1. INTRODUCTION:
Industrial waste water is considered as one of the major pollutants of the environment. Moreover, in country textile industries are the basic industries and have colored wastewater due to making use of colored materials (1). The dyes are used in many industries such as carpets, plastics, cosmetics, paper, food and textile in order to color their product (2). The World Bank has estimated that 17 to 20 percent of industrial water pollution comes from textile dyeing and treatment. Discharge of dyes into river from these industries cause several problems as dyes give toxicity to the aquatic life and also damaging the asthetic nature of the environment (3). The presence of dye upsets the biological activity which leads to the destruction of aquatic communities present in ecosystem. Hence the wastewater containing dyes require proper treatment before it is released into the various environmental source of water (4). A variety of physical, chemical and biological methods are currently available for color removal. The conventional methods for treating waste water containing dyes are coagulation and flocculation (5), Hydrogen peroxide (6), Fenton’s reagent (7), Ozonation (8), photo catalysis (9), biological treatment (10) and adsorption using activated carbon (11).
In this work it is planned to utilize the adsorption of dye using activated carbon, due to its excellent efficiency. The activated carbon is by far most common adsorbent used in waste water treatment since during adsorption the pollutant is removed by accumulation at the interface between the activated carbon (adsorbent) and the waste water (liquid phase) the adsorbing capacity of activated carbon is always associated with very high surface area for unit volume (13).Several activated carbons are synthesized from different natural plant material. The present study is undertaken to evaluate the efficiency of carbon adsorbent prepared from acid activated Musa paradisiaca sheath fibre for the removal of dye from the aqueous solution. In order to design adsorption treatment system knowledge of kinetic and mass transfer process is essential (12). In this paper, it is reported that the applicability of kinetics, batch experiment studies, mass transfer model and characterization studies like SEM for the adsorption onto activated carbon.
2. MATERIALS AND METHODS:
2.1 Preparation of Activated Carbon:
The Musa paradisiaca sheath fibre was collected from local agriculture land N.V. Kudikadu, Papanasam (T.K.), Thanjavur (D.T), Tamil Nadu – 613 502. The fibre material to be carbonized is impregnated with a boiling solution of 30 % H3PO4 for 2 hours and soaked in the same solution for 24 hours. At the end of 24 hours the excess solution decanted off and air dried. Then the material was carbonized in muffle furnace at 400o C for 2 hours. The dried material was powdered and activated in a muffle furnace at 800o C for a period of 10 minutes, and then the material was washed with plenty of water to remove residual acid, after that it is dried and powdered.
2.2 Preparation of Dye Solution:
The Bismark brown dye used is Himedia grade. The dye stock solution was prepared by dissolving accurately weighted Bismark brown dye in distilled water to the concentration of 1 mg/L-1. The experimental solutions were obtained by diluting the dye stock solution in accurate proportions to get required initial concentrations (14).
Batch Experiment:
Dye solution adsorption experiments were performed by taking 50 mL stock solution of dye (10 mg/L-1) and treated with 1 gram of adsorbent dose. Various studies were performed by varying pH, adsorbent dose, agitation time and initial concentration. After the desired times of treatment, samples were filtered to remove the adsorbent and progress of adsorption was determined using UV- Spectrometer (Systronics PC based double beam spectrophotometer (2202)) at 465 nm for Bismark brown dye, in which the maximum absorbance (λmax) takes place.
3. RESULTS AND DISCUSSION:
3.1 Effect of pH:
The pH of the aqueous solution is an important parameter that controlled the adsorption process. The experiments were done with pH (1to7), temperature (±33oC), contact time (2 hrs), agitation speed (350 rpm), initial concentration 10 mg/L and the adsorbent dose is 1 g. The experimental results are shown in table -1. The graph was plotted between pH and dye uptake shown in figure -1. The figure shows that the optimum pH of solution was adsorbed at pH of 5 and by increasing pH, no changes of adsorption was observed. This might be due to the weakening of electrostatic force of attraction between the positive charged adsorbate and adsorbent that ultimately lead to the reduction in sorption capacity.
3.2 Effect of adsorbent dose:
The effect of adsorbent dose was also investigated for the removal of dye from aqueous solution. The experiments were carried out with adsorbent dose varied from (0.25 to 1.25 g) with keeping other parameter as constant such as pH 5, initial concentration 10 mg/L, temperature (±33o C ), contact time (2 hrs), agitation speed (350 rpm). The experimental results are shown in table - 2. The influence of adsorbent dose in removal of dye is shown in figure - 2. The figure shows that adsorbent dose 0.5 g is sufficient for the removal of dye. Further increment in adsorbent dose did not cause significant improvement in the adsorption.
Fig 1 Effect of pH on the dye uptake, Time 120 min, Adsorbent dose 1 g, Volume of the solution 50 mL, Initial dye concentration 10 mg/L and Temperature 33±1o C.
Table 1 Effect of pH on the dye uptake, Time 120 min, Adsorbent dose 1 g, Volume of the solution 50 mL, Initial dye concentration 10 mg/L and Temperature 33±1o C.
|
Dye concentration (ppm) |
pH |
Dye concentration after Adsorption (ppm) |
|
10 |
7 |
5.0 |
|
10 |
6 |
4.9 |
|
10 |
5 |
4.8 |
|
10 |
4 |
5.2 |
|
10 |
3 |
5.7 |
|
10 |
2 |
6.2 |
|
10 |
1 |
6.7 |
Table 2 Effect of adsorbent dose on the dye uptake, Time 120 min, pH 5 Volume of the solution 50 mL, Initial dye concentration 10 mg/L and Temperature 33±1o C.
|
Dye concentration (ppm) |
Adsorbent dose (g) |
Dye concentration after Adsorption |
|
10 |
0.25 |
5.8 |
|
10 |
0.5 |
4.8 |
|
10 |
0.75 |
4.6 |
|
10 |
1.0 |
4.6 |
|
10 |
1.25 |
4.6 |
Fig 2 Effect of adsorbent dose on the dye uptake, Time 120 min, pH 5, Volume of the solution 50 mL, Initial dye concentration 10 mg/L and Temperature 33±1o C.
3.3 Effect of Equilibrium time on adsorption:
Equilibrium time is one of the effective factors in batch adsorption process. In this study all of the parameter except contact time, including temperature (±33o C), adsorbent dose (0.5 g), pH 5, initial concentration (10 mg/L), and agitation speed (350 rpm) were kept constant. The experimental data are shown in table - 3 and the effect of contact time on dye adsorption efficiency showed in figure - 3.The figure showed that a contact time of 180 minutes was sufficient to achieve equilibrium and the adsorption does not change with further increasing contact time, therefore the uptake of dye solution at the end of 180 minutes are given as the equilibrium value qeq(mg/g) and Ceq(mg/L) as 1.56 and 2.2 respectively.
Table 3 Effect of equilibrium time on dye adsorption, pH 5, adsorbent dose 0.5 g, Volume of the solution 50 mL, Initial dye concentration 10 mg/L and Temperature 33±1o C.
|
Dye concentration (ppm) |
Time (min) |
Dye concentration after Adsorption (ppm) |
|
10 |
30 |
2.6 |
|
10 |
60 |
5.2 |
|
10 |
90 |
7.8 |
|
10 |
120 |
10.4 |
|
10 |
150 |
11.6 |
|
10 |
180 |
15.6 |
|
10 |
210 |
15.6 |
|
10 |
240 |
15.6 |
Fig 3 Effect of equilibrium time on dye adsorption, pH 5, adsorbent dose 0.5 g, Volume of the solution 50 mL, Initial dye concentration 10 mg/L and Temperature 33±1o C.
3.4 Effect of Initial concentration:
The rate of adsorption is a function of initial concentration. The experiment were done with variable concentration (10 to 50 mg/L) and constant temperature(±33oC ), adsorbent dose (0.5 g), pH 5, contact time (3 hrs), agitation speed (350 rpm). The experimental data are shown in table - 4 and the graphs are plotted between dye uptake and times are shown in figure - 4. This increase (15.6 to 46 mg/g) is a result of the increase in the driving force i.e., concentration gradient. These results indicate that the adsorption of dyes is much dependent on concentration of the solution because removal decreases with increase of initial concentration of dye.
Table 4 Effect of initial concentration on dye adsorption, Time 180 min, pH 5, Adsorbent dose 0.5 g, Volume of the solution 50 mL, Initial concentration 10 to 50 mg/L and Temperature 33±1o C.
|
Dye Concentration (ppm) |
Dye Concentration after Adsorption (ppm) |
|
10 |
15.6 |
|
20 |
28.0 |
|
30 |
37.2 |
|
40 |
43.2 |
|
50 |
46.0 |
Fig 4 Effect of initial concentration on dye adsorption, Time 180 min, pH 5, Adsorbent dose 0.5 g, Volume of the solution 50 mL, Initial concentration 10 to 50 mg/L and Temperature 33±1o C.
3.5 Adsorption Isotherm:
Langmuir Isotherm:
Langmuir isotherm takes an assumption that the sorption occurs at specific homogeneous sites within the adsorbent.
A general form of Langmuir equation is,
qe = 
The linear form of isotherm equation can be written as,
qmax = Maximum dye uptake corresponding to the saturation capacity of the adsorbent b = Energy of adsorption Variable Ce and qe respectively.
The constant qmax and b are the characteristic of the Langmuir isotherm and can be determined from the above equation. Therefore a plot of 1/qe Vs 1/Ce gives a straight line of a slope (1/qmax) and intercepts 1/qmax. So the data fit Langmuir isotherm. The linearity of the plot indicates application of Langmuir equation supporting monolayer formation on the surface of the adsorption.
Freundlich Isotherm:
Freundlich isotherm is an empirical equation based on a heterogeneous surface. The general form of Freundlich equation is,
qe = kf Ce1/ n
and the linearized form is, log qe = log kf + 1/n log Ce where the intercept log kf is a measure of adsorption
capacity and slope 1/n is the intensity of adsorption. The variable qe and Ce are dye adsorbed and the equal dye concentration in solution. Langmuir and Freundlich plots were arrived using the table - 5 and the plot was shown in figure - 6 and figure - 7. It appears that Langmuir and Freundlich model both best fit the experimental results over the experimental range with good correlation coefficient.