International Journal of Environmental Pollution Control & Management
Vol. 3, No. 1, January-June 2011; pp. 1-10
REMOVAL OF CATIONIC DYE METHYLENE BLUE (MB) FROM
AQUEOUS SOLUTION BY ADSORPTION ON BIOSOLID ADSORBENT
Tushar Kanti Sen1*
1
Department of Chemical Engineering, Curtin University, GPO Box U1987, 6145 Western Australia
Abstract: The kinetics and mechanism of methylene blue (MB) adsorption onto raw biosolid was
investigated under various physico-chemical parameters. The extent of the methylene blue dye adsorption
increased with increases in initial dye concentration, contact time, solution pH, amount of adsorbent, and
temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process
followed pseudo-second-order kinetic model. The different kinetic parameters including rate constant
are determined at different physicochemical conditions. Equilibrium data was fitted with Freundlich
adsorption isotherm. Freundlich constant, n give an indication of favourable adsorption.
Keywords: Biosolid; MB adsorption; kinetic model; isotherm.
1. INTRODUCTION
Biological wastewater treatment generates a biological sludge, called biosolid which also
contain inert materials and microorganisms. However waste activated sludge (WAS) consists
of the non-living microorganisms (Sarioglu and Atay, 2006). With increasing population
worldwide, biosolid production is likely to continue to increase in the future requiring increased
reuse options for the waste material (Kim and Owens, 2010). In Australia, the annual total
production of biosolids was estimated at 2.5 x 10 5 Mg (Cameron et al., 1997). On the other
hand many industries including textile, rubber, paper, leather, plastics, cosmetic, printing etc
are producing high volume of dye bearing wastewater because of using synthetic dye-stuff
during their various dyeing operation (Yao and Wang, 2009; Rafatullah et al., 2009).This
dye-bearing wastewater exhibit high colour and high chemical and biochemical oxygen
demands (COD and BOD) (Yao and Wang, 2009). The discharge of these dyes effluents in
the environment is worrying for both toxicological and esthetical reasons (Tan et al., 2007).
Cationic dyes like methylene blue are more toxic than anionic dyes (Hao and Chiang, 2000).
Therefore, an increased interest has been focused on removing of such dyes from the
waste water.
Many investigations have been conducted on physicochemical methods for the removal of
dye such as such as adsorption, coagulation/flocculation, advanced oxidation, ozonation,
membrane filtration and liquid-liquid extraction (Yao and Wang, 2009; Abd EI-latif et al 2010;
Vimonses et al., 2009). The removal of dyes and organics in an economic way remains an
*
Corresponding author: [email protected]
2 / INTERNATIONAL JOURNAL OF ENVIRONMENTAL POLLUTION CONTROL & MANAGEMENT
important problem although a number of systems have been developed with adsorption
technique. Physical adsorption is an efficient and cost effective process to eliminate dyes from
waste streams (Yao and Wang, 2009; Abd EI-Latif et al., 2010; Mohammad et al., 2010).
A commonly used adsorbent, activated carbon has a high capacity for the removal of dye/
organics (Sharma et al., 2010; Wang et al., 2005). But some of its disadvantages are the high
price of treatment and difficult to regenerate which gives the increase in cost of the wastewater
treatment. Thus there is demand for the other adsorbents which are made up of inexpensive
material and does not require any additional pre-treatment such that the adsorption process will
become economically viable. Adsorption is one of the most effective alternative processes of
advanced wastewater treatment, especially if the adsorbent is inexpensive and naturally available
or industrial solid waste which industries employ to reduce hazardous organic and inorganic
wastes in effluents. Therefore the basic objective of this study was to utilise biosolid as biosrbent
in the removal of methylyne blue from aqueous solution. There are various adsorbents have
been used for the removal of methylene blue from its aqueous solution and readers are encouraged
to go through review articles by Rafatullah et al., 2009 and by Srinivasan et al., 2010 respectively.
But research on the utilization of biosolid as an effective biosrbent towards methylene blue
(MB) removal is limited.
This present research work will explore the mechanism of adsorption and adsorption kinetics
of methylene blue by using biosolid and will determine the various physicochemical controlling
factors on the rate of adsorption and also on the capacity of adsorbent. The effect of solution
pH, initial dye concentration, adsorbent dose, and temperature on methylene blue adsorption
has been investigated.
2. MATERIALS AND METHODS
2.1. Adsorbent
The adsorbent used in the present study was biosolid which was obtained from wastewater
treatment plant of Water Corporation, Beenyup, WA. Biosolid was taken from belt filter press
dewatering equipment. It was used as such without further grinding and sieving. The biosolid
o
sample was stored at 4 C in a laboratory refrigerator. The general characteristics of biosolid
(as provided by the supplier) were: pH value = 7 – 9, % volatiles < 10%, soluble in water,
composition of 70% organic compounds, 10% of Ca, 10% of TN (total nitrogen compounds)
and 10% of TP (total phosphorus compounds
2.2. Adsorbate and other Chemicals
All chemicals used were of analytical grade. Mythelene Blue (MB), the typical basic cationic
dye was selected as the adsorbate in the present study. The formula of cationic methylene blue
dye is C16 H18 N3SCl.3H2O which was supplied by Sigma-Aldrich Pty. Ltd., NSW, Australia
and of analytical grade. It was used without further purification. A stock solution of 1000 mg/
l was prepared by dissolving the appropriate amount (1000 mg) of MB in a litter of deionised
water .The working solutions were prepared by diluting the stock solution with deionised water
REMOVAL OF CATIONIC DYE METHYLENE BLUE (MB) FROM AQUEOUS SOLUTION BY… / 3
to give the appropriate concentration of the working solutions. The pH of the solutions was
adjusted by addition of either 0.1 M HCl or 0.1 M NaOH solutions respectively. All sample
bottles and glassware were cleaned, and then rinsed with deionised water and oven dried at
o
60 C.
The SP-8001 UV/VIS Spectrophotometer was used to determine the concentrations of
Methylene blue dye in solution. pH measurements were done using Orien pH meter. The
concentration of the residual dye was measured using UV/visible spectrometer at a λmax
corresponding to the maximum adsorption for the dye solution (λmax = 667 nm) by withdrawing
samples at equilibrium, centrifuged and the supernatant was analysed for residual methylene
blue (MB). Calibration curve was plotted between absorbance and concentration of the dye
solution to obtain absorbance-concentration profile.
2.3. Adsorption Experiment
2.3.1. Kinetic Experiments
Adsorption measurement was determined by batch experiments of known amount of the
adsorbent with 50 ml of aqueous methylene blue solutions of known concentration in a series
of 250 ml conical flasks as per method by Arias and Sen, 2009. The mixture was shaken at a
constant temperature using Thermo line scientific Orbital Shaker Incubator at 120 rpm at
o
30 C temperature for 180 minutes. At equilibrium time, the bottles were withdrawn from the
shaker and the residual dye concentration in the reaction mixture was analysed by centrifuging
the reaction mixture and then measuring the absorbance of the supernatant at the wavelength
that correspond to the maximum absorbance of the sample. Dye concentration in the reaction
mixture was calculated from the calibration curve. Adsorption experiments were conducted
by varying initial solution pH, contact time, adsorbent dose, initial methylene blue dye
concentration, and temperature under the aspect of adsorption kinetics, adsorption isotherm
and thermodynamic study.
The amount of dye adsorbed onto biosolid at time t, q t (mg/g) was calculated by the
following mass balance relationship:
qt =
( C0 – Ct )V
m
(1)
And dye removal efficiency i.e. % of adsorption was calculated as:
% Adsorption =
C0 − Ct
x 100
C0
(2)
Where C0 is the initial dye concentration (mg/L), Ct is the concentration of dye at any time t,
V is the volume of solution (L) and m is the mass of biosolid (g).
All measurements are, in general, reproducible within ± 10%
4 / INTERNATIONAL JOURNAL OF ENVIRONMENTAL POLLUTION CONTROL & MANAGEMENT
2.4. Theory
2.4.1. Freundlich Isotherm
The Freundlich adsorption isotherm, which assumes that adsorption takes place on heterogeneous
surfaces, can be expressed as
ln qe = ln K f +
1
( ln Ce )
n
(3)
Where qe is the amount of dye adsorbed per unit of adsorbent at equilibrium time (mg/g), Ce is
equilibrium concentration of dye in solution (mg/L). Kf and n are isotherm constants which
indicate the capacity and the intensity of the adsorption respectively (Aries and Sen, 2009).
2.4.2. Adsorption Kinetics
2.4.2.1. Pseudo-first Order Model
The integral form of the pseudo-first-order model generally expressed as (Vimonses et al.,
2009; Mohammad et al., 2010)
(
)
Log qe – qt = Log qe –
k1
t
2.303
(4)
Where qt and qe represents the amount of dye adsorbed (mg /g) at any time t and at equilibrium
time respectively and k1 represents the adsorption first-order rate constant (min-1) and t is the
contact time (min). The adsorption rate constant K1 were calculated from the plot of log (qe –qt)
against t.
2.4.2.2. Pseudo-second-order Model
The adsorption data was then analysed in terms of pseudo-second-order mechanism, described
by (Vimonses et al., 2009; Mohammad et al., 2010).
dqt
2
= k2 ( qe – qt )
dt
(5)
Where k2 is the pseudo-second order rate constant (g/mg min).
Integrating and applying boundary conditions t = 0 to t = t and q = 0 to q = qt gives:
t
1
1
=
+ t
2
qt
k2 qe qe
(6)
A plot between t / qt versus t gives the value of the constants K2 (g/mg h) and also qe
(mg/g) can be calculated.
REMOVAL OF CATIONIC DYE METHYLENE BLUE (MB) FROM AQUEOUS SOLUTION BY… / 5
The Constant k2 is used to calculate the initial sorption rate h, at t’!0, as follows:
h = k2 q2e
(7)
Thus the rate constant K2, initial adsorption rate h and predicted qe can be calculated from
the plot of t / q versus time t using Eq. (6).
3. RESULTS AND DISCUSSION
3.1. Effect of Initial Solution pH on MB Dye Uptake
The initial pH of the MB dye solution was an important parameter which controlled the adsorption
process, particularly the adsorption capacity. The efficiency of adsorption is dependent on the
solution pH because variation in pH leads to the variation in the degree of ionization of the
adsorptive molecule and the surface properties of adsorbent (Rosemal et al., 2009; Nandi et al.,
2009). Figure 1 shows the adsorption of dye (MB) at different pHs. The amount of dye adsorption
increases with the increase in pH or alkalinity. The percentage removal of dye was also found
to increase when the solution pH was increased from pH 3. to pH 11. As the pH increases, it is
usually expected that the cationic dye adsorption also increases due to increasing negative
surface charge of the adsorbent. With the increasing pH values, the adsorption of methylene
blue on biosolid tends to increase, which can be explained by the electrostatic interaction of
dye cationic species with the negatively charged surfaces. This electrostatic force of attraction
is more with increasing negative surface charge of adsorbent. Moreover, the high percentage of
dye removal at high pH is also due to presence of less H+ competing for sorption sites on the
biosolid adsorbent.
Figure 1: The Effect of pH on the Results of Methylene Blue (Initial MB Concentration,
C0 = 60 mg/L, V = 100 mL, Adsorbent Dosage = 5 g/L, T = 25 °C, Equilibrium Time = 140 Minutes)
6 / INTERNATIONAL JOURNAL OF ENVIRONMENTAL POLLUTION CONTROL & MANAGEMENT
3.2. Effect of Adsorbent (Biosolid) Dosage on Dye Adsorption
Figure 2 shows that at equilibrium the the percentage dye removal was increased from 65% to
85% with the increase of adsorbent mass from 1 to 7 g. It was also found that the increase in
adsorbent dosage from 1 to 7 g resulted in decrease of amount of adsorbed dye from 3.9 to 0.73
mg/g. A similar behaviour was observed for methylene blue adsorption on rice husk (Sharma
et al., 2010; Vadivelan and Kumar 2005), on cashew nut shell (Kumar et al., 2010). At higher
biosolid to methylene blue concentration ratios, there is a very fast superficial sorption onto
biosolid surface that gives a lower methylene blue concentration in the solution compared to
the lower biosolid to methylene blue concentration ratio. This is because a fixed mass of biosolid
can only adsorb a fixed amount of dye. Therefore, the more the adsorbent dosages, the larger
the volume of effluent that a fixed mass of biosolid can purify. The decrease in amount of dye
adsorbed, qe (mg/g) with increasing adsorbent mass is due to the split in the flux or the
concentration gradient between solute concentration in the solution and the solute concentration
in the surface of the adsorbent (Vadivelan and Kumar, 2005; Kumar et al., 2010). Thus with
increasing adsorbent mass, the amount of dye adsorbed onto unit weight of adsorbent gets
reduced, thus causing a decrease in qe value with increasing adsorbent mass concentration
(Vadivelan and Kumar, 2005).
Figure 2: The Effect of Adsorbent Dosages on the Results of Methylene Blue
(Initial Dye Concentration, C0 = 60 mg/L, V = 100 mL, Normal pH = 7, T = 25 °C, Equilibrium
Time = 140 Minutes)
3.3. Effect of Temperature on Dye Adsorption Kinetics
Figure 3 shows that amount of methylene blue adsorption on biosolid increased with increasing
temperature of the solution. As the temperature increases, rate of diffusion of adsorbate molecules
across the external boundary layer and interval pores of the adsorbent particle increase and
therefore changing the equilibrium adsorbent capacity.
REMOVAL OF CATIONIC DYE METHYLENE BLUE (MB) FROM AQUEOUS SOLUTION BY… / 7
Figure 3: The Effect of Temperature on the Results of Methylene Blue (Initial Concentration, C0 = 60
mg/L, V = 100 mL, Normal pH = 7, Adsorbent Dosage = 5 g/L, Equilibrium Time = 140 Minutes)
3.4. Effect of Contact Time and Initial MB Dye Concentration on Adsorption Kinetics
The initial dye concentration has a pronounced effect on its removal from aqueous solutions.
The effect of contact time on the adsorption of methylene blue dye was investigated at different
initial dye concentration onto biosolid adsorbent and results are presented in Figure 4. It was
found that the removal of dye increased from 65 to 98% with decreasing initial concentration
of methylene blue dye from 60 to 10 ppm (Figure 4). It was also found that the amount of
adsorption i.e. mg of adsorbate per gram of adsorbent increases with increasing contact
time at all initial metal ion concentrations and equilibrium is attained within 180 minutes for
which plot is not presented here. Further it was observed that the amount of metal ion uptake,
qt (mg/g) is increased with increase in initial metal ion concentration. Basically the adsorption
percentage decreases and the extent of adsorption increases with increasing initial dye
concentration. This is so because the initial dye concentration provides the driving force to
Figure 4: The Effect of Concentration on the Result of Methylene Blue (V = 100 mL, Normal pH = 7,
T = 25 °C, Adsorbent Dosage = 1 g/L, Equilibrium Time = 140 Minutes)
8 / INTERNATIONAL JOURNAL OF ENVIRONMENTAL POLLUTION CONTROL & MANAGEMENT
overcome the resistance to the mass transfer of dye between the aqueous and the solid phase.
For constant dosage of adsorbent, at higher initial dye concentration, the available adsorption
sites of adsorbent become fewer and hence the removal of methylene blue depends upon the
initial concentration (Shahryari et al., 2010). The increase in initial concentration also enhances
the interaction between adsorbent and dye. Therefore, an increase in initial dye concentration
leads to increase in the adsorption uptake of dye.
3.5. Adsorption Kinetics
In the present study, the applicability of the pseudo-first-order (equation 4) and pseudo-secondorder model (equations 5-7) was tested for the adsorption of methylene blue onto biosolid
particles. In the pseudo-first-order model, the rate constant k1 and linear correlation coefficient,
R2, were determined by plotting log (qe–qt) against time, t which is not shown here with
comparatively poor regression coefficient, R2 of 0.81. The plot t/qt versus t should give a straight
line with higher linear correlation coefficients if pseudo-second-order kinetics is applicable for
which plot is not presented here. The value of qe, k2 and h can be determined from the slope and
intercept of the plot respectively. All kinetic parameters including linear correlation coefficient
(R2) obtained from fitting model plots with experimental data under different initial MB
concentrations which is presented in Table 1. The linear correlation coefficients (R2) for the
pseudo-first-order kinetic model are poor (Table 1). Higher linear regression coefficients (R2)
(Table 1) with respect to fitted pseudo 1st-order model (Table 1) suggest that adsorption of
methylene blue on biosolid follows pseudo second-order kinetics. Moreover, calculated,
q-e cal values from pseudo-second-order fitting model (Table 1) is very close to the experimental
qe values (Table 1) also suggest the suitability of this model whereas pseudo-first-order kinetic
model predicts a much lower value of the equilibrium adsorption capacity than the experimental
value (Table 1) and hence it gives the inapplicability of this model.
Table 1
Pseudo-first and Second Order Adsorption Kinetics at Different Initial Dye
Concentrations for the Adsorption of Methylene Blue Onto Biosolid at 25°C
Pseudo-first order rate constants
Pseudo-second order rate constants
Ci
(mg/L)
qe, exp
(mg/g)
k1
(min-1)
qe, calc
(mg/g)
R2
k2
(g/mg.min)
qe, calc
(mg/g)
R2
1000
60
50
40
30
20
10
65.786
3.902
3.868
3.684
2.927
1.970
0.981
-0.0283
-0.0161
-0.1819
-0.0246
-0.0246
-0.0299
-0.0801
157.25
0.964
2.748
4.816
4.686
4.768
25.316
0.899
0.881
0.907
0.858
0.955
0.948
0.810
0.0008
0.0474
0.0128
0.0071
0.0250
0.0313
4.6047
69.930
3.982
4.193
4.303
3.065
2.090
0.981
0.942
0.998
0.974
0.942
0.969
0.950
0.999
h
4.057
0.753
0.225
0.132
0.235
0.137
4.435
3.6. Adsorption Equilibrium Isotherm
Analysis of adsorption isotherm is of fundamental importance to describe how adsorbate
molecules interact with the adsorbent surface. Equilibrium studies determine the capacity of
REMOVAL OF CATIONIC DYE METHYLENE BLUE (MB) FROM AQUEOUS SOLUTION BY… / 9
the adsorbent and describe the adsorption isotherm by constants whose values give information
on the surface properties and affinity of the adsorbents. Figure 5 gives results on Freundlich
isotherm fittings for biosolid with linear correlation coefficient (R2) of 0.99. Freundlich constants
i.e. adsorption capacity, Kf and rate of adsorption, n, are calculated from this plot which are
2.45 mg/g and 1.1 respectively. The value of ‘n’ is larger than 1 which indicates the favourable
nature of adsorption and a physical process (Mohammad et al., 2010; Arias and Sen, 2009).
Figure 5: Freundlich Plot for MB-biosolid System
4. CONCLUSION
Biosolid a by-product of waste water treatment plant can be used as an effective alternative low
cost adsorbent for the removal of methylene blue from its aqueous solutions. The amount of
methylene blue dye uptake was found to increases with increase in initial dye concentration,
contact time, solution pH, adsorbent dose and system temperature. Overall, the kinetic studies
showed that the methylene blue adsorption process followed pseudo-second-order kinetics
models. Freundlich isotherm model is applicable to describe the adsorption of methylene blue
on biosolid within this initial dye concentration range. Freundlich constant, n, give an indication
of favourable adsorption.
ACKNOWLEDGEMENT
Author acknowledges Nelson Kho Han Hui- for his final year project work at at Curtin University
of Technology, Perth.
References
Abd EI-Latif, M. M., Ibrahim, A. M., EI-Kady, M. F. (2010), Adsorption Equilibrium, Kinetics and
Thermodynamics of Methylene Blue from Aqueous Solutions Using Biopolymer Oak Sawdust Composite.
J. Am. Sci., 6(6) 267-283.
10 / INTERNATIONAL JOURNAL OF ENVIRONMENTAL POLLUTION CONTROL & MANAGEMENT
Arias, F., Sen, T. K. (2009), Removal of Zinc Metal Ion (Zn2+) from its Aqueous Solution by Kaolin Clay
Mineral: A Kinetic and Equilibrium Study, Colloids and Surfaces A: 348, 100-108.
Cameron, K. C., Di, H. J., McLaren, R. G. (1997), Is Soil an Appropriate Dumping Ground for Our Wastes?
Aus. J. Soil Res., 35, 995-1036.
Hao, J. O., Kim, H., Chiang, P. C. (2000), Decolourization of Wastewater. Crit. Rev. Environ. Sci. Technol.,
30, 449-505
Kumar, P. S., Ramalingam, S., Senthamarai, C., Niranjanaa, M.,Vijayalakshmi, P., Sivanesan, S. (2010),
Adsorption of Dye from Aqueous Solution by Cashew Nut Shell: Studies on Equilibrium Isotherm,
Kinetics and Thermodynamics of Interactions, Desalination, (doi:10.1016/j.desal.2010.05.032)
Kim, K. W., Owens, G. (2010), Potential for Enhanced Phytoremediation of Landfills Using Biosolids-A
Review, J. Environ. Management, 91, 791-797.
Mohammad, M., Maitra, S., N. Ahmad, A. Bustam, T. K. Sen, Dutta, B. K. (2010), Metal Ion Removal from
Aqueous Solution Using Physic Seed Hull. J. Hazard. Mater., 179, 363-372
Nandi, B. K., Goswami, A., Purkait, M. K. (2009), Removal of Cationic Dyes from Aqueous Solutions by
Kaolin: Kinetic and Equilibrium Studies, Apply. Clay Sci., 42, 583-590.
Rafatullah, M., Sulaiman, O., Hashim, R., Ahmad, A. (2009), Adsorption of Methylene Blue on Low-cost
Adsorbents; A Review. J. Hazard. Mat.(doi:10.1016/j.jhazmat.2009.12.047
Rosemal, H. M., Haris, M., Sathasivam, K. (2009), The Removal of Methyl Red from Aqueous Solution
Using Banana Pseudo Stem Fibers, Am. J. Appl. Sci., 6(9) 1690-1700.
Sarioglu, M., Atay, U. A. (2006), Removal of Methylene Blue by Using Biosolid, Global NEST Journal, 8(2),
113-120.
Sharma, P., Kaur, R., Baskar, C., Chung, W. J. (2010), Removal of Methylene Blue from Aqueous Waste
Using Rice Husk and Rice Husk Ash. Desalination, 259, 249-257
Shahryari, Z., Goharrizi, A. S., Azadi, M. (2010), Experimental Study of Methylene Blue Adsorption from
Aqueous Solutions Onto Carbon Nano Tubes. Int. J. Water Resour. Environ. Eng., 2(2), 16-28.
Srinivasan, A.,Viraraghavan, T. (2010), Decolourization of Dye Wastewaters by Biosorbent: A Review. J.
Environ. Management, (doi:10.1016/j.jenvman.2010.05.003)
Sharma, Y. Uma, C. (2010), Optimization of Parameters for Adsorption of Methylene Blue on a Low-cost
Activated Carbon, J. Chem. Eng. Data, 55, 435-439
Tan, I. A. W., Hameed, B. H., Ahmad, A. L. (2007), Equilibrium and Kinetic Studies on Basic Dye Adsorption
by Oil Palm Fibre Activated Carbon. Chem. Eng. J., 127 111-119.
Vadivelan, V., Kumar, K. V. (2005), Equilibrium, Kinetics, Mechanism and Process Design for the Sorption
of Methylene Blue Onto Rice Husk. J. Colloid Int. Sci., 286, 90-100.
Vimonses, V., Lei, S., Bo Jin, C. W. K. Chow, Saint, C. (2009), Kinetic Study and Equilibrium Isotherm
Analysis of Congo Red Adsorption by Clay Materials. Chem. Eng. J., 148, 354-364.
Wang, S., Zhu, Z. H., A. Coomes, F. Haghseresht, Lu, G. Q. (2005), The Physical and Surface Chemical
Characteristics of Activated Carbons and the Adsorption of Methylene Blue from Wastewater, J. Colloid
Int. Sci., 284, 440-446.
Yao, Z. L., Wang, J. Q. (2009), Biosorption of Methylene Blue from Aqueous Solution Using a Bioenergy
Forest Waste: Xanthoceras Sorbifolia Seed Coat. Clean, 37(8) 642-648.