Ind. J. Sci. Res. and Tech. 2015 3(3):43-51/Pierini & Ratto Online Available at: http://www.indjsrt.com Research Article
ISSN:-2321-9262 (Online)
YARD TRIMMINGS' LIFE CYCLE: COMPOSTING vs. LANDFILLING *
Verónica Inés Pierini and Silvia Ratto Department of Soil Science, University of Buenos Aires, Av. San Martin 4453, Buenos Aires, Argentina *Author for Correspondence ABSTRACT Landfilling of yard trimmings is no good for many reasons. Landfill's space is scarce and yard trimmings occupy a lot of it. When buried, yard trimmings decompose in anaerobic conditions so they emit methane to the atmosphere increasing global warming. Finally, if we bury this biomass we are missing the opportunity to make compost. Objective: to compare greenhouse gases (GHGs) emissions of two management alternatives for Autonomous City of Buenos Aires and Metropolitan Area of Buenos Aires’s yard trimmings: landfilling and composting. We calculated, by means of IPCC, UNFCCC and European Commission’s models, methane and carbon dioxide emissions of the whole composting and landfilling processes and compared them. GHGs emissions were calculated for CEAMSE's (Coordinadora Ecológica Área Metropolitana Sociedad del Estado) composting plant in Buenos Aires, Argentina. Composting a year of yard trimmings biomass would emit 1.55Gg carbon dioxide eq if composted or 458.25Gg carbon dioxide if landfilled. This is long cycle carbon dioxide which is important for global warming. Composting is the best option as we avoid emitting global warming gases to the atmosphere; we slow down landfills clogging and we obtain compost. These figures extend knowledge of GHGs emissions scenario in our country. Key Words: Landfill, Yard Trimmings, Composting, Methane, Carbon Dioxide and Global Warming INTRODUCTION Landfilling of yard trimmings is no good for many reasons. Yard trimmings represent 6% of municipal solid waste (MSW) in Autonomous City of Buenos Aires (CABA) and 13% in Metropolitan Area of Buenos Aires (AMBA) (Instituto de Ingeniería Sanitaria, 2011). When buried, this important amount of yard trimmings decomposes in anaerobic conditions emitting methane to the atmosphere. Landfills emissions represent 6-18% of global methane emissions (Bingemer & Crutzen, 1987; Bogner & Matthews, 2003). There are two more reasons why landfilling is not good: landfills space is scarce while yard trimmings occupy a lot of it and burying this biomass is burying resources. So, we miss the opportunity to make compost from green waste. Compost is the product of aerobic degradation of organic matter in a controlled process. During this process emissions are mainly carbon dioxide and little quantities of methane and nitrous oxide (Teichmann & Schempp, 2013). Methane and nitrous oxide are greenhouse gases (GHGs) that have a global warming potential of the atmosphere 25 times and 298 times, respectively, higher than carbon dioxide (IPCC, 2007). Carbon dioxide that has global warming potential is called long cycle carbon dioxide. It is a product of combustion or degradation of substances of ancient carbon which was not available to reach the atmosphere easily, for example carbon in carbon fuel (Smith et al., 2001). On the contrary, short cycle carbon dioxide is carbon that completes its cycle fast and is available to be taken up by plants when degraded aerobically by microorganisms (Brown et al., 2008; Lou & Nair, 2009). The goal of this investigation was to choose the best option between landfilling and composting of CABA and AMBA’s yard trimmings, comparing GHGs emissions. To measure GHGs emissions of each step for the two alternatives is complicated and even impossible. So we used international proven models to estimate machinery, landfilling and composting emissions. MATERIALS AND METHODS Composting process Composting process takes place in CEAMSE’s composting plant in Complejo Ambiental Norte III, Buenos Aires, Argentina. In average, the plant receives 1200 Mg month-1 (3429 m3) of yard trimmings. This material is classified and 25-35% (in weight) of the original biomass is discarded. Selected material is chipped (rejects 3-5% in weight of this mass) and moistened to facilitate microorganisms’ decomposition. Composting process is aerobic and static. First, the material is introduced in silo bags where air is supplied and temperature and humidity of the piles are regulated. Then static piles are formed to end biological degradation (50-60% in weight of chipped mass is mineralized). After that, composted material is sieved. 27%, in weight, of that material has coarse particles and it is used for daily capping at landfill. 18%, in weight, of composted sieved material is 1.8-4cm long and is used in landscaping. Finally, 55%, in weight, is compost which has the finest particles.
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Ind. J. Sci. Res. and Tech. 2015 3(3):43-51/Pierini & Ratto Online Available at: http://www.indjsrt.com Research Article
ISSN:-2321-9262 (Online)
Estimation of GHGs emissions in carbon yard trimmings’ life cycle Scope: From total MSW we only consider yard trimmings that enter CEAMSE’s composting plant. From composting process (alternative) we analyzed: 1. carbon dioxide emissions from fuel combustion and electricity consumption by composting machinery; 2. carbon dioxide emissions from biological composting process and 3. Fugitive emissions (methane and nitrous oxide) from biological composting processes. From landfilling (baseline): 1. Landfilling methane potential generation; 2. Landfilling methane emissions and 3. carbon dioxide emissions from fuel combustion during landfilling. We worked with some stages for both alternatives (Fig.1).
Figure 1: Scheme of green waste life cycle: resources inflows and outflows and impacts on the environment. Details are given on the possibility of estimate the amount of material and emissions coming from each process: Dotted line impossible to estimate; Dashed line: not estimated, baseline and alternative are equal, Full line: estimated; Double line: it will be estimated in the future. Assumptions General emission models for total MSW are applicable for just a portion of MSW. 2. Every month enter the composting plant 1200 Mg of yard trimmings. 3. At CEAMSE there are 6 working days a week. Working days were calculated for every year between 2007 and 2015 in Argentina. Median was 245 days year-1. This assumption is necessary to calculate annual carbon dioxide emissions by machinery We considered two scenarios, one of maximum compost production and one of minimum. This was based on coefficients presented in item 2.1 for rejects (initial rejects, chipping rejects and sieving rejects) and mineralization occurred during composting process. The maximum compost production scenario reflects the best scenario when all rejects are minimized and mineralization is minimum, process’ efficiency is the best expected. The minimum compost production scenario is the worst case; process’ efficiency is the lowest. Between these two scenarios, others can exist that arise from all the combinations of all composting process’ coefficients. Figures of green waste’s total carbon dry base and humidity were obtained from green waste’s quality dairy data from 2007 to 2009. Based in 215 registers, total carbon maximum, minimum and mean, wet base, (Teichmann &
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Ind. J. Sci. Res. and Tech. 2015 3(3):43-51/Pierini & Ratto Online Available at: http://www.indjsrt.com Research Article
ISSN:-2321-9262 (Online)
Schempp, 2013) were calculated. Results were: Mean: 21.0% (SD: 4.2); maximum: 38.2%; minimum: 8.31% and limits of the confidence intervals (CI95): 20.45-21.58%. Composting process emissions Short cycle carbon: Carbon dioxide annual emissions were calculated with mineralized biomass during composting process in CEAMSE’s plant and the carbon dioxide emission factor obtained from European Comission’s Final Report (Smith et al., 2001). Mineralized biomass is calculated as: the remaining biomass after chipping multiplied by the percentage of that biomass mineralized during composting at CEAMSE (0.5 or 0.6 by weight). For mineralized biomass and total carbon we used our data (2.2.2. item), for the other parameters we used that given by the European Comission. This was calculated for the two compost production scenarios. Long cycle carbon: Total long cycle carbon emissions were calculated with CDM EB 65’s (2011) model. Total emissions are the sum of: 1.fossil fuel combustion and electricity consumption emissions by composting machinery, 2. fugitive methane and nitrous oxide emissions from anaerobic spots during composting process and 3. methane emissions that will be produced by anaerobic decomposition of the organic portion of first selection’s rejects landfilled. We did not considered emissions from co-composting because it is not carried out in CEAMSE’s plant. At CEAMSE’s composting plant fossil fuel consumption was 96,448 L y-1 and electricity consumption was 97,804 KW y-1. These figures were used to calculate carbon dioxide emissions. In both cases a first approximation was made with Oficina Catalana del Canvi Climàtic’s (2013) conversion coefficients. The other estimations were made with CDM EB 41’s (2008) model and CDM EB 39’s (2008) model for scenario A. Oficina Catalana del Canvi Climàtic’s conversion coefficients are: for fuel combustion: 2.79 Kg carbon dioxide L-1 gasoil and for electricity: 0.3 Kg carbon dioxide KWh-1. To calculate CDM’s coefficient for fuel consumption the following factors were used: 20.2 Mg C TJ-1 for diesel as carbon content factor (IPCC, 1996); 42.47 GJ Kg-1 of diesel (IDAE, 2014) as conversion factor and 850 Kg m-3 at 15ºC as diesel density (Viloria, 2013). To estimate CDM’s coefficient for fuel consumption the following factors were used: for Emission Factor (EF EL,j,y) 1.3 Mg carbon dioxide MWh-1 was used as default value and for the average technical transmission and distribution losses for providing electricity to source (TDLj,y) 0.2 was used as default value (CDM EB 39, 2008). Methane and nitrous oxide fugitive emissions were estimated with two different factors to compare results. For methane, 0.000604 Mg methane Mg-1 wet green waste (Amlinger et al., 2008) and 0.002 Mg methane Mg-1 wet green waste were used (CDM EB 65, 2011). For nitrous oxide 0.000178 Mg nitrous oxide Mg-1 wet green waste (Amlinger et al., 2008) and 0.0002 Mg nitrous oxide Mg-1 wet green waste (CDM EB 65, 2011) were used. Biomass used for estimations was biomass for composting. That is: Biomass for chipping – (Biomass for chipping * reduction coefficient). Reduction coefficient=0.05 or 0.1. Finally, initial rejects emissions were studied because estimations of the other rejects’ organic fraction were lacking. Organic fraction (30%in weight) represents 1296Mg a year (9% of initial biomass of green wastes). This would reflect an ineffectiveness of sorting process. This amount, estimated in carbon dioxide equivalents, was calculated with the same models as for total yard trimming biomass buried (described later). Total carbon used was that of 2.2.2. item. Methane landfilling emissions Methane emissions were calculated with two approximations: methane potential and methane emitted. Both models were taken from the IPCC’s Final Report (IPCC, 2006a). Carbon dioxide emissions from fossil fuel combustion during operation at the landfill were added. Methane generation potential (L0): The organic part of initial rejects and yard trimmings biomass for chipping was considered to be the biomass that decomposes anaerobically inside the landfill (W i). For Fraction of methane in the SWDS gas (F) we used 0.5 (Smith et al., 2001). For Fraction of dissimilable organic carbon (DOCf) that can decompose we used 0.5 (IPCC, 2006a). For Methane correction factor (MCF), considering CEAMSE’s landfill cells have a compacted capping over the MSW, we used a value of 1(Börjesson et al., 2009). Dissimilable degradable organic carbon mass (DDOC) is obtained as: Wi*DOCf* MCF*DOC (total carbon degradable fraction). Methane emissions over time: A first order decay (FOD) multi phase model was used. Modeling was started in 2007. Thirty years later (2036) biomass burial ended. Emissions were modeled until they were 0.55 Mg y-1. We did not estimate recovered methane (RT), so RT=0. For oxidation factor (OX) we used the default value 0.1 (CDM EB 55, 2010). For reaction constant (k) we used 0.1 given the rainfalls (annual mean: 1039 mm,(SMN, 2014)) and temperature (annual mean: 16.8 ºC,(SMN, 2014)) conditions in CABA and AMBA and quality of green wastes. The other parameters were described in 2.2.4.1. Emissions started on the 13th month after biomass was buried. These results were converted to carbon dioxide equivalent using a Global Warming Potential factor for methane: 25(IPCC, 2007). Carbon dioxide emissions from landfilling operations: Energy consumption for landfilling operations is not known. So, only carbon dioxide emissions from fuel combustion were estimated with conversion factor of 0.5 million Btu
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Ind. J. Sci. Res. and Tech. 2015 3(3):43-51/Pierini & Ratto Online Available at: http://www.indjsrt.com Research Article
ISSN:-2321-9262 (Online)
ton-1 of MSW (492,126 Btu Mg-1)(FAL, 1994). There was no description of activities accounted to generate this factor. So it was supposed that all activities in a controlled landfill were the same and this factor was used. It was also supposed that diesel was used for landfilling operations. This makes landfilling comparable to composting emissions at local and global scale (ROU, 2007). So, conversion factor utilized was 14.31 L diesel Mg-1 MSW (1 Btu = 0.00105MJ; diesel calorific power= 42.45 MJ Kg-1; diesel density (15 °C) = 0.85 g cm-3). Emissions were calculated for green wastes that arrive at CEAMSE during a year. GHGs emissions balance Initially, fuel combusting carbon dioxide emissions for composting were added to carbon dioxide equivalent emissions for initial rejects. Only estimations made with CDM EB’s models were used. Secondly, landfilling carbon dioxide equivalent emissions were added to long cycle carbon dioxide emissions from fuel combustion. Finally, a comparison between landfilling and composting GHGs emissions was made. For a correct comparison between alternatives, total emissions for each alternative were divided by total amount of green wastes entering CEAMSE’s plant in a year (14,400 Mg y-1). RESULTS AND DISCUSSION We worked with green waste because this fraction of MSW is collected separately from the other waste in Gran Buenos Aires. Globally yard trimmings are composted more often and in bigger proportion than organic waste from kitchens (Smith et al., 2001). Composting emissions Carbon dioxide short cycle carbon emissions from aerobic biomass decomposition during composting process present a very high variability depending on which carbon content in fresh biomass is used (Table 1). It represents between 55 and 259 Kg carbon dioxide Mg-1 of composted biomass taking into account all carbon contents and scenarios. However, this figure is, at CEAMSE, lower than in Europe (420 Kg carbon dioxide Mg -1waste) (Smith et al., 2001).
Anaerobic decomposition
Table 1: Estimation of: methane emissions (Mg), methane emission potential (L 0; Mg) and carbon dioxide eq emissions (Mg) from chipped biomass and rejects material deposited during a year. A scenario of maximum and minimum compost production is shown with three contents of organic carbon (average, maximum and minimum the last two between parenthesis and in that order). Estimation of methane emissions (Mg) from 30 years of biomass deposited in landfill. Methane Carbon dioxide equivalent Maximum Minimum Maximum Minimum production production production production ------2017 2054 Aerobic decomposition (3668-798) (3736-813) 761 20800 19025 L0 material for chipping + 832 (1513-329) (1384-301) (37825-8225) (34600-7525) rejects 76 106 1900 2650 L0 rejects (138-30) (193-42) (3450-750) (4825-1050) 679 18575 16975 Emission from chipping 743 (1356-291) (1240-266) (33900-7275) (31000-6650) material + rejects (1 year) 62 90 1550 2250 Emission from rejects (118-21) (168-32) (2950-800) (4200-525) (1 year) 22453 20548 Emission from chipping (40714-8885) (37259-8131) material + rejects (30 years) Carbon dioxide long cycle carbon emissions during composting were estimated for fuel combustion and electricity consumption. When estimated with Oficina Catalana’s coefficient, fuel combustion emissions were 269 Mg carbon dioxide y-1 (18.7 Kg carbon dioxide Mg-1 of green waste). These figures were similar when calculated with CDM’s formula: 255 Mg carbon dioxide y-1 (17.7 Kg carbon dioxide Mg-1 of green waste). Other coefficients proposed are similar to those used here (Smith et al., 2001; Brown et al., 2008). This is, possibly, because fuel combustion emissions can be quantified directly. It is not the same for electrical consume emissions. Electrical consume emissions estimated with Oficina Catalana’s coefficient were 29 Mg carbon dioxide y-1 (2 Kg carbon dioxide Mg-1 of green waste). But when CDM’s formula was applied, electrical consume generated 127 Mg carbon dioxide y-1, a bigger figure than before. These numbers
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Ind. J. Sci. Res. and Tech. 2015 3(3):43-51/Pierini & Ratto Online Available at: http://www.indjsrt.com Research Article
ISSN:-2321-9262 (Online)
are even larger if we add the emissions caused by system inefficiencies: 153 Mg carbon dioxide y-1 (10.6 Kg carbon dioxide Mg-1 of green waste). Other coefficients published are similar to that of the Oficina Catalana (Smith et al., 2001; Brown et al., 2008). This variability can be explained because electricity emissions cannot be estimated directly and because all types of electrical sources have to be taken into account. In addition, CDM incorporates a factor that accounts for system losses which increases the difference between results. Comparing CEAMSE’s energy consumption it can be seen that CEAMSE’s plant has bigger fuel consumption than composting plants in USA or Australia and similar electricity consumption to this last country (USEPA, 2002; ROU, 2007). Compared to plants in Australia CEAMSE’s plant consumes more fuel during the reception and maintaining stages. Methane fugitive emissions, calculated with Amlinger et al., (2008) factor, were 134 and 158 Mg carbon dioxide e y-1 when compost production was minimum or maximum respectively. When calculated with CDM’s coefficient, emissions were higher: 445 and 524 Mg carbon dioxide eq y-1 compost production was minimum or maximum respectively). In contrast, estimations of nitrous oxide fugitive emissions were similar when calculated with both coefficients: 472-556 and 530-624 Mg carbon dioxide eq y-1 when compost production was minimum or maximum and for Amlinger et al. (2008) and CDM’s coefficients, respectively. Methane emission from anaerobic digestion of initial rejects’ organic fraction (1296 Mg y-1) can be seen in table 1. This emission is added to composting long cycle carbon emissions. There are authors who claim that fugitive emissions are very low or null and they discard them. But fugitive emissions were studied because there are studies that demonstrate that those emission are high (Zeman et al., 2002; IPCC, 2006b; Amlinger et al., 2008; CDM EB 65, 2011). Rejects’ methane emissions are also important. Landfilling emissions As can be seen in table 1 potential emissions are variable depending on composting scenario and total carbon content. Methane potential emission can be used as a first approximation to methane emitted from landfills. This would be the maximum that could be emitted by landfilled green waste biomass (10.9 -11.9 Gg waste y-1). We chose IPCC’s FOD model because it is an international organism that receives information of national emissions from many countries. So we expect their model to fit a bigger number of climate and geographical situations than others. This model is applied globally (Mor et al., 2006; Börjesson et al., 2007; Machado et al., 2009; Abushammala et al., 2010) because it allows to incorporate climatic conditions and distinguish different fractions of waste making it more precise than others (Oonk, 2010). The difficulties in applying FOD model are a few. 1. It was not validated itself but other models, in which it is based, were validated. 2. It was not made to fit individual sanitary landfills but to fit the entire group of landfills of a country or region (Scharff & Jacobs, 2006). So this could diminish IPCC’s model accuracy. 3. There is lack of national data to estimate model’s parameters. 4. Existing information about these parameters is very variable (Bogner & Matthews, 2003) and the units in which they are expressed also vary, making it difficult to work. However, we consider the FOD model used to be the best option we could choose because of its accessibility, applicability to different regions and its differentiation of wastes fractions. If we concentrate in methane emissions (fig. 2), we observe that methane emission curves always initiate the year after first deposit is made and continue to grow while organic waste is landfilled. They persist during 50 and 105 years when the landfilling of waste occurs during 1 year or 30 years respectively. Maximum methane emission takes place the year after last deposit is made when the input of biomass is in 1 year and occurs the year before last deposit is made when the input last 30 years. Methane emission curves for different DDOC follow the same trend for both scenarios and depend on the number of years where deposit of green waste is made. If the maximum DDOC is taken into account maximum emissions can be compared. When biomass deposit last 1 year and compost obtained is minimum, methane emissions maxima is 109 Mg (fig. 2). When compost obtained is maximum, emission will be of 100 Mg. When deposit of yard trimmings last 30 years and the amount of compost obtained is minimum, total maximum emission will be 1090 Mg (fig. 2). If compost obtained is maximum then those emissions will be 998 Mg. Total emissions for 1 and 30 years can be seen in table 1. Gasoil consume generated an emission of 355-409 Mg carbon dioxide y-1 using EPA’s (2014) coefficient. Shape of the curves is modeled to follow biological degradation of waste by anaerobic microorganisms in landfills. Methanogens and other anaerobic organisms degrade labile organic matter first and then degrade the subproducts from less degradable fractions. As every year there is a new deposit with fresh material, emissions continue to grow. When deposit ceases, emissions decrease because microorganisms die as they do not have enough food. Emissions over time can be seen as the emissions that could really be produced if attenuation factors were to be considered. FOD model can be used to study the emissions dynamics and to make adjustments to reach good landfill management. For example, study the installation or improvement of a recovery system.
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Ind. J. Sci. Res. and Tech. 2015 3(3):43-51/Pierini & Ratto Online Available at: http://www.indjsrt.com Research Article
ISSN:-2321-9262 (Online)
Figure 2: Methane emissions in time (Mg y-1) from decomposition of green waste in CEAMSE’s landfill according to: average, minimum and maximum Dissimilable degradable organic carbon (DDOC), a scenario of minimum or maximum compost production, and for one and thirty years of biomass deposit in landfill. If we set a recovery system of biogas and it recovered 50% of generated biogas, there would be no emissions for any of two scenarios if DDOC is minimum. More over if recovering was 90% there would be no emissions in both scenarios when DDOC is the average or the minimum. So we can try different scenarios to find one in which economic, technical and environmental scopes match. Carbon balance Composting at CEAMSE is aerobic and emits, in average and for 14400 Mg waste a year, 2.04 Gg of short cycle carbon dioxide (table 2). This amount of carbon is bigger than carbon generated by the rest of the process but does not have global warming potential. It represents between 24-29% of carbon contained initially in chipping biomass (depending on compost production scenario). Composting emission with global warming effect is 1.55 Gg carbon dioxide. Fugitive emissions followed by fuel combustion emissions are the fractions that have more influence in this figure. Landfilling methane emissions were of 18.32 Gg carbon dioxide eq year-1 (table 2). This figure was a little less than potential methane emission, where no attenuation factors are considered. Machinery emissions (long cycle carbon) were much smaller than landfilling emissions. Considering the same mass of green material, long cycle carbon emissions because of landfilling are 12 times bigger than that emitted by aerobic composting process. Thanks to composting 17 Gg carbon dioxide eq are avoided to reach the atmosphere in comparison to landfilling.
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Table 2: Emission balance of composting process and landfilling (Gg carbon dioxide; 1 Gg= 1000 Mg) for a year of green waste deposit COMPOSTING PROCESS 0.26 Fuel consume emission 0.15 Energy consume emission 0.48 Fugitive emission (methane) 0.58 Fugitive emission (nitrous oxide) 0.08 Initial reject emission (methane) Total long cycle C emission 1.55 Total Short cycle C emission 2.04 LANDFILLING Potential emission (methane) Real emission (methane) Fuel consume emission Total emission
potential real
19.91 17.78 0.55 20.46 18.32
We show strong evidence, in terms of GHGs emission balance, that composting is a better option to treat green waste than burying it in a sanitary landfill. Emissions avoided with composting process are 457 Gg carbon dioxide. For other compostable materials, depending on the efficiency with which landfills recover landfill gas and C sequestered by landfills, composting is a less suitable option to treat them (Smith et al., 2001; USEPA, 2014). We think that composting may be a less suitable option in terms of GHGs balance but, as it is in our case, there are many other reasons why it is a good idea to compost or recycle organic materials. We can obtain a new product (compost, paper if we are recycling paper or cupboard, etc) and we do not need, or need less, new materials to do so. In addition, we retard landfills clogging and reduce impact on soil and water. There are other options to treat our organic waste (Kranert et al., 2010) but there is no solution which will “save” us all. Finally, it would be interesting, to close life cycles, to estimate the quantity of carbon stocked in soil after application of compost or in the landfill (Bogner & Spokas, 1993; Barlaz, 1998; De la Cruz et al., 2013; USEPA, 2014). Although this results may have very limited application because of great variation of variables (amount, proportion and type of MSW composted or landfilled, characteristics of composting processes or landfilling processes, climate conditions, etc.). CONCLUSION The use of green waste to produce compost reduces methane emissions. Also, it reduces volume of waste buried in landfills which slows down landfills clogging and has multiple benefits when applied to crops or in ornamentation. It has been demonstrated, with verifiable formulas, that yard trimmings composting is an alternative viable and positive to landfilling. Even though this first approximation can be improved, it is important to remember its great value because is the first step in this subject in our country. These figures are a very important contribution to GHGs balance in Argentinian Republic. Following steps in this subject could be, to adapt model’s parameters to fit the characteristics of our country and to estimate lacking information in this green waste’s carbon cycle. ACKNOWLEDGEMENT This research was made in collaboration with Dr. Alejandro Cittadino who is in charge of environmental monitoring CEAMSE and Joaquín Guillot. This research is part of a Masters degree scholarship UBACyT, Resolution (CS) Nº 5621/2012; And its extension: Res. 1128 EXP-UBA: 49805/2014. REFERENCES Abushammala MFM, Basri NEA, Basri H, Kadhum AAH & El-Shafie AH (2010). Estimation of Methane Emissions from Landfills in Malaysia using the IPCC 2006 Model. Journal of Applied Sciences, 10 1603-1609. Amlinger F, Peyr S & Cuhls C (2008). Green house gas emissions from composting and mechanical biological treatment. Waste Management & Research, 26 47-60. Barlaz MA (1998). Carbon storage during biodegradation of municipal solid waste components in laboratory-scale landfills. Global Biogeochemical Cycles, 12 373-380.
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