INTRODUCTION:

A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs. They are capable of being shaped or molded. Plastics are strong, light-weighted, and durable. However, they are disadvantageous as they are resistant to degradation, leading to pollution, harmful to the natural environment.

The successful production and marketing of biodegradable plastics will help alleviate the problem of environmental pollution. In the past 10 years, several biodegradable plastics have been introduced into the market. However, none of them is efficiently biodegradable in landfills.

Bioplastics or organic plastics are a form of plastics derived from renewable biomass sources, such as vegetable oil, corn starch, pea starch, or microbiota, rather than fossil-fuel plastics which are derived from petroleum. Some, but not all, bioplastics are designed to biodegrade.

Biodegradable plastics (Bioplastics) are natural biopolymers that are synthesized and catabolized by various organisms. These materials do not cause toxic effects in the host and have advantages over petroleum-derived plastic.

Plastics are the most widely used materials for the production of various consumer products because of their cost, durability and resistance to degradation. They have become a major part of many of the components which we use in our daily life. Plastics play a major role in packaging in almost all industries by replacing glass and paper. Due to uncontrollable increase in the population and a need to adopt cheaper ways, non-degradable materials have gained enormous importance in past few decades. But, as plastics are disposable and non-degradable, their accumulation in environment has become a major problem.

Synthetic plastics not only take several long years for degradation, but also release toxic chemicals during the process. These concerns paved way to dig out mechanisms to produce plastics that are readily degradable and are gaining attention as “Eco-friendly plastics”. In this process, there took place discoveries of a wide range of microbial species which can synthesize plastics and some which can degrade them.

Historical perspective on production of Bioplastics:

Singh and Parmar (2011) utilized the biodiversity of bacteria to isolate various species from different environments and screen them for their ability to produce PHB. Sixteen unknown samples were collected, assayed and compared with known bioplastic producers (Ralstonia, Bacillus and Pseudomonas). Conditions were extensively optimized by varying the temperature, carbon, nitrogen and substrate sources for maximal PHB production. Presence of accumulation of PHB in these strains was confirmed by microscopic staining.

Chaijamrus and Udpuay (2008) have studied the accumulation of PHB granules in the cells of Bacillus megaterium was significantly depended on the ratio of C-source and N-source in the medium culture. Sugarcane molasses (MOL) and corn steep liquor (CSL) were used as renewable raw materials, since they were rich in carbon and nitrogen respectively, leading to develop a low cost process of PHB production. The highest PHB production was observed after 45h of growth (43% w/w, dry matter) when 4% molasses and 4% CSL were used, whereas the highest biomass (7.2 g/l) was obtained at 4% molasses and 6% CSL. This indicated that bacterial growth increased as CSL concentration increased, whereas the PHB accumulation decreased. The formation rate of PHB up to 0.016 h^-1and specific growth rate up to 0.25 h^-1 were observed during growth. The chemical structure and thermal properties of PHB produced from molasses and CSL were obtained the same properties as commercial PHB, except for the higher molecular mass (approx. 3.9 x 106 Da) and the lower degree of crystallinity (60% XC).Thus, the present data indicate that molasses and CSL could be alternatively used for PHB production by this bacterium with high PHB content and adequate properties of biopolymer from a low cost process.

Gouda et al. (2001) used cane molasses and corn steep liquor, two of the cheapest substrates available in Egypt to reduce the cost of producing such biopolyesters. The effect of different carbon sources was studied and maximum production of PHB was obtained with cane molasses and glucose as sole carbon sources (40.8, 39.9 per mg cell dry matter, respectively). The best growth was obtained with 3% molasses, while maximum yield of PHB (46.2% per mg cell dry matter) was obtained with 2% molasses. Corn steep liquor was the best nitrogen source for PHB synthesis (32.7 mg per cell dry matter), on the other hand, best growth was observed when ammonium chloride, ammonium sulphate, ammonium oxalate or ammonium phosphate were used as nitrogen sources.

Sayed et al. (2009) investigated batch and two-stage batch culture of Ralstonia eutropha and Alcaligenes latus for producing the intracellular bioplastic poly-β-hydroxybutyric acid (PHB) using shake flasks technique. The highest growth and PHB production of Ralstonia eutropha and Alcaligenes latus were recorded on medium containing glucose or sucrose (as a carbon source), respectively. Ammonium sulfate was the best nitrogen source for PHB production by both strains. The productive medium which contains carbon source and ammonium sulfate in C/N ratio of 12.57 gave the highest PHB either by Ralstonia eutropha and Alcaligenes latus. Applying the two stage batch fermentation with nitrogen limitation increased the PHB content (%) of R.eutropha and A.latus cells about 48.43 % and 14.29 %, respectively.

Guocheng et al. (2001) investigated the continuous production of PHB in a two-stage continuous culture system. The ﬁrst-stage produced cell mass giving the maximal cell dry weight of 27.1 g l^-1at 0.21 h^-1 of dilution rate. High speciﬁc cell growth rate results in the decrease of PHB synthesis under glucose-limited and nitrogen-rich conditions in the ﬁrst-stage. The second-stage produced PHB giving the maximal PHB concentration of 47.6 g l^-1 at 0.14 h^-1 of dilution rate. Speciﬁc PHB synthetic rate reached highest value at low dilution rate under nitrogen-limited condition in the second-stage, and decreased with the increase of ammonium concentration in the culture. In the continuous culture system, the maximal PHB productivity could reach 1.43 g l^-1h^-1at a dilution rate of 0.12 h^-1, but with relatively low PHB content of 47.6%. Maximal yield of PHB on glucose could reach 0.36 g g^-1 glucose at 0.075 h^-1 of dilution rate with relatively high PHB productivity of 1.23 g l^-1h^-1 and PHB content of 72.1%.

Santhanam and Sasidharan (2010) screened the effect of different nutrient conditions on production of PHA by Alcaligens eutrophus, Alcaligens latus and Pseudomonas oleovorans and characterized. The influence of different carbon sources on PHA production showed that, medium with glucose as carbon source produced the maximum PHA content of 4.14 g/l from A. eutrophus. P. oleovorans produced 2.06 g/l from n-octane as carbon source. The functional groups of the extracted PHA granules were identified as C=O group by fourier transform infrared (FTIR) spectroscopy analysis. Biodegrability studies showed that, the PHA produced is degradable by a number of soil microbes making it an ideal environmentally friendly material for regular human use.

Haas et al. (2008) showed that saccharified starch can be used as a viable alternative carbon source in high cell density PHB production. Using Ralstonia eutropha NCIMB 11599 with phosphate limitation, 179 g/l biomass, 94 g/l PHB, Y_biomass_/starch = 0.46 g/g, Y_PHB/starch= 0.33 g/g, and PHB productivity = 1.47 g/ (l*h) were achieved. Residual maltose accumulated in the fed-batch reactor but caused no noticeable inhibition. Performance with saccharified starch was virtually identical to that with glucose.

Naheed et al. (2012) carried out research was conducted to check the cane molasses as a media for the production of polyhydroxybutyrate (PHB). Out of the 54 bacteria isolated from three types of organic waste contaminated environments, two were selected for their highest intensity of fluorescence under UV by Nile blue A viable colony staining method and they produced maximum amount of PHB from glucose (66.61±0.05% and 76.92±0.04%) in a shake flask culture at pH 7.0, 37°C and 150 rpm. The best growth and polyhydroxyalkanoates (PHA) production was observed in media with 2% molasses and 0.2% ammonium sulphate in mineral medium.

Fernanda et al. (2006) studied among a wide variety of polyhydroxyalkanoates, bacterial biodegradable polymers known as potential substitutes for conventional plastics. This work aimed at evaluating the use of enzymes to recover and purify the PHB produced by Ralstonia eutropha DSM545. Screening experiments allowed the selection of trypsin, bromelain and lysozyme among six enzymes, based on their efficiency in lysing cells of a non-PHB producing R. eutropha strain. The best result was achieved with 2.0% of bromelain (enzyme mass per biomass), equivalent to 14.1 U ml⁻¹, at 50 °C and pH 9.0, resulting in 88.8% PHB purity.

Yoga et al. (2010) discussed economical strategies to reduce production costs of PHA as well as its applications in various fields as the selections of suitable bacterial strains, inexpensive carbon sources, efficient fermentation and recovery processes are important aspects that should be taken into consideration for the commercialization of PHA.

Boonsawang and Thongchai (2008) optimized polyhydroxyalkanoate production from palm oil fiber by Ralstonia eutropha using response surface methodology. The effects of propionic acid, butyric acid, (NH4)₂SO₄ and K₂HPO₄ addition were examined. The result showed that the nutrient optimum for PHA production was fermented broth with nutrient addition (2.50 g/l propionic acid, 6.53 g/l butyric acid, 1.53 g/l, (NH4)2SO4 and 0.03 g/l K2HPO4). The cell concentration, PHA concentration, and PHA content were 1.53 g/l, 0.70 g/l and 46.5%, respectively.

Ramadas et al. (2009) have done optimization studies on production of Poly (β- hydroxyl) butyrate using Central Composite Design. They have optimized three parameters namely inoculum age, pH and substrate concentration. On the basis of results obtained from “one variable at a time” experiment, inoculum age, jackfruit seed hydrolysate concentration, and pH were selected for response surface methodology studies. Analysis of variance exhibited a high coefficient of determination (R₂) value of 0.910 and 0.928 for biomass and PHB concentration, respectively, and ensured that the quadratic model with the experimental data was a satisfactory one. The data used in our wok was taken from this paper and further optimized using Artificial Neural Networks and Simulated Annealing.

Chisti et al. (1999) have studied fermentation optimization for the production of poly (b-hydroxybutyric acid) microbial thermoplastic. Batch culture of Alcaligenes latus was investigated for producing the intracellular bioplastic poly (β-hydroxybutyric acid) (PHB).A central, composite experimental design (RSM) was used to optimize the productivity of PHB. Investigated were the effects of temperature, the initial culture pH, the ionic strength of the medium, the concentration of trace elements, the type of nitrogen source, and the carbon-to-nitrogen ratio. The optimal temperature for growth and PHB synthesis appeared to be 33°C; an initial pH value of 6.5 gave the best results. Typical culture characteristics were: 0.075/h maximum specific growth rate, 0.38 g/l h maximum specific sucrose consumption rate and 0.15 g/l h maximum specific PHB production rate.

Shahhoseini and et al. (2003) worked on “Simulation and Model Validation of Batch PHB producton process using Ralstonia eutropha”. They have used Mulchandani Kinetic model using MATLAB for optimization of the yield.

Synthesis of bioplastics:

It is possible to make biodegradable plastics from sugars and organic acids using bacteria. One procedure is similar to the fermentation process, that produces ethyl alcohol, except that the bacteria used. Alcaligenes eutrophus, converts feed material into plastic material known as polyhydroxybutyrate-valerate, or PHBV. The bacteria accumulates the PHVB as a store of energy in the same way that animals and humans accumulate fat. When the bacteria have accumulated up to 80% of their dry body weight as PHVB, the cells are burst open with steam and the plastic is collected. The product is reported to have been made by Imperial Chemical Industries, Ltd. In Great Britain at a cost of $15 a pound, compared to less than a $1 a pound for common plastics.

How is PLA made ?

Lactic acid can be produced by two different routes. By petrochemical feed stock and fermentation. The most popular route is fermentation in which corn starch is converted into lactic acid by bacterial fermentation using a optimized stains of genus lactobacillus.

The starting material for poly lactic acid is starch from a renewable resource such as corn. Corn is milled , which separates starch from the raw material. Unrefined dextrose is then processed from the starch. Dextrose is turned into lactic acid using fermentation, similar to that used by beer and wine producers. Turning the lactic acid into a polymer plastic takes some specialized chemistry. Through a chemical process called condensation, Two lactic acid molecules are converted into one cyclic molecule called lactide. This lactide is purified through vaccum distillation. A solvent free melt process causes the ring shaped lactide polymers to open and join end to end to form long chain polymers. A wide range of products that vary in molecular weight and crystallinity can be produced allowing the poly lactic acid to be modified for a variety of applications Materials such as a polyhydroxy alkanoate (PHA) biopolymer are completely compostable in an industrial compost facility. Polylactic acid (PLA) is another 100% compostable biopolymer which can fully degrade above 60C in an industrial composting facility. Fully biodegradable plastics are more expensive, partly because they are not widely enough produced to achieve large economies of scale.

Certain additives when added to conventional plastics attract the microbes to the molecular structure by allowing the hydrocarbons to be sensed once again by microbial colonies. When oil is in the ground, the microbes attach themselves onto the hydrocarbons consuming the oil and creating natural gas, 50% of which is methane gas. When the oil is cracked 4% is used for the plastic industry, if the plastic industry did not use this 4% the 4% would be considered waste and be thrown away or removed and dumped into a waste disposal facility, another 4% is used in the generation of your consumer product. During this phase of cracking the organic compound which attracts the microbes to the molecular structure of the plastic is burnt out. The organic compound which is burnt out and other proprietary compounds which increase quorum sensing of the microbes and pH balance for the microbes are placed into the molecular structure of the plastic, to create a plastic product that can biodegrade 100 times faster than normal plastic.

Bacteria used for production of various kinds of PHA:

Strains	PHA type	Substrates	PHA content (wt %)
Alcaligenes latus DSM 1124	P(3HB)	Soya waste, malt waste	33, 71
Bacillus megaterium	P(3HB)	Beet molasses, date syrup	~50
Burkholderia sp. USM (JCM 15050)	P(3HB)	Palm oil derivatives, fatty acids, glycerol	22- 70
Comamonas testosteroni	MCL-PHA	Castor oil, coconut oil, mustard oil, cottonseed oil, groundnut oil, olive oil, sesame oil	79-88
Cupriavidus necator	P(3HB)	Bagasse hydrolysates	54
Cupriavidus necator H16	P(3HB-co-3HV)	Crude palm kernel oil, olive oil, sunflower oil, palm kernel oil, cooking oil, palm olein, crude palm oil, coconut ,oil + sodium propionate	65-90
Cupriavidus necator DSM 545	P(3HB)	Waste glycerol	50
Recombinant Cupriavidus necator	P(3HB-co-3HHx)	Palm kernel oil, palm olein, crude palm oil, palm acid oil	40-90
Recombinant Escherichia coli	P(3HB-co- 3HHx-co-3HO)	Soybean oil	6
Pseudomonas aeruginosa IFO3924	mcl PHA	Palm oil	39
Pseudomonas aeruginosa NCIB 40045	mcl PHA	Waste frying oil	29
Pseudomonas guezennei biovar. tikehau	mcl PHA	Coprah oil	63
Thermus thermophilus HB8	P(3HV-co- 3HHp-co-3HN- co-3HU)	Whey	36

Plastic Types:

Based on the constituents present bioplastics are classified as follows

· Starch based plastics: Constituting about 50 percent of the bioplastics market, thermoplastic starch, such as Plastarch Material, currently represents the most important and widely used bioplastic. Pure starch possesses the characteristic of being able to absorb humidity and is thus being used for the production of drug capsules in the pharmaceutical sector.

· Polylactic acid (PLA) plastics: Polylactic acid (PLA) is a transparent plastic produced from cane sugar or glucose. It resembles conventional petrochemical mass plastics (like PE or PP) in its characteristics. PLA and PLA-Blends generally come in the form of granulates with various properties and are used in the plastic processing industry for the production of foil, moulds, tins, cups, bottles and other packaging.

· Poly-3-hydroxybutyrate (PHB): The biopolymer poly-3-hydroxybutyrate (PHB) is polyester produced by certain bacteria processing glucose or starch. Its characteristics are similar to those of the petroplastic polypropylene. It produces transparent film at a melting point higher than 130 degrees Celsius, and is biodegradable without residue.

· Polyamide 11 (PA 11): PA 11 is a biopolymer derived from natural oil. It is also known under the trade name Rilsan B, commercialized by Arkema. PA 11 belongs to the technical polymers family and is not biodegradable. It is used in high-performance applications like automotive fuel lines, electrical cable anti-termite sheathing, flexible oil & gas pipes, sports shoes, and electronic device components.

· Bio-derived polyethylene: The basic building block (monomer) of polyethylene is ethylene. Bio-derived polyethylene is chemically and physically identical to traditional polyethylene - it does not biodegrade but can be recycled. It can also considerably reduce greenhouse gas emissions.

· Genetically modified bioplastics: Genetic modification (GM) is also a challenge for the bioplastics industry. None of the currently available bioplastics - which can be considered first generation products - require the use of GM crops

Table 1: Major companies in Bioplastics production

Product	Company	Location	Capacity (tonnes)	Price, $/lb
PLA	Nature Works	US	140,000	0.85-1.20
PLA	Hisun	China	5,000	1.25
PHAs	Metabolix	US	300/50,000 (2010)	2.50-2.75
PHBV	Tianan	China	2,000	2.40-2.50
Mater-Bi	Novamont	EU	75,000	2.0-3.0
Cereplast	Cereplast	US	25,000	1.50 2.50
Others	DuPont, Plantic, Innovia, Arkema & others	Global	2,000	1.50 4.00

Degradable plastic:

An oil-based plastic containing a chemical additive that undergoes significant change in its chemical structure causing it to break down into smaller particles. The degradation process is triggered only when material is exposed to specific environmental conditions (such as UV, heat and moisture). Residues are not food matter for microorganisms and are not biodegradable or compostable. There are five different kinds of degradable plastic:

· Biodegradable

· Compostable

· Hydro-biodegradable

· Photo-degradable and

· Bioerodable.

These can be either organically based from renewable resources or synthetic with a

petroleum base.

Biodegradable plastic:

A degradable plastic, in which the degradation must result from the action of naturally occurring microorganisms over a period of time (up to 2-3years in a landfill).

Compostable plastic:

A plastic that undergoes biological degradation during the composting process (up to 2-3 months in a windrow) to yield carbon dioxide, water, inorganic compounds and biomass at a rate consistent with other known compostable materials and leaves no visually distinguishable or toxic residues

Hydro-biodegradable:

These plastics contain additives that are degraded under the moisture conditions. The end result is converted to carbon dioxide (CO₂), water (H₂O) and biomass.

Photo-degradable :

Photo-degradable plastics -conventional plastics with photo-degradable additives that are degraded under the sunlight

Bioerodible:

Bioerodible polymers which degrade completely into nontoxic residues over a clinically useful period of time, including polyanhydrides, polyorthoesters, polyglycolic acid, polylactic acid, and copolymers thereof, are used for the delivery of bioactive agents, including antibiotics, chemotherapeutic agents, inhibitors of angiogenesis, and simulators of bone growth, directly into bone.

Biodegradability of Bioplastics:

In a biological system, PHBs can be degraded using microbial depolymerase as well as by non enzymatic and enzymatic hydrolysis in animal tissue. The biodegradability of a polymer is governed primarily by its physical and chemical properties. It has been found that low molecular weight PHAs are more susceptible to biodegradation. The melting temperature is another important factor to be considered. As the melting point increases, the biodegradability decreases with the increases in melting temperature, the enzymatic degradability decreases. Biodegradation of solid polymers is also influenced by chemical structure (especially functional groups and hydrophobicity - hydrophilicity balance) and highly ordered structures (mainly crystallinity, orientation and morphological properties). Highly ordered structures have lower biodegradability. In addition the microbial population in a given environment and the temperature also contribute to the biodegradability in the polymer (Tokiwa and Calabia, 2004).

Methods of degradation:

Chemical degradation:

The Polymer Energy system uses catalytic pyrolysis to efficiently convert plastics (primarily polyolefins) into crude oil. Conversion process takes place in reactors provided. The reactors are provided with catalyst and molten metal. Catalysts are used for reducing or speed up the actual process. Molten metal is used for maintaining high temperature in the reactor. Depolymerisation process takes place in the process. In this process the pressed plastic wastes were placed in the reactor at high temperature. At high temperatures polymer chains of the plastics are breakdown there taking depolymerisation process. The depolymerisation process will takes place in one reactor and the exhaust of one reactor is in gaseous state and these were condensed in condensate reactor and the final product which is in liquid state are stored in thermally insulated storage tanks and forwarded to refineries for further proccessings.

Thermal degradation:

Thermal degradation of polymers is molecular deterioration as a result of overheating. At high temperatures the components of the long chain backbone of the polymer can begin to separate (molecular scission) and react with one another to change the properties of the polymer. Thermal degradation can present an upper limit to the service temperature of plastics as much as the possibility of mechanical property loss. Indeed unless correctly prevented, significant thermal degradation can occur at temperatures much lower than those at which mechanical failure is likely to occur. The chemical reactions involved in thermal degradation lead to physical and optical property changes relative to the initially specified properties. Thermal degradation generally involves changes to the molecular (and molecular weight distribution) of the polymer and typical property changes include reduced ductility and embrittlement, chalking, color changes, cracking, general reduction in most other desirable physical properties.

Photo degradation:

Photo degradation is degradation of a photodegradable molecule caused by the absorption of photons, particularly those wavelengths found in sunlight, such as infrared radiation, visible light, and ultraviolet light. However, other forms of electromagnetic radiation can cause photo degradation. Photo degradation includes photo dissociation, the breakup of molecules into smaller pieces by photons. It also includes the change of a molecule's shape to make it irreversibly altered, such as the denaturing of proteins, and the addition of other atoms or molecules. A common photo degradation reaction is oxidation. This type of photo degradation is used by some drinking water and wastewater facilities to destroy pollutants.

Role of additive:

d2w® turns ordinary plastic at the end of its useful life into a material with a completely different molecular structure. At that stage it is no longer a plastic. It has become a material which can be bio-assimilated in the open environment in the same way as a leaf.
d2w® is an additive technology that is included in the basic polymer resin during the manufacturing process. It breaks the molecular chains after a pre-determined lifespan.
All plastics will eventually become embrittled, and will fragment and be bioassimilated, but the difference made by Symphony’s d2w® technology is that the process is accelerated.

Biodegradable plastics:

Biodegradable plastics are plastics that will decompose in natural aerobic (composting) and anaerobic (landfill) environments. Biodegradation of plastics can be achieved by enabling microorganisms in the environment to metabolize the molecular structure of plastic films to produce an inert humus-like material that is less harmful to the environment. They may be composed of either bioplastics, which are plastics whose components are derived from renewable raw materials, or petroleum-based plastics which utilize an additive. The use of bio-active compounds compounded with swelling agents ensures that, when combined with heat and moisture, they expand the plastic's molecular structure and allow the bio-active compounds to metabolize and neutralize the plastic.

Composting the wastes:

Compost may be the key to maximizing the real environmental benefit of biodegradable plastics. One of the big impediments to composting our organic waste is that it is so mixed up with non-degradable plastic packaging that it is uneconomic to separate them. Consequently, the entire mixed waste-stream ends up in landfill. By ensuring that biodegradable plastics are used to package all our organic produce, it may well be possible in the near future to set up large-scale composting lines in which packaging and the material it contains can be composted as one. The resulting compost could be channeled into plant production, which in turn might be redirected into growing the starch to produce more biodegradable plastics. With intelligent use, these new plastics have the potential to reduce plastic litter, decrease the quantities of plastic waste going into landfills and increase the recycling of other organic components that would normally end up in landfills. Whilst several biodegradable plastics are used for these applications worldwide, the current market penetration is low.

Applications:

Biodegradable bioplastics are used for disposable items, such as packaging and catering items (crockery, cutlery, pots, bowls, and straws). Biodegradable bioplastics are also often used for organic waste bags, which can be composted together with the food or green waste. Some trays and containers for fruit, vegetables, eggs and meat, bottles for soft drinks and dairy products and blister foils for fruit and vegetables are manufactured from bioplastics.

Non-disposable applications include mobile phone casings, carpet fibers, and car interiors, fuel line and plastic pipe applications, and new electro active bioplastics are being developed that can be used to carry electrical current. In these areas, the goal is not biodegradability, but to create items from sustainable resources.

Biodegradable plastics are a new generation of polymers emerging in the market. Biodegradable plastics have an expanding range of potential applications, and are driven by the growing use of plastics in packaging and the perception that biodegradable plastics are 'environmentally friendly', their use is predicted to increase. However, issues are also emerging regarding the use of biodegradable plastics and their potential impacts on the environment and effects on established recycling systems and technologies.

Ideology:

Using genetically modified organisms, we can speed up the process of degradation of both common as well as biodegradable plastics. By isolating the gene from a plastic degrading microbe and introducing into a species with a high copy number such as Escherichia coli, the population of microbes can be increased rapidly at the site of degradation, which fastens the process.

CONCLUSION:

The development of bioplastics is best viewed in the wider context of the "greening" of industrial chemistry. In future years, itwill be largely driven by three factors: the need to derive morecarbon for chemical processes from renewable substances insteadof oil reserves, to develop cleaner chemical processes, and toavoid perturbing the ecosystem

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Received on 17.09.2014 Accepted on 30.09.2014

Research J. Engineering and Tech. 5(3): July-Sept. 2014 page 158-165