Manufacture of biodegradable Plastics is a newly emerged sector, which originated to design degradable plastics by common biological organisms such as, bacteria, algae and fungi. Innovation of bioplastics specifically resulted to conquer the monopoly of petrochemical plastics in the market since; petrochemical plastics have become a burdensome issue due to economic stress, environmental impacts and resource shortage caused by utilization of non-renewable petroleum oil. Since biodegradable plastics are designed to degrade in the biological environments, the most common and feasible method of end of life scenario is landfills. Objective of the present study is to estimate maximum additional methane generation via biodegradable plastics under landfill anaerobic conditions. Literature was reviewed on currently available types of biodegradable plastics, individual polymers comprised, production capacity (year 2007) and methane production data from individual polymers. Empirical data for methane generation were based on the published experimental literature on individual polymers under laboratory simulated landfill conditions using thermophilic anaerobic sludge digestion. Methane generation in organic molecules was theoretically calculated based on derived currently available chemical equations, assuming standard temperature and pressure conditions. Global methane contribution by biodegradable plastics was calculated only using theoretical values since no sufficient data were available at experimental conditions. Study demonstrates 0.011% of global contribution of methane by biodegradable plastics if entire production capacity in year 2007 is assumed to be landfilled and completely biodegraded. 1.52% of methane is contributed to global emissions, if 90% of petrochemical plastics are substituted by biodegradable plastics, which the percentage of petrochemical plastics could be technically substituted according to the reports of PROBIP (2009). In comparison of theoretical and experimental data, experimental data was in the range of 55.9- 68.84% upon theoretical data. The estimated values demonstrate a low level of methane emission compared with other anthropogenic methane sources, presenting a negligible impact to global methane emission and/or global warming by biodegradable plastics.
Introduction
Plastics are synthetic, typically long chain polymeric molecules. Substitution of natural materials by plastics came about to the scenario back in 1907 after invention of synthetic polymer "Bakelite" from phenol and formaldehyde (Thompson et al., 2009). Improvement of the synthesis methods and techniques have ameliorated the quality of plastics with more stable and durable properties (Shah et al., 2008 ). Today plastics have become an indispensable part of the humans' life particularly due to their extensive use in packaging, cosmetics, chemicals, and detergents. Plastics we use today are synthesized materials extracted from crude oil, coal and natural gas (Seymour, 1989) which is termed as Petroleum based plastics. Property of high persistency (very slow biodegradation rate) of plastics have created being resistant to environmental degradability which mounted societal awareness and concerns of proper disposal and management (Albertsson et al., 1987). Wide variety of plastics are manufactured including polypropylene, polystyrene, polyvinyl chloride, polyethylene, polyurethane and nylons with estimated global production of approximately 140million tons per year (Shimao 2001). Thus excessive uses of plastics have exerted a huge pressure globally in terms of saving of confined crude oil, waste disposal and management, and environmental recreation.
To overcome the problems related to petroleum based plastics attention of scientists have devoted their attention that lead to promote research activities to give rise to alternative materials, intended to degrade through biological processes (Shah et al., 2008, Lenz and Marchessault, 2004, Amass et al., 2001). A new type of thermoplastic polyester was first produced by Imperial Chemical Industries Ltd- London in 1982, which was considered to be completely biodegradable (Anderson and Dawes, 1990). The invented product is known as biodegradable plastic since, it's degraded by environmentally available microorganisms. Term Bioplastic (BP) is perplexingly used today to interpret bio-based and bio-degradable materials. However the study will mainly consider on the Biodegradable plastics (BDP), which is intended to use as a promising solution for the petroleum based plastics. According to ASTM definition of BP, BP is a degradable plastic in which the degradation results from the action of naturally-occurring microorganisms such as bacteria, fungi, and algae (Narayan, 1999).
Many different types of BPs have been successfully produced and have invaded the market during past few years. BPs are synthesized using plant extracted polymers or use of growth of microorganisms. Tailoring the properties of plant extracted polymers via chemical modification of the main polymer by hydrolysable or oxidisable groups and using polymer blends (Amass et al., 1998) have amended BP to use in a broad range of applications contained with novel and beneficial characteristics. The primary goal expected over invention of BPs was the environmental concerns including waste management, reduction of greenhouse gas release, and saving of non-renewable energy (petroleum oil and gas). Apart from that secondarily, economic aspects and new technical opportunities came into scenario (PROBIP, 2009).
Today BPs are popular compounds used in packaging materials, surfactants, as biomedical materials (eg: wound dressings, drug delivery, Surgical implants), and agricultural compounds (eg: control the fertilizer and pesticide release). BPs used as packaging materials has led to excellent management strategy mainly to prevent environmental accumulation (Amass et al., 1998). Only 0.3% (0.36 million metric tons) of the worldwide production of conventional plastics has replaced by biodegradable plastics by the year of 2007. In year 2007 world plastic generation was reported as 205 million tons (Gervet and Nordell., 2007). However 90% of the conventional plastics are estimated the percentage is capable of technically substituted by BPs. There is an upsurge in generation of bio based plastics globally that resulted in an estimated global growth of 38% from 2003 to 2007 (PROBIP, 2009).
Initially when BPs were entering to the market (1990) no standard procedures were existed to investigate the biodegradability of the plastics. To prevent misconceptions with biodegradability of BPs, standards have been developed by standard organizations to identify the literal biodrgradability of BPs in commodity (Mohee et al., 2007). At the end of the service life BPs wind up in landfills, anaerobic treatment plants or composting facilities. Based on the degradable properties and the properties of the material end of life, the alternatives vary. Landfill disposed BPs will ultimately undergo anaerobic biodegradation where, the materials are disintegrated to methane, carbon dioxide, hydrogen sulphide, ammonia, hydrogen and water as a result of series of microbial metabolic interactions (ATSDR, 2010). Methane gas is a well-known and important by product which public attention has paid as a global warming gas and also as an economically viable biofuel. The study is a preliminary attempt to investigate the levels of additional methane gas released if end of life option is chosen to be a landfill using commonly available types of BPs globally, with different biodegradability levels.
Back ground
Types of BPs
Literature reports numerous types of BPs in the market today, such as starch plastics, Poly glycolic acid (PGA), Poly lactic acid (PLS), poly lactic acid-co-glycolic acid, poly 3- hydroxybutanoate (P3HB), Poly 3- hydroxyl valerate (PHV), Polyethylene succinate (PES), Poly butylenes succinate, Poly propiolactone (PPL), starch blends, etc (Figure 1)(Shah et al., 2008, PROBIP, 2009), derived from renewable resources such as starch, plant based oils, or cellulose (Beta analytic, 2010). The study covers 5 major groups of BDPs currently available in the market with details on different manufacturers engaged in manufacturing process (Table 1). Except these main groups mentioned, chitin (polysaccharide), protein (collagen, casein), and amino acid based BDPs are manufactured in insignificant levels, which are not covered in this study. Main group of polymer contributes the global BP production is Cellulose plastics, which the production capacity is approximately 4000Mt per annum. To be considered as a bioplastic, it should be certified legally through standards, EN 13432 or EN 14995 in Europe, ASTM D-6400, ASTM D6868, ASTM D6954, ASTM D7081 in United States, DIN V4900 in Germany or ISO 17088 in other countries (Beta analytic, 2010, ASTM, 2010). As mentioned earlier all BPs are not biodegradable and the biodegradability is based essentially on the molecular structure of the compound. ASTM D-6400 requires 60-90% decomposition of BPs within 180 days in natural environment in order to be considered as a biodegradable plastic. ASTM has demonstrated both aerobic and anaerobic standard methods to identify (respectively in composting environments and anaerobic digestion processes) the extent of biodegradability of BDPs (Narayan, 1999).
Decomposition
Degradation and potential degradability of a particular BDP varies depending on the environment exists: anaerobic or aerobic (Ishigaki et al., 2004). Based on the degradation property of a particular BDP, end of life option should be chosen, whether it is to be disposed in a landfill or composting facility. Different types of soil microorganisms (bacteria and fungi) are responsible for the biodegradation of different types of BPs specifically (Shah et al., 2008). Rate and process of biodegradation of BPs rely on the Soil properties, nature of the pretreatment, characteristics of the polymer such as tactility, mobility, molecular weight, functional groups present, additives, availability and optimal growth of specific microorganisms (Artham and Doble, 2008, Glass and Swift, 1989, Gu et al., 2000). Initially biodegradation starts with disintegration of the polymer via physical and biological forces. Some fungal hyphae are able to penetrate the polymer structure and cause cracks and swelling of the material (Griffin, 1980). Heating, cooling, freezing thawing, wetting and drying like physical forces also contribute the mechanical degradation process (Kamal and Huang, 1992). Generally high molecular weighted polymers have a lesser potential to biodegrade than the low molecular weighted compounds. Broadly extracellular and intracellular microbial enzymes are responsible for biodegradation process, and then converted into oligomers, dimers and monomers which can be easily penetrable into bacterial cells. Thus utilizes for bacterial energy production releasing CO2, CH4, and H2O (Hamilton et al., 1995, Gu et al., 200). Present study will be given emphasis landfills, as the end of life time option. Less data is available on the biodegradation of BDP in landfill anaerobic conditions than aerobic composting. Thence more investigations have to be implemented and few have been reported (Yagi et al., 2009). In a landfill high percentage is readily degraded by anaerobic communities in anoxic conditions. As a result of series of physical, chemical,l and biological reactions that take place in a landfill, landfill gas is produced, with varying compositions based on the type of waste contained (Barlaz et al., 1990). Anaerobic degradation of carbon, Hydrogen and Oxygen containing substance is given by the Buswell equation as follows (Yagi et al., 2009).
CnHaOb + (n- a/4 - b/2) H2O (n/2 + a/8 - b/4) CH4 + (n/2 - a/8 + b/4)CO2 (A)
Anaerobic decomposition of Carbon, Hydrogen, Oxygen and Nitrogen containing substance is given as follows (Behera et al., 2010).
CaHbOcNd + ((4a-b-2c+3d)/4) H2O ((4a+b-2c-3d)/8) CH4 + ((4a-b+2c+3d)/8) CO2 +
d NH3 (B)
CO2 and CH4 are the main gaseous substances released during anaerobic degradation of any compound. Methane produced in landfills is recovered as an energy source where provides an economic advantage. However if not recovered, methane would readily enter to the atmosphere, which is listed as one of the major contributor to global warming. Methane is an effective heat trapping agent in the atmosphere and over 20 times more potent than CO2 (USEPA, 2010 a). Studies have reported on methane yields obtained via anaerobic biodegradation for few polymers (Cellulose ester, Polycaprolactone and Poly lactic acid) and most are yet to be studied.
Methane as a potent global warming gas
Global warming is understood as the main causation of global climate change. Global warming is caused due to increase of green house gases in the atmosphere such as Carbon dioxide, methane, Nitrous oxide, and water vapor (US composting council, 2009). Methane is considered as a green house gas with high heat trapping capacity which lasts approximately 9- 15 years in the atmosphere. Global warming potential (GWP) of green house gases are represented in relation to a reference gas, CO2, where GWP is considered as 1. Global warming potential of methane gas is 21 which infers, 21 times more effective heat trapping agent than CO2. Methane is emitted to the atmosphere mainly from anthropogenic and natural sources. 50% of methane in the atmosphere is attributed to anthropogenic sources such as fossil fuel combustion, biomass burning, rice cultivation, animal husbandry, and waste management. Contribution of anthropogenic methane to global green house gas emission was 282.6 million tons in the year 2000 (22.9%) as declared by USEPA (2006). Natural sources of methane emissions include emissions from wetlands, permafrost, termites, oceans wild fires and fresh water bodies. Levels of methane emitted from each region or country depends on factors, such as climatic conditions, industrial and agricultural lands, energy type used and waste management procedures. Largest methane emission human related sources in USA are landfills, animal husbandry, and manure management where the second highest of the list goes to landfills. In the aspect of global methane production, landfills attributed the third highest source of emission and globally methane contribution by landfills was over 12% for year 2000 (USEPA, 2010 b). Organic compounds in a landfill, upon decomposition release methane as mentioned above and recent estimation suggests that 72% of MSW stream contained with organic substances: paper, food scraps, yard debris, textiles/ leather, and wood. Percentages of each MSW component landfilled was respectively, 34%, 12%, 13%, 7%, and 6% (US composting council., 2009). Thus methane generation from each MSW component may be assumed being in the same order as above from each MSW component, since methane production is proportional to the carbon amount in an organic substance. Thus paper is the main methane gas contributor to the atmosphere from a landfill while others play a minor role. BDPs is novel emerging organic compound set in the landfills and also a new global source of methane emitting from a landfill.
Gas Generation model
Landfill gas estimation is useful for landfill operators, regulators, energy users and energy recovery project owners to investigate how gas is produced and recovered in a particular time period. USEPA has generated a Landfill methane gas estimation model to simulate the gas production in landfills using first order decay curve, which is written as, M(t) = M0 e -kt. Where M(t) is the mass of a batch waste remaining at any time, M0 is the initial mass of waste, k is the decay rate (time -1) and t is the time since decay was begun. Gas production is directly correlated to mass lost, which is termed as L0 (m3 of methane per metric ton of waste). Total Volume of gas (G0) that can be produced by the degradation of mass of weight (M0) is, calculated using the equation, G0 = L0 M0. BDP is a newly emerging landfill component which contributes the global methane generation. The study will provide an estimation of additional methane produced upon this new arrival.
Methods
Study was based on estimation of additional methane gas amount produced from landfills with subsequent emergence of BDPs to the market. Literature was reviewed related to brand names, quantity, polymer types incorporated and biodegradability (especially in terms of methane production) of BDPs commonly found in the global market (Table1 and Table 2). Manufacturer and quantity data obtained were associated with the year 2007. This study has considered only biobased and non biobased BDPs and non degradable bio based or non biobased plastics have not been used for analysis as they are incapable of degrade in a landfill and release methane. Study was carried out in 4 steps.
Step 1: Methane production per day was calculated using published experimental data on methane gas production in simulated landfill conditions assuming total manufactured BDPs were being landfilled (Table 2). Biodegradability of a particular BDP is likely to vary based on the percentages of individual polymers contained in the blend. Although production capacity was available in respect to a particular brand name, no production data was available for individual polymers separately. Since a particular producer manufactures different types of BDP materials related to textile, agriculture, biomedical items and packaging, percentages of individual polymers used for blends vary largely from each other even within the same brand name. Therefore it's difficult to pinpoint a distinct percentage for each polymer in a particular BDP being manufactured. Further data on percentages of each polymer are neither readily available from the manufacturers' website nor descriptive studies have done regarding percentages. Therefore brand names with multiple polymer types were assumed to be equally distributed, thus manufactured capacity from each polymer was obtained by averaging the manufactured capacity of the particular brand name. Most published literature was based on the biodegradability of individual polymer types rather than the biodegradability of a particular brand name except for Mater Bi starch BDP (Mohee et al., 2007).
Step 2: Methane production per day was calculated using theoretical stoichiometric methane production data assuming total biodegradation of the compound and total manufactured BDPs (2007) were being landfilled. Brands with multiple numbers of polymers, percentages of individual polymers are assumed equally distributed as mentioned in step1 (Table 3). Methane gas amount released is theoretically calculated using the chemical equations (A) and (B). Maximum biogas (CO2, CH4 and NH3) amount produced by degradation of 1 kilo ton of Poly lactic acid ((C2H4O2)n) was calculated to be 7.5 x 10 5 m3 ((106/60) x 22.4x 2) at standard temperature and pressure. CH4: CO2 ratio for poly lactic acid is 1:1. Theoretical maximum volume of CH4 produced calculated according to the combined gas law was reported to be 3.73 x 10 5m3, assuming total biodegradation of the compound. Table 3 displays the maximum theoretical methane volume produced at standard temperature and pressure for C, H, O and N related polymers intended to discuss in this study.
Step 3: Maximum methane production was calculated considering the amount of BDPs being landfilled per year when 90% (the possible amount that can be technically substituted by BPs from petrochemical plastics in use today) of petrochemical plastics were substituted over BPs. All BDPs produced are assumed to be readily (during a period of year) biodegradable in this scenario.
Step 4 : Contribution of landfilled BDPs to global methane emission was calculated using the total methane emission data obtained from step 3 and step 4.
RESULTS AND DISCUSSION
Data on methane generation (Table 2, step 1) was obtained from published experiments on anaerobic decomposition of individual polymer compounds, simulating landfill, thermophilic conditions by using anaerobic sludge as the medium in controlled laboratory conditions. However, since different authors have used different conditions with different types of sludges and diversed microbial communities, (affects diversity of microbial communities) (Abou-Zeid et al., 2004) would affect the reliability of the study in utilizing the values for comparison, due to introduction of many biases. It was not possible to estimate global methane production based on published experimental data since sufficient data were not available to cover a reasonable number of polymers attended this study. However, estimation for global methane production from BDPs was able to obtained by using theoretical calculation to approach the objectives as showed in step 2, Table 3 (see appendix for calculations). If assumed the entire manufactured BDPs in year 2007 were landfilled and total landfilled is completely biodegraded, the methane amount produced was calculated to be 8.31 x 10 8m3. Global contribution resulted was 0.011 % in this scenario (see appendix). MSW stream is declared to be composed of 205 million tons of petrochemical plastics in year 2003 (Garnet and Nordell, 2007). The amount of BDPs that could possibly substitute to petrochemical plastics was calculated to be 184.5 million tons. Assuming equal proportions of different BDPs tabulated in Table 2 are being landfilled, the amount of methane released is calculated to be 1.06 x 1011m3 / year. 90% substitution scenario is an estimation undertaken to understand whether methane released causes significant contribution to global anthropogenic methane gas emission, in its maximum level of BDP manufacture. The scenario is responsible for 1.38% of global methane contribution. This was 116% of total landfill methane generation based on the year 2006 total methane emission (USEPA, 2006), which is higher than the total current landfill methane generation. The values were obtained on the basis of 2007 BDP manufacture data however expected total plastic production will also be raised apparently at the time of 90% substitution petrochemical plastics upon BDPs. Total BP production capacity amounted to be in year 2020 is 1.5-4.4 million tons (PROBIP 2009).
In comparison of the methane yields (m3/kt) from theoretical stoichiometric calculations and laboratory measurements (Table 4), highly vary. It is obvious that, experimental methane production in laboratory conditions is lower than the theoretical data. Percentage of experimental methane emission was in the range of 55.9-68.84% of the theoretical values, when compared the methane emission levels of available experimental data (PCL and PCL). Methane amounts will be further diminished if methane emission is calculated considering the experimental data. Efficiency of biodegradation process occur in a landfill governs the rate and amount of methane generated into the atmosphere. Numerous factors such as size of waste particle, composition of waste, pH, temperature, design of the landfill, nutrients and as the most important factor moisture control the methane emission in a landfil (Micales and Skog, 1996, Augenstein and Pacey, 1991). Rathje and Murphy (1992) have demonstrated mummification of refuse under levels where, a landfill does not receive optimum level of moisture impeding degradation or methane release (Barlaz et al., 1987). Bogner and Spokas (1993) have shown that carbon conversion value of 25-40% for even readily degradable materials in a landfill and Aragno (1988) reported 35-40% organic matter degradation to Carbon dioxide and methane under ideal laboratory conditions. However in the present study Methane generation resulted was higher than the published literature, demonstrating higher methane emissions from BDPs than other sources such as wood, paper, etc. Therefore under actual landfill conditions released methane amounts is lesser than the controlled laboratory obtained values as confirms by published data and data from the present study . Further degradation process in a landfill takes place over decades of periods and even after 20-30 years of period large quantities of non-degraded portions have been observed even for readily degradable materials (Micales and Skog, 1996). Therefore methane yields per year should be more lessen than the quoted values in the study. Efficient and effective use of landfill methane as a beneficial fuel or enrgt source would further alleviate the methane release into the atmosphere in landfills (Gregg, 2010).
SUMMARY AND CONCLUSIONS
The study estimates maximum additional global theoretical methane resulted from decomposition of BDPs which is a novel methane source emerged from landfills. Results suggest that the global contribution of BDPs to methane generation is comparatively less compared with other anthropogenic sources. However in comparison of the methane emission from BDPs, with other landfill components, BDPs are likely to contribute a considerable amount of methane, which demonstrated the highest amount of methane emission other landfill components. Experimental data evidences an overestimation of the theoretical estimates. Study has come across with many assumptions in each depiction scenario, which weakens the estimation. However study provides an estimation of the additional methane gas released globally due to BDP landfilling, where no studies or estimations have done so far in a maximum possible logical and scientific way utilizing available data. Further studies on individual polymer degradation are essential in order to strengthen and verify the results obtained for sound literal estimations.
REFERENCES
ATSDR (Agency for Toxic substances & Disease Registry). 2010. http://www.atsdr.cdc.gov/hac/landfill/html/ch2.html. Accessed July 2010.
Albertsson, A. C., Andersson, S. O., Karlsson, S. 1987. The mechanism of biodegradation of polyethylene. Polym Degrad Stab 18,73-87.
Amass, W., Amass, A., Tighe, B. 1998. A review of biodegradable polymers: Used, Current Developments in the synthesis and characterization of biodegradable polyesters, blends of biodegradable polymers and Recent advances in biodegradation studies. Polymer international. 47, 89-144.
Anderson. A. J., Dawes, E. A. 1990. Occurrence, metabolism, metabolic role and industrial uses of bacterial polyhydroxyalkaonates. Microbiol Rev. 54:4, 450-472.
Aragno, M. 1988. The landfill ecosystem: a microbiologists look inside a "black box". In the Landfill. Lecture notes in Earth Sciences #20, ed. P. Baccini. Springer Verlag. New York. 15-38. In: Micales, J. A., Skog, K. E. 1996. The decomposition of Foresy products in landfills. International Biodeterioration & Biodegradation 39. 2-3. 145-158
Artham, T., Doble, M. Biodegradation of Aliphatic and Aromatic Polycarbonates. Macromol Biosci 2008;8(1):14-24.
ASTM Standards and Engineering Digital library. 2010. ASTM international. http://www.astm.org/DIGITAL_LIBRARY/TOPICS/PAGES/section08_stds.htmHYPERLINK "http://www.astm.org/DIGITAL_LIBRARY/TOPICS/PAGES/section08_stds.htm Accessed October 2010" Accessed October 2010.
Augestein, D., Pacey, J. 1991. Landfill methane models, Proceedings from the Technical sessions of SWANA's 29th Annual International Solid waste exposition, SWANA, Silver Spring, MD. 87-111. In: Micales, J. A., Skog, K. E. 1996. The decomposition of Foresy products in landfills. International Biodeterioration & Biodegradation 39. 2-3. 145-158.
Barlaz, M. A., Ham, R. K., Schaefer, D. M. 1990. Methane production from Municipal refuse: A review of enhancement techniques and microbial dynamics. Environmental Science and Technology. 19, 6. 557-584.
Barlaz, M. A., Milke, M. W., Ham, R. K. 1987. Gas production parameters in sanitary landfill simulators. Waste manag. And Res. 5, 27-39.
Bertoldi. M., Sequi, P., Lemmes, B. 1996. The Science of composting. 1st edition, Glasgow. Chapman & Hall.
Beta analytic Corporation. 2010. <http://www.betalabservices.com/biobased.html. Accessed october 2010>.
Bogner, J., Spokas, K. 1993. Landfill CH4:rates, fates and role in global carbon cycle. Atmosphere. 25. 369-386.
Gervet, B., Nordell, B. 2007. The use of crude oil in plastic making contributes to global warming. Renewable energy research group, Division of Architecture and Infrastructure, Lulea University of Technology, Sweden.
Glass, J. E., Swift, G. 1989. Agricultural and Synthetic Polymers, Biodegradation and Utilization, ACS Symposium Series, 433. Washington DC: American Chemical Society. 9-64.
Gregg, J. S. 2010. national and regional generation of municipal residue biomass and the future potential foe waste-to-energy implementation. Biomass and Bioenergy. 34. 379-388.
Griffin, G. J. L. 1980. Synthetic polymers and the living environment. Pure Appl Chem. 52. 399-407. In: Shah, A. A., Hasan, F., Hameed, A., Ahmed, S. 2007. Biological degradation of plastics: A comprehensive review. Biotechnology Advances. 26, 246-265.
Gu, J. D., Ford, T. E., Mitton, D. B., Mitchell, R. Microbial degradation and deterioration of polymeric materials. 2000. In: Revie W, editor. The Uhlig Corrosion Handbook. 2nd Edition. New York: Wiley.. 439-60. In: Shah, A. A., Hasan, F., Hameed, A., Ahmed, S. 2007. Biological degradation of plastics: A comprehensive review. Biotechnology Advances. 26, 246-265.
Hamilton, J. D, Reinert, K. H, Hogan, J. V, 1995. Lord WV. Polymers as solid waste in municipal landfills. J Air Waste Manage Assoc. 43. 247-51.
Ishigaki, T., Sugano, W., Nakanishi, A., Tateda, M., Ike, M., Fujita, M. 2003. The degradability of biodegradable plastics in aerobic and anaerobic waste landfill model reactors. Chemosphere. 54. 225-233.
Kamal, M. R., Huang, B. Natural and artificial weathering of polymers. In: HamidSH, Ami MB, Maadhan AG, editors. Handbook of Polymer Degradation. New York, NY: Marcel Dekker; 1992. p. 127-68.
Lenz, R. W., Marchessault, R. H. 2004. Bacterial Polyesters: Biosynthesis, biodegradable plastics and biotechnology. American Chemical society. 6:1.
Micales, J. A., Skog, K. E. 1996. The decomposition of Foresy products in landfills. International Biodeterioration & Biodegradation 39. 2-3. 145-158.
Mohee, R., Unmar, G. D., Mudhoo, A., Khadoo, P. 2007. Biodegradability of biodegradable/degradable plastic materials under aerobic and anerobic conditions. Waste Management. 28, 1624-1629.
Narayan, R. 1999. ASTM standards help define and grow a new biodegradable plastics industry. ASTM standardization News. 36-42.
PROBIP (Product overview and market projection of emerging bio-based plastics). 2009. Europen polysaccharide Network of excellence and European Bioplastics.
Rathje, W., Murphy, C. 1992. Rubbish:The archeology of garbage, new York: Harper Collins.250.
Seymour, R. B. Polymer science before&after 1899: notable developments during the lifetime of Maurtis Dekker. J Macromol Sci Chem 1989;26:1023-32.
Shah, A. A., Hasan, F., Hameed, A., Ahmed, S. 2007. Biological degradation of plastics: A comprehensive review. Biotechnology Advances. 26, 246-265.
Shimao, M. 2001. Biodegradation of plastics. Curr Opinion Biotechnol 12,242-247.
Behera, S. K., park., J., Kim, K., Park, H. 2010 Methane production from waste leachate in laboratory-scale simulated landfill. Waste management. 30. 1502-1508.
Thomas, N., Clarke, J., McLauchlin, A., Patrick, S. 2010. Assessing the environmental Impacts of oxo-degradable plastics across their life cycle. Loughborough University.
Thompson, R.C., Swan, A. H., Moore, C. J., Saal, F. S. 2009. Our Plastic Age. Phil. Trans. Soc. 364, 1973-1976.
United States Composting Council. 2009. USCC Position statement: Keeping organics out of landfills.
USEPA (United States Environmental protection Agency). 2010a. http://www.epa.gov/climatechange/glossaary.html#GWP. Accessed October 2010.
USEPA (United States Environmental protection Agency). 2010b. http://www.epa.gov/methane/. Accessed October 2010.
USEPA (United States Environmental protection Agency). 2008. Municipal Solid waster generation, Recycling and Disposal in the United States: Facts and Figures.
USEPA (United States Environmental protection Agency). 2006. Global Mitigation of Non-CO2 Green house gases. Office of Atmospheric programs, Washington, DC. EPA 430-R-06-005.
Yagi, H., Ninomiya, F., Funabashi, M., Kunioka, M. 2009. Anaerobic biodegradation tests of polylactic acid and polycaprolactones using new evaluation system for methane fermentation in anaerobic sludge. Polymer Degradation and Stability. 94. 1397- 1404.
List of Tables
Table 1 Manufacturers and amounts of BDP manufactured in year 2007
Table 2 Literature published on methane production, biodegradability of polymers incorporated to BDPs and calculated methane production levels
Table 3 Maximum theoretical methane amounts released during anaerobic biodegrdation of major polymer types in standard temperature and pressure
Table 4 Comparison of theoretical and experimental methane emission levels
List of Figures
Figure 1 Molecular structures of polymers involved in the production of common BDPs
Table 1 Manufacturers and amounts of BDP manufactured in year 2007.
Producer
Country of production
Trade Name
Polymer type
Polymer Name
Worldwide production (kt.p.a.) in 2007
Biodegradability
A
Cellulose Plastics (with regerated cellulose and cellulose esters)
2046
1
Lenzing
GLO
Lenzing viscose Lenzing modal Tencel
Viscose modal and encel fibers
Cellulose ester (CA) Cellulose acetate propionate(CAP)
Cellulose acetate butyrate(CAB
590
Fully biodegradable
2
Birla
India, Thailand, Indonesia
Birla Cellulose
Viscose modal and encel fibers
Cellulose acetate Cellulose acetate propionate Cellulose acetate butyrate
500
Fully biodegradable
3
Formosa Chemicals &Fibre
Taiwan
NA
Viscose Staple fibres
Cellulose xanthate
140
Fully biodegradable
4
Kelheim
Germany
Danufil, Galaxy, Viloft
Viscose Staple fibres
Cellulose ester Cellulose acetate propionate Cellulose acetate butyrate
72
Fully biodegradable
5
Celanese
US
NA
CA flakes, tows and filament
Cellulose ester (Cellulose acetate)
250
NA
6
Eastman
US
NA
CA tows and filament, CAB, CAP
Cellulose ester Cellulose acetate propionate Cellulose acetate butyrate
200
NA
7
Rhodia Acetow
Germany
NA
CA tows
Cellulose ester (Cellulose acetate)
130
NA
8
Daicel
Japan
NA
CA tows
Cellulose ester (Cellulose acetate)
90
NA
Other
74
Producer
Country of production
Trade Name
Polymer type
Polymer Name
Worldwide production (kt.p.a.) in 2007
Biodegrad
ability
B
Polylactic Acid (PLA) polymers
151
9
PURAC
Taiwan
PURAC
Polylactic acid (PLA)
75
Fully biodegradable
10
Nature Works
US
Ingeo
Polylactic Acid
70
Fully biodegradable
Other
6
C
Starch blends
153
11
Novamont
Italy
Mater Bi
Starch blends
Starch/ Polycaprolactone (PCL)*
40
Fully biodegradable
12
Rodenburg
Newzealand
Solanyl
Fermented starch
40
Fully biodegradable
13
Biotec
Denmark
Bioplast
starch blends
20
Fully biodegradable
Other
53
D
Polyhydroxy alkanoates
2
14
Tianan
Canada
Enmat
PHBV, PHBV and Ecoflex (petrochemical polymer)
poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)
2
Fully biodegradable
E
Polyurethane from Biobased polyol
12.3
15
Dow
US
Renuva
Polyurethane
8.8
Fully biodegradable
Other
3.5
Producer
Country of production
Trade Name
Polymer type
Polymer Name
Worldwide production (kt.p.a.) in 2007
Biodegrad
ability
F
Other biodegradable polymers
140
16
DuPont
Japan
Biomax
PBST/PET copolymer
Poly(butylene succinate terephthalate) Poly(ethylene terephthalate) (PET)
90
NA
17
Novamont
Japan
EatBio
Polytetramethylene adipate- co- terephthalate (PTMAT)
15
Fully biodegradable
18
BASF
Denmark
Ecoflex
Poly butylene adipate-co-butylene terephthalate (PBAT)
14
Fully biodegradable
Other
21
Data Source: (PROBIP, 2009), NA-Data Not Available
* Data source: Bertoldi et al., 1996.
Table 2 Literature published on methane production, biodegradability of polymers incorporated to BDPs and calculated methane production levels.
.
Polymer
Initial mass (g)
Methane volume (L)
Days of incubation
Methane production (%)
Biodegrada
Bility (%)
Methane volume (m3/ kt)/ L0*
Global polymer production (kt/annum) M0
Volume of methane gas (G0) (m3/day)**
References
Polylactic acid
10
2.57
22
53.8
91
257,000
151
3.9 x 107
Yagi et al., 2009
Mater Bi (Starch Blend)
1.96
0.245
32
99.11
26.9
24,500
40
9.8 x 106
Mohee et al., 2007
Polycaprolactone
10
6.59
22
65.8
92
659,000
20
1.3 x 10 7
Yagi et al., 2009
* Calculated methane volume (m3/kton) based on published data.
** Calculated methane amounts according to the USEPA gas estimation model.
Table 3 Maximum theoretical methane amounts released during anaerobic biodegrdation of major polymer types in standard temperature and pressure conditions.
Major polymer type
Polymer
Production capacity (kt/annum)
Theoretical methane production (m3/kt)
Theoretical methane production (m3/yr)
Cellulose based
Cellulose acetate
668.76
6.2 x 10 5
4.1 x 10 8
Cellulose acetate butyrate
448.76
4.0 x 10 5
1.8 x 10 8
Starch blends (Mater Bi)
Starch
20
4.1 x 10 5
8.3 x 10 7
Polycaprolactone
20
7.36 x 10 5
1.5 x 10 7
Poly lactic acid
Poly lactic acid
151
3.73 x 10 5
5.6 x 10 7
Polyhydroxy alkaonates
poly(3-hydroxybutyrate-co-3-hydroxyvalerate)
20
1.1 x 10 6
2.2 x 10 7
Polyurethane based polyol
Polyurethane
8.8
5.5 x 10 5
1.3 x 10 4
Other
Polyethylene terephthalate
45
6.5 x 10 5
2.9 x 10 7
Polytetramethylene adipate -co- terephthalate
15
1.47 x10 6
2.2 x 10 7
Polybutylene adipate -co-butylene terephthalate
14
7.0 x 10 5
9.8 x10 6
Total theoretical Methane production due to C, H, O polymers in year 2007 if assumed all manufactured polymers being landfilled
1411.32
7.0 x 10 7
8.31 x 10 8
Theoretical total methane generation per year is estimated to be 8.4 x10 8m3 based on year 2007 manufactured BDP capacity.
Table 4 Comparison of theoretical and experimental methane emission levels.
Polymer
Experimental Methane volume (m3/ kt)
Theoretical methane amount (m3/ kt)
% experimental emission in relation to theoretical emission
Polylactic acid
257,000
373,333.33
68.84
Polycaprolactone
659,000
1,178,947.37
55.9
Figure 1 Molecular structures of polymers involved in the production of common BDPs
