ABSTRACT
This study investigated the adsorption of Methylene Blue (MB) present in aqueous solution onto the activated carbon produce from almond shell. The agricultural material (almond shell) was activated using hydrochloric and phosphoric acid (1:1). The Activated almond shell was used for the adsorbtion. Batch model experiments were conducted at 20˚C to study the effects of contact time and initial concentration of methylene blue. The Methylene Blue (MB) uptake increased as contact time increased from 0 – 120 mins, and reached equilibrium at 120 minutes. The percentage removal increased with increasing initial dye concentration for the almond shell. This study suggests that adsorbent prepared from almond shell can be used effectively for the adsorption of methylene blue in wastewater.
CHAPTER ONE
- INTRODUCTION/BACKGROUND
Methylene blue is a common dye mostly used by industries involve in textile, paper, rubber, plastics, leather, cosmetics, pharmaceutical and food industries. Effluents discharged from such industries contain residues of dyes. Consequently, the presence of very low concentrations in effluent is highly visible. Discharge of colored wastewater without proper treatment can results in numerous problems such as chemical oxygen demand (COD) by the water body, and an increase in toxicity. Methylene blue is a colored dye. Colored dye wastewater is created as a direct result of the production of the dye and also as a consequence of its use in the textile and related industries[1]. Currently, there are about 10,000 different commercial dyes and pigments exist and over 7×105 tones of synthetic dyes are produced annually world-wide. It is estimated that 10–15% of the dyes are lost in the effluent during the dyeing processes while 10% was discharged from textile and associated industries [2].
Among industries, textile factories consume large volumes of water and chemicals for processing of textiles. Wastewater stream from the textile dyeing operation contains unutilized dyes (about 8%–20% of the total pollution load due to incomplete exhaustion of the dye) and auxiliary chemicals along with a large amount of water. It is estimated that 10%–20% of dyes in the textile dying process will be lost in residual liquors through incomplete exhaustion and washing operations. The rate of loss is approximated to be 1%–10% for pigments, paper and leather dyes. Effluent treatment processes for dyes are currently able to eliminate only half of the dyes lost in wastewater streams. Therefore, hundreds tones daily find their way into the environment, primarily dissolved or suspended in water[3].
Major problems associated with colored effluent are lowering light penetration, photosynthesis and damages the aesthetic nature of the water surface. Moreover, their degradation products may be mutagenic and carcinogenic. Many dyes may cause allergic dermatitis, skin irritation, dysfunction of kidney, liver, brain, reproductive and central nervous system [4]. The presence of toxic pollutants in water sources has stimulated much attention in recent decades because of their potential to involve the environmental problems. Moreover, they lead to undesirable effects in the color, odor and taste of source waters [4]. Organic dyes are harmful to human beings, the need to remove color from wastewater Effluents become environmentally important. It is rather difficult to treat dye effluents because of their synthetic origins and mainly aromatic structures, which are biologically non-degradable. Among several chemical and physical methods, adsorption process is one of the effective techniques that have been successfully employed for color removal from wastewater. There are currently numerous treatment processes for effluent discharged from industrial processes containing dyes; amongst which we can mention biodegradation, chemical oxidation, foam flotation, electrolysis, adsorption, electro-coagulation and photocatalysis. However, all these treatment methods are costly, suffering from many restrictions and cannot be utilised by small industries to treat the wide range of wastewater [5]. Hence, adsorption process has been preferred for the treatment of the wastewater due to its cheapness, simple design and easy operation, less energy intensiveness, no effect by toxic substances and high quality of the treated effluents particularly for well-designed sorption processes [6][7]. Therefore, the major advantages of an adsorption system for water pollution control are less investment in terms of initial cost, simple design and easy operation, less energy intensiveness, no effect by toxic substances and greater removal of organic waste ingredients as compared to the conventional treatment methods[8].
1.1 STATEMENT OF THE PROBLEM
There exist some difficulties in the removingdyes at low concentration from wastewater, which is partly as a result of high cost of conventional methods. Therefore, there is a need for a more reliable and cheap method which is biosorption, which offers promise as an alternative for potentially economically attractive treatment.
1.2 AIMS AND OBJECTIVES
The aim of this study was to determine the biosorptive activity of almond shell in removing methylene blue (MB) from aqueous solution.
The objectives of the study are outlined below:
- To study the influence of contact time on the uptake of methylene blue (MB) by almond shell at different initial concentrations.
- Investigate the effect of adsorbent dosage on equilibrium adsorption of methyl blue at different concentrations.
- To investigate the effect of adsorbent dosage on dye removal efficiency of methyl blue onto almond shell at different concentrations.
1.3 SIGNIFICANCE OF THE STUDY
Environmental pollution caused by the release of a whole range of compounds, has a consequence of industrial progress, as well on human health. Hence, there is need for environmental cleanup. Adsorption is eco-friendly, reliable and also addresses the demerits of the conventional methods. Although using agricultural waste materials in environmental cleanup has been in practice for a while, yet, this research hopes to show the economical advantage of using almond shellas the activated carbon and its effectiveness in removing methylene blue dye from aqueous solutiononto fixed bed.
1.4 JUSTIFICATION OF THE STUDY
Although, there are numerous studies published on adsorption using batch processes. However, there’s paucity of information in regards to adsorption of methylene blue dyes onto activated carbon using almond shell.
1.5 LITERATURE REVIEW
1.6 Dye
Dye can be said to be coloured, ionising and aromatic organic compounds which shows an affinity towards the substrate to which it is being applied. It is generally applied in a solution that is aqueous. Dyes more used in industries such as food, pharmaceutical, cosmetic, printing, textile and leather industries. Synthetic dyes are easier and low cost in synthesis, firmness, more stable in light, detergent and microbial attack. Other than that, synthetic dyes are made in varieties of colour compared to natural colour[8].
Although dyes are useful, but it can be classified as problematic compounds because can pollute the environment otherwise it been treated nicely. Dye is water soluble and cannot be remove easily from the waste water although using biological wastewater treatment [9].Dye usually withstand to biological attack, light, heat and oxidation. According to [10]and [11], dye has very low concentration and need to remove before water can be discharged or disposal. There are two key of dye molecule which is the chromophores and auxochromes. Chromophores are use for produce the colour and auxochromes to give the molecule soluble in the water and increased affinity toward the fibres.
Figure 1.0: Chromophores and auxochromes in dye
Many types of dyes are poisonous and have carcinogenic and mutagenic effects that can affect aquatic lives and also humans being. The carcinogenic was prepared from known carcinogens such as benzene or other aromatic compound that might be formed as a result of microbial metabolism. Different dyes will have different chromophoric group. Besides, there is more than one type of dyes in the industries[12].
1.6.0Methylene Blue
Methylene blue, also known as methylthioninium chloride, is a medication and dye.[13] As a medication it is mainly used to treat methemoglobinemia. Specifically it is used to treat methemoglobinemia levels that are greater than 30% or in which there are symptoms despite oxygen therapy. It has previously been used for cyanide poisoning and urinary tract infections but this use is no longer recommended. It is typically given by injection into a vein.[14]
Common side effects include headache, vomiting, confusion, shortness of breath, and high blood pressure. Other side effects include serotonin syndrome, red blood cell breakdown, and allergic reactions.Use often turns the urine, sweat, and stool blue to green in color.While use during pregnancy may harm the baby, not using in methemoglobinemia is likely more dangerous.Methylene blue is a thiazine dye. It works by converting the ferric iron in hemoglobin to ferrous iron.
Methylene blue should not be confused with methyl blue, another histology stain, new methylene blue, nor with the methyl violets often used as pH indicators. Methylene blue is a heterocyclic aromatic chemical compound (a phenothiazine derivative) with the chemical formula C16H18N3SCl. At room temperature it appears as a solid, odorless, dark green powder that yields a blue solution when dissolved in water. The hydrated form has 3 molecules of water per unit of methylene blue. Methylene blue has a pH of 3 in water(10g/l) at 25 °C (77 °F).[15]
1.6.1 Methods of Dye Removal
Generally, dye is water soluble and has very low concentration. So, dye need toremove before water can be discharged or disposal by dye although this activity is very difficult. Otherwise, the environment and human body will be affecting by dye industries. Due to this problem, human now have concern on potential adverse effects to the chemical industry in environment. Hence, for protecting the environment and to meet the stringent government law, many researchers try to find out this problem. There are many ways to remove the dye, which are classified into three main categories namely physical, chemical and biological methods. All of them have advantages and disadvantages respectively. Considerable amount of research has been undertaken on the treatment to decrease the impacts of the environment[16] [17].
1.6.1.0 Biological Method
Biological treatment method can be defined as a process in which microorganisms such as bacteria are used to biochemically decompose the dye wastewater and stabilize the end of product [18]. Biological treatment methods usually more cheap and simple to apply and currently used toremove dye wastewater. Most of existing process includes an initial step of activated sludge treatment to remove the organic matters, follow by oxidation, membrane, activated carbon and so on[19].
Biological treatment methods that used for wastewater treatment can be classified into two types, which are aerobic and anaerobic method. The commonest treatment of wastewater has been based on aerobic biological process that involvedmainly conventional and extended activated sludge process. In activated sludge process, the wastewater flows into a tank after primary settling. The microorganism in activated sludge is suspended in the wastewater as aggregates. The operation of activated sludge process likes of mixing and stirring raw sewage with recycled by activated sludge[20].
Aerobic degradation of the pollution takes place by thoroughly mixing the purifying the microorganism to be treated. Then, the purified water and purifying sludge phases are separated. Meanwhile, an anaerobic process is an organism that does not need oxygen as based metabolism. There is an interest in anaerobic bacteria used for bioremediation of polychlorinated biphenyls (PCBs) in river sediments, chlorination of the solvent trichloroethylene (TCE), and chloroform [21].
Sometimes, aerobic and anaerobic processes have been use together or separately for the treatment of dye wastewater. Conventional biological treatment methods are not effective for removal dye because many commercial dyestuffs are toxic to organism being used and also because of low biodegradability of many textile chemicals and dyes.
1.6.1.1 Physical Method
Physical methods different also widely used, such as membrane-filtration processes (nanofiltration, osmosis relapse, electrodialysis) and adsorption techniques.Physical methods use strictly physical processes to improve or treat the wastewater and no gross chemical or biological changes. The major weaknesses of membrane processesis they have lifetimes limited before membrane cancel is happen and the periodic replacement cost must be became included in any their economic viability analysis. In line with enormous literature data, liquid phase adsorption is one of methods that most popular for pollutant isolation of material from wastewater since suitable design adsorption process will produce one high quality treat effluent. This process provides an alternative pulled to the treatment polluted waters, especially if sorbent inexpensive and does not require an additional pre-treated stepped before the application[22].
Adsorption is famous balance separation process and one of the effective processes for water purification applications. Adsorption has been found in order to be great for other techniques for deep water salvage in term of initial cost, flexibility and design moderation, operations facility, and not sensitive for toxic pollutants. It is an effective of lowering the concentration of solution in the effluent water. Adsorption also did not result in dangerous materials formation. Decolourisation is a result of two mechanisms that included adsorption and ion exchange, and is influenced by many physiochemical factors, such as, dye or material interaction, material surface area, particle size, temperature, pH, and contact time. Flotation also is a method of physical wastewater treatment processes. Flotation is used to remove suspended matter and to concentrate biological sludge. Flotation uses air exclusively as the floating agent so that particles can be removed faster and smoothly[23].
1.6.1.2 Chemical Method
Chemical treatment method is used the chemical reactions to achieved treatment. This chemical technique is often expensive, and although dyes are removed, concentrated sludge collection holds a disposal problem. There is also possible that oneis a secondary pollution problem will be submerged due to excess chemistry use. The most common using chemical treatment is chlorination. Chlorine is used to kill the bacteria which lead to decomposition of water and to decrease the rate of decomposition. It is important to note that chlorination will not remove toxic by products because it has already been produced. Coagulating chemicals in wastewater treatment is a conventional treatment method to remove of high turbidity and this is more consistent performance. This method is suitable to treat the water employed in dyeing. Metals that have more than one valence (e.g. lime and aluminiumsulphate) are some commonly used coagulants. The main advantage of the conventional coagulation is removal of the waste stream due to the removal of dye molecules from the dye bath effluent and not due to partial decomposition of dyes. Besides, disinfection involves in chemical treatment process. Disinfection with aggressive chemicals like chlorine or ozone is normally the last step in purifying water.Water is disinfected to destroy any pathogens which passed through the filters[24].
Chemical oxidation is the most commonly used method of decolourization by specific chemical to its simplicity. Chemical oxidation uses strong agents which are hydrogen peroxides, chlorine and others to force degradation of resistance organic pollutant. An advantage of oxidation is the volume of wastewater and sludge does not increase[25].
Physical and chemical treatment techniques are effective for dye removal but use more energy and chemicals substance than biological technique. They also focussed to the additional treatment disposal to treat liquid or solid pollution that through into the rivers[26].
1.7 Adsorption Method
Adsorption is a process of collecting soluble substances in a solution on asurface. In adsorption processes, one or more components of a gas or liquid stream areadsorbed on the surface of a solid adsorbent and a separation is accomplished. Thisseparation process use a solid phase with large surface area, which selectively retainsthe components to be separated. Adsorption is simple to apply and currently use for theremoval of wastewater and dye. For many industrial treatment applications, it hasproved to be the least expensive treatment option. Adsorption is particularly effective intreating low concentration waste streams and in meeting stringent treatment levels[26] [27].
The adsorbing phase is known as adsorbent and the material concentratedadsorbed at the surface of the phase is called adsorbate. Adsorption process is operative in natural physical, chemical, and biological systems. Adsorption operations with anactivated carbon and synthetic are widely used in industrial applications for thepurification of water and wastewater. In the bulk material, all the bonding requirementsionic, covalent or metallic of the constituent atoms of the material are filled. The exactnature of the bonding depends on the details of the species involved, which the processis generally classed as physisorption or chemisorption. In physisorption, adsorbedmolecules are held by the weaker Van der Waals’ forces [28].
Physisorption is generally considered to be an effective method for quickly lowering theconcentration of dissolved dyes in an effluent. For chemisorption, the moleculesundergo a chemical bonding with the solid molecules, and this attraction may bestronger than the forces holding the solid together [27].
The configuration of the adsorption system, which is the fluid (feed) and solid(adsorbent) are contacted, is divided into two main categories. There are batch andcolumn adsorption. Batch adsorption is often used for amount of quantities treated aresmall, as in the pharmaceutical. In this process, the volume of feed solution contact with a quantity of adsorbent in a vessel. For column adsorption, a column is used to hold the adsorbent in a fixed position. In column, adsorbate is always continuously in contact with an adsorbent thus providing the required concentration [29].
Mechanism of adsorption occurs in three steps. First step, the adsorbate diffuses from the major body of the stream to the external surface of the adsorbent particle.
Second step, the adsorbate migrates from the relatively small area of the external surface to the pores within each adsorbent particle. The bulk of adsorption usually occurs in these pores because there is the majority of available surface area. And final step, the contaminant molecules go to the surface in the pores[30].
Application of liquid-phase adsorption includes removal of organic compound from water or organic solution, coloured impurities from organic, and various fermentation products from fermentor effluence. While, application for gas-phase adsorption include removal of water from hydrocarbon gases, sulphur compounds from natural gas, solvents from air and other gases, and odours from air. However, solid can be a good adsorption if it has a surface composed of molecules which provide a good attractive force[31].
Recently, adsorption techniques have been considered due to their efficiency in the removal of pollutants that could not be achieved by conventional methods. Adsorption produces a high quality product, and is a process, which is economically feasible. Decolonization may be a result of two mechanisms: adsorption and ion exchange, and is influenced by many physico-chemical factors, such as, dye/adsorbent interaction, adsorbent surface area, particle size, temperature, pH and contact time[21].
On the basis of type of forces of attraction existing between adsorbate and adsorbent, adsorption can be classified into two types: Physical Adsorption or Chemical Adsorption which is also known as phsisorption or chemisorption.[14]
1.7.0 Physical adsorption or Physisorption
This type of adsorption results from the action of weak van der Waals forces. These are comprised of London dispersion forces and classical electrostatic forces that are related with interactions between the dipole moments of adsorbate and adsorbent molecules.
1.7.1 Chemical adsorption or Chemisorption
Chemical adsorption involves strong adsorbate-adsorbent interactions resulting in a change in the chemical form of the adsorbate. Here, the gas molecules or atoms are held to the solid surface by chemical bonds. The resulting chemisorptive bond is generally stronger than that derived from the physical van der Waals forces and is very similar in strength to a covalent bond. It is highly specific and occurs only if there is some possibility of chemical bonding between adsorbent and adsorbate. The bonds that form between solute molecules and specific surface chemical groups have all the properties of true chemical bonds and are characterized by relatively large heats of adsorption[32].
1.8 Adsorption mechanism
Biosorption mechanisms are complicated, and not fully understood. An extensive
literature exists which is concerned with the mechanism and modelling of biosorption referring to specific elements and microbial strains.[15,16] The key factors controlling and characterizing these mechanisms are:
- The type of biological ligands available for metal adsorption;
- The status of the biomass, i.e. living /non-living
- The chemical, stereochemical and coordination characteristics of the targeted metals and metal species
- The characteristics of the metal solution such as pH and the presence of competing co-ions.[17]
Biomass possesses an abundance of functional groups that can passively adsorb metal ions. The term adsorption can be used as a general term and includes several passive, i.e. non-metabolic, mechanisms such as: complexation; chelation; co-ordination; ion exchange and precipitation.
- Complexation
As noted above complex formation of metal ions with organic molecules involves ligand centres in the organic species. It is also referred to as the ability of the metal ion to form a complex with one functional group of the biomass present in solution.
- Chelation
Organic molecules containing more than one functional group with donor electron pairs can simultaneously donate these to a metal atom. This can result in the formation of a ring structure involving the metal atom a process termed ‘chelation’. Thus, chelation mechanism can be referred to as the ability of the metal to form a complex with two or more functional group of the biomass present in solution.
- Co-Ordination
Metal atoms have preferences for specific donor atoms (“hard/hard” “soft/soft”) and the stereochemical arrangements that play an important role in the binding with the available ligands on the biomass cell. Limited information of surface complexation models, based on the theory of surface co-ordination chemistry, is available to describe metal biosorption; however the preferences of the metal species should be considered to explain observed metal biosorption capacities and to elucidate biosorption mechanisms.
- Precipitation
This occurs as a result of the effect of pH.Biosorption researches so far proves that within the ranges of 1-6 biosorption is said to occur at a higher pH above 6, precipitation is said to occur i.e the metals are been precipitated out of solution instead of it been adsorbed on the surface of the biomass.
1.9 Adsorption technology
The research for the new technologies adsorption involving the removal of toxic metals from wastewaters has directed attention to biosorption, based on metal binding capacities of various biological materials. Biosorption can be defined as the ability of biological materials to accumulate heavy metals from wastewater through metabolically mediated or physiochemical pathway of uptake. The major advantages of biosorption over conventional treatment methods include low cost, high efficiency, minimization of chemical or biological sludge, no additional nutrient requirement, and regeneration of biosorbents and possibility of metal recovery. Agricultural materials mainly those containing cellulose and lignin show potential metal binding capacity. The basic components of the agricultural waste biomass include hemicelluloses, lignin, extractives, lipids, proteins, simple sugars, water hydrocarbons, and starch containing variety of functional groups that facilitates metal complexation or precipitation and which assists the heavy metals sequestration process.[18]
1.10Agro waste for adsorption
Agricultural wastes (AW) can be defined as the residues from the growing and processing of raw agricultural products such as fruits, vegetables, meat, poultry, dairy products and crops. Agricultural wastes can be in the form of solid, liquid or slurries depending on the nature of agricultural activities. Furthermore, agricultural industry residues and wastes constitute a significant proportion of worldwide agricultural productivity. Although the quantity of wastes produced by the agricultural sector is significantly low compared to wastes generated by other industries, the pollution potential of agricultural wastes is high on a long-term basis. However, agricultural waste has serve as a biosorbent for removing metals and dyes from waste water. Example of agro waste that have been used in biosorption study includeCationized sawdust, Compost sorbent, Maize waste, Orange peel, Peat, Polysaccharides, Red mud, Shale oil ash, Bottom ash, de-oiled soya, BagassFlyash, Blast Furnace Sludge, Clinoptilolite and Amberlite, Compost sorbent, Dried Activated Sludge, Fly Ash, Giant duckweed, Linseed Cake, Maize Waste, Natural Zeolite, Peat, Shale oil ash, Silk worm pupa, Chitosan, Coal based sorbent, Compost sorbent, Fly Ash Chitin, Eggshell membrane, Eucalyptus bark, Polysaccharides, Activated carbon, andSugar beet pulp
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