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ABSTRACT
Huge quantity of dyes and pigments produced annually throughout the world are used by textile industries. Effluents from these industries are colour dye wastewater and the disposal of these wastes into freshwater bodies causes damage to environment. Among the treatment technologies, the adsorption is an attractive and viable treatment. The use of low cost, recycled waste and eco-friendly absorbent has been investigated as an alternative process for replacement of currently expensive process for removing dyes from wastewater. In this study, Neem Bark was used to remove dyes from aqueous solution in a adsorption techniques. Neem bark is an excellent low cost adsorbent and may have significant potential as a colour removal from textile wastewater. The effectiveness of Neem Bark in absorbing vat dyes from aqueous solutions was studied as a function of agitation time, adsorbent dosage, agitation speed, pH, temperature. The experimental data were fitted to Langmuir and Freundlich Isotherm and found that adsorption process follows both the isotherm. The values of Langmuir and Freundlich constants indicate favorable and beneficial adsorption. This was backed by a series of laboratory experiments. The results of which provide a better scientific understanding of the biodegradable material like Neem Bark and help realize their potential as commercial products.
Keywords: Neem Barks, Adsorption, Green Olive-B, Kinetics, Isotherms.
INTRODUCTION
About 15% of the total world production of dyes is lost during the dyeing process and is released as liquid effluents. Colour removal from such wastes is one of the most difficult requirements, faced by the textile finishing, dye manufacturing, pulp and paper industries. Among the various types of dye, various vat dyes, including green olive b, are used in dye and wool dyeing. Vat dyes is also used in cotton, wool, silk, nylon and other fibre making industries and it is a organic pollutants. The effluent containing dyes are highly coloured, resulting in major environmental problems. As International Environmental Standards are becoming more stringent, these coloured wastes need treatment before disposal. Several methods for the removal of dyes have been developed. Physical methods, mainly adsorption on various supports, are the most frequently used. Biological methods such as biodegradation have been proposed. However, due to the low biodegradability of dyes, conventional biological waste water treatment processes are not very efficient for the treatment of dyeing wastes. Chemical treatment processes (ozonation and chlorination) are more effective. However, adsorption is one of the promising methods to remove the dye pollutants from aqueous system completely. It was, therefore, thought worthwhile to develop highly efficient and effective adsorbents for the removal of dye from the textile effluents.
ADSORPTION
Adsorption is the adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid (the absorbate) permeates or is dissolved by a liquid or solid (the absorbent). Adsorption is a surface-based process while absorption involves the whole volume of the material. The term sorption encompasses both processes, while desorption is the reverse of it. Adsorption is a surface phenomenon.
Similar to surface tension, adsorption is a consequence of surface energy. In a bulk material, all the bonding requirements (be they ionic, covalent, or metallic) of the constituent atoms of the material are filled by other atoms in the material.
However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and therefore can attract adsorbates. The exact nature of the bonding depends on the details of the species involved, but the adsorption process is generally classified as physisorption (characteristic of weak Vander Waals forces) or chemisorption (characteristic of covalent bonding). It may also occur due to electrostatic attraction Adsorption is present in many natural, physical, biological, and chemical systems, and is widely used in industrial applications such as Neem leaves, orange peel and banana peel capturing the dyes from industrial wastewater.
DYE WASTEWATER
Textile dyeing industry is one of the most water consuming industries after thermal, engineering pulp and paper industries. In India water consumed by textile industries in the year of 2010 was around 1900 Mm3 (Million cubic meters) and effluent water generated was around 75 per cent of its intake.
Discover the dos and don'ts of industrial water treatment. As the textile industry is one of the most water consuming industries in the country. The dye stuff lost in the textile industry poses a major problem to wastewater sources and indeed, textile industry produces high levels of dye and floating solid materials.
It is estimated that 5000 tons of dyeing materials are discharged into the environment every year. These poisonous materials absorb the oxygen of the water and this has risen much as it threatens human life and the environment. Industrial wastewaters contain various kinds of toxic substances such as cyanides, alkaline cleaning agents, degreasing solvents, oil, fat, and metals.
MATERIALS AND METHOD
The Biomass of Neem Barks used in this study was collected from local fields. The collected biomass material was extensively washed with tap water to remove soil and dust sprayed with distilled water then dried in an oven at80o C to a constant weight. These dried Neem Barks were crushed in mechanical crusher to a constant powder size which were fractionated to 600 µ and preserved as an adsorbent in air tight glass bottles.
ADSORBENT MATERIALS
Artificial and naturally occurring solids with a highly developed surface which readily adsorbs matter from solutions surrounding the adsorbent bed. The adsorptive properties of an adsorbent depend on its chemical composition, its physical surface condition, the degree of its porosity and its specific surface area. Nonporous adsorbents such as pulverized crystals, fine crystalline sediments, particles of smoke, soot and aerosol present a specific surface area ranging from 1 to 500 square meters per gram.The specific surface area presented by porous adsorbents such as silica gels, alumogels, aluminosilicate catalysts and charcoal may be as great as 1000 m2/g. Nonporous highly dispersed adsorbents are produced primarily by thermal decomposition or incomplete combustion of hydrocarbon, as in the production of soot, and in combustion of heterogenic compounds or halides, as in the production of highly dispersed silica aerosol.
NEEM BARK
Neem tree barks can be used to remove some highly polluting dyes from aqueous solutions. This is the most important thing we must remember from the project we are going to consider. It is very useful to communities in need. In fact, pollution by dyes is often underestimated despite its seriousness. But now a great natural method can really solve the issue. The today’s suggested publication comes from india, where a very interesting and potentially life-saving project has been carried out.
Its aim is to remove chemical dyes from the polluted water. More precisely, the removal action targeted green olive b vat dye. This does not mean that the method only addresses this chemical. In fact, green olive b vat dye has been selected because it is a reliable model for many dyes. In other words, if the method is prove effective for removing green olive b dye, it is expected that it may work even in the presence of several other dyes.
The application of neem tree barks represents a great value and a very important opportunity for both environmental restoration and local development. In fact this tree already is very important because of its many applications, such as for traditional medicine and personnel care. If barks can prove their application on a wide scale shoule start immediately. Several countries still are dealing with pollution by dyes and india is among these.
Many efforts are made for reducing this very important threat, and use of neem tree barks would be an asset for water cleanup. As we can read, the method envisages the application of mature neem tree barks in powdered form. Several parameters are able to influence the method: pH value, agitation speed, agitation time, temperature, adsorbent dosage. By working on these features it may be possible to control and optimize the process towards a more effective result. A biosorbent, Neem bark powder was prepared from the mature bark of Azadirachta indica (Neem) tree by initial cleaning, drying, grinding to pigments and redrying. The powder was characterized with respect to specific surface area (21.45 m2g-1), surface topography and surface functional groups and the material was used as an adsorbent in a batch process to remove Vat dye such as green olive B from aqueous solution under conditions of different pH, agitation time, adsorbent dosage, agitation speed and temperature.
METHOD OF DYE REMOVAL
ADSORPTION AS A PROCESS
Porous or finely divided solids can hold more adsorbate because of the relatively large exposed surface area. The adsorbent surface of a liquid is increased if the liquid is divided into fine droplets. In some cases, the atom of the adsorbate shares electrons with atoms of the adsorbent surface, forming a thin layer of chemical compound. Adsorbent is also an important part of catalysis and other chemical processes. Adsorption has been regarded as superior to other methods.
Adsorption used mostly in industries for the removal of waste depends on numerous factors. Dyes are a kind of organic compounds with complex aromatic molecular structure that gave bright and firm color to other substances. However, the complex aromatic molecular structure of dyes makes them more stable and more difficult to biodegrade. The extensive use of dyes often poses pollution problems in the form of colored wastewater discharged into environmental water bodies.
Dyes are coloured compounds suitable for colouring textiles, wools, and fibres; natural dyes such as indigo have been used for over 5,000 years. There are more than 10,000 dyes with different chemical structures available commercially. Dyes are classified into different classes: (a) anionic, direct, acid, and reactive dyes, (b) cationic: all basic dyes, and © non-ionic, disperse dyes. There are also synthetic and natural dyes but the synthetic dyes have replaced natural dyes because of their low cost and vast range of new colours. Today, over 9,000 types of synthetic dyes have been incorporated.
Discharge of dye from various industries such as textile, food processing, and ink production imposes threat to the environment and ecosystem resulting to toxicity in human and aquatic organisms. It also blocks sunlight penetration thereby inhibiting photosynthesis.
DYE ADSORPTION PROCEDURE
The adsorption study was carried out by batch experimentation. The adsorption experiments were performed through batch method by contacting different amounts of adsorbent with 20 ml of solution containing various amounts of dye. The pH of the solution was adjusted to the required value using NaOH and HCl aqueous solutions (1N and 0.1 N, respectively). Batch experiments were conducted for maximum bio sorption of dye ions, through the following parameters.
1. Effect of initial concentration, 2. Effect of contact time, 3.Effect of pH, 4.Biomass dose, 5.Adsorption Isotherms and 6.Kinetics. Adsorption studies were conducted by placing 1, 1.5, 2, 2.5, 3 grams of adsorbent in 20 ml of dyes with in 100 ml Erlenmeyer flacks. The solutions were agitated at 100, 120, 140 rpms for 27⁰ C, 30⁰ C, 33⁰ C temperature levels of the solution agitated at 15, 30, 45 minutes to check the effective contact time for maximum dye uptake by bioadsorbent. The effect of bioadsorbent dose, size and dye concentration was also measured. The system was maintained at constant temperature in a thermostatic bath, under stirring. After reaching the equilibrium time (24 hours), the amount of unretained dye was determined using a spectrophotometric method.
The percentage of dye removal and the bioadsorbent capacity for dye uptake was calculated using the equations below.
Ci - Cf
Percentage Dye Removal = × 100
Ci
Where
Ci = initial dyes concentration (mg/l),
Cf = final dyes concentration (mg/l).
RESULT AND DISCUSSION
EFFCTS OF pH ON ADSORPTION KINETICS
The results showed that using adsorbent material, the percent removal of Green Olive B was decreased when the Ph was increased at constant other variables. It is well recognized that the pH of the aqueous solution is an important parameter in affecting adsorption of heavy metal ions. High adsorption of Congo red at pH = 7.2 can be explained in both terms; the species of Green Olive B and the adsorbent surface. For this case, at low pH, acidic conditions, the surface of the adsorbent becomes highly protonated and favours adsorb of above group of Green Olive B in the anionic form.
With increasing the pH of wastewater sample, the degree of protonation of the adsorbent surface reduces gradually and hence adsorption is decreased. Furthermore, as pH increases there is competition between hydroxide ion and species of Green Olive B, the former being the dominant species at higher pH values. The net positive surface potential of sorbent media decreases, resulting in a reduction the electrostatic attraction between the (sorbent) Green Olive B species and the (sorbate) adsorbent material surface, with a consequent reduced sorption capacity which ultimately leads to decrease in percentage adsorption of Green Olive B. Finally the adsorption capacity is very higher level of ph=7.2
EFFCTS OF CONTACT TIME ON ADSORPTION KINETICS
The results demonstrated that when the treatment time of Green Olive B of dyes increased the percent removal of dyes increased at constant other variables as shown in figure 4.2. This may be due to the fact that when the time of treatment of Green Olive B of dyes increasing and the velocity of Green Olive B in the column packed with the adsorbent material was remaining constant, the solution spend longer time than that spend it when the time of treatment decreased, so the adsorbent material uptake more amount of dyes from Green Olive B, therefore the percent removal of dyes from Green Olive B was increased.
EFFCTS OF TEMPERATURE ON ADSORPTION KINETICS
The results demonstrated that when the temperature of feed which was Green Olive B of dyes was increased, the percent removal of dyes was increased too at constant other variables as shown in figure 4.3. The effect of temperature is fairly common and increasing the mobility of the acidic ion. Furthermore, increasing temperatures may produce a swelling effect within the internal structure of the adsorbent media enabling dyes ions to penetrate further. It was indicated that dyes adsorption capacity increased with increasing feed temperature from 27 to 33°C. This effect may be due to the fact that at higher temperature an increase in active sites occurs due to bond rupture.
EFFCTS OF ADSORPTION DOSE ON ADSORPTION KINETICS
The results elucidated that when the adsorbent dosage amount was increased, the percent removal of dyes was increased too at constant other variables as shown in figure 4.4. The increased in the amount of adsorbent dosage Neem Bark, thus increasing the surface area of adsorbent material, hence increased the number of active sites in the adsorbent material surface increased the availability of binding sites for adsorption and consequently increase dyes removal capacity on Neem Bark. This lead to increase the ability of adsorbent dosage to adsorb greater amount of dyes from Green Olive B at different PH and ultimately the percent removal of dyes level increased.
EFFCTS OF AGITATION SPEED ON ADSORPTION KINETICS
Agitation is an important parameter in adsorption phenomena, influencing the distribution of the solute in the bulk solution and the formation of the external boundary film. Figure 4.5 shows the adsorption capacity of the reactive dyes (Green Olive B) at different agitation speed (100, 120 and 140 rpm). From the figure, it is clear that the dye uptake increases from 100 rpm to 120 rpm and shows a slight decrease at 140 rpm.
It is confirmed that 120 rpm is the optimum agitation for the adsorption process. At higher agitation speed there may be a process of desorption at the equilibrium time. Thus, the difference in agitation speed causes change in kinetics of the adsorption, as well as the equilibrium adsorption capacity. The increase in dye uptake at the optimum speed (120 rpm) reduces the film boundary layer surrounding particles, thus increasing the external film transfer coefficient and hence the percentage dye removal.
ADSORPTION ISOTHERMS
The analysis of the isotherm data by fitting them to different isotherm models is an important step to find the suitable model that can be used for design of adsorption systems. Two adsorption isotherm models Langmuir and Freundlich were used in this work. Adsorption isotherms play a very important role for understanding adsorption mechanism.
LANGMUIR ISOTHERM
The Langmuir isotherm assumes monolayer adsorption onto a surface containing a finite number of adsorption sites of uniform strategies of adsorption with no transmigration of adsorbate in the plane of surface. The Langmuir equation can be expressed in mathematical
form as shown in Equation 1:
Ce / qe = 1 / Qo b + Ce / Qo (1)
Where, Ce is the equilibrium concentration (mg/L), qe is the amount adsorbed at equilibrium (mg/g), Qo is the adsorption capacity (mg/g) and b is the energy of adsorption (Langmuir constant, l/mg). The maximum adsorption of Langmuir constant were calculated from the linear plots Ce/qe versus Ce to determine the value of Qo (mg/g) and b (L/mg), which gives a straight line of slope 1/Qo, corresponding to complete monolayer coverage (mg/g) and the intercept is 1/Qo b.
The maximum adsorption capacity Qo was found to increase with the temperature, thereby enhancing the mobility of the dye ions. This led to a higher chance of the reactive dyes being adsorbed onto the adsorbent and an increase in its adsorption capacity which resulted in the enlargement of pore size or activation of the adsorbent surface. The isotherm showed no linear variation for the Langmuir constant b and hence the kinetic energy of the dye was independent. This indicates the applicability of the isotherm (Langmuir isotherm) and the surface.
CONCLUSION
High Dye Removal efficiency is 81.23 %. These experimental studies have indicated that the Neem bark has the potential to act as an adsorbent for the removal of the Green Olive B from aqueous solutions. The effects of contact time, adsorbent dosage, agitation speed, temperature and pH on the reactive dye removal were determined with the experimental data. The adsorption data correlated well with Freundlich model as compared to the Langmuir isotherm model. The Freundlich plot of Green Olive B showed higher adsorbent capacity.