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Adsorption equilibria of basic dyestuff onto palm-fruit bunch particles
8)
Pergamon
WaL ScI. Tech. Vol. 32, No. 11.pp. 27-32, 1995. CopyrightC 1996IAWQ.Puhlishedby ElsevierScienceLtd. Printedin Oreat Britain.All righlareserved. 0273-1223/9S$9'SO + 0-00
Pll:S0273-1223(96)OO114-X
ADSORPTION EQUILmRIA OF BASIC DYESTUFF ONTO PALM-FRUIT BUNCH PARTICLES M. M. Nassar", M. F. Hamoda** and G. H. Radwan* • Chemical & Petroleum Engineering Department, Faculty of Engineering. UAEUniversity, P.O. Box 17555, AI-Am, United ArabEmirates •• CivilEngineering Department, Faculty of Engineering, UAEUniversity, P.O. Box 17555. AI-Am, United ArabEmirates
ABSTRACT Particles prepared from palm-fruit bunch have been used for the adsorption of a basic dye (BR 18) over range of initial dye concentrations and varying adsorbent particle size in the range of 106 to 300 m, using batch tests. The results revealed the potential for palm-bunch particles as low cost adsorbents. Uptake of the basic dye was higher at smaller adsorbent particle size. The adsorption isotherm follows both the Langmuir and Freundlich models. Values of the separation factor. R. indicate favourable adsorption for the basic dye· palm fruit bunch particles system, that is, 0< R <1 and Freundlich constant n >1. Copyright Cl 1996 IAWQ. Published by Elsevier Science Ltd.
KEYWORDS Palm-fruit bunch; basicdyes;particle size; adsorption isotherms, INI'RODUCTION Many industries use dyes and pigments to colour their products. Wastewater effluentsfrom such industries containdyes and pigments whichare inert and may be toxic at the concentrations discharged into receiving waters. Moreover, the colourcontributed by the dyes and pigments causesenvironmental problems. The removal of dyes from wastewater effluents in an economic way remains a major concern although a number of successful systems using adsorption techniques have recently been investigated. Activated carbon, whichis predominantly used in the adsorption of pollutants, is costly both to use and to regenerate. Therefore there is a growing interestin using low-cost, easily available materials for the adsorption of dye colours. Suchmaterials can be used once,then disposed of by burning themas fuel. Investigations have been undertaken to determine whetherlow cost, commercially available materials hold promise in the treatment of wastewater. The initialfindings indicated that bagasse pith (McKay et at, 1987, 1988; Nassarand EI Geundi, 1991, 1994) and wood (Asfour et al., 198580 b) have adsorptive capacities for dyes and were relatively cheap. Studies have been reported on the use of peat as an adsorbent for the removal of acid dyes (Poots et at, 1976) but basic dyes are more difficult to remove from wastewater. Moreover, many reports have appeared on the development of activated carbon from cheaper and readily
28
M. M. NASSAR et al.
available materials such as rice husk, coconut shell and peanut hull (Azab and Peterson, 1989) for removal of various pollutantsfrom water. In tropical countries the palm tree is one of the most abundant and important trees. Usually, its fruit bunches are either discarded or burnt As the palm tree fruit bunch is a rather cheap material and very abundant in the UAE and Gulf countries, this research considers that it would be interesting to study the ability of chopped/groundpalm fruit bunches to adsorb dyes. A basic dye was chosen for a detailed investigationsince basic dyes are usually difficult to remove from solution. This paper examines the adsorption of basic dye from aqueous solution by palm fruit bunch particles through the effect of particle size of the adsorbent on the equilibrium isotherms (Langmuir and Freundlich).
MATERIALS AND METHODS The palm-fruit bunches used in this study were collected from trees grown in Al-Ain City, United Arab Emirates. Dry fruit bunches were used and were cut applying planing, slicing and crushing to the minimum possible size and sieved to different particle sizes. The material was not subjected to any form of pretreatmentprior to its use in experimentation.All data are presentedon a dry weight basis. The dyestuff used in this study was Basic Red 18 (Maxilon Red BL-N) supplied by Ciba-Geigy as a commercial salt The concentration of dyestuff in the aqueous solution was determined using a PU8620 UV/vislNIR spectrophotometer (Philips). All measurements were made at the wavelength corresponding to the maximum absorbance, [max =490 rn, Dilutions were undertaken when the absorbance exceeded a value of 0.6. Adsorptionequilibria were obtained by contacting a constant mass (l g) of palm fruit bunch particles with a 0.05 dm3 dye solution in sealed glass bottles. The bottles were placed on a shaker for a sufficient period to ensure that equilibrium had been reached. Preliminary experiments showed that such equilibrium was established within 2-3 days; however, all equilibrium experiments were allowed to run for 5 days. After that time the samples were centrifuged and their equilibrium concentration in the clear supernatant was determined by spectrophotometric methods. The difference between the initial concentration (CO> and the equilibrium concentration (C~ was used to compute the amount of dye removed (q~ from the solution containing a mass of adsorbent (M) as follows: qe =[0.05 (Co - Ce)] 1M All batch tests were carried out at 252°C to eliminate any temperature effects while the effect of palm fruit bunch particle size was studied in the range of 106 to 300 m. RESULTS AND DISCUSSION Adsorption isotherms were determined for the adsorption of the basic dye onto palm fruit bunch particles shown in Fig. 1. The isotherms rise in the initial stages with higher slope at low Ce and qe values. This indicates that, initially, there are numerous readily accessible sites. However, a plateau is reached eventually in all the curves, indicating that the adsorbent is saturated at this level. Analysis of isotherm data is important in order to develop an equation which accurately represents the results and could be used for design purposes. Several isotherm equations are available for such analysis. In this study two models have been selected, that is, the Langmuir and Freundlich isotherms. The Langmuir isothermcan be represented by the following equation:
(2)
29
Adsorption equilibria of basic dyestuff
where qe is the amount of dye adsorbed per unit mass of bunch particles at equilibrium and Ce is the equilibrium liquid-phase concentration of dye. Equation (2) can be converted into a linear form convenient for plottingand determining the constantsK L and aL as follows: Ce!qe
=IIKL + (aLIKL) c,
(3)
160 140 -
Particle Size (IJ.m)
-106-150 +150-220 -&220-300
120 100 -
~
.s
,J
80 60 40
-
20 - • 0 0
20
40
60
80
100
120
140
c. (mgldm-') Figure 1. Adsorption isotherm forBR18 onto Palm Fruit Bunch particles.
1.2 1 . 0.8 -
Particle Size
(um)
"-106-150 +150-220 -&220-300
~
e ~
~
0.6 0.4 0.2 . 0 0
20
40
60
80
100
120
140
C. (mgldm-')
Figure 2.Langmuir plots corresponding to the adsorption of BR18onto Palm Fruit Bunch particles. Figure. 2 shows a linear relationship of CJqc against Cc using experimental data obtained at different particle size "ranges". suggesting the applicability of the Langmuir Model. It demonstrates monolayer coverage of adsorbate at the outer surface of the adsorbent (Pandey et al., 1984). Values of KL and aL at different particle sizes (d ) have been calculated from plots shown in Fig. 2 using the least squares method.
~.~.~ASSAJletaL
30
The results obtained are displayed in Table 1 and indicate high correlation coefficients. The values of the constant KJ..!0L correspond to the maximum adsorption capacity of palm-fruit bunch particles for a basic dye. Table 1 also shows that the adsorption capacity of the palm-bunch increases with a decrease in the particle size of adsorbent since a larger surface area is obtained. The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter. R. which is defined by the folIowing equation (Weber and Chakkravorti, 1974):
(4) Table 1. Parameters in the Langmuir Adsorption Model
KL
dp
m3mg-1
J.lID 106-150 150-220 220-300
2.67 2.32 2.13
aL
qmax
R
dm3mg-1
0.110 0.012 0.010
Correlation coefficient
242 225 213
0.061 0.373 0.417
0.98 0.86 0.87
The equilibrium indicates the shape of the isotherm as folIows: value ofR
Ixpe of isotherm
R>l R 1 O
Unfavourable Linear Favourable Irreversible
=
R=O
2.5 Particle Size
2 1.5 -
(~m)
-106-150 ....150-220 -&220-300
0.5 -
Oo ....--------...:.----~--.....--2.5 0.5 1.5 2 101(
c;)
Figure 3. Freundlichplotscorresponding to the adsorptionof BRlS onto Palm Fruit Bunchparticles.
31
Adsorption equilibriaof basicdyestuff
Values of R for the system of basic red dye plus palm-fruit bunch particles have been calculated as shown in Table l. The R values indicate that the palm-fruit bunch particles are favourable for the adsorption of basic red dyes. The Freundlich model was also used to explain the observed phenomena.The experimentalequilibrium data for the adsorption of basic dye stuffs onto palm-fruit bunch particles were analysed using the Freundlich isothermas given by the following equation: - KF Ce lin qe-
(5)
where qe =x1n is the amount of dye adsorbed per unit mass of palm-fruit bunch particle and K F is a constant The equation may be linearized using a logarithmicplot which enables the exponent n and the constant K F to be determined, that is, log qe
=log KF + (lin) log Ce
(6)
Fig. 3 shows a linear relationship of log qe against log Ce at different particle sizes indicating the applicability of the Freundlich model. The parameters K F and n for the basic dye have been calculated from experimental data using the least squares method and the results obtained are given in Table 2; they show high correlation coefficients. These results also show that the values of the Freundlich exponent, n, are greater than one, indicating that the basic dyes are favourably adsorbed by palm-fruit bunch particles (Trebal, 1985). Table 2 Parameters in the Freundlich AdsorptionModel dp
IJ.Il1
KF
n
dm3.mg- 1
coefficient ---~--
106-150 150·220 220-300
608 5.37 4.81
Correlation
1.54 1.50 1.46
f-----
0.99 0.98 0.99
CONCLUSIONS The experimental results showed that palm-fruit bunch particles can remove basic dyes from effluent solutions by adsorption. The adsorption isotherms have been determined and data were analysed according to the Langmuir and Freundlich models. The values of separation factor indicate that the basic dye-palm bunch particles system shows favourable adsorption, that is, 0 < R < 1 and n > 1. NOMENCLATURE Parameter of Langmuir isotherm (dm3/mg) Equilibrium liquid-phaseconcentration(mgldm3) Initial liquid-phaseconcentration (mgldm3) Adsorbent particle size range ( m) Parameter of Freundlich isotherms (dm3/g) Parameter of Langmuir isotherms (dm3/g) Mass of adsorbent (g) Freundlichexponent (dimensionless)
M. M. NASSAR et al;
32
qe R
Equilibrium solid-phase concentration (mglg) Dimensionless equilibrium parameter, defined by equation (4)
REFERENCES Asfour, M., Fadali, O. A., Nassar, M. M. and EI-Geundi, M. S. (l985a). Equilibrium studies on adsorption of basic dyes on hardwood. J. Chem: Tech.Biotech; 35A,21. Asfour, M., Nassar, M. M., Fatal, O. A. and El-Geundi, M. S. (l985b). Colour removal from the textile effluents using hardwood saw dust as an adsorbent J. Chem; Tech. Biotech; 35A, 28. Azab, M. S. and Peterson, P. J. (1989). The removal of cadmium from water by the use of biological sorbents. Wat. Sci. Technol. 21 (12) 1705-6. McKay, G., El-Geundi, M. and Nassar, M. M. (1987). Equilibrium studies during the removal of dyestuffs from aqueous solutions using bagasse pith. Wat. Res. 21 1513-20. McKay, G., El-Geundi, M. and Nassar, M. M. (1988). External mass transport processes during the adsorption of dyes onto bagasse pith. Wat. Res. 22 1527-33. Nassar, M. M. and El-Geundi, M. S. (1991). Comparative cost of the colour removal from textile effluents using natural adsorbents. J. Chem. Tech.Biotech:41A, 50. Nassar, M. M. and El-Geundi, M. S. (1994). Studies on the dimensionless mass transfer coefficient during the adsorption of basic dyes onto bagasse pith, AdsorptionSci. Tech. n (No 3). Panday, K. K., Prasad, G. and Singh, V. N. (1984). Removal of Cr (VI) from aqueous solution on flyasb-woUastonite. J. Chem: Tech. Biotech. 34A, 367. POOlS, V. J. P., McKay, G. and Healy, J. J. (1976). The removal of acid dye from effluent using natural adsorbents (peat). Wat. Res. 10, 1061. Trebal, R. E. (1985). Mass TransferOperations. 3rd edn, McGraw Hill, Singapore, pp. 182-185. Weber. T. W. and Chakkravorti, R. K. (1974). Pore and solid diffusion models for fixed bed absorbers. AICHEJ. 20228.
Pergamon
WaL ScI. Tech. Vol. 32, No. 11.pp. 27-32, 1995. CopyrightC 1996IAWQ.Puhlishedby ElsevierScienceLtd. Printedin Oreat Britain.All righlareserved. 0273-1223/9S$9'SO + 0-00
Pll:S0273-1223(96)OO114-X
ADSORPTION EQUILmRIA OF BASIC DYESTUFF ONTO PALM-FRUIT BUNCH PARTICLES M. M. Nassar", M. F. Hamoda** and G. H. Radwan* • Chemical & Petroleum Engineering Department, Faculty of Engineering. UAEUniversity, P.O. Box 17555, AI-Am, United ArabEmirates •• CivilEngineering Department, Faculty of Engineering, UAEUniversity, P.O. Box 17555. AI-Am, United ArabEmirates
ABSTRACT Particles prepared from palm-fruit bunch have been used for the adsorption of a basic dye (BR 18) over range of initial dye concentrations and varying adsorbent particle size in the range of 106 to 300 m, using batch tests. The results revealed the potential for palm-bunch particles as low cost adsorbents. Uptake of the basic dye was higher at smaller adsorbent particle size. The adsorption isotherm follows both the Langmuir and Freundlich models. Values of the separation factor. R. indicate favourable adsorption for the basic dye· palm fruit bunch particles system, that is, 0< R <1 and Freundlich constant n >1. Copyright Cl 1996 IAWQ. Published by Elsevier Science Ltd.
KEYWORDS Palm-fruit bunch; basicdyes;particle size; adsorption isotherms, INI'RODUCTION Many industries use dyes and pigments to colour their products. Wastewater effluentsfrom such industries containdyes and pigments whichare inert and may be toxic at the concentrations discharged into receiving waters. Moreover, the colourcontributed by the dyes and pigments causesenvironmental problems. The removal of dyes from wastewater effluents in an economic way remains a major concern although a number of successful systems using adsorption techniques have recently been investigated. Activated carbon, whichis predominantly used in the adsorption of pollutants, is costly both to use and to regenerate. Therefore there is a growing interestin using low-cost, easily available materials for the adsorption of dye colours. Suchmaterials can be used once,then disposed of by burning themas fuel. Investigations have been undertaken to determine whetherlow cost, commercially available materials hold promise in the treatment of wastewater. The initialfindings indicated that bagasse pith (McKay et at, 1987, 1988; Nassarand EI Geundi, 1991, 1994) and wood (Asfour et al., 198580 b) have adsorptive capacities for dyes and were relatively cheap. Studies have been reported on the use of peat as an adsorbent for the removal of acid dyes (Poots et at, 1976) but basic dyes are more difficult to remove from wastewater. Moreover, many reports have appeared on the development of activated carbon from cheaper and readily
28
M. M. NASSAR et al.
available materials such as rice husk, coconut shell and peanut hull (Azab and Peterson, 1989) for removal of various pollutantsfrom water. In tropical countries the palm tree is one of the most abundant and important trees. Usually, its fruit bunches are either discarded or burnt As the palm tree fruit bunch is a rather cheap material and very abundant in the UAE and Gulf countries, this research considers that it would be interesting to study the ability of chopped/groundpalm fruit bunches to adsorb dyes. A basic dye was chosen for a detailed investigationsince basic dyes are usually difficult to remove from solution. This paper examines the adsorption of basic dye from aqueous solution by palm fruit bunch particles through the effect of particle size of the adsorbent on the equilibrium isotherms (Langmuir and Freundlich).
MATERIALS AND METHODS The palm-fruit bunches used in this study were collected from trees grown in Al-Ain City, United Arab Emirates. Dry fruit bunches were used and were cut applying planing, slicing and crushing to the minimum possible size and sieved to different particle sizes. The material was not subjected to any form of pretreatmentprior to its use in experimentation.All data are presentedon a dry weight basis. The dyestuff used in this study was Basic Red 18 (Maxilon Red BL-N) supplied by Ciba-Geigy as a commercial salt The concentration of dyestuff in the aqueous solution was determined using a PU8620 UV/vislNIR spectrophotometer (Philips). All measurements were made at the wavelength corresponding to the maximum absorbance, [max =490 rn, Dilutions were undertaken when the absorbance exceeded a value of 0.6. Adsorptionequilibria were obtained by contacting a constant mass (l g) of palm fruit bunch particles with a 0.05 dm3 dye solution in sealed glass bottles. The bottles were placed on a shaker for a sufficient period to ensure that equilibrium had been reached. Preliminary experiments showed that such equilibrium was established within 2-3 days; however, all equilibrium experiments were allowed to run for 5 days. After that time the samples were centrifuged and their equilibrium concentration in the clear supernatant was determined by spectrophotometric methods. The difference between the initial concentration (CO> and the equilibrium concentration (C~ was used to compute the amount of dye removed (q~ from the solution containing a mass of adsorbent (M) as follows: qe =[0.05 (Co - Ce)] 1M All batch tests were carried out at 252°C to eliminate any temperature effects while the effect of palm fruit bunch particle size was studied in the range of 106 to 300 m. RESULTS AND DISCUSSION Adsorption isotherms were determined for the adsorption of the basic dye onto palm fruit bunch particles shown in Fig. 1. The isotherms rise in the initial stages with higher slope at low Ce and qe values. This indicates that, initially, there are numerous readily accessible sites. However, a plateau is reached eventually in all the curves, indicating that the adsorbent is saturated at this level. Analysis of isotherm data is important in order to develop an equation which accurately represents the results and could be used for design purposes. Several isotherm equations are available for such analysis. In this study two models have been selected, that is, the Langmuir and Freundlich isotherms. The Langmuir isothermcan be represented by the following equation:
(2)
29
Adsorption equilibria of basic dyestuff
where qe is the amount of dye adsorbed per unit mass of bunch particles at equilibrium and Ce is the equilibrium liquid-phase concentration of dye. Equation (2) can be converted into a linear form convenient for plottingand determining the constantsK L and aL as follows: Ce!qe
=IIKL + (aLIKL) c,
(3)
160 140 -
Particle Size (IJ.m)
-106-150 +150-220 -&220-300
120 100 -
~
.s
,J
80 60 40
-
20 - • 0 0
20
40
60
80
100
120
140
c. (mgldm-') Figure 1. Adsorption isotherm forBR18 onto Palm Fruit Bunch particles.
1.2 1 . 0.8 -
Particle Size
(um)
"-106-150 +150-220 -&220-300
~
e ~
~
0.6 0.4 0.2 . 0 0
20
40
60
80
100
120
140
C. (mgldm-')
Figure 2.Langmuir plots corresponding to the adsorption of BR18onto Palm Fruit Bunch particles. Figure. 2 shows a linear relationship of CJqc against Cc using experimental data obtained at different particle size "ranges". suggesting the applicability of the Langmuir Model. It demonstrates monolayer coverage of adsorbate at the outer surface of the adsorbent (Pandey et al., 1984). Values of KL and aL at different particle sizes (d ) have been calculated from plots shown in Fig. 2 using the least squares method.
~.~.~ASSAJletaL
30
The results obtained are displayed in Table 1 and indicate high correlation coefficients. The values of the constant KJ..!0L correspond to the maximum adsorption capacity of palm-fruit bunch particles for a basic dye. Table 1 also shows that the adsorption capacity of the palm-bunch increases with a decrease in the particle size of adsorbent since a larger surface area is obtained. The essential characteristics of the Langmuir isotherm can be expressed in terms of a dimensionless constant separation factor or equilibrium parameter. R. which is defined by the folIowing equation (Weber and Chakkravorti, 1974):
(4) Table 1. Parameters in the Langmuir Adsorption Model
KL
dp
m3mg-1
J.lID 106-150 150-220 220-300
2.67 2.32 2.13
aL
qmax
R
dm3mg-1
0.110 0.012 0.010
Correlation coefficient
242 225 213
0.061 0.373 0.417
0.98 0.86 0.87
The equilibrium indicates the shape of the isotherm as folIows: value ofR
Ixpe of isotherm
R>l R 1 O
Unfavourable Linear Favourable Irreversible
=
R=O
2.5 Particle Size
2 1.5 -
(~m)
-106-150 ....150-220 -&220-300
0.5 -
Oo ....--------...:.----~--.....--2.5 0.5 1.5 2 101(
c;)
Figure 3. Freundlichplotscorresponding to the adsorptionof BRlS onto Palm Fruit Bunchparticles.
31
Adsorption equilibriaof basicdyestuff
Values of R for the system of basic red dye plus palm-fruit bunch particles have been calculated as shown in Table l. The R values indicate that the palm-fruit bunch particles are favourable for the adsorption of basic red dyes. The Freundlich model was also used to explain the observed phenomena.The experimentalequilibrium data for the adsorption of basic dye stuffs onto palm-fruit bunch particles were analysed using the Freundlich isothermas given by the following equation: - KF Ce lin qe-
(5)
where qe =x1n is the amount of dye adsorbed per unit mass of palm-fruit bunch particle and K F is a constant The equation may be linearized using a logarithmicplot which enables the exponent n and the constant K F to be determined, that is, log qe
=log KF + (lin) log Ce
(6)
Fig. 3 shows a linear relationship of log qe against log Ce at different particle sizes indicating the applicability of the Freundlich model. The parameters K F and n for the basic dye have been calculated from experimental data using the least squares method and the results obtained are given in Table 2; they show high correlation coefficients. These results also show that the values of the Freundlich exponent, n, are greater than one, indicating that the basic dyes are favourably adsorbed by palm-fruit bunch particles (Trebal, 1985). Table 2 Parameters in the Freundlich AdsorptionModel dp
IJ.Il1
KF
n
dm3.mg- 1
coefficient ---~--
106-150 150·220 220-300
608 5.37 4.81
Correlation
1.54 1.50 1.46
f-----
0.99 0.98 0.99
CONCLUSIONS The experimental results showed that palm-fruit bunch particles can remove basic dyes from effluent solutions by adsorption. The adsorption isotherms have been determined and data were analysed according to the Langmuir and Freundlich models. The values of separation factor indicate that the basic dye-palm bunch particles system shows favourable adsorption, that is, 0 < R < 1 and n > 1. NOMENCLATURE Parameter of Langmuir isotherm (dm3/mg) Equilibrium liquid-phaseconcentration(mgldm3) Initial liquid-phaseconcentration (mgldm3) Adsorbent particle size range ( m) Parameter of Freundlich isotherms (dm3/g) Parameter of Langmuir isotherms (dm3/g) Mass of adsorbent (g) Freundlichexponent (dimensionless)
M. M. NASSAR et al;
32
qe R
Equilibrium solid-phase concentration (mglg) Dimensionless equilibrium parameter, defined by equation (4)
REFERENCES Asfour, M., Fadali, O. A., Nassar, M. M. and EI-Geundi, M. S. (l985a). Equilibrium studies on adsorption of basic dyes on hardwood. J. Chem: Tech.Biotech; 35A,21. Asfour, M., Nassar, M. M., Fatal, O. A. and El-Geundi, M. S. (l985b). Colour removal from the textile effluents using hardwood saw dust as an adsorbent J. Chem; Tech. Biotech; 35A, 28. Azab, M. S. and Peterson, P. J. (1989). The removal of cadmium from water by the use of biological sorbents. Wat. Sci. Technol. 21 (12) 1705-6. McKay, G., El-Geundi, M. and Nassar, M. M. (1987). Equilibrium studies during the removal of dyestuffs from aqueous solutions using bagasse pith. Wat. Res. 21 1513-20. McKay, G., El-Geundi, M. and Nassar, M. M. (1988). External mass transport processes during the adsorption of dyes onto bagasse pith. Wat. Res. 22 1527-33. Nassar, M. M. and El-Geundi, M. S. (1991). Comparative cost of the colour removal from textile effluents using natural adsorbents. J. Chem. Tech.Biotech:41A, 50. Nassar, M. M. and El-Geundi, M. S. (1994). Studies on the dimensionless mass transfer coefficient during the adsorption of basic dyes onto bagasse pith, AdsorptionSci. Tech. n (No 3). Panday, K. K., Prasad, G. and Singh, V. N. (1984). Removal of Cr (VI) from aqueous solution on flyasb-woUastonite. J. Chem: Tech. Biotech. 34A, 367. POOlS, V. J. P., McKay, G. and Healy, J. J. (1976). The removal of acid dye from effluent using natural adsorbents (peat). Wat. Res. 10, 1061. Trebal, R. E. (1985). Mass TransferOperations. 3rd edn, McGraw Hill, Singapore, pp. 182-185. Weber. T. W. and Chakkravorti, R. K. (1974). Pore and solid diffusion models for fixed bed absorbers. AICHEJ. 20228.