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Table of Contents
1.2 Physical Chemical Characteristics of molasses waste water
1.3 Problem statement
2 LITERATURE REVIEW
2.2 USES OF MOLASSES
2.3 Molasses waste water pigments
2.4 Post treatment methods for spent wash
2.6 Adsorption kinetic models
2.7 Equilibrium Isotherms
2.8 Derivation of freundlich equation
2.9 The Langmuir isotherm
2.10 Chitosan Biosorption
2.10.1 Sorption process on chitosan biopolymer
2.11 Powdered Activated Carbon
2.12 Types of Activated Carbon
3.1 Apparatus and Reagents
4 Experimental Results and Analysis
4.1 Calibration Analysis
4.2 Contact Time Comparison
a) Activated Carbon Data
4.3 Adsorbent Dose Comparison
a) Activated Carbon Data
4.4 PH Comparison
4.5 Concentration of Molasses Waste Water
4.6 Combination Dose
4.7 ADSORPTION ISOTHERM
4.8 Freundlich Isotherm;
4.9 Langmuir Isotherm
4.10 Freundlich Isotherm;
4.11 Langmuir Isotherm
5 Conclusion and Recommendation
Sugarcane molasses is the by-product of the sugar production industry which are generated during sugar production. Sugarcane molasses contains 50% fermentable sugar is dark brown, putrid and viscous liquid. Sugarcane molasses is a feedstock for ethanol production and is used in a ratio of 1:1 for fermentation and purification of spirit. The product collected as bottom products form spent wash which is the major constituent of molasses waste water.
Properties of molasses include high acidity, strong odor, coloring pigments due to presence of melanoidins, metal sulfides and phenolics giving it brown color. Spent wash is one of the serious pollution problems of countries producing alcohol from fermentation and subsequent distillation of cane molasses. According to (Prakash, Vimala, & Sitarama, 2014) distillery spent wash is characterized as one of the caramelized and recalcitrant wastes containing extremely high Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), inorganic solids and low in pH 1-2. The post methanation distillery effluent produced from treatment is characterized by high BOD, COD, intense brown colour due to presence of melanoidin pigments and high levels of salts and nutrient rich.
The biomethanation of distillery waste effluent under anaerobic conditions brings down it BOD from 50,000mg/l to 8000mg/l, due to their high organic load post treatment is needed. If these effluents are discharged to water streams the suspended solids present in the effluent impart turbidity in water, reduce light penetration and impair biological activity of aquatic life. Hence an economic viable and environmental friendly method is needed to dispose and handle large volumes of post methanation distillery effluent
1.2 Physical Chemical Characteristics of molasses waste water
The physical-chemical properties of concern for post treatment of molasses spent wash include;
The distillery waste water contains dark brown colored recalcitrant organic compounds that are not amenable to conventional biological treatment. The degree of discoloration is related primarily to pH and temperature. The discoloration in molasses increases three fold for every 10°C rise in processing temperature. The colour of spent wash is dark brown due to presence of a derivative of caramelized sugar formed during distillation, termed as melanoidin and melanins. The two compounds structure are not known and are thought to be nitrogen containing groups according to (Moletta, 2005). The compounds are described below briefly;
a. Melanoidin: - is formed by Maillard reactions which are initiated by condensation of an amine with a carbonyl group, often from a reducing sugar. The structural determination of melanoidines has remained a challenge for several years. A wide range of reactions takes place in the formation of melanoidin and include cyclizations, dehydrations, retroadolizations, rearrangement and further condensations, leading to formation of brown co polymer. The melanoidins formed are recognized as being acidic in nature. As reaction time and temperature increases, total carbon content increases, thus promoting the unsaturation of molecules. The colour intensity increases with the polymerization degree, as measured via absorbance spectrometer.
b. Melanins: - they are polyphenol oxidases with a copper active group. When exposed to air it introduces the oxidation of various aromatic compounds (pyrocatechol, tyrosine) and produces blackish-grey discoloration. This reaction known as melanin formation requires only the enzymatically catalyzed oxidation for its initiation and proceeds as a chain reaction passing through red and red brown intermediate stages to orthoquinone like compounds.
Odor of distillery effluent is offensive, odorous compounds from distillery waste water consist mainly volatile fatty acids such as butyric and valeric acid have a high color index. Distillery has distinct organic composition, the anaerobic bacteria ferment these compounds and generate the volatile fatty acids for example glycerol is fermented to butyric acid by clostridium butyricum.
The pH of raw spent wash is acidic in value with a mean pH value ranging between 3.5 to 5.1. This is due to presence of melanoidines and caramel compounds.
- Electrical conductivity
The spent wash has an electrical conductivity of 8388-16450mS this is due to presence of metal cations like potassium and potassium in the spent wash.
- Chemical Oxygen Demand
Theoretical values of Chemical Oxygen Demand are high ranging between 54164128000 mg/l
- Biological Oxygen demand
Theoretical values of Biological Oxygen Demand range between 32300-43000mg/l
Table 1.1 Agrochemical and food company spent wash from distillery
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Impacts of distillery waste on the environment
1. Color and odor of effluent of distillery is red brown in color with unpleasant color odor of indol and sketol compounds. This dark colour increases water turbidity and makes water unsafe for domestic or agricultural use.
2. Industrial waste water changes pH of receiving water body. These changes affect ecological aquatic systems, which may become too acidic for fish and plant life.
3. Total suspended solids in waste water reduce the light penetration, this affects plants activity due to less sunlight being received and these solids may clog the gills of fish.
4. High amount of BOD in waste water leads to decomposition of organic matter under the anaerobic condition that produces highly objectionable products including methane, ammonia and hydrogen sulphide gas.
5. Spent wash has many mineral cations including potassium, calcium, magnesium and calcium, when dumped in moving water increases water hardness which may lead to fouling of process equipment when used as process water in downstream industries.
1.3 Problem statement
Many sugar industries and alcohol distillery plants handling molasses are faced with the problem of treating molasses waste water. This is due to presence of compounds like melanoidin and caramel compounds which cannot be treated by conventional system of water treatment like aerobic and anaerobic systems.The properties of these compounds include highly acidic, strong odor coloring pigments due to presence of melanoidin, metal sulfides and phenolics giving its brown color. Spent wash contains 2% melanoidin which is formed by maillard reaction between amino acids and sugars.
Melanoidin has high molecular weight and is non-biodegradable and if release to rivers and other water bodies it hampers the photosynthesis process by blocking sunlight and also contains toxic components which affects aquatic plants and animals. This research is evaluating a way of using physical chemical methods of treatment i.e use of adsorption method by applying a combination of chitosan an emerging biopolymer and powdered activated carbon a known adsorbent to remove the colour pigments and adsorb metals present thus also solving the problem of high COD in the waste water.
- Perform and utilize a thorough literature review on odors, color removal and COD reduction in treatment of molasses waste water combining with Chitosan and powdered activated carbon adsorbent.
- Development of a bench-scale testing protocol that stimulate full scale molasses waste water treatment to assess chitosan-powdered activated carbon performance is color, odor removal as well as COD reduction.
2 LITERATURE REVIEW
The term 'molasses' is applied to the final effluent obtained in the preparation of sugar by repeated crystallization. The amount of molasses obtained and its quality provide information about the nature of the cane and the processing in the sugar factory, such as the efficiency of the juice clarification, the method of crystallization during boiling, and the separation of the sugar crystals from the low-grade massecuite.
Molasses is one of the major co-products of sugar processing. It comes out of the last boiling evaporator in a triple effect evaporator. Molasses is a heavy, viscous, dark brown liquid consisting mainly of sucrose, water, reducing sugars and other organic compounds. It forms about 3% weight of cane processed.
2.2 USES OF MOLASSES
A. Production of alcohol from molasses
Molasses is widely used as a feedstock in bioethanol. Alcohol is produced from molasses combined with the manufacture of yeast. The manufacture of ethanol from molasses is composed of these 4 main steps;
i. Feed preparation
Molasses is diluted to about 20-25 brix in order to obtain desired sucrose level and pH is adjusted to below 5 using sulfuric acid before fermentation. It is then supplemented with assimilable nitrogen source like ammonium sulfate or urea. If necessary, it is also supplemented with phosphate.
The composition of molasses varies with the variety of cane, the agro climatic conditions of the region, sugar manufacturing process, handling and storage.
In general, yeast culture ( Saccharomyces cerevisiae ) is prepared in the laboratory and propagated in a series of fermenters. The feed is inoculated with about 10% by volume of yeast inoculum. This is an anaerobic process carried out under controlled conditions of temperature and pH. Sucrose is broken down to ethanol and carbon dioxide. Fermentation can be carried out in either batch or continuous mode. Ethanol accumulates up to 8-10% in the fermented mash. The fermented mash is then distilled, fractionated and rectified after the removal of yeast sludge. The residue of the fermented mash which comes out as liquid waste is termed as distillery slop or spent wash.
Distillation is a two-stage process and is typically carried out in a series of bubble cap fractionating columns. The first stage consists of the distillation column and is followed by rectification columns. The cell free fermentation broth is preheated to about 90OC by heat exchange with the effluent ("slop'') and then sent to the degasifying section of the distillation column. Here, the liquor is heated by live steam and fractionated to give about 50% alcohol. The wastewater discharge from the distillation column is the slop. The alcohol vapors are led to the rectification column where by reflux action, 95 -97% alcohol is tapped, cooled and collected. The condensed water from this stage, known as "spentlees'' is usually pumped back to the distillation column.
Rectified spirit is marketed directly for the manufacture of chemicals such as acetic acid, acetone, oxalic acid and absolute alcohol. Denatured ethanol for industrial and laboratory uses typically contains 60- 95% ethanol as well as between 1% to 5% each of methanol, isopropanol, methyl isobutyl ketone (MIBK), ethyl acetate.
B. Production of glycerin from molasses
In normal alcoholic fermentation, about 3% of the weight of the sugar is converted into glycerin, which thus represents theoretically a by-product. In weak alkaline solution the fermentation can be guided in such a manner that glycerin and acetaldehyde are the predominant products, together with alcohol and carbon dioxide.
C. Molasses as Additive to Silage
Molasses is added directly to animal fodder, i.e. by mixing it into the basic fodder or into commercial feeds, molasses has special importance as a safety additive in the preparation of fermented feeds, the so called silage. Sugar-containing food supplements increase the concentration of fermentable carbohydrates and provide the indispensable nutrients to the lactic acid bacteria, so that they grow rapidly and produce adequate amounts of lactic acid.
2.3 Molasses waste water pigments
In general colourants can be divided into enzymatic colourants such as melanins and non-enzymatic colourant such as melanoidin, alkaline degradation product of hexoses and caramel according to (Jiranuntipon, 2009). Cane molasses contains around 2% of melanoidins that imparts colour to the effluent. There is high concentration of sulphate also in sugarcane molasses, which is added to molasses during the cleaning of sugar crystals. High level of sulfate can lead to the production of sulfides in anaerobic digestion of the effluent, these precipitate out along with the existing metal as metallic sulfides in Post Methanated Distillery, consequently increasing the total solid (TS) of effluent.
Some of the process colourants that contaminate the spent wash include;
- Phenolics are plant pigments, low molecular weight, may be attached to polysaccharides, pH sensitive, darker at high pH, pale yellow to arrange colour, reacts with iron to produce very dark colour, may dimerise or oxidize to form darker colour.
- Caramel is a process colourant, formed by thermal degradation of sugar. It has high molecular weight and low net charge.
- Alkaline degradation product of fructose is a process colourant that is reddish to dark brown in colour. It has low molecular weight depending on the degree of degradation.
- Melanoidin is the most important colorant since it occurs in the highest percentage in the spent wash. It is a browning reaction products of sugars and amino acids they have a high molecular weight.
- Sulfide this is a process colourant obtained from sulfite added to sugar, as a decolourising agent. It is toxic to microorganisms since it reacts forming hydrogen sulphide gas that has a strong foul smell. It forms strong bonds with metals.
- Heavy metals these are process colourants that are toxic to microorganism, plants and animal life
2.4 Post treatment methods for spent wash
Spent wash which is our product of concern after aerobic and anaerobic treatment can be treated by a variety of physical-chemical methods and biologically by bacteria and fungi to reduce the chemical oxygen demand, the heavy metal contaminants, the dark brown colour and the bad odor in the waste water sample. These methods are;
Biological treatment of molasses wastewater is either aerobic or anaerobic but in most cases a combination of both is used. Anaerobic treatment is an accepted practice and various high rate reactor designs have been tried at pilot and full scale operation. Aerobic treatment of anaerobically treated effluent using different microbial populations has also been explored. Majority of biological treatment technologies remove color by either concentrating the color into sludge or by partial or complete breakdown of the color molecules. The systems are described for anaerobic and aerobic treatment as follows;
1. Anaerobic systems
Anaerobic digestion is viewed as a complex ecosystem in which physiologically diverse groups of microorganisms operate and interact with each other in a symbiotic, synergistic, competitive or antagonistic association. In the process methane and carbon dioxide are generate. According to (Patil & Khandeshwar, 2014) processes have been sensitive to organic shock loadings, low pH and showed slow growth rate of anaerobic microbes resulting in longer hydraulic retention times. The anaerobic system commonly employed is the Upflow anaerobic sludge blanket reactors (UASB).
- Upflow anaerobic sludge blanket reactors systems according to (Bailey, Hansford, & Dold, 1994) belong to the category of high rate anaerobic wastewater treatment and hence it is one of the most popular and extensively used reactor designs for treatment of distillery wastewaters globally. The success of UASB depends on the formation of active and settleable granules. These granules consist of aggregation of anaerobic bacteria, self-immobilized into compact forms. This enhances the settelability of biomass and leads to an effective retention of bacteria in the reactor. Particularly attractive features of the UASB reactor design include its independence from mechanical mixing, recycling of sludge biomass and ability to cope up with perturbances caused by high loading rates and temperature fluctuations
2. Aerobic systems
Anaerobically treated distillery wastewater still contains high concentrations of organic pollutants and then cannot be discharged directly. The partially treated spent wash has high BOD, COD and suspended solids and must be treated in aerobic reactors. It can reduce the availability of essential mineral nutrients by trapping them into immobilized organic forms, and may produce phytotoxic substances during decomposition. Stringent regulations on discharge of colored effluent impede direct discharge of anaerobically treated effluent. Therefore, aerobic treatment of sugarcane molasses wastewater has been mainly attempted for the decolorization of the major colorant, melanoidins, and for reduction of the COD and BOD. A large number of microorganisms such as bacteria, cyanobacteria, yeast and fungi have been isolated in recent years and are capable of degrading melanoidins and thus decolorizing the molasses wastewater. The aerobic method listed here is the most popular system and is;
- Activated sludge process
The most common wastewater treatment is the activated sludge and it is studied considerably by (Gupta, Sunil , & Gurdeep, 1998). The treatment system consisted of a primary settling tank, an intermediate retention trough, two storage tanks and an aerobic treatment tank. A startup period of 7 days was given to the aerobic reactor and the system resulted in 93% COD and 97.5% BOD removal. The activated sludge process and its variations utilize mixed cultures
Phytoremediation of effluents (Ayub & Usmani, 2010)is an emerging low cost technique for removal of toxicants including metals from industrial effluents and is still in an experimental stage. Aquatic plants have excellent capacity to reduce the level of toxic metals, BOD and total solids from the wastewaters carried out the treatment of distillery effluent in a constructed wetland which comprised of four cells. This treatment eventually led to 64% COD, 85% BOD, 42% total solids and 79% phosphorus content reduction.
4. Fungal systems
Increasing attention has been directed towards utilizing microbial activity for decolorization of molasses wastewater. According to reports by (Asthana, Mishra, Chandra, & Guru, 2001)have indicated that some fungi in particular have such a potent. One of the most studied fungus having ability to degrade and decolorize distillery effluent is Aspergillus such as Aspergillus fumigatus G-2-6, brought about an average of 69-75% decolorization along with 70- 90% COD reduction.
The phenomenon where by atoms or molecules (substances) get attached to a surface is called adsorption. Adsorption operations exploit the ability of certain solids to preferentially concentrate specific substances from the fluid phase onto their surfaces. Among the physical chemical treatment methods, adsorption of activated carbon is the most widely employed method for removal of color and specific organic pollutants. Adsorption of an adsorbate from a solution is caused by physical and chemical forces. Adsorption as a result of physical forces mainly van der Waals forces is known as physisorption. It occurs as a result of van der Waals and electrostatic attraction between an adsorbate and the atoms conforming the adsorbent surface. While chemisorption involves electron transfer between solids and liquid phases. Adsorption from solution occurs because of differences in concentration of the solution, and in the adsorbent pore. The mechanism of adsorption includes 5 major steps and they include;
i. The molecule to be removed migrates from bulk of solution to liquid boundary layer due to difference in concentration gradient between bulk liquid and the film surrounding the adsorbent particle. This is governed by Frieundlich/Langmuir equations isotherms. The capacity of an adsorbent for a particular adsorbate involves the interaction of these properties, namely the concentration C, of the adsorbate in fluid phase, the concentration Cs of the adsorbate in the solid phase and the temperature T of the system.
ii. The molecule has to migrate through the surface film of the particle to reach to its outer surface. The film encounters a resistance known as mass transfer film coefficient, this resistance determines the rate at which it can reach the surface of the particle.
iii. The molecule now has to diffuse through the particle surface to the active sites of the adsorbent. This diffusion is against a resistance known as internal mass transfer coefficient, it slows the molecule motion to access the active size of particle.
iv. The molecule is now adsorbed by the active site, and for it to be adsorbed will depend on its ionic charge and number of active sites remaining. The more the active sites the higher the rate of adsorption of molecules.
v. The final stage is Desorption, desorption is the reverse of adsorption and its main objective is the removal of the adsorbed constituent from the adsorbent in what is commonly known as regeneration of adsorbent. This enables one to recover the adsorbent materials for future reuse in case of using a contactor
The most commonly used adsorbent are granular activated carbon, powdered activated carbon, zeolite, alumina, bone char and newer adsorbents like metal oxides and chitosan.
2. Oxidation Process
This method employs a powerful oxidant for discoloration of molasses pigments and destabilization of melanoidines present in waste water. The most commonly used is ozonation method (Prakash, Vimala, & Sitarama, 2014) and to a lesser extent the Fenton's method. Ozone is a powerful oxidant for waste water treatment. Once dissolved in water, ozone reacts with a great number of organic compounds in two different ways; by direct oxidation as molecular ozone or by indirect reaction through formation of secondary oxidants like free radical species, in particular the hydroxyl radicals. Oxidation by ozone can achieve 80% decolourization for biologically treated molasses waste water with chemical oxygen reduction of 1525%. However the limitation of ozone is that it only transforms the chromophore groups but does not degrade the dark colored polymeric compounds in the effluent.
The Fenton's oxidation technology according to (Raghu & Gaikwad, 2001) is based on the production of hydroxyl radicals OH, which has an extremely high oxidation potential. Fenton's reagent, which involves homogeneous reaction and is environmentally acceptable, is a mixture of hydrogen peroxide and iron salts (Fe2+or Fe3+) which produces hydroxyl radicals which ultimately leads to decolourization of the effluent.
3. Coagulation and Flocculation
Coagulation is the destabilization of colloids by neutralizing the forces that keep them apart. Cationic coagulants provide positive electric charges to reduce the negative charge of the colloids, as a result the particles collide to form large particles called floccs. Flocculation is the action of polymers to form bridges between the floccs and binds the particles to form agglomerates or clumps. Bridging occurs when the segment of the polymer chain adsorb on different particles and help the particles aggregate. Generally coagulation is an expensive method considering the chemical coagulants used that cannot be regenerated and the cost of sludge disposal. Commonly used coagulants include; aluminium sulphate, poly aluminium chloride, ferric chloride and poly ferric sulphate.
4. Membrane Treatment
Pretreatment of molasses waste water with ceramic membranes prior to anaerobic digestion was reported to halve the Chemical Oxygen Demand from 36000 to 18000mg/l, (Chang et al. 1994). The total membrane area was 0.2m2 and the system was operated at a fluid velocity of 6.08m/s with 0.5 bar transmembrane pressure. Electrodialysis has been explored for desalting molasses wastewater using cation/anion exchange membranes resulting in 50-60% reduction in potassium content. According to recent study by Nataraj et al (2006), reported pilot trials on distillery spent wash using a hybrid of nano filtration and reverse osmosis process. Nano filtration was primarily effective in removing the color and colloidal particles accompanied by 80% and 45% reduction in total dissolved solids and chloride concentration respectively operating at an optimum pressure of 30-50 bars.
Chitin is the world's second most abundant naturally occurring polysaccharide. Much of this occurs as a significant component in the shells/exoskeletons of crustaceans. Due to its widespread abundance, its chemical and physical versatility, and the problems of its disposal as a waste material, a wide range of value-added applications of chitin and chitosan is being initiated, investigated, and developed. Chitin and its derivative, chitosan, both highly stable and difficult to degrade materials, can be obtained as 10-20% w/w from the waste seafood shells by suitable chemical processing.
Chitosan (Rinaudo, 2006) is the deacetylated form of chitin, and this process produces a chain of amino groups along the chitosan structure. Many researchers are now looking at the ability of this amino group to adsorb metal ions from industrial wastewaters and leachates.
Uses of Chitosan
I. Medical uses:-due to its enhanced healing properties, chitosan has stimulated research into uses for cuts and abrasions; studies to produce chitosan fibers for such uses and medical stitches have been carried out, but to date the fibers are quite friable. Materials suitable for burn dressings, artificial skin grafting, bandages, and medical sponges are being developed. Optical applications are being developed and tested, including eye humor fluids and the use of the flexible polymeric films/membranes for contact lenses. The use of chitosan for blood cholesterol control is under investigation, as is its use in the production of artificial blood vessels.
II. Agriculture uses:-due to its permeability and its ability to form flexible protective membranes, chitin has been used as a seed coating, leaf coating, and a hydrophonic fertilizer.
III. Food Industry:-Its uses in the food industry include food preservatives and biodegradable packaging. A major application in the food/health care products area includes the development and extremely rapidly growing market to incorporate chitosan as a significant ingredient in weight loss products or fat reducers.
IV. Chemical industry:- chitosan has been used as a basic raw material for the production of a number of selective high-value-added products including glucosamine and glucosamine sulfate, oligosaccharides and chitosan derivatives
V. Waste Management: - Most interest and research, however, have been generated by the ability of chitosan to remove metal ions from wastewaters by the process of adsorption. Adsorption is the ability of certain solids to selectively concentrate solute from solution onto their surface. Chitosan has demonstrated the potential to adsorb significant amounts of metal ions, and this has generated a large amount of interest in assessing its feasibility to remove metal ions over a wide range of effluent systems and types including that of organic compounds like melanoidins.
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- Jan Hendriok (Autor:in), 1998, Die Bundeswehr in der Demokratie - Funktion, Ziel und Inhalt der Inneren Führung, München, GRIN Verlag, https://www.grin.com/document/97858