Adsorptive Elimination of an Acidic Dye from Synthetic Wastewater using Yellow Green Algae along with Equilibrium Data Modelling
Surabhi Sagar1*, Dr. Arshi Rastogi2
1Research Scholar, K.L.D.A.V. (PG) College, Roorkee Dist. Haridwar� Uttarakhand
2Assistant Professor, K.L.D.A.V. (PG) College, Roorkee Dist. Haridwar� Uttarakhand
*Corresponding Author E-mail: arshirastogi@gmail.com
ABSTRACT:
Present research discussed the adsorptive elimination of Methyl Orange [MO] by yellow green algae, Vaucheria sp. from synthetic wastewater. The adsorption process was found to be highly dependent on various operative variables, such as the pH of aqueous solution, contact time to reach equilibrium, the dosage of adsorbent, temperature and the chemical pretreatment for dye removal. Adsorption of the dye over the adsorbent has been monitored through Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) isotherms with Langmuir isotherm showing the best-fit. To describe the adsorption mechanism kinetic models such as pseudo-first order, pseudo-second order and intra particle diffusion were applied and pseudo-second order kinetic model was found to adequately describe the kinetic data. Thermodynamic analysis of the adsorption process of MO dye on this yellow green alga confirms their spontaneity and endothermicity. In order to explore various properties of the adsorbent used i.e. Vaucheria sp., surface area was calculated by BET method, surface morphology studies by SEM and functional group studies by FTIR. Thus, this study demonstrated that easily available, Vaucheria sp. could be used as an efficient adsorbent for the treatment of wastewater bearing MO dye.
KEYWORDS: Methyl Orange, Vaucheria sp., Adsorption isotherms, Kinetic models, Synthetic wastewater.
The immeasurable use of dyes in various industrial applications has resulted in the release of toxic dye effluents into the water streams every year. Presence of these dye effluents poses a significant threat to the environment. Dyes are water soluble and intensely coloured substances and are mainly used in textiles, plastics, pharmaceuticals, paper, and electroplating and paint industries1. Dyes are considered to be obnoxious type of pollutants as they cause highest aquatic environment contamination among all the industrial sectors2,3. Dyes are known to be mutagenic, toxic, carcinogenic, they are generally resistant to light, water, oxidizing agents and difficult to degrade5.Therefore, it is essential; to treat the wastewater containing dyes before being discharged.
Methyl orange [MO], an acidic dye, is used extensively in various branches of textile and paper printing industry and is available in excess as industry effluent. It is hazardous in case of its ingestion, inhalation or its contact with eyes or skin and severe over-exposure can result in death also. Hence, great deal of attention is given using new technologies, for the removal of such coloured substances from contaminated waters6. In past few years, literature survey shows various adsorbents investigated for removal of MO from wastewater include Chitosan7, Humicola fuscoatra8, Pine cone derived activated carbon9, Ficus caria fibre10and aminated pumpkin seed powder11.
Several treatments have been proposed for the removal of synthetic dyes from aqueous solutions such as precipitation, coagulation, flocculation, ionexchange, membrane separation, photocatalysis and photo oxidation12 but their practical usage is sometimes restricted due to technical reasons and relatively high cost of exploitation or may not be capable of treating large volumes. Among various treatment technologies, adsorption process has been successfully employed for the treatment of wastewaters12-16. This process is gaining importance due to its ease of operation and comparably low cost application in treatment of dyes17-19. In recent years, algal biomass has gained a wide attention as a vital option for the treatment of water containing dyes. Uptake of dye molecules by algal biomass is believed to occur through interaction of various functional groups that make up a cell wall20. Algae are biological and renewable resources which are widely available in many parts of the world.
In the present study, Xanthophyta alga, Vaucheria sp. was used as an adsorbent, for the adsorptive elimination of MO dye, as it is abundantly available freshwater algae. Also, there are very few reports which show that Vaucheria sp. can effectively remove certain toxic heavy metals 21, 22 and dyes 23 from aqueous solutions. So, the aim of study was to investigate the adsorption efficiency of Vaucheria sp algae for MO dye from synthetic wastewater. To understand the adsorption process better, the isotherms, kinetics and thermodynamic for dye removal in batch system were studied, in addition to chemical pre-treatment of algae and sorption�desorption reuse studies. The characterization of adsorbent was performed using FTIR, SEM and BET method.
MATERIALS AND METHODS:
Equipment:
The pH measurements were made using a pH meter (PERFIT, India) and the aqueous solution was analysed using a UV-Vis spectrophotometer -119 (Systronics India Ltd.). Infrared spectra were recorded using KBr pellets on a Thermo Nicolet FTIR (Germany) within 4000-400 cm-1. To examine the morphological characteristics of the alga before and after adsorption of MO dye, samples were viewed using a SEM (model ZEISS EVO 40 EP, Cambridge, UK) with analytical software Quantax 200. Elemental analysis of the adsorbent was carried out on an Elementar analyse system Vario MICRO CHNS V3.1.1 (GmbH, Germany) and the Brunauer-Emmett-Teller (BET) surface area of the adsorbents was measured by nitrogen adsorption isotherms on a Micrometrics ASAP 2010 surface area analyser (England, UK).
Chemicals and Reagents:
All the chemicals used in this study were of analytical grade. Double distilled water was used throughout the experiments. MO used as an adsorbate was of commercial purity and used without further purification. Synthetic wastewater for the study was prepared in the laboratory using MO and distilled water.
Algal Biomass Preparation:
For this study, the test algae Vaucheria sp. was acquired from a fresh water pool, near Roorkee and Haridwar.� It was then washed thoroughly with distilled water to remove the filth and unwanted materials. After Sun drying, the biomass was dried in the oven at 343K for 24 hrs. and then it was ground and sieved to obtain particle size of 100�m mesh size. Prior to use, the powdered adsorbent was maintained in vacuum desiccator.
Dye Solution Preparation:
Stock dye solution (1g/L) was prepared according to the standard procedure by dissolving the required amount of MO in distilled water. Synthetic wastewater that is an artificially prepared wastewater containing desired concentration of MO dye was prepared by diluting the above prepared stock solution with suitable volume of distilled water. The initial pH was adjusted with 0.1M HCl and 0.1M NaOH solutions using a digital pH meter calibrated with standard buffer solutions. Table 1 summarizes some important characteristics of the studied dye.
Table 1: Chemical structure and characteristics of the dye used as adsorbate in the present study
Dye |
Methyl orange |
Molecular formula |
C14H14N3NaO3S |
Chemical structure |
|
MW� (g mol-1) |
327.33 |
λ max (nm) |
463 |
Ionization |
Acid |
Characterization of Adsorbent:
Surface area of the adsorbent was determined by BET method24and the surface morphology after gold coating was studied using Scanning Electron Microscope (SEM). Elemental analysis was done to examine the percentage composition of Carbon, Nitrogen, Hydrogen and Sulphur and finally the Infra-red analysis was used to identify the principal chemical functional groups present at the surface of the adsorbent.
Adsorption Experiments:
Studying the effect of various parameters on dye removal from synthetic waste water was followed according to pH values (2-12), biomass dosage (1-10g/L), contact time (0-160 min), and temperature (298, 308, 318 K). Each experiment was conducted in triplicate and mean values of data were reported. Since standard deviations never exceeded � 1.5%, the error bars were not shown in the figures. All experiments were performed for 100 min, as the contact time experiment revealed that at this time, the reaction reached its equilibrium condition. After 100 min of contact time the solution was filtered and the residual dye in the solution was determined quantitatively by the UV/Vis Spectrophotometer at λ maxof the dye. The adsorption capacity was calculated using mass balance equation given as follows.
������������������������������������������������� (1)
Where qe is the adsorption capacity of algae (mg/g), Co and Ce are the initial and the equilibrium concentration of dye (mg/L), V is the volume of reaction mixture (L) and M is the mass of adsorbent used (g).
Adsorption Isotherm Models:
For predicting and comparing the adsorption performance of the adsorbent, modelling of adsorption isotherm data is important. Therefore, the equilibrium data was fitted using different isotherm models namely Langmuir, Freundlich, Temkin and Dubinin-Radushkevich (D-R) 25-28.
Equilibrium experiments under optimised conditions were performed at three different temperatures (298, 308, 318 K) using 2g/L of adsorbent dose at 200mg/L dye concentration for 100min.The Langmuir isotherm preassumes monolayer adsorption on the surface that contains a finite number of adsorption sites via uniform strategies of adsorption with no migration of adsorbate taking place along the plane of the surface and the energy of adsorption is constant. It can be expressed as:
����������������������������������������������������������� (2)
where qe is the amount adsorbed (mg/g), Ce is the equilibrium dye concentration of adsorbate (mg/L), Q0 is the Langmuir constant related to maximum monolayer adsorption capacity (mg/g) and b is the constant related to free energy. The values of these constants were calculated by plotting a graph of 1/ qe versus 1/ Ce.
Dimensionless separation factor, RL, can be calculated from Langmuir constant, b, as:
�������������������������������������������������������������������������� (3)
The values of RL were computed at different temperatures, and the nature of the adsorption isotherm depends on the criterion that if the RL value is greater than 1then the adsorption isotherm is unfavourable, if it is equal to 1 then it� is considered to be Linear , if the value of� RL falls between 0 and 1 it a favourable and� irreversible in case the value is equal to 0
Freundlich isotherms assume a multilayer heterogeneous adsorption for which the energy term in Langmuir equation varies as a function of surface coverage.� This model can be expressed as:
�������������� �������������������������������������������� (4)
where KF is a Freundlich constant (mg1-1/n L1/n g-1) and n is the intensity of adsorption. The plot between ln qe versus ln Ce was drawn and the intercept and slope were used to calculate the value of KF and n.
The Dubinin and Radushkevich (D-R) isotherm was chosen to calculate the porosity apparent free energy. This isotherm does not assume a homogeneous surface or constant adsorption potential but is related to the porous structure of the adsorbent. The linear form of D-R isotherm equation is given as:
����������������������������� ������� (5)
�������������������������������������������� (6)
where qm is maximum adsorption capacity(mg/g), β is constant related to adsorption energy (mol2kJ-2), ε is a Polanyi potential, R is the gas constant (8.314Jmol-1K-1), T is temperature(K). The mean adsorption energy can be calculated from formula
�������������������������������������������������������������������������� (7)
In order to find certain indirect adsorbate-adsorbent interactions on the dye adsorption and that the fall in the heat of adsorption is linear rather than logarithmic, Temkin isotherm was modelled. Temkin model is given by:
����������������������������� ����������������������������� (8)
where R is the gas constant, T is the absolute temperature in kelvin. The constants bT(g kg mg-1 mol-1) and AT(L mg-1)associated with the heat of adsorption were calculated from slope and intercept of qe versus ln Ce.
Adsorption Kinetic Models:
Kinetic studies for adsorption of dyes were conducted with dye concentration of 100 and 200mg/L containing 2g/L of adsorbent at temperature 318K. Samples were collected at various time intervals, filtered and analysed for unremoved dye concentration as described earlier.
Among various kinetic models, pseudo-first order, pseudo-second order, and intra particle diffusion models were selected in order to find an efficient model for the best description of adsorption kinetics 29-31.The linear form of the pseudo-first order equation can be expressed as follows.
�������������� ����������������������������� (9)
where qt (mg/g) is the amount of dye adsorbed by biomass at equilibrium time t, k1 is the pseudo-first order rate constant (min-1). The graph between log (qe�qt) versus log qe was plotted in order to calculate the constants.
The linear form of pseudo-second order model and be written as follows.
�������������������������������������������� (10)
Where qe and q are the amounts of the dye adsorbed by the algal biomass (mg/g) at equilibrium and time t, respectively and k2 (g mg-1 min-1) is the rate constant of second order adsorption.qe and k2 can be computed from the slope and intercept obtained from the plots of t/q versus t.
The mathematical formula for the intraparticle diffusion rate constant can be expressed as follows.
�������������� �������������������������������������������� (11)
where qt is the amount of MB adsorbed per unit mass of adsorbent (mg/g) at time t and kid the intra-particle diffusion rate constant (mg/g min-1/2).
Adsorption Thermodynamics:
In order to investigate the main thermodynamic variables such as standard free energy changes (ΔGo, kJ/mol), enthalpy (ΔHo, kJ/mol) and entropy(ΔSo, kJ/mol/K), adsorption of MO were studied at three different temperatures (298, 308, 318 K) using the following equations.
����������������������������� �������������� (12)
�������������� ��� ���������� (13)�������
�������������� ������������ ���������������� (14)
Desorption Studies:
For desorption studies, MO dye solution(1g L-1) were mixed with Vaucheria sp. at pH 4 and 318K for 100 min. Remaining dye concentration in the solution was measured in order to calculate the adsorbed dye. The adsorbent was then filtered and dried in vacuum oven at 343K for 24 h. The MO loaded adsorbent was then allowed to contact with 50ml of 0.1 M HCl (acid), 0.1 M NaOH (base), and EDTA(Ethylene diamine tetra acetic acid) (chelating agent) each in 100 ml conical flask at 318K, for 100 min, for five consecutive cycles using the same adsorbent. One complete cycle followed the sequence consisting of adsorption followed by desorption. The amount of dye desorbed was determined using UV-Vis Spectrophotometer. Desorption ratio is given as the amount of dye desorbed to the amount of dye adsorbed multiplied by 100.
Chemical Pre-treatment:
Five different chemical reagents (Hydrochloric acid, Nitric Acid, Sodium Hydroxide, Sodium Chloride and Ethanol) were selected for the chemical treatments. Chemical pretreatment test were conducted using a known quantity of a yellow green algae, suspended in 1 mol/L pretreatment solution. The mixtures were stirred at 110 rpm at 300K for 5 h. Treated algal biomass were separated from the mixture by filtration. The collected samples were oven dried at 343K for 24 h and later used for adsorption studies.
RESULTS AND DISCUSSION:
Characterization of Adsorbents:
The physical and chemical properties of algal biomass were determined by the standard methods. The surface area of Vaucheria sp. was found to be 3.248 m2/g by BET method and the Elemental analysis depicted the composition of adsorbents as C, 35.93%; N, 4.28%; H, 4.59% and S, 0.744%.
As can be seen from the SEM micrograph (Fig. 1A) the surface of the algae comprises of grooves and cavities. This large surface area and grooved structure of yellow green algae might allow the molecules of MO dye to penetrate into the algal tissue and interact there in with the surface functional groups. Figure 1B shows the tangled dye molecules at the outer grooves of the algal surface.
��������������������������������������������������������������������������
A
B |
Figure1: SEM micrographs of (A) Vaucheria sp. before adsorption (B) Vaucheria sp. after adsorption of MO
To understand any possible interaction between the functional group on the surface of the test alga and MO dye, dried powder of the algae before and after adsorption was examined using FTIR spectroscopy. The FTIR spectra of algal biomass before and after adsorption of the dye was recorded, and as seen from the Table 2, there was a shift in the peaks indicating the presence of ionisable functional groups(i.e. carboxyl, amino, amide and hydroxyl). This shifting of peaks suggests the formation of new bonds and the binding that takes place on the surface of algal biomass.
Table 2:IR absorption bands and corresponding possible functional groups present on algal biomass Vaucheria sp.
Vaucheria sp. before MO adsorption (cm-1) |
Vaucheria sp. after MO adsorption (cm-1) |
Bonds indicative of functional groups |
3423.09 |
3417.07 |
Carboxylic/OH stretch and N-H stretch |
2925.13 |
2924.19 |
Phenolic/carboxylic |
1644.72 |
1644.18 |
=C=O stretch, >C=C, >C=N, Amide I band |
1535.31 |
1536.22 |
Amide II band |
1068.79 |
1069.68 |
≡C-N< |
478.11 |
469.60 |
C-N-S scissoring |
Preliminary Adsorption Studies:
There are many operational parameters affecting dye adsorption such as solution pH, contact time, adsorbent dose and temperature. The effects of these parameters were therefore taken into account.��
pH edge :
Earlier studies have shown that the pH of the solution is one of the vital factors influencing the adsorption process as it affects the solubility of adsorbent and the ionizing of functional groups present on the cell walls. Figure 2show the effect of pH values on the removal of MO at different initial dye concentrations, when the temperature, adsorbent dose and contact time were kept constant. The highest adsorption was observed at acidic pH (4.0). The results are consistent with prior researchers in which maximum adsorption of anionic dyes such as Acid orange II by brown algae32 and Acid orange 7 by green alga Spirogyra sp.33 were determined at pH 2-4. This can be understood on the basis of isoelectric point of yellow green algae around pH 4. The cell wall functional groups get protonated at a pH lower than isoelectric point, therefore the adsorption of anionic dye MO gets stimulated and the dye removal was increased.
Figure 2: Effect of pH on the extent of adsorption of MO on Vaucheria sp., (pH 2-12, initial dye concentration 50, 100, 150 and 200 mg/L, contact time 100 min, adsorbent dose 2.0 g/L, temperature 318 K)
The Influence of Contact Time:
Ideal adsorption materials are effective in quickly adsorbing high dye concentrations from wastewater and attain equilibrium. The effect of contact time on removal of MO dye is depicted in Figure 3. The figure shows that the rate of adsorption of dye was rapid at early stage and then it gradually slowed down until equilibrium was achieved at 100 min. After the saturation levels the amount of MO dye adsorbed on the algal biomass did not significantly change further with time. The high adsorption rate at the beginning can be regarded to the effect of easy availability of the active sites on the surface of the adsorbent. Later there was not only the decrease in the available active sites but also the accumulation of dye molecule on the surface of biomass thus causing the repulsion among the dye molecules and significantly causing decline in the adsorption process. A similar trend was also reported for other dyes by different adsorbents34.
Figure 3: Effect of contact time on the extent of adsorptionof MOon Vaucheria sp., (contact time 0-160 min, initial dye concentration 50, 100, 150 and 200 mg/L, pH 4, adsorbent dose 2.0 g/L and temperature 318 K)
Influence of Adsorbent Loading:
The dependence of dye adsorption on the amount of algal biomass was studied for different adsorbent dosages (1-10 g/L).From Figure 4 it was apparent that dye adsorption increased on increasing the adsorbent dose from 1-2 g/L, and it further decreased when the adsorbent dosage was over 2 g/L. This may be regarded to the fact that as the amount of adsorbent dose increases, the surface area and consequently the number of available adsorption sites also increases thereby increasing the adsorbed dye amount. At higher adsorbent dose the adsorption decreases due to interaction between adsorbent particles, aggregation of adsorbent leads to a decline in adsorbent total surface area35.
Figure 4: Effect of adsorbent dose on the extent of adsorption of MO on Vaucheria sp, (adsorbent dose 1.0 - 10.0 g/L, initial dye concentration 50, 100, 150 and 200 mg/L, contact time 100 min,pH 4, temperature 318 K)
Influence of Temperature and Thermodynamic Studies:
The influence of temperature on adsorption of dye by Vaucheria sp. was investigated at three different temperatures (298, 308 and 318 K) at optimum pH and contact time of 100 min. Figure. 5. depicts the effect of temperature on dye adsorption. As it can be seen that there was an increase in adsorption process as the temperature was increased and signifies the endothermic nature of the reaction10. The increase in temperature increases the active sites of algal biomass surface and also reduces the thickness of the boundary layer surrounding the adsorbent, resulting in an increase in the adsorption capacity.
Figure 5: Adsorption isotherms at three different temperatures for Vaucheria sp.(temperature 298, 308, 318 K, adsorbent dose 2 g/L, contact time 100 min, pH 4)
Thermodynamic parameters including standard free energy changes (ΔGo, kJ/mol), enthalpy changes (ΔHo, kJ/mol) and entropy changes (ΔSo, kJ/mol/K)were calculated using equilibrium constants changing with temperature. Table3. represents the values of ΔGo, ΔHo, and ΔSo for adsorption onto Vaucheria sp. The negative value of ΔGo, implies the spontaneity and thermodynamic feasibility of the adsorption. On increasing the temperature the absolute value of ΔGo increased confirming the increase in feasibility of adsorption at higher temperature and indicates that high temperature plays a positive role in adsorption. The positive value of ΔHo� indicates that adsorption process of dye onto the dried algal biomass is physical and endothermic. The adsorption process is generally considered as physical process if ΔHo< 25 kJ/mol and as chemical process when ΔHo< 40 kJ/mol10. The positive values of ΔSo corresponds to the randomness at the solid/liquid interface during adsorption process. Similar thermodynamic studies have been reported in earlier studies 36.
Adsorption Isotherm Models:
�The distribution of adsorption molecules between the solid and liquid phase of adsorbent and adsorbate on reaching the equilibrium state is well explained by adsorption isotherms which describe the potentiality of the adsorbent. In the present study the Langmuir, Freundlich, Temkin and Dubinin �Radushkevich (D-R) isotherm models were applied to find the model that describes the experimental data. The values of isotherm models constants and their respective correlation coefficients are presented in Table 3. The experimental data produced a higher value of correlation coefficient (0.996) with Langmuir model indicating the homogeneous adsorption phenomenon on a uniform surface for the algal-dye system.
The results were also found to fit well with Temkin model (see Table 3) which suggested the reduction in heat of adsorption with the increase of coverage of adsorbent, and adsorption could be characterized by a uniform distribution of binding energies up to maximum value
The Dubinin-Raduskevich (D-R) isotherm model has been considered to determine the mean adsorption energy. The experimental results were found to fit well with relatively good correlation coefficient values (0.80-0.90). The value of E determines the physical and chemical nature of reaction. If the value of E falls between 8kJ/mol and 16kJ/mol, then the adsorption process is chemically controlled, and if the value of E is < 8 kJ/mol then it progresses physically. The calculated value of mean energy (E)was found to be less than 8kJ/mol, indicating that the adsorption of MO on to Vaucheria sp. was a controlled and physical process.
Table 3: Adsorption isotherms constants for the adsorption of Methyl orange on Vaucheria sp. at different temperatures
Isotherm Parameters |
Vaucheria sp. |
||
|
298K |
308K |
318K |
Langmuir isotherm |
|||
b(L/mg) |
0.0344 |
0.03497 |
0.04563 |
�qe�(mg/g) |
108.69 |
120.48 |
126.58 |
R2 |
0.991 |
0.993 |
0.996 |
Thermodynamic parameters |
|||
ΔGo�(kJ/mol) |
-23.113 |
-23.931 |
-25.411 |
ΔSo�(kJ/mol/K) |
0.114933 |
0.13857 |
0.11494 |
ΔHo*�(kJ/mol) |
|
11.137 |
|
Freundlich isotherm |
|||
N |
1.9538 |
2.1468 |
2.5303 |
KF(mg/g) |
12.222 |
13.365 |
23.268 |
R2 |
0.9637 |
0.922 |
0.9405 |
Temkin isotherm |
|||
AT |
0.7057 |
0.8810 |
0.9622 |
bT |
65.705 |
69.358 |
78.406 |
R2 |
0.910 |
0.941 |
0.953 |
D-R isotherm |
|||
qm(mg/g) |
104 |
118 |
120 |
E(kJ/mol) |
0.100 |
0.111 |
0.158 |
R2 |
0.807 |
0.8289 |
0.904 |
Dimensionless separation factor |
|||
RL |
0.126 |
0.125 |
0.098 |
|
|
|
|
Adsorption Kinetic Studies :
The results obtained from three kinetic models, namely the pseudo-first order, the pseudo-second order and intra particle diffusion models at two initial MO concentrations (100 and 200mg/L) at 318 K are given at Table 4. The best fit model was determined based on the linear regression correlation coefficient values. It can be seen that, the pseudo-second order model generated the best fit in comparison to the pseudo-first order kinetics, as the value of R2for pseudo-first order was lower than the value of R2 for pseudo-second order model.
Intra particle diffusion model was fitted to experimental kinetic data in order to gain information about the mechanism and rate controlling steps affecting the kinetics of adsorption. In this study the plots at both the concentrations (Figure 6) were not linear and did not pass through the origin, which indicates that intra-particle diffusion is not the only rate controlling step. Similar results were also found in earlier literature37.
Figure 6: Intra-particle diffusion model plot of adsorption of MO on Vaucheria sp.
Table 4: Kinetic parameters estimated by pseudo-first order, pseudo-second order and intra-particle diffusion for algal biomass Vaucheria sp. at two different concentrations of dye.
Algae |
Initial dye concentration (mg/L) |
|
First-order model |
Second-order model |
Intra-particle model |
|||||
qe(exp) (mg/g) |
K1 ( x 10-3 min-1 ) |
qe(cal) (mg/g) |
R2 |
K2 �x 10-3 (g/mg/min ) |
qe(cal) (mg/g) |
R2 |
KW (mg/g min0.5) |
R2 |
||
Vaucheria sp. |
100 |
97.92 |
12.206 |
74.473 |
0.939 |
0.174 |
97.08 |
0.999 |
1.668 |
0.919 |
200 |
122.58 |
12.666 |
144.37 |
0.943 |
0.397 |
123.45 |
0.995 |
2.914 |
0.946 |
Sorption - Desorption and Reuse Study :
Desorption ability of Vaucheria sp. were studied using three different eluents, HCl, NaOH and EDTA. It was observed that among all the other desorbents HCl was the most efficient, while EDTA and NaOH showed negligible desorption. More than 85% of the adsorbed MO was desorbed from yellow green algal biomass using HCl as an eluent (Figure 7). Interaction between adsorbent surface and dye molecule consists of strong binding and weak binding forces. The reversibility of adsorption depends on the presence of these binding forces. In the present study both strong and the weak binding forces could be present between algal biomass and the dye molecules10.
Figure 7: Adsorption/desorption cycles for Vaucheria sp. using HCl as an eluent.
Pretreatment Studies:
Earlier studies reported that pretreatment can increase or decrease the efficiency of adsorbent. The results regarding the effect of initial concentration of MO (25-200 mg/L) on the adsorption capacity of chemically pretreated algal biomass, at optimum conditions of pH, contact time and temperature, is given in Figure 8. Present results showed that the cell wall of the algal biomass played an important role in the success of chemical pretreatment. HCl pretreatment eliminated some of the impurities and exposed more binding sites and increased the dye adsorption. The acidic pretreatment process also changes the negatively charged surface of the algal biomass to positively charge and increased the interaction between biomass and dye38, 39.
Figure 8: Effect of initial concentration of MO (25-200 mg/L) on the extent of adsorption of MO on Vaucheria sp., (contact time 100 min, pH4, adsorbent dose 2.0 g/L, temperature 318 K)
CONCLUSION:
The present study revealed that the dead algal biomass of Vaucheria sp. could be effectively used to remove MO from synthetic wastewater. Acidic pH, high dye concentration, high temperature and HCl modification favoured the adsorption capacity of dyes. The algae fitted well in Langmuir isotherm model that proves monolayer adsorption of dye. The thermodynamic estimates indicates feasibility, endothermic and spontaneous nature of the adsorption at the temperature ranging from 298 K to 318 K. Based on the results from Langmuir isotherm, the maximum adsorption capacity for Vaucheria sp. was found to be 126.58 mg/g. Pseudo-second order kinetic studies showed the best fit. It may be concluded that Vaucheria sp. acts as a potential adsorbent for the removal of methyl orange dye from synthetic wastewater.
ACKNOWLEDGEMENT:
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
CONFLICT OF INTEREST:
The authors declare no conflicts of interest.
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Received on 16.07.2018���� Modified on 08.08.2018
Accepted on 11.10.2018���� � AJRC All right reserved
Asian J. Research Chem. 2018; 11(5): 778-786.
DOI: 10.5958/0974-4150.2018.00137.2