CSSR 06’07 THE REMOVAL OF BASIC DYE (METHYLENE BLUE) FROM AQUEOUS SOLUTIONS BY ADSORPTION ON ACTIVATED CARBON PREPARED FROM PALM OIL FIBRE Fairus Muhamad Darus, Rusdin Laiman and Mohd Nizam Yusof Department of Environmental Technology Faculty of Applied Sciences, Universiti Teknologi MARA, Shah Alam
Abstract Adsorption is as an alternative technology to remove colour from wastewater. In this study, activated carbon, prepared from low cost palm oil fibre has been utilised as the adsorbent for the removal of basic dyes from aqueous solution. A basic dye, Methylene Blue has been used as the adsorbate. Experiments were conducted by varying several parameters namely pH, adsorbent dose, initial concentration of dye and contact time. Colour was effectively been removed at all selected pH, and the increase in activated carbon dose showed an increase in the removal’s percentage. The percentage of colour removal decreased with increasing of initial dye concentration. The adsorption equilibrium for colour was reached after 90 minutes of contact time. The adsorption followed both Langmuir and Freundlich isotherms. Results obtained indicate that palm oil fibre could be employed as a low cost alternative to commercial activated carbon in wastewater treatment for dye removal.
1. Introduction Colour can be considered as the earliest pollutant to be detected in polluted water. The extensive use of dyes, in both dye manufacturing and consuming industries create significant problems due to the discharged of coloured wastewater. The presence of very small amounts of dyes in water (less than 1 ppm for some dyes) is highly visible and affects the quality of waterbodies (Banat et.al, 1996). Dyes can be divided into several categories, based on their chemical nature whether anionic or cationic dye, and basic or reactive dyes. The discharge of highly coloured industrial wastewater also contributes appreciable concentrations of materials with highly biochemical oxygen demand (BOD) and significant amount of suspended solids (Mckay, 1984). Besides the effect to the environment, dyes can also cause deterioration in human’s health. Some dyes are found to be toxic, mutagenic and carcinogenic (Chen et al., 2003). Dyes released by the industries can get into the water bodies and eventually contaminate the water supply system. Consumption of dye-polluted water can cause allergy reactions, dermatitis, skin irritation, cancer and mutation both in babies (Garg et al., 2003) and grown-ups. In addition, this problem can impact several vital activities such as fisheries, livestock and agriculture since the polluted water is no longer suitable for their particular use. Many regulations have been enacted to regulate the effluent discharged by the industries. These regulations aim to control and limit several parameters in the effluent wastewater. Colour is one of the parameters concerned. For instance, the Environmental Quality (Sewage and Industrial Effluents) Regulation, 1979, limits the colour present in the final discharged by the industries to 10 Hazen for Standard A and 50 Hazen for Standard B (Environmental Quality Act, 1974). Dyes discharged, mainly from textile industries, are
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CSSR 06’07 often found exceeding these limits along with other parameters such as COD, BOD, dissolved oxygen and total iron (Tan et al., 2000). Removing colour from wastewater can be done via several methods namely chemical, biological and physical (Walker et al., 1998; Chern et al., 2001; Namasivayam et al., 2001a; Yang et al., 2001; Annadurai et al., 2002; Robinson et al., 2002b; Gupta et al., 2003; Janos et al., 2003; Rozada et al., 2003). Chemical methods use coagulation or flocculation combined with flotation and filtration, precipitation-flocculation, electroflotation, electrokinetic coagulation and ozonisation to remove colour. Biological colour treatment utilizes fungi, bacteria or other biomass (either dead or alive) and is widely accepted due to its economical advantage. This method however requires longer treatment period. Physical methods often applied are either using membrane filtration or adsorption techniques. Among these two, adsorption has been found to be superior due to advantages it offers in initial cost, flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants. Generation of harmful substances also can be avoided by applying this technique (Crini, 2006). Many types of sorbent are available for sorption. However, activated carbon is found to be the most popular adsorbent. Commercial activated carbons were prepared from various sources such as charred bone, wood and incomplete combustion of gases. Yet, it is quite expensive and ineffective against disperse and vat dyes. Therefore, many studies were carried out to vary the sources of raw material which can be activated. Wastes from agrobased industries are of attention mainly because of their abundance. Production of activated carbon from this source may reduce the cost of wastewater treatment, and at the same time open new market for low-cost agricultural by-product. In this study, waste fibre generated from oil palm mill has been chosen as the raw material to be activated. The availability of this source together with its characteristics has made palm oil fibre a suitable choice to be activated. The result of this study is hoped to provide useful information on the efficiency of activated carbon prepared from palm oil fibre for colour removal. 2. Methodology 2.1 Preparation of activated carbon from palm oil fibre 300g of sun-dried palm oil fibre was mixed with concentrated H2SO4 (17.5M) (1:2 v/w) and left to dry at room temperature for 24 hours. Dried material was put into an oven, heated at 180oC for 24 hours. The samples were then allowed to cool at room temperature in an inert atmosphere. The product resulting from the activation step was blended in order to form a granular activated carbon and washed with 3M NaOH per 100 g of product. The carbon product then was vacuum-filtered through Whatman 2 V filter paper and washed repeatedly with distilled water to remove all traces of the acid and alkali i.e until the pH of the rinsed water was constant. The product was wet-screed and dried at 80°C overnight. 2.2 Aqueous solution Stock solution of Methylene Blue (1000 mg/l) was prepared and diluted to the required initial concentration. Adsorption experiments were carried out at room temperature.
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CSSR 06’07 2.3 Adsorption experiments The initial and final concentrations of Methylene Blue were determined by measuring at 663 nm using spectrophotometer. 100 ml of Methylene Blue solution with required dose of activated carbon was shaken 200 rpm. The initial pH of the solutions was adjusted to the required value (range: 3-9) by adding 1M NaOH or 1M H2SO4 solution. Experimental variables considered were (i) different initial concentration of dye; (ii) pH; (iii) adsorbent dose and (iv) contact time between adsorbent and dye solution.
2.4 Separation techniques For separation between adsorbent and solution, the sample was centrifuged at 200 rpm at predetermined times. The supernatant was measured using UVspectrophotometer at 663 nm to determine the percentage of colour removed.
2.5 Analysis of the data Data was analysed by calculating the percentage removal of dye and the amount adsorbed (in mg/g) using equations below: Percentage removal = 100 (Ci . Cf) / Ci = (Ci . Cf) / m Amount adsorbed (qe) where Ci and Cf are initial and final concentration (in mg/L) of dye respectively, and m is the mass of activated carbon (in mg/L). Deionised water was used for each series of experiments as controls. The average values of duplicates run were obtained and analysed. The adsorption data was analysed with the help of the following linear forms of Freundlich and Langmuir isotherms: Freundlich Isotherms: log qe = log kf + (1/n) log Ce Langmuir Isotherms: (Ce/qe) = (1/Qob) + (Ce/Qo) where; log kf = 1/n = = qe
the adsorption capacity, an indictor of adsorption effectiveness, amount of dye adsorbed per unit mass of adsorbent (in
mg/g) Ce
=
the equilibrium concentration of dye (in mg/L),
Qo and b were the Langmuir constants, which measures of monolayer (maximum) adsorption capacity (in mg/g) and energy of adsorption (in g/L), respectively. The values of Freundlich and Langmuir parameters were obtained from the linear correlations between the values of: i)
log qe and log Ce (Freundlich)
ii)
(Ce/ qe) and Ce (Langmuir)
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CSSR 06’07 The observed statistically significant (at 95% confidence level) linear relationships as evidence by r-values (close to unity) indicate the capability of these two adsorption isotherms. Other essential characteristics of the Langmuir isotherms can be described by a separation factor RL; defined by the following equation: RL = 1/(1 + b Ci) Where; = =
Ci b
initial concentration of dye (in ppm or mg/L) and the Langmuir constant (in g/L).
The characteristics of separation factors can be referred in Table 1. Table 1:The characteristics of separation factor, RL
RL value process
Nature of adsorption
RL > 1
Unfavourable
RL = 1
Linear
0 < RL < 1
Favourable
RL = 0
Irreversible
3. Result and discussion 3.1 Effect of pH on dye removal in aqueous solution The effect of pH on the amount of adsorption was studied by varying the initial pH of dye solution and keeping the other process parameters as constant. The experiments were carried out at different pH (pH 3 – 9) for different dye concentration (50, 70 and 100 mg/L) and constant carbon dosage of 2.0 g. The results are shown in Figure 1. The data indicates that the colour removal using activated carbon prepared from palm oil fiber is pH independent.
Amount Removal (%)
50 mg/l
70 mg/l
100 mg/l
100.0 99.5 99.0 98.5 98.0 97.5 3
4
5
6
7
8
9
pH Figure 1: Effect of pH on dye removal using activated carbon prepared from palm oil fibre (dose = 2 g, temp = 27 ± 1 oC, time: 120 min, particle size: < 105 µm)
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CSSR 06’07 3.2 Effect of different initial dye concentration The removal of dye increased with increase in initial dye concentration (Figure 2). The amount of dye removed increased when initial dye concentration is increased from 50 mg/L to 100 mg/L with 99.5% and 99.4% for 1 and 2 g adsorbent dose respectively. It is clear that the removal of dye was dependent on the concentration of dye. These results are comparable to other similar previous studies (Kannan and Meenakshisundaram, 2002; Namasivayam et al., 2001a; 2001b).
Amount Removal (%)
1g
2g
100.0 99.5 99.0 98.5 98.0 50
60
70
80
90
100
Initial Dye Concentration (m g/L) Figure 2: Effect of different initial dye concentration on dye removal using activated carbon prepared from palm oil fibre o (pH = 7.2, temp = 27 ± 1 C, time: 120 min, particle size: < 105 µm)
3.3 Effect of adsorbent dose and contact time The effect of adsorbent dose on the amount of dye adsorbed is shown in Figure 3. The removal percentage increases when the adsorbent dose increased from (0.2-2.0 g/100 ml) at 50, 70 and 100 mg/L dye concentration. Varying the adsorbent mass may affect the porosity of the adsorbent suspension. A larger mass of adsorbent could adsorb larger amount of dyes due to the availability of more surface area of the adsorbent (Namasivayam et al., 1996; 2001a; 2001b).
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Amount Removal (%)
50 mg/l
70 mg/l
100 mg/l
120.0 100.0 80.0 60.0 40.0 20.0 0.0 0.2
0.4
0.8
1.2
1.6
2
Adsorbent Dose (g) Figure 3: Effect of adsorbent dose on dye removal using activated carbon prepared from palm oil fibre o (pH = 7.2, temp = 27 ± 1 C, time: 120 min, particle size: < 105 µm)
The colour’s removal percentage increases with the increase of contact time and remains constant after a particular time as shown in Figure 4. Removal of dyes increased rapidly in the beginning but then slowed down until it reaches the equilibrium time. The equilibrium times for all different initial dye concentration were reached after 90 min treatment. After reaching the equilibrium the adsorbate species normally forms a surface layer, which is only one molecule thick, on the surface of the adsorbent which prevent further attachment of dyes molecule to it (Kannan and Meenakshisundaram, 2002). 50 mg/l
70 mg/l
100 mg/l
Amount Removal (%)
100.0 98.0 96.0 94.0 92.0 90.0 30
60
90
120
150
180
Contact Tim e (m inute)
Figure 4: Effect of contact time on dye removal using activated carbon prepared from palm oil fibre o (dose = 2.0 g, pH = 7.2, temp = 27 ± 1 C, particle size: < 105 µm)
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CSSR 06’07 3.4 Adsorption isotherms Adsorption data for a wide range of adsorbate concentration and adsorbent doses have been analyzed using Langmuir and Freundlich isotherms in order to find the adsorption capacity of activated carbon prepared from palm oil fibre (Figure 5 and 6).
Ce/qe (mg/g)
4.0 3.0 2.0 1.0
y = 0.0399x + 0.0735 R2 = 0.9986
0.0 0
20
40 60 Ce (m g/L)
80
100
Figure 5 : Langmuir isotherms for the removal of Methylene Blue by adsorption of activated carbon prepared from palm oil fibre
log qe
1.5 1.0 0.5
y = 0.1825x + 0.8669 R2 = 0.823
0.0 0.0
0.5
1.0 1.5 log ce
2.0
2.5
Figure 6: Freundlich isotherms for the removal of Methylene Blue by adsorption of activated carbon prepared from palm oil fibre
The linear plots of Langmuir isotherms will determine whether the activated carbon prepared from palm oil fiber can be used as low cost adsorbent by calculating the separation factor RL by using Langmuir equation. The linear graph of Langmuir isotherms also represents the correlation coefficient and the value of intercept that is interpreted in Table 2. The linear plots of log qe and log Ce show the strength of adsorption capacity.
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CSSR 06’07 Table 2:
Dye
Methylene blue
The Langmuir and Freundlich parameters of adsorption isotherms
Langmuir isotherm Freundlich isotherm b Correlation RL Intercept Slope Correlation Qo (1/n) coefficient coefficient (kf) (r) (r) 26.65 0.005 0.9986 0.8000 0.8669 5.479 0.8230
The applicability of the Langmuir isotherm with the RL values showed to be in the range of 0-1 indicates that the adsorption process is favourable as low cost adsorbents. According to Choy et al., (1999), Namasivayam et al., (2001a, 2001b, 2002), Tsai et al., (2001), Rozada et al., (2003) and Wong et al., (2004), Langmuir isotherms based on the assumption that maximum adsorption corresponds to saturated monolayer of dye molecules on the adsorbent surface. The energy of adsorption is constant and there is no transmigration of adsorbate in the plane of the surface of activated carbons. The Freundlich isotherm describes equilibrium on a heterogeneous surface where energy of the adsorption was not equivalent for all adsorption sites, thus allowing multi-layer adsorption. The larger the value of adsorption capacity, kf , the higher the adsorption. The more heterogeneous the surface will bring the 1/n value closer to zero (Tsai et al., 2001; Azira et al., 2004). Values of kf and n were calculated from the slope and intercept of the Freundlich plots respectively. The magnitude of the exponent ‘n’ gives an indication of the favourability and kf the capacity of the adsorbent/adsorbate system. Result from this experiment shows the n values ranging between 1 and 10, indicating beneficial adsorption. Comparison of Langmuir and Freundlich isotherms between previous studies and the present study can be referred in Table 3. Table 3: material
Langmuir and Freundlich isotherms of activated carbon prepared from various
Activated carbon
Langmuir isotherm B RL
Palm oil fiber Bamboo dust
0.8000
0.005
0.083
0.120
0.683b
0.514b
Coconut shell
0.001
0.091
0.620b
0.677b
Groundnut shell Coir pith
0.072
0.128
0.698b
0.524b
a
a
0.62
5.17
Freundlich isotherm Slope Intercept (1/n) (kf) 0.8669 5.479
Dye: Methylene Blue a Langmuir isotherm was not followed b Freundlich isotherm was not followed
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Reference
This work Kannan et al., 2001
Namasivayam et al., 2001
CSSR 06’07 4. Conclusion The results of present study show activated carbon prepared from low cost palm oil fibre have suitable adsorption capacity in removing Methylene Blue from its aqueous solution. The adsorption is highly dependent on contact time, adsorbent dose and adsorbate concentration. Adsorption trends are found to follow both Freundlich and Langmuir isotherms.
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