (mainly dye effluents) from difficult industries leading to aquatic and environmental pollution is a serious global problem of great concern [1,2]. Due to toxicity of dyes, it is necessary to remove them from wastewater before them discharge to the natural environment. Various physical-chemical and biological wastewater treatment methods such as anaerobic bioremediation, oxidative process, ozonation, electrochemical destruction, irridation, ion-exchange, membrane filtration and adsorption have been used for the dye removal from effluents , as each method has some limitations.
Among all of these methods, the adsorption is one the most effective method for wastewater treatment . The adsorption method is superior to other technique in terms of low-cost, high efficiency, simplicity of design, and ease of operation and insensitive to toxic substances . The cost effectiveness, availability and adsorptive properties are the main criteria in selection of low-cost adsorbent to remove toxic compounds from wastewater .
Adsorption by agricultural by-products used recently as an economical and realistic method for removal of different pollutants, also application of bio-adsorbent especially based on non-toxic and eco-friendly with high surface area and active sites is a great demand . The main objective of this work was to study the decolourization of synthetic dye effluent using activated sago waste by adsorption technique.
In the experimental studies, Elico-UV-spectrophotometer was used for determination of dye concentrations. Equip-Tronics digital pH meter model EQ-610 was used in pH measurements for adsorption experiments.
Naphthol Blue Black-B (NBB-B) used in the adsorption studies was obtained from Loba Chemie Pvt. Ltd., Mumbai. Brilliant Green (BG) and Alizarine Red-S (AR-S) were procured from Hi Media Laboratory Pvt Ltd., Mumbai.
Preparation of stock dye solution
Stock solution of synthetic dye effluent (NBB-B, BG and AR-S) was prepared by dissolving 0.05 g of dyes in distilled water and making it up to 100 ml in a standard flask.
Preparation of activated sago waste (ASW)
The sago waste was obtained from sago industries in Rasipuram (Karur district, Tamil Nadu). It was washed with distilled water, dried and powdered in a mixer grinder. The dry sample was sieved and then dried at 110°C for 6 hours. Finally, it was preserved in a desiccator.
The batch experiments were carried out in 250 ml pyrex bottle with 100 ml of Synthetic Dye Effluent (SDE) contains 2 g of ASW, shaken in an orbital shaker at 250 rpm to investigate the effects of contact time, initial dye concentration, dosage of sago waste, temperature, pH, agitation speed and desorption. Before and after adsorption of the (SDE) dye concentration is measured by using Elico UV-spectrophotometer at wave length of 618 nm. The amount of dye adsorbed on the ASW (mg/g) and percentage of adsorption of (SDE) dye are calculated using eqn. 1 and 2 respectively .
Where, qe is the adsorption capacity (mg/g) of ASW at equilibrium, Ci and Ce are initial and equilibrium concentration of SDE dye solution (mg/L) respectively, V is the volume of SDE dye solution and M is the weight of ASW.
Kinetic and thermodynamic study
In order to find out the adsorption rate of synthetic dye effluent by ASW kinetic study was determined by variation of contact time. Thermodynamic parameters were calculated by executing the experiment at different temperature (34°C-4°C).
Results and Discussion
SEM is widely used to study the morphological features and surface characteristics of adsorbent materials. The surface morphology of the ASW was examined using Scanning Electron Microscopy (SEM) and the results are shown in Figure 1. SEM image in Figure 1 shows regular surface texture, porosity, holes and cave type openings on the surface of the ASW .
The FT-IR spectrum of the ASW in Figure 2 exhibits broad bands at 3345.55 cm-1 due to the -OH stretching frequency. The absorption band at 2929.37 cm-1 is due to contribution from C-H stretching. The stretching vibration obtained in the range 1250-1050 cm-1 is attributed to the presence of C-O-C bond. The strong band at 1026.76 cm-1 denotes the presence of C-OH stretching vibration .
Availability of more surface area due to typical holes and cave openings type of structure of the ASW surface was clearly witnessed in the SEM micrograph and FT-IR spectrum was confirmed that starch and cellulose moieties are present in the ASW sample.
Variation of contact time
Batch experiment was performed at 34°C with initial dye concentration of 4 mg/L using ASW dose at 20 g/L at pH 7 with agitation speed of 250 rpm in an orbital shaker. The equilibrium data shows that the variation of contact time from 10 to 50 min on SDE dyes removal. It was observed that 78.3% of SDE dye removed at 50 min; thereafter it becomes constant shown in Figure 3. As all the adsorption sites were occupied, further adsorption was not possible and 50 min was considered as optimum time for maximum adsorption.
Variation of initial dye concentration
The effect of different initial dye concentrations is studied by (3-5 mg/L) maintaining the dose of ASW at 20 g/L, contact time to 50 min, temperature at 34°C, pH 7 and agitation speed at 250 rpm. The adsorption data depicts that the % decolourisation follows decreasing trend with increasing initial dye concentration shown in Figure 4. This may be due to the formation of monolayer of dyes on the surface of ASW which hinders the further layer.
Variation of ASW dosage
The effect of ASW dose was carried out by varying the ASW mass from 10 to 30 g/L keeping contact time to 50 min, dye concentration to 4 mg/L, temperature at 34°C, pH 7 and agitation speed at 250 rpm. Figure 5 shows that the dye removal increased with increase in ASW dosage due to increased amount of adsorption sites.
Variation of temperature
The effect of temperature (Figure 6) was studied by varying the different temperatures (34, 37 and 40°C) maintaining contact time to 50 min, dye concentration to 4 mg/L, ASW dose 20 g/L, pH 7 and agitation speed at 250 rpm. The equilibrium data evident that % decolourisation increased with increasing temperature due to the excitation of adsorbent particles.
Variation of pH
The effect of pH was studied by varying different pH (4, 7 and 9) keeping contact time to 50 min, initial dye concentration 4 mg/L, ASW dose 20 g/L, temperature at 34°C and agitation speed at 250 rpm. Figure 7 depicts that the adsorption of SDE increases with the decrease of pH of the solution . The initial pH may affect the charge on the adsorbent surface, altering its adsorption capacity .
Variation of agitation speed
The effect of agitation speed of SDE on ASW was studied by varying the agitation speed from 50 to 250 rpm, keeping the other parameters is constant. It is evident from Figure 8 that the adsorption of SDE is found to increase with increasing agitation speed due to the fact that with the increased turbulence, there is a decrease in boundary layer thickness around the adsorbent particles.
Desorption studies help to elucidate the nature of adsorption and recycling the spent adsorbent and dye is essential . The desorption experiment was carried out with 0.1 N NaOH. Figure 9 shows that the desorption efficiency increases with increase in strength of NaOH due to ion substitution.
Adsorption isotherm studies
The adsorption isotherm is widely used to elucidate the relationship between the amount of dye adsorbed at constant temperature and its concentration in equilibrium solution. It is an important tool of both theoretical and practical point of view. In order to optimize the adsorption design and also to predict its corresponding parameters. The parameters obtained from different isotherm models provide information about adsorption mechanism and the surface properties of the adsorbent. Linear regression coefficient is frequently used to determine the best fitting isotherm.
The Freundlich isotherm  is an empirical relation between the concentrations of a solute on the surface of an adsorbent to the concentration of the solute in the liquid with which it is in contact.
The linear form of Freundlich equation (Figure 10) is given by the following expression:
Where, qe is the amount of the dye adsorbed per unit mass of adsorbent (mg/g) at equilibrium, Kf and n are Freundlich constants. The slope 1/n indicates the favourable adsorption with the attractive force between adsorbed species .
Langmuir isotherm  is precise for the monolayer adsorption of a solute from a liquid on the adsorbent surface containing a definite number of identical active sites. The linear equation of Langmuir isotherm is expressed by:
Where, Q0 and b are Langmuir constants. In the present study, the experimental data was fitted into Langmuir equation (eqn. 4) and the plot of Ce/qe versus qe was found to be linear which indicates that the adsorption of SDE dye on ASW follows Langmuir isotherm (Figure 11).
Langmuir isotherm can also be expressed in terms of separation factor, RL which is referred as equilibrium parameter and expressed as:
RL value indicates the shape of the isotherm and nature of adsorption process. When, the RL value>1 adsorption is unfavorable, 0<RL<1 it is favorable, if RL=0 it is irreversible. In the present study, the RL value was found to be 0.4123. This indicates that the adsorption of SDE using ASW is a favorable process.
Where, BD is related to the free energy of sorption, qD is the Dubinin- Radushkevich isotherm constant. The apparent energy of adsorption can be computed using the following equation:
The apparent energy (E) of the adsorption of SDE using ASW was obtained as 57.7350.
Temkin isotherm  is assumed that the heat of adsorption decreases linearly with increasing coverage. The temkin isotherm (Figure 13) is represented by the following linear equation:
Where, KT is the equilibrium binding constant (L/mg), BT is the variation of adsorption energy (KJ/mol).
Jovanovic model  is derived for describing the adsorption behaviour on heterogeneous surfaces. The linear form of Jovanovic isotherm (Figure 14) equation is,
Where, qm and KJ are Jovanovic constants.
Scatchard analysis  is employed to analyse the binding isotherm of dye molecules and adsorbent. The Scatchard (Figure 15) equation can be expressed as:
Where, Q is the equilibrium adsorption amount at each concentration, Qmax is the maximum adsorption amount; Kd is the equilibrium dissociation constant at binding sites.
Flory-Huggins isotherm  is the model describing the degree of surface coverage characteristics of adsorbate onto adsorbent. The linear plot (Figure 16) of Flory-Huggins equation is expressed as:
Where, KFH is the Flory-Huggins equilibrium constant, nFH is the model exponent; θ is the degree of surface coverage.
The kinetics of decolourisation of SDE dye solution over ASW has been studied using pseudo-second order kinetic model.
Pseudo-first order kinetic model
Pseudo-first order model  is given by Lagergren as:
Where, qe and qt are the adsorption capacity at equilibrium and at time t respectively, k1 is the rate constant of the pseudo-first order adsorption.
After integration, the integrated form of the above equation becomes,
The equilibrium data shows (Figure 17) that the adsorption of SDE onto ASW cannot be applied and the reaction mechanism is not a firstorder reaction.
Pseudo-second order kinetic model
Pseudo-second order kinetics  is expressed as:
Where, k2 is the rate constant of pseudo-second order adsorption.
After integration, the form of rearranged equation is,
The plot (Figure 18) was perfect linear shows that the reaction kinetics follows pseudo-second order model. The correlation coefficients (R2) are also confirmed that the adsorption better fitted by the pseudo-second order kinetic model.
Weber and Morris intra particle diffusion model
Weber-Morris intra-particle diffusion model  is mainly used to elucidate the diffusion mechanism. The Weber-Morris intra-particle diffusion rate equation can be given as:
Where, qt is the amount of sorbate on the surface of the sorbent at time t, Kd is the intra-particle diffusion rate constant, C is a constant that gives idea about the thickness of the boundary layer.
The plot of qt versus √t is linear indicates occurrence of intraparticle diffusion (Figure 19).
The Gibbs free energy change of the adsorption process  is related to the equilibrium constant by the Van’t Hoff equation,
Where, KL (L/g) is equilibrium constant obtained by multiplying the Langmuir constants Q0 and b, T is the absolute temperature (Kelvin), R is the gas constant (8.314 J/mol/K). The graph is plotted by taking ΔG° in y-axis against T in x-axis. The relationship between the changes in the Gibbs free energy, entropy (ΔS°) and enthalpy (ΔH°) can be expressed as follows:
The plot (Figure 20) of ΔG° versus T was perfect linear which helps ΔS° and ΔH° could be calculated from the slope and intercept of the plot respectively. The negative value of ΔG° (-2.7311) and ΔH° (-2 × 10-15) indicate that the process is spontaneous and feasible process and exothermic nature of the adsorption. The negative value of ΔS° (-0.0089) suggests that decreased randomness at the solid/solution interface during the adsorption.
In this study, ASW was prepared by simple process and used for the adsorption of SDE from aqueous solution. Adsorption efficiency of ASW for SDE at equilibrium time of 50 min was found to be 78.3%. The parameters influencing adsorption rate such as contact time, initial dye concentration, temperature, etc. were optimized. The equilibrium results were analyzed using several adsorption isotherm models. The equilibrium data were better fitted by the Langmuir model than other isotherm models. The adsorption process was found to follow pseudosecond order kinetics and the experimental data were found to fit into Weber-Morris intra particle diffusion model. In thermodynamic study, negative value of ΔG° and ΔH° indicate that the adsorption process is spontaneous, feasible process and exothermic in nature. The negative value of ΔS° reveals that the process is enthalpy driven. Thus, the present study has proved that ASW could be used as an efficient adsorbent for the removal of SDE dye from aqueous solution. Moreover, the use of ASW as adsorbent not only to solve the environmental pollution but also to decrease the overall cost of waste water treatment and to reduce the amount of industrial by-products.
We thank the Department of Chemistry, Seethalakshmi Ramaswami College, Trichy, for financial support.
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Citation: Karthika M, Vasuki M (2018) Adsorptive Removal of Synthetic Dye Effluent Using Sago Waste as Low-Cost Adsorbent. Int J Waste Resour 8: 344. DOI: 10.4172/2252-5211.1000344
Copyright: © 2018 Karthika M, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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