Universidade Federal de Santa Maria

Ci. e Nat., Santa Maria, v. 41, e50, 2019.

DOI: http://dx.doi.org/10.5902/2179460X36777

Received: 06/02/2019 Accepted: 13/04/2019

Section Environment

Estimation of greenhouse gas emissions in the agro-industrial system of sugarcane in Piauí, Brazil.

Lilian de Castro Moraes Pinto^I

^IUniversity of Brasilia, DF, Brazil - lilian.moraes@gmail.com

Abstract

The present study presents an estimate of greenhouse gas emissions throughout the production process of ethanol and sugar originated from sugarcane in Piauí. The field research was carried out in a mill with an attached distillery, where the harvest was conducted manually, from January to December 2015. Life Cycle Assessment principles were considered in the quantification of total CO₂, CH₄ and N₂O emissions in the stages of agriculture, industrialization and distribution, converting them according to their global-warming potential into carbon-equivalent (CO₂eq). The use of fuels, agriculture inputs, sugarcane burning, manufacture of machinery and physical structure of the mill, application of pesticides, seeds, use of chemical reagents in the production process and human labor were considered in this study. The results show a total emission of 2,413.3 kg CO₂eq /ha.year, and the main key sources were sugarcane burning (48%) and use of chemical products (29.6 %). The industrial and distribution stages contributed with 2% of the emissions each. There was an emission of 29.9 kg CO₂eq per ton of sugarcane processed and it was estimated that there would be a net reduction of 83% of emissions if the harvesting could be thoroughly conducted mechanically.

Keywords: Ethanol; Sugar; Life cycle assessment

1 Introduction

Oil-based fuels have been introduced to replace coal as an energy source in order to avoid the release of pollutant particles into the air, which pose a serious problem to the health of the world's population (BARTRA et al., 2007). However, the burning of fossil fuels has increased the concentration of carbon dioxide (CO₂) in the atmosphere, aggravating the greenhouse effect, which retains a portion of the heat emitted by the sun in the Earth's atmosphere, keeping the planet warm. According to Pearce (2002), the intensification of this phenomenon has become a problem whose most serious consequence is the increase in global temperature. This problem, along with geopolitical conditions and the price of fossil fuels, as well as advances in biofuel production technologies, environmental conditions, concern with emission reduction and energy supply have led to the search for alternative energy matrices (HAHN-HÄGERDAL; LINDEN; ZACCHI, 2006).

Thus, this search evidenced a group of liquids derived from vegetable matter, known as biofuels (CLANCY, 2008). Brazil produces ethanol since 1975, which places the country in an internationally favorable position in terms of CO₂ emissions. As a result of the use of this biofuel that derives mainly from sugarcane, the country became the world leader in the agroenergy sector, responsible for about 30% of the energy offered in 2011 (BRAZIL, 2011).

In addition to ethanol, sugarcane serves as a raw material for the production of sugar. According to the Companhia Nacional de Abastecimento (CONAB), while between 2005/2006 sugar production was 26.42 million tons, between 2013/2014 it was 37.87 million. In the same way, ethanol production in 2005/2006 was 16.99 billion liters, while in 2013/2014 it increased to 27.95 billion liters. Both productions showed a growing trend in Brazil over the period under analysis (CONAB, 2014). Moreover, the Ministry of Agriculture, Livestock and Food Supply estimates for the 2019 crop, a production of 47.34 million tons of sugar, and 58.8 billion liters of ethanol (BRAZIL, 2014).

However, the belief that the substitution of fossil fuels with ethanol would nullify the chances of climate change in the future is incorrect, since the production of ethanol and sugar from sugarcane requires the use and burn of fossil fuels, emitting GHG (GARCIA; SPERLING, 2010).

It is noteworthy that at the 21st Conference of the Parties (COP21) of the United Nations Framework Convention on Climate Change in 2015 in Paris, Brazil vowed to reduce GHG emissions by 37% below 2005 levels by 2025, with a subsequent reduction by 43% until 2030 (MMA, 2016).

Several studies have focused on assessing the mitigating potential of ethanol's GHG emissions, although there are different technological scenarios in which ethanol is produced, including distinct agricultural and industrial practices (GARCIA; SPERLING, 2010). Therefore, the present study aims to present an estimate of GHG emissions originated in the production process of ethanol and sugar from sugarcane in Piauí, thus identifying the stages or activities in which the highest GHG emissions occur and their respective emissions. The nature of the current research is exploratory due to the lack of previous studies in this area. As a result, it did not test any hypotheses and did not interpret the results by applying any theoretical bases. The results were used to evaluate the potential mitigation of GHG emissions by the replacement of fossil fuels with ethanol in the context of Piauí.

2 Methods

This study was carried out regarding the 2015 crop year in Piauí, which contains a single sugar-alcohol plant, established in 1979, with a total area of 16,000 ha and 12,000 ha cultivated and harvested in 2015. Hereby, this enterprise is referred to as the Plant. Data were collected through interviews and document analyses. Calculations were made with the use of Microsoft Excel software (U.S.).

In order to estimate the GHG emission, principles of the Life Cycle Assessment (LCA) methodology were adopted, according to the standards ABNT NBR ISO 14040 and ABNT NBR ISO 14044 and recommendations of the IPCC (2006). Sugar and alcohol production systems were described separately, and GHG outputs in the two processes were identified to estimate their emission for each activity: raw material cultivation, industrial processing and distribution. The basic quantities of all input items were used to estimate GHG emissions, considering one hectare of land cultivated for one year (functional unit). Emission factors from the IPCC (2006) were applied.

Carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) emissions were considered, because they are the most important anthropogenic GHGs in agriculture-related systems (IPCC, 2006). Total emissions are expressed in kg of CO₂ equivalent (kg CO₂eq).

This study applied the standard average of Macedo, Seabra and Silva (2008) for the management of the sugar cane crop: a six-year planting cycle, with one reforestation, four crops and five cuts. The aspects related to the cultivation of sugar cane were defined considering the data related to the implantation of the crop, which was a unique activity, for the subsequent five years of production, divided equally for the six years of cultivation. GHG emissions from the harvest and maintenance of the crop were estimated taking into account the production of 2015.

The survey of emissions in the studied Plant was conducted with average values of consumption and production. As the objective of the study was to determine the steps or activities in which most GHG emissions occurred, no data uncertainty analysis was performed. GHGs were classified into three categories: agricultural phase emissions, industrial processing emissions and emissions from the distribution of sugar and ethanol.

The Plant did not use gasoline in any of the agricultural or industrial operations, and such fuel was not taken into account in the quantification of emissions. Similarly, the Plant did not use fuels in the industrial stage, since the electric energy was generated by the burning of the sugarcane bagasse. In order to calculate GHG emissions, the emission factors of diesel, oil and coal were applied according to IPCC (2006).

In the studied Plant, agricultural operations were characterized by semi-mechanized cultivation (mechanized grouting and fertilization, with manual planting) and manual harvesting with previous burning of the cane field. It was not possible to determine the amount of machinery used and the consequent consumption of fuels in agricultural operations; thus, data reported in Macedo, Leal and Silva (2004) were adopted. It is significant that the authors analyzed a plant that performed mechanized harvesting, which implies in greater use of machinery than what actually occurred in Piauí.

The consumption data of lime and fertilizers were applied according to Alves, Boddey and Urquiaga (2009), even though it was an overestimated value since the plant destined the whole amount of filter cake, ashes and sediments generated in the industrial stage to the sugarcane fields.

For the calculation of the emissions due to the consumption of pesticides (herbicides and insecticides), the recommendations of Alves, Boddey and Urquiaga (2009), BNDES (2008) and PIMENTEL (1980) were followed. Regarding the transportation of cane from the crop to the industry, it was considered: the Plant's agricultural productivity, the average distance traveled of 17 km (BRAZIL, 2013), and the type of truck, with an average capacity of 28 tons of cane, whose fuel efficiency varied from 1.6 km /L of diesel when full and 3 km /L when empty. Emissions from the transport of inputs to the Plant and to the crop were defined according to Boddey et al. (2008).

  The emissions of manual labor in the cultivation of sugarcane were estimated considering the energy consumed by rural work (kcal / work day) of 14,975 kcal/day, according to Giampietro and Pimentel (1990), and the employment of 128 man hours per hectare in one year. The emissions resulting from the construction of the Plant, associated to the material used in the constructions and the equipment, were determined according to Pimentel and Patzek (2007).

GHG emissions from the distribution of sugar and ethanol considered the trucks owned by the Plant, with a capacity of 3,000, 5,000 and 15,000 L, with an average fuel efficiency of 2.5 km/L, and the average distance of 360 km, in the round trip (COMVAP, 2016).

The burning of sugarcane field before the harvest was also responsible for GHG emissions, calculated according to Alves, Boddey and Urquiaga (2009), for whom the total amount of cane straw deposited is 16.4 t/ha.year.

3 Results and Discussion

Total emissions of ethanol and sugar production in Piauí were calculated based on Table 1, which summarizes the results of the 2015 crop at the Plant.

Table 1 – Summary of the 2015 sugarcane crop in Piauí

Item	Production
Harvested area (ha)	12,000.00
Total sugarcane (t)	967,427,41
Average yield (Mg/ha)	80.60
Ethanol sugarcane (t)	152,282.14
Total ethanol (m^3)	32,679.50
Sugar sugarcane (t)	815,145.27
Total sugar (kg)	66,914,600.00

Source: Research data

Considering that the total amount of sugarcane harvested in 2015 corresponded to 100%, it was verified that 84.3% of sugarcane was used to produce sugar and 15.7% was destined to the production of ethanol.

Table 2 presents the result of the LCA on the basic quantities of all entry items in the sugarcane agroindustrial system, considering one hectare of land cultivated during the 2015 harvest.

Table 2 – Input data of the sugarcane agroindustrial system in Piauí, in 2015, and the respective amount of energy they required.

Inputs			Energy
ITEM	Basic quantity	Basic unit	Energy factor (MJ/basic unit)		MJ/ha.year
Machinery	136.6	kg	8.52		1,163.83
Diesel oil	22.26	L	35.52		790.80
Lime	333.00	kg	1.31		436.20
Phosphorus	16.00	kg	3.19		51.04
Potassium	83.00	kg	5.89		488.87
Nitrogen	57.00	kg	54.00		3,078.00
Herbicides	2.20	kg	451.66		994.40
Insecticides	0.12	kg	363.83		43.66
Seeds ^1	2,000	kg	-		190.34
Input transportation	5.80	L	35.52		206.00
Sugarcane transportation	35.50	L	35.52		1,260.90
Construction cement	8.32	kg	6.61		54.99
Structural light steel	20.30	kg	30.00		609.00
Equipment light steel	18.20	kg	30.00		546.00
Stainless steel	2.90	kg	71.70		208.18
Rectification up to 99.5%^2	-	-	-		225.30
Chemical reagents used in the plant^2	-	-	-		487.60
Workforce	128.00	h	7.84		1,003.50
Ethanol distribution	26.14	L	35.52		928.60
Sugar distribution	19.11	L	35.52		679.10
Total				13,446.31

Source: Research data

Note: ¹ Estimated as 2,0% of all agricultural inputs (Pimentel and Patzek, 2007).

² Alves, Boddey and Urquiaga (2009).

The basic quantities of all input items, shown in Table 2, were used to estimate GHG emission using emission factors for each of the considered gases (CO₂, CH₄ and N₂O) and knowing the amount of each GHG generated by the production of 1 MJ of energy by burning oil, diesel or coal, according to IPCC (2006). In order to do so, the most representative primary energy source for each of the items was determined.

According to Alves, Boddey and Urquiaga (2009), GHG emissions resulting from labor, herbicides, insecticides and seeds from different sources are better represented by oil as the primary energy source required for manufacturing, processing or development. An emission of 162.9 kg of CO₂eq per hectare per year from processes using petroleum as the primary energy source was determined. Mineral coal was considered the primary source of energy for the manufacture of agricultural machinery. An emission of 110 kg of CO₂eq was observed due to the burning of this fuel and the estimates were based on the amount of steel contained in the composition of the machinery. Diesel oil was recognized as a source of energy for the transport of inputs and cane, for agricultural machinery and for the distribution of products. Thus, it is noteworthy that the burning of diesel oil generated 217.46 kg of CO₂eq per hectare per year.

In addition, regarding fertilizers and lime, the CO₂eq emission factor for each kilo of input was applied according to Garcia and Sperling (2010). The amount of CO₂eq emitted due to the use of nitrogen, phosphorus and potassium fertilizers by the Plant in the harvest of 2015 totaled 402.64 kg. According to IPCC (2006), the CO₂ emissions from the addition of lime were estimated by the amount applied to the planting, multiplied by the emission factor of 0.75 kg of CO₂/kg of lime which resulted in an emission of 225 kg of CO₂.

As there is no specific data for the burning of sugarcane straw concerning the emissions of CH₄ and N₂O, the factors provided by the IPCC (2006) for the burning of agricultural waste were used. It reports that for each ton of burnt straw with an efficiency of 80%, there is an emission of 2.7 kg of CH₄ and 0.07 kg of N₂O. It was estimated that the burning of the sugarcane straw during the harvest was responsible for the emission of 425,088 kg of CH₄ and 11,020.8 kg of N₂O. Converting these values by their respective greenhouse effect potentials, an emission of 1,159,3 kg of CO₂eq per hectare was found.

Results showed that 48% of the GHG emission (Figure 1) during the stages of agriculture and industrialization of sugarcane for ethanol and sugar production occurred during the burning of the sugarcane field, when there was emission of CH₄ and N₂O. During the crop management, there was also emission of 26.82 kg of CO₂eq from the nitrogen present in the filter cake. According to Soares, Biruir and Baldos (2009), there are 5.5g of N in each kilogram of filter cake, and usually 10t are added per hectare. This means an addition of 55kg/ha of N in the planting, or 9,1 kg/ha.year. It is added that, according to the IPCC (2006), 1% of the applied nitrogen is emitted as N₂O.

In the Plant, vinasse was distributed by fertigation and, according to Alves, Boddey and Urquiaga (2009), doses of vinasse traditionally vary from 80 to 150 m³/ha.year, containing approximately 1 to 2% of soluble carbon and 0.2% of the contained carbon is emitted as CH₄. Therefore, the equivalent CO₂ emission caused by the fertirrigation totaled 59.67kg/ha.year. The N₂O emissions were estimated based on IPCC (2006), which defined that 1% of the applied N is emitted in the form of N₂O. Resende et al. (2006) estimated that 80m³ of vinasse contains 23kg of N. In order to facilitate the calculation, in this research the dose of 80m³/ha.year of vinasse was considered, containing 20kg of nitrogen and 2% of soluble carbon, which meant 1.6m³.

The emissions of CO₂eq caused by the construction and maintenance of the Plant's physical structure totaled 49.6 kg/ha in 2015, according to the methodology of Boddey et al. (2008). Emissions from the burning of the bagasse in the boilers were not accounted for, since the chimney of the boilers has a gas washing system, which hold solid particles and cleans the smoke before its release into the atmosphere.

In order to synthesize GHG emissions into the sugar and ethanol production process by the Plant in 2015, all those originating from agricultural, industrial and distribution activities were converted into CO₂eq and the results are summarized in Table 3.

Table 3 – GHG emissions by sugar cane processing in Piauí in 2015

Stages	GHG emission (kg/ha.year)
	CH4	N2O	CO2	CO2eq	Total CO2eq
Agricultural phase	35.410	14.2	1,067.3	1,246.1	2,313.4
Industrial phase	-	-	-	49.6	49.6
Distribution	0.002	0.00004	50.2	0.061	50.2
Total emission	35.400	14.2	1,117.5	1,295.8	2,413.3

Source: Research data

According to Table 3, CO₂ emissions were predominant in the cultivation of the sugarcane. This is due to the burning of the straw during the harvest, the use of energy from fossil fuels in machinery and transportation, and the application of fertilizers and lime. The emission derived from the production of ethanol and sugar reached approximately 2.0% of the emissions calculated for the complete cycle, as well as the emissions from the distribution of these products.

In contrast with the results obtained by Macedo, Leal and Silva (2004), it was observed that the total emissions estimated in this study (2,413.3 kg CO₂eq/ha.year) were lower. While they found the emission of 34.5 kg CO₂eq per tonne of sugarcanecane (tc), in Piauí this value was 29.9 kg CO₂eq/tc, considering the average productivity of 80.6 Mg/ha. Therefore, the main difference was in the emissions corresponding to the burning of sugarcane. In the study by Macedo, Leal and Silva (2004), such emissions amounted to 32.84% of the total, considering 100% of combustion efficiency, different from our research, in which it was 48%. Nevertheless, the total amount of GHG emitted in Piauí in 2015 was lower than that found by these authors, who analyzed two technological scenarios: one representing average values of consumption by the distilleries and the other, considering optimal values of input consumption. This research was in line with the second scenario, since the analyzed distilleries used industrial waste in sugar cane agriculture, which contributes to the reduction of total GHG emissions.

The Plant's efforts to reuse agricultural and industrial waste in the field and in the processing of alcohol and sugar have resulted in mitigation of the amount of GHG emitted in 2015, despite the need to continue improving techniques and replace practices which are harmful to the environment, such as the burning of straw before the harvest.

Results show that the life cycle of ethanol and sugar in Piauí in 2015 generated the amount of 2,413.3 kilograms of CO₂eq per hectare cultivated. Figure 1 presents the proportion of atmospheric emissions related to the different stages of the production system.

Figure 1 - GHG atmospheric emissions by activity in Piauí in 2015

Source: Research data.

Note: ¹ Emissions referring to the application of filter cake and vinasse were counted with the inputs.

The stage that emitted the greatest amount of GHG was agricultural, mainly the harvest, corresponding to the burning of the straw (48% of the emissions), and in part to the application of fertilizers (29.6%). The burning of diesel oil caused by the transport of inputs to the crop and to the Plant, of sugarcane from the field to the Plant and the distribution of sugar and alcohol was responsible for 9% of total emissions.

CO₂ emissions from sugarcane burning were not taken into account because we believe that the released carbon was reassimilated by the vegetation during the following crop. Nevertheless, this stage of sugar and alcohol production emitted the most GHG into the atmosphere. If the insertion of 100% mechanical harvest in Piauí was possible, the emissions would result in an additional consumption of 2,628.48 MJ/ha.year and an approximate release of 194.7 kg CO₂eq/ha.year, considering that the machinery consumes fossil fuels in a rate of 74L/ha (MACEDO; LEAL; SILVA, 2004). The emissions from the burning of the cane in the field would be zero, resulting in an emission of 1,159.3 CO₂eq/ha.year. Thus, the introduction of mechanized harvesting could reduce burning emissions by 83%. Therefore, the replacement of manual for mechanized harvesting is a viable alternative to make the productive process in Piauí more sustainable.

In 2015, the Plant in Piauí was responsible for the emission of 2,413.3 kg of CO₂eq per hectare cultivated and processed, with each hectare generating 6,228.00 L of ethanol, resulting in the emission of 0, 39 kg of GHG per liter of manufactured alcohol. Macedo, Seabra and Silva (2008) considered both the agricultural and industrial phases and obtained total emissions of 0.42 and 0.43 kg of CO₂eq during the production of hydrated and anhydrous ethanol, respectively. The amount of GHG emitted in Piauí was lower and closer to the scenario predicted by the aforementioned authors for 2020, when the average emission of 0.33 kg of CO₂eq is expected.

Oliveira, Vaughan and Rykiel Jr. (2005) estimated GHG emissions from the production of ethanol from sugarcane in Brazil in two different scenarios, varying the yield of sugarcane per hectare, the conversion rate of liters of ethanol per Mg of sugarcane and demand for energy. They reached an emission of 0.46 kg of CO₂eq/L under the best conditions and 0.57 kg of CO₂eq/L under the worst conditions. In Piauí, the value obtained in 2015 was below their estimate under the most advantageous circumstances, which reveals a procedure favorable to the environment.

Moreover, according to the ANP (2015), 41.13 billion liters of gasoline were consumed in Brazil in 2015. The area required for the total substitution of this volume of gasoline for ethanol, without considering the difference in average consumption between vehicles powered by each fuel, would be 6.37 million hectares (Brazil, 2013). This amount is close to the total area planted with sugarcane in Brazil in the 2015/2016 harvest, which was 8.6 million hectares (CONAB, 2016). In other words, in order to completely replace the use of gasoline with ethanol, it would be necessary to double the area devoted to sugarcane, which could lead to other consequences such as deforestation, competition with food crops and expropriation. Because the prospects for expanding planted areas are limited, raising productivity in the field and in the industry tends to be one of the only viable solutions for sustaining the sector, and it is directly related to the adoption of new technologies and, consequently, to the increase of investments.

4 Conclusions

In summary, because the Plant adopted manual harvesting in 2015, most GHG emissions from ethanol and sugar production occurred during the burning of sugarcane and straw, due to the release of CH₄ and N₂O. Nonetheless, results found for emissions in Piauí were considerably lower than in other plants situated in more developed areas of the country, such as in the Southeast region. Procedures followed by the Plant studied, such as the reuse of agricultural and industrial waste in the field and in the processing, were considered favorable to the environment, for their reduction of GHG emissions.

However, the complete replacement of fossil fuels with ethanol, considering the context of Piauí, would not be advantageous to the environment because of the need for lands to cultivate the sugarcane. More research is needed in order to enhance productivity both in the agricultural and industrial stages and diminish GHG emissions without enlarging the area of sugarcane cultivation.

References

ALVES BJR, BODDEY RM, URQUIAGA S. Mitigação das emissões de gases efeito estufa pelo uso de etanol da cana de açúcar produzido no Brasil. Circular Técnica, EMBRAPA, Seropedica – RJ. 2009;13p.

ANP. Anuário estatístico brasileiro do petróleo, gás natural e biocombustíveis 2015. Rio de Janeiro: MME, ANP. 2015;249p

BARTRA J, MULLOL J, CUVILLO A, DÁVILA I, FERRER M, JÁUREGUI I. Air pollution and allergens. Journal of investigational allergology and clinical immunology, 2007;17(2):3-8.

BNDES. Bioetanol de cana de açúcar - Energia para o desenvolvimento sustentável. CEPAL, 1, Rio de Janeiro. 2008;72-76.

BODDEY RM, SOARES LHB, ALVES BJR, URQUIAGA S. Biofuels, solar and wind as renowable energy sistems. In: PIMENTEL, D. (Ed.). Bio-ethanol production in Brazil. New York, USA, Springer. 2008;321-356.

BRASIL. Ministério de Agricultura, Pecuária e Abastecimento. Brasil é líder mundial no setor de agroenergia [internet].  Brasília: MAPA; 2011 [cited 2015 sep]. Available from: http://www.agricultura.gov.br/comunicacao/noticias/2011/12/brasil-e-lider-mundial-no-setor-de-agroenergia

BRASIL. Ministério de Agricultura, Pecuária e Abastecimento. Perfil do setor do açúcar e do álcool no Brasil. Edição para a safra 2011-2012. Brasília: MAPA. 2013;5:1-88.

BRASIL. Ministério de Agricultura, Pecuária e Abastecimento. Cana-de-Açúcar [internet]. Brasília: MAPA; 2014 [cited 2015 sep]. Available from: http://www.agricultura.gov.br/vegetal/culturas/cana-de-acucar

CLANCY JS. Are biofuels pro-poor? Assessing the evidence. The European journal of development research. 2008;20(3):416-431.

COMVAP. Relatório acerca da safra 2015. Teresina, 2016.

CONAB. Séries históricas de área plantada, produtividade e produção, relativas às safras 2005/06 a 2014/15 de cana-de-açúcar [internet]. 2014 [cited 2015 feb]. Available from: http://www.conab.gov.br/conteudos.php?a=1252&ordem=produto

CONAB. Acompanhamento da safra brasileira: cana de açúcar. Safra 2015/16. Brasília. 2016;2(4):1-76.

GARCIA JCC, SPERLING EV. Emissão de gases de efeito estufa no ciclo de vida do etanol: estimativa nas fases de agricultura e industrialização em Minas Gerais. Engenharia Sanitaria e Ambiental. 2010;15(3):217-222.

GIAMPIETRO M, PIMENTEL D. Assessment of the energetics of human labor. Agriculture, Ecosystems and Environment. 1990;32:257-272.

HAHN-HÄGERDAL B, LINDEN G, ZACCHI G. Bio-ethanol – the fuel of tomorrow from the residues of today. Trends biotechnology. 2006;24:549-556.

IPCC. Good Practice Guidance and Uncertainty Management in National Greenhouse Gas Inventories. In: IPCC. 2006 IPCC Guidelines for National Greenhouse Gas Inventories. IPCC, 2006.

MACEDO IC, LEAL MRLV, SILVA JEAR. Balanço das emissões de gases do efeito estufa na produção e no uso do etanol no Brasil. São Paulo: Secretaria de Meio Ambiente do Estado de São Paulo. 2004;37p.

MACEDO IC, SEABRA JEA, SILVA JEAR. Greenhouse gases emissions in the production and use of ethanol from sugarcane in Brazil: The 2005/2006 averages and a prediction for 2020. Biomass and Bioenergy. 2008;32(7):582 – 595.

MMA. Acordo de Paris [internet]. 2016 [cited 16 nov]. Available from: http://www.mma.gov.br/clima/convencao-das-nacoes-unidas/acordo-de-paris.

OLIVEIRA MED, VAUGHAN BE, RYKIEL JR EJ. Ethanol as fuel: energy, carbon dioxide balances, and ecological footprint. Bioscience. 2005;55(7):10p.

PEARCE F. O aquecimento global. São Paulo-SP: Publifolha. 2002;72p.

PIMENTEL D. Handbook of energy utilization in agriculture. 1980;487p.

PIMENTEL D, PATZEK T. Ethanol production: energy and economic issues related to U.S. and Brazilian sugarcane. Natural Resources Research. 2007;16(3):235 – 242.

RESENDE ASD, SANTOS A, XAVIER RP, COELHO CH, GOLDIM A. Efeito da queima da palhada da cana-de-açúcar e de aplicações de vinhaça e adubo nitrogenado em características tecnológicas da cultura. Revista Brasileira de Ciência do Solo. 2006;30:937-941.

SOARES LHB, BIRUIR D, BALDOS U. Mitigação das emissões de gases efeito estufa pelo uso de etanol da cana de açúcar produzido no Brasil. Relatório Técnico. Seropédica, RJ: EMBRAPA. 2009;14p.