COMPARATIVE STUDY ON ADSORPTION OF METHYL ORANGE USING SEEDS (MELON, WATERMELON AND MUSKMELON SEEDS)
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Abstract
In the present study, three types of adsorbents; garlic peel, onion peel and coconut were used for the removal of methyl orange from water, which is considered to be a carcinogenic dye, and it was observed that the efficiency of the three adsorbents was dependant on these parameters; concentration of analyt, concentration of adsorbent, particle size, pH, temperature, time and stirring. The comparative behaviour of these three adsorbents indicates that garlic peel is a better adsorbent than onion peel and coconut peel.
Introduction
Color is the most obvious indicator of water pollution. The discharge of colored wastes into receiving streams not only affects the aesthetic nature but also interferes with transmission of sunlight into streams and therefore reduces photosynthetic activity. Dyes and pigments represent one of the problematic groups; they are emitted into wastewaters from various industrial branches, mainly from the dye manufacturing and textile finishing. Dyes can be classified as anionic (direct, acid, and reactive dyes), cationic (basic dyes) and non-ionic (disperse dyes). Wastewaters offer considerable resistance for their biodegradation due to presence of these heat and light stable dyes, thus upsetting aquatic life. Hence, the conventional methods used in sewage treatment, such as primary and secondary treatment systems, are unsuitable. The adsorption process provides an attractive alternative treatment, especially if the adsorbent is inexpensive and readily available.
Over the last few decades, society has become increasingly sensitive towards the protection of the environment. Due to this problem, mankind nowadays has concern about the potential adverse effects to the chemical industry on the environment, although the response in some parts of the world has been much faster and more intense than in others. The impact and toxicity of dyes that are released in the environment have been very important and extensively studied. The source of such pollution lies in the rapid increase in the use of synthetic dyes because of their ease of use, inexpensive cost of synthesis, stability and variety of color compared with natural dyes. More than 10,000 chemically different dyes are being manufactured. These dyes are mainly consumed in textiles, tanneries, pharmaceuticals, pulp and paper, paint, plastics, electroplating and cosmetics industries [1]. During the processing of dye manufacturing and dye application, up to 15% of the used dyestuff are released into the process water so the effluents from these industries are highly colored [2-3].Dyes and pigments are highly visible material. Thus even minor release into the environment may cause the appearance of colour, for example in open waters, which attracts the critical attention of public and local authorities. Most of the dyes are toxic, carcinogenic and can cause allergic dermatitis, skin irritation, mutation, etc. [4-6]. Beside these they impart intense color to wastewater streams causing reduced photosynthesis of aquatic plants due to inhibition of the sunlight penetration [7-8]. Thus endanger aquatic life.
There is thus the requirement on industry to minimize environmental release of colour, even in cases where a small but visible release might be considered as toxicologically rather innocuous. A major source of release of colour into the environment is associated with the incomplete exhaustion of dyes onto textile fiber from an aqueous dyeing process and the need to reduce the amount of residual dye in textile effluent has thus become a major concern in recent years. An alternative approach to addressing the problem of colour in textile dyeing effluent has involved the development of effluent treatment methods to remove colour. Available methodologies in this regard such as flocculation combined with coagulation, nanofiltration, micellar enhanced ultrafiltration ,membrane separation, oxidation or ozonation etc., are either expensive or inadequate in removing dye from wastewater [9-14].
Adsorption has been recognized as the most popular treatment process for the removal of the dyes in aqueous solution with the advantages of high efficiency, simple operation, and easy recovery and reuse of adsorbent. Activated carbon adsorption shows high effectiveness in removal of dyes [15]. However the use of this promotes search for adsorbents mainly from biological origin such as peat, fly ash, coir pith, banana pith, biogas residual slurry, hardwood sawdust, maize stalk, rice husk, peanut hull, bagasse pith, jute processing wastes, wheat shells etc., for this purpose [16-29].
Still depending upon the availability and cost there is always a necessary to search for new effective adsorbent. In this study, we attempt to use an agricultural by-product, melon seed, watermelon seed and muskmelon seed as an adsorbent for the removal of Methyl Orange from water. The objective of this study is to study the removal of Methyl Orange from aqueous solutions using melon, watermelon and muskmelon seeds as abundant and low-cost sorbent.
Dyes
Dyes may be defined as intensely colored substances which, when applied to substrate impart color to this substrate by a process, which at least temporarily destroy a crystal structure of the colored substance. The dyes are retained in the substrate by absorption, solution and mechanical retention or by ionic or covalent chemical bonds. They are soluble completely or at least partially in the media from which they are applied in contrast to pigments, dyes must possess a specific affinity to the substrate from which they are used.
Retention of color as well as stability is required functional property and is accomplished by chemical and physical forces. Such as chemical bonding, H-bonding, Vander Wall’s forces , adsorption, solution, electrostatic interaction of visible light with the electron system of the dye molecule. Several hundred thousand known compounds qualify as dyes based on their light absorption in the visible region of the electromagnetic spectrum. However, of these only about 1500 have proved to be of practical value and are being manufactured. Commercial uses of dyes include the coloration of textile paper, leather, wood, inks, fuels, food items and metals. Dyes are used also in photographic paper as indicators in analysis and as biological stains.
Acid dyes
Acidic dyes are water soluble. These are sodium salts usually of sulphonic acids, but in a few cases, carboxylic acids. The –ve ion is responsible for the color of dye. These are used to dye animal fibers such as wool and silk directly. Most of them have no affinity for cellulose fibers. Acid dyes are also used by several industries, such as textile, paper, printing, cosmetic and plastics to colour their products [30-31].
Methyl Orange Orange
Azo Dyes
The name azo comes from azote, the French name of nitrogenthat is derived from the Greek a (not) + zoe (to live). Azo compounds are compoundsbearing the functional group R-N=N-R', in which R and R' can be either aryl or alkyl. The N=N group is called an azo group, although the parent compound, HNNH, is called diimide. The more stable derivatives contain two aryl groups.
As a consequence of п-delocalization, aryl azo compounds have vivid colors, especially reds, oranges, and yellows. Therefore, they are used as dyes, azo dyes for example Disperse Orange 1. Some azo compounds, e.g methyl orange and congo red are used as acid-base indicators due to the different colors of their acid and salt forms. The development of azo dyes was an important step in the development of the chemical industry [32]
Azo dyes are widely used in textile dyeing, paper printing and other industrial processes such as the manufacture of pharmaceutical drugs, toys and foods including candies. These dyes are highly recalcitrant to conventional wastewater treatment processes.
Methyl Orange
Methyl orange is a pH indecator frequently used for titration involving weak base its mager physical properties are as follows:
Properties of Methyl Orange
IUPAC name 4-dimethylaminobenzene-4-sulfonic acid sodium salt
Other name p-dimethyl amino azo benzene sulfonic acid
Molecular formula C14H14N3O3SNa
Molar mass 327.33 g/mol
Appearance orange powder
Odor Odorless
Melting point >300oC (not precisely defined)
Solubilityin water soluble in hot water
Specific gravity 1:00
Density 1.28 g/cm3 solid
Boiling point Decomposes
Dye content ~95%
Transition range 3.0 – 4.4 pH
Absorttivity (pH 3.0) 501 – 504nm
Absorttivity (pH 4.4) 467 – 471nm
Loss on drying (110oC) <5%
Structure:
Fig. 1 Structure of Methyl Orange dye
Methyl Orange
Technologies for Color Removal
There are more than 100,000 commercially available dyeing existing and more than 7x105 tonnes per year are produced annually [36-37]. Wastewater containing dyes is very difficult to treat, since the dyes are recalcitrant organic molecules, resistant to aerobic digestion, and are stable to light. A synthetic dye in wastewater cannot be efficiently decolorized by traditional methods. This is because of the high cost and disposal problems for treating dye wastewater at large scale in the textile and paper industries [38] The technologies for colour removal can be divided into three categories: biological, chemical and physical [39]. All of them have advantages and drawbacks.
Biological Methods
Biological treatment is the often the most economical alternatives when compared with other physical and chemical processes. Biodegradation methods such as fungal deodorization, microbial degradation, adsorption by (living or dead) microbial biomass and bioremediation systems are commonly applied to the treatment of industrial effluents because many microorganisms such as bacteria, yeasts, alges and fungi are able to accumulate and degrade different pollutants [40]. However, their application is often restricted because of technical constraint. In particular, due to their xenobiotic nature, azo dyes are not totally degraded.
Chemical Methods
Chemical methods include coagulation or flocculation combined with flotation and filtration, precipitation-flocculation with Fe (II)/Ca (OH)2, electroflotation, electrokinetic coagulation, conventional oxidation methods by oxidizing agents (ozone), irradiation or electrochemical processes [9-14]. These chemical techniques are often expensive, and although the dyes are removed, accumulation of concentrated sludge creates a disposal problem. Recently, other emerging techniques, known as advanced oxidation processes, which are based on the generation of very powerful oxidizing agents such as hydroxyl radicals, have been applied with success for the pollutant degradation. Although these methods are efficient for the treatment of waters contaminated with pollutants, they are very costly and commercially unattractive. The high electrical energy demand and the consumption of chemical reagents are common problems.
Physical Methods
Different physical methods are also widely used, such as membrane – filtration processes (nanofiltration, reverse osmosis, electrodialysis) and adsorption techniques. The major disadvantages of the membrane processes is that they a limited lifetime before membrane fouling occurs and the cost of periodic replacement must thus be included in any analysis of their economic viability.
Adsorption is a well known equilibrium separation process and an effective method for water decontamination applications [41]. Adsorption has been found to be superior to other techniques for water re-use in terms of initial cost, flexibility and simplicity of design, ease of operation and insensitivity to toxic pollutants.
An Efficient Technique To Remove Dyes From Water
Adsorption
Adsorption may be in principle occurring at all surfaces. Its magnitude is noticeable when porous solids which have a high surface area are contacted with gases and liquids e.g. alumina, fuller’s earth; chitin etc. adsorption process may involve either simple unimolecular adsorbent layers or multi-layers. So, adsorption may be defined as, “it process where one or more components (adsorbates) are attracted and bounded to the surface of a solid (adsorbent) with which they in contact” [42].
The substance attached to a surface is said to be the “adsorbed phase” while the substance to which it is attached is called adsorbent. The substance being adsorbed is called adsorbate or solute. When the adsorption is accomplished by absorption either in physical or in chemical phenomenon, the process is termed as sorption.
The major advantage of adsorption over the conventional method is;
•The low cost;
• The high efficiency;
• The minimization of chemical and biological sludge;
• No additional nutrient requirement;
• The regeneration of biosorbent; and
The forces which bind the adsorbent to the surface, may be physical or chemical in nature.
Driving Force for Adsorption
The driving force for adsorption is the reduction in interfacial (surface) tension between the fluid and the solid adsorbent as a result of the adsorption of the adsorbade on the surface of the solid.
The surface or interfacial tension, 
is the change in free energy, G, resulting when the area between two phases, A, is increased. The definition of
is:
is the change in free energy, G, resulting when the area between two phases, A, is increased. The definition of is:
Theory
A solid surface in contact with a solution tends a surface of solute molecules. Because of the unbalance of the surface forces chemical adsorption results in the formation of monomolecular layer of adsorbent on the surface through forces of residual valence of the surface molecules. Physical adsorption results from the condensation in the capillaries of the solid. In general substances of highest molecular weight are more easily adsorbed. There is a rapid formation of equilibrium concentration followed by the slow diffusion into carbon particles. The overall rate of adsorption is controlled by the rate of diffusion of solute molecules within the capillary forces of the carbon particles. The relation varies reciprocally with the square of the particles diameter increases with increasing temperature and decreases with increasing molecular weight of the solute.
Adsorption from Solutions
The number of molecules, which adsorb at the surface of a solid or a liquid from solution is proportional to the concentration C
σ = KC
Where, K is constant
The kinetic picture is very similar to that of the adsorption of gases on solute molecule moving in all directions so does the molecules of solvent. Each molecule is, however, constantly in contact with a few other molecules of the solute and solvent. Their movements, therefore in any direction are far more restricted though not in vigor. The restriction is in free path. They can hardly move over any length without being influenced by molecules. This is the reason that diffusion in liquids proceeds so much slowly then in gases. The time of adsorption depends on the energy of adsorption. When an aqueous solution of dye is shaken with charcoal, the color intensity of the solution is often lowered to zero. This is striking example of chemical adsorption.
Adsorption Isotherms
The relationship between amount of substance adsorbed, pressure and concentration of adsorbate at constant temperature is called “Adsorption Isotherm”. The Langmuir adsorption isotherm and Freundlich adsorption isotherm are included in the present study.
Langmuir Isotherm
This isotherm was chosen for the estimation of maximum adsorption capacity corresponding to complete monolayer coverage on the adsorbent surface[43].
It is described by:
q = qmax b Ce / (1+ bCe)
or
1/q = 1/bqmax Ce + 1/qmax
Where
q = The adsorption density (mg of adsorbate per g of biosorbent).
qmax= Max. amount (adsorption capacity) of Methyl Orange dye forming a complete monolayer on the biomass surface (mg/g).
b = Langmuir constant related to energy of adsorption (L of biosorbent per mg of biosorbate)
The Freundlich Adsorption Isotherm
The Freundlich model was chosen to estimate the adsorption intensity of the sorbate on the sorbent surface. The Freundlich equation is an empirical equation based on adsorption on heterogeneous surface [44] and is given by:
q = Kf (Ce) 1/n
log q = log Kf + 1/n log Ce
Where
q = The adsorption density (mg of adsorbate per g of biosorbent).
Ce = Equilibrium concentration of adsorbate in solution (mg/L).
n = Empirical constant (Freundlich exponent).
KT = Max. adsorption capacity (Freundlich adsorption constant)
Factors Affecting Adsorption
The adsorption is affected by the following factors:
1. Effect Of Temperature
Generally heat is evolved during the process of adsorption. So according to Lie Chatelier`s principal the magnitude of adsorption should increase with falls in temperature.
2. Effect Of Pressure
Since adsorption of a gas causes decrease of pressure, so the magnitude of adsorption should increase with increase of pressure.
3. Effect Of Density
At constant temperature, adsorption decreases with the density of the adsorbade or if it is mixed with another fluid, with the adsorbade content of the fluid.
4. Effect Of pH
It depends upon the composition of adsorbent. This is due to solubility of constituents of adsorbent which leads to smaller number of available sites for adsorption incase of alumina, the solubility of different constituents in acidic solutions percentage values increases with increase in pH.
5. Nature Of Adsorbade
For a given adsorbent, the absorbability of different substances may vary widely so that in the presence of mixture of substances selective adsorption will occur. Although at the beginning of the run, several substances may be adsorbed simultaneously the less, clear-cut segregation will be obtained according to the relative densities of the substance in the mixture.
6. Nature Of Adsorbent
The help of examples will explain the importance of this factor. Although activated carbon may show the same or even greater saturation value for the water vapor than does bauxite or silica gel, its efficiency is so poor that it is worth less as a desiccant. On the other hand the benzene vapors has maximum efficiency for charcoal, silica gel and it is lowest for activated alumina so, it should be kept in mind the term like silica gel, activated carbons and clay are merely expressions for general type since each exits in the numerous varieties according to the mode of preparation although called the same name, they may produce quite different results.
Types Of Adsorption
Based on the interaction between the adsorbent and adsorbade, there are following types of adsorption [45].
1. Physical Adsorption
“The adsorption in which the molecules or atoms are held to the solid or liquid surface by Vander Wall’s forces is called physical adsorption.”For example, the adsorption of toxic metals on clay. It provides information about the structure of solids and its surface area.
2. Chemical Adsorption
“The adsorption of a substance at a surface involving the formation of chemical bond between the adsorbade and the adsorbent which may be covalent or ionic is called chemical adsorption”.The chemical adsorption is fundamental importance in heterogeneous catalysis.
3. Polar Adsorption
Adsorption may be polar when the material adsorbed consists of positive and negative ions. So, that adsorbed film has an overall electric charge, the term adsorption is chiefly attributable to attraction between polar groups of adsorbents and adsorbade.
4. Specific Adsorption
Specific adsorption is preferential adsorption of one substance over another, or the quality of the adsorbent held per unit area of the adsorbent.
5. Biosorption
Biosorption is defined as the accumulation and concentration of organic and inorganic pollutants including metals, dyes and odour causing substances from aqueous solutions by the use of biological materials. These biological materials are typically live or dead microbial biomasses, which may be bacteria, fungi and algae. Biosorption is a complex phenomenon where the dyes species could be deposited in the solid biosorbent through different sorption processes of ion exchange, complexation, chelation and micro precipitation. Biosorption in natural or uncontrolled situations typically involves a combination of active and passive transport mechanisms.
The Most Effective Method (Biosorption)
The main attractions of biosorption are high selectivity and efficiency, cost effectiveness, good removal performance, possible regeneration at low cost, availability of known process equipment, sludge free operation and recovery of the sorbate. Raw materials which are either abundant (sea weeds) or wastes from other industrial industrial operations (fermentation wastes, activated sludge process wastes) can be used as biosorbents. The use of dead microbial cells in biosorption is more advantageous for water treatment in that dead organisms are not affected by toxic wastes, they do not require a continuous supply of nutrients and they can be regenerated and reused for many cycles [46-51].
The work is aimed at,
Ø Screening of efficient biosorbent
Ø Characterization of biosorbent mechanism
Ø Modeling if dyes removed by biosorbent
Development of biosorption process and search for a low cost and easily available adsorbent has led to the investigation of materials of agricultural wastes having biological origin, along with industrial by-products, as potential dye sorbent.
Mechanism
There is believed to be a variety of ways in which cells take up dye ions and these include ion exchange, chelation, adsorption by physical forces, and ion entrapment in inter and intra fibrillar capillaries and spaces of the structural polysaccharide network as a result of the concentration gradient and diffusion through cell wall and membranes. Fungal pigments have also been implicated in dye uptake and resistant by some fungal species. There are several chemical groups that could attract dyes ions in biomass. The cell wall of fungi consists of amino or non amino-polysaccharides. These polysaccharides play an important role in the uptake of dye anions from solution. The amino, carboxyl and hydroxyl groups and the nitrogen and oxygen of the peptide bond could be available for characteristic coordination bonding with dye anions.
A number of different dye anions binding mechanisms have been postulated to be active in biosorption such as;
Ø Chemisorptions: by ion-exchange, complexation, coordination, and chelation.
Ø Physical adsorption: micro precipitation.
Due to complexity of biomaterials used it is quiet possible that at least some of these mechanism are acting simultaneously to varying degrees depending upon the biosorbent and the solution environment. Simple and economically feasible pretreatment procedures for the suitable biomaterials may be divided based on better understanding of the biosorbent mechanisms.
Advantages Of Biosorption
It has following advantages,
Ø Biosorption can be used under a broad range of operating conditions (pH, temperature, dye concentration etc.)
Ø It is cost effective, cheap raw materials can be used like suitably abundant biomass types or industrial wastes by product biomass. In the later case, an additional benefit is that waste from one industry can be used to clean the waste from other processes.
Ø Another advantage of biosorption is that it offers high effluent quality and avoids the generation of toxic sludge.
Ø Its main target is; however to remove dyes which can be quite toxic even at low concentrations.
Biosorption can become a good weapon in the fight against carcinogenic dyes threatening our environment. While the biosorption process could be used even with low degree of understanding of its dye binding mechanisms, better understanding will make for its more effective and optimized applications.
Adsorbent
Adsorbents are specific in their nature and properties. The adsorbing solid or adsorbent generally is extremely porous “solid foam” surface with large internal surfaces. Its external surface comprising of a small part of total surface. Amorphous solids in general are more adsorbent than crystalline material. The extent of the surface area, structure of surface, size, distribution of pores, the cleanliness of surface and the activation process employed in preparation of adsorbent all play important role. The commercially important solid adsorbents are fuller’s earth, bauxite, and acid treated clays, bones, char, decolorizing carbon, alumina, base exchange silicates, synthetic resin exchanges, metal adsorbent chars, bentonite and magnesia.
Agricultural Stuff as A Low Cost Adsorbent For Dye Removal From Waste Water
Agricultural waste materials have little or no economic value and often pose a disposal problem. So, activated carbon prepared from these wastes help to solve the waste disposal problem. Agricultural wastes include peat, fly ash, coir pith, banana pith, biogas residual slurry, hardwood sawdust, maize stalk, rice husk, peanut hul, bagasse pith, jute processing wastes, wheat shells etc., for this purpose [16-29].
In a developing country like Pakististan agriculture is the primary occupation, agricultural waste by-product such as melon seeds, water melon seeds and musk melon seeds are abundantly available. Therefore, it would be worthwhile to develop a low-cost adsorbent from these seeds.
1. Melon
Melon is a term used for various members of the Cucurbitaceaefamily with fleshy fruit. Melon can refer to either the plant or the fruit, which is a false berry. Many different cultivars have been produced, particularly of muskmelons. Melon can be round, oval, or obvoid in shape, up to 12 inches long, smooth skin, grooved, ribbed or netted, varieties vary in color the plant grows as a vine. The protein content of melon is 29.55, fat contents are 42.67, and carbohydrate contents are 6.39. Crude fibre contents are 2.94 and ash contents are 1.67 [52].
Melons are known to contribute to a person's health by being a rich source of beta-carotene (for muskmelon), but are less well known for their ascorbic acid, carbohydrate, dietary fiber, potassium, calcium and iron contents. Melons have at least thirty-eight (38) of these chemical compounds with beneficial human biological activities. These compounds are called phytochemicals and can have anti-arthritic, cataract, cold, depressant, glaucomic, migraine, obesity, parkinson, ulcer, properties in addition to cancer-preventive attributes. Recommended for Persons suffering from Bladder and Kidney Problems and used against certain types of Intestinal Parasites. Melon can be used as a cooling light cleanser or moisturizer for skin. They are also used as first aid treatment for burns and abrasions.
In addition to consumption of the fresh fruit, melons are sometimes dried and stored as melon leather. Other varieties are cooked as vegetables or grown for their seeds, which are processed to produce melon oil. Still other varieties are grown only for their pleasant fragrance.
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