Assessment of agricultural biomass residues to replace fossil fuel and hydroelectric power energy: A spatial approach.

Abstract Despite the recent discoveries of considerable fossil fuel reserves, Brazil is one of the only great economic and industrial powers with very high amounts of renewable energy in its electricity matrix. Approximately 79.3% of the electric energy supply comes from renewable resources, of which hydroelectric power represents 70.6%. The two primary concerns regarding hydroelectricity are the damage caused to the environment by the construction of dams and the uncertainty of the supply in cases of long drought seasons. This article presents an analysis on the availability and energy exploitation of sugarcane straw and forest residues derived from eucalyptus for decentralized generation using a Geographic Information System–based model. The potential bioelectricity and bioethanol production from sugarcane and eucalyptus biomass in the Administrative Region of Campinas (ARC) is higher than the demand in this region. The results provide guidelines for designing alternatives to the intended Nationally Determined Contributions in Brazil within the scope of the ARC, and they can be used to provide energy empowerment, electric matrix diversification, and new policies that address the residue availability and demand.


| INTRODUCTION
Because of the impacts caused by extreme events associated with increased levels of carbon dioxide (CO₂) and other gases, 1,2 people around the world have been discussing how to address this issue since 2003. 3,4 Many countries have committed to an effort to decrease their production of greenhouse gases (GHG), primarily CO₂, to prevent an increase in temperature above 2°C, with the temperature of the pre-industrial era used as the baseline. In this context, one point can be highlighted, namely the sustainable use of bioenergy.
The signatory countries of the Intergovernmental Panel on Climate Change (IPCC) have adopted different measures to contain the emissions of harmful gases; however, they all consider bioenergy as a source of renewable energy (RE). The European Union (EU), whose contribution to energy consumption (starting from 2458 PJ in 2005) will reach 4605 PJ in 2020, has adopted ambitious goals for using RE and bioenergy. 5 The Conference of the Parties (COP21) of the United Nations Framework Convention on Climate Change (UNFCCC) resulted in an agreement to save the planet in the case that the expected scenario for extreme events and climate change is established. All the member countries committed to adopting measures to reduce GHG effects, and, in doing so, to mitigate the impacts of climate change. At the COP21, the participant countries presented their mitigating goals by their intended Nationally Determined Contributions (iNDCs). Each member country has established its iNDCs in the context of its national priorities, jurisdictions, and expertise, and these goals were endorsed in November 2016 at the COP22. For its iNDC, Brazil made a commitment to reduce its emissions of greenhouse gases by 37% below its 2005 levels by 2025, with a subsequent intention to reduce its emissions of greenhouse gases to 43% below the 2005 levels by 2030. 4,6,7 Agricultural biomass residues are important and strategic inputs for bioenergy in the above context. Agricultural biomass residues were previously considered as an input of low aggregated value and were left behind in the field or burned; however, they are now seen as essential in a low-carbon economy in several respects, including the composition of carbon in the soil, the mitigation of GHG effects, and the generation of renewable energy. 5,8,9 Brazil has already made important sustainability advances in its use of agricultural biomass for energy generation. The production of ethanol, which may be used in pure form or in a mixture with gasoline as automobile fuel or for electric power generation (sugar mill cogeneration), provides two important examples. [10][11][12] Additionally, it has been proposed that Brazil should adopt measures that are coherent with the temperature increase up to 2°C. Among these measures, expanding the use of renewable energy sources, except those derived from hydroelectricity, such as biomass, wind, and solar power energy, is highlighted. However, energy from hydroelectric power plants has also decreased due to the problems of water scarcity [13][14][15] and supply sources. 16 In addition, the new hydroelectric power plants are located in the northern region, which is far from the region with the highest demand (in the southeast). 17 Moreover, Brazil is engaged in implementing low-carbon agriculture that focuses, among other things, on the use of biofuels and on increasing the alternative sources that biomass offers. 18 Brazil is a country with great resources and varied agriculture, and it has enormous potential to engage in energy production using agricultural biomass residues. 19 Many factors can define the major use of bioenergy. Among them is the relative geographic distribution of the sources of origin for agricultural biomass that could increase the diversity of the energy supply and contribute to improved energy security. [20][21][22] Few studies have explored the availability of agricultural biomass residues as materials for exploitation as renewable energy sources in Brazil, 23,24 despite their widespread use around the world.
Therefore, key points need to be addressed, such as spatial aspects in the context of a low-carbon economy. Agricultural biomass residues are spread over wide-ranging territories. The Geographic Information System (GIS) is a powerful tool for assisting decision makers regarding agroenergy systems once the spatial variables are considered. [25][26][27] Many authors have used spatial analyses to address the optimal energy use of agricultural residues, 5,28-31 in which residues were exploited for potential energy generation. These studies considered spatial aspects and helped to create subsidies for the European community regarding public policy decision making. Other studies from around the world can also be mentioned; these studies include Voivontas et al 32 in Greece, to estimate the biomass quantity potential for bioelectricity production; Sacchelli et al 33 in Italy, who used a GIS model to quantify forestry biomass; Wakeyama and Ehara 34 in Japan, who assessed the potential use of renewable energy in northern Tohoku; and Yousefi et al 35 in Iran, who estimated renewable energy production from different sources of biomass.
In the United States of America (USA), the National Renewable Energy Laboratory (NREL) constantly performs evaluations on technological options for electric energy generation. 36,37 The evaluation of potential electrical energy generation is performed based on several sources, including those originating from agricultural residues and spatial analyses via GIS as a first step, without considering the cost. Voivontas et al 32 studied plant capacities and the spatial distribution of residues, which are the primary parameters to consider regarding the location and size of the plant capacity.
The majority of studies consider spatial analyses as part of the decision support system at the municipality level and for the given electricity demand. However, in the energy sector, ethanol is currently the most important liquid biofuel, 38 and performing an analysis via GIS can assist in managing both demands. Our proposal addresses a specific way to identify residues that is different from the usual analysis using satellite data, and it provides much greater accuracy in identifying the areas that have relevant residues.
Therefore, the objective of this study was to estimate the potential for electric energy generation and ethanol production by treating agricultural residues, namely sugarcane straw (SS) and eucalyptus forestry residues (EFR), while considering a spatial analysis. This paper is organized as follows. Section 2 introduces the study area and the methods adopted to achieve the goal. Section 3 describes the results, and finally, Sections 4 and 5 present the discussion and conclusion, respectively.
(ARC). The ARC occupies an area of 27 079 km 2 and represents 10.9% of the total territory in the state of São Paulo. 39 This region has intensive agriculture that primarily consists of sugarcane to produce ethanol and sugar as well as forestry for the paper industry. The ARC is an intense energy consumer due to its industrial park and car fleet.
Part of the energy consumed by the ARC is provided by sugar mills that produce ethanol, which can be used in car engines directly or in mixture with gasoline. The other part is electric energy, which is provided by hydroelectric power plants or thermoelectric sources (fed by diesel). 39 Determining the potential ethanol and electric energy production is the target of this work.

| Sugarcane and eucalyptus locations
To identify and georeference the occupied area locations used for sugarcane production in the ARC (Figure 2), a satellite database obtained from the CanaSat Project was used along with information from the 2013/2014 harvest. 40 This method identified the sugarcane areas by using medium-resolution spatial images (30 m) from Landsat series satellites. The digital processing of the images was then supported by visual inspection. This area is very stable in terms of land cover. Because there is no more land available, the area occupied by sugarcane will not change. Thus, the sugarcane area from 2013/2014 has not changed, and this area was used in this study.
For the areas occupied with eucalyptus in the ARC (

Electrical energy consumption by municipality
The information in Table 1 was extracted from the Annual Energetic Report by municipality for the state of São Paulo in 2016 42 and for the energy balance of the state of São Paulo. 42 The annual report is based on information from 2015, and it was prepared by the State Secretary for Energy and Mining. The annual report includes consolidated data about the primary energy consumption by the 645 municipalities in the state of São Paulo. Table 1 shows information about the electricity consumption by the municipalities in the ARC. The total consumption was almost 93 000 terajoules (TJ). These data will be compared with those calculated from the available production of biomass residues, and an evaluation of the demands and consumption and the deficits and surplus in the region is provided.

| Ethanol Consumption in the ARC by municipality
The information included in Table 2 was extracted from the State of São Paulo Energy-per-Municipality Yearbook of 2016 42 and the Energy Balance of the State of São Paulo. 43 Table 2 provides information about ethanol consumption for each municipality in the ARC. The total consumption was 1850 megaliters (ML).

| Estimated amounts of agricultural residues
In this study, the estimated agricultural residues are calculated by considering one process for the same power plant as separated by each type, as follows:

Estimated residue availability from sugarcane
Sugarcane is the most cultivated crop in the ARC. Sugarcane residues that come from agricultural production can be used as raw material to produce electrical power and bioproducts.
Despite Brazil's demonstrably positive conditions for developing second-generation ethanol derived from sugarcane biomass, 44 we only consider first-generation ethanol production in this study.
Specifically, in relation to sugarcane straw (SS is dry leaves, green leaves, and tops), according to Menandro et al, 45 the performance of dry mass SS in the field is 14 Mg. ha -1 . From this total mass, the same authors suggested that 60% (8.4 Mg ha -1 ) of the dry leaves could be exploited to guarantee agronomic sustainability. The availability of the residues was then estimated using those parameters along with the sugarcane area obtained by CanaSat.

Estimate of Eucalyptus Forestry Residue availability (EFR)
Eucalyptus plantations are present in approximately 40% of the municipalities in the ARC. Mogi Guaçu (MG), Espírito Santo do Pinhal (ESP), Casa Branca (CB), and Brotas (BRO) are the leading municipalities for producing wood that originates from eucalyptus. Because of wood exploitation, forestry residues are important sources of the lignocellulosic biomass used for energy. 46,47 The amount of forestry residues, which basically include bark, leaves, and stalks in designated areas for eucalyptus forestry use, varies from 10 to 70 Mg.ha -1 , according to Wrobel-Tobiszewska et al 48 In this study, only the bark  and stalk dry basis was considered, because these residues are present in higher amounts. According to Foelkel,49 in Brazil, the availability of eucalyptus residues (such as bark and stalks) in the field is 30 Mg ha -1 , which is within the range presented in Wrobel-Tobiszewska et al 48 Therefore, the value of 30 Mg ha -1 was used to calculate the amount of available residues by considering the total eucalyptus area from satellite data.

Residue availability
We are assuming that the residues will be available during the harvest time for sugarcane and eucalyptus. The sugarcane harvest begins in April and ends in December. The eucalyptus harvest was considered throughout the year. Therefore, the total amount of residues was divided into 9 months for sugarcane, for 598 × 10 3 Mg per month, and 12 months for eucalyptus, for 79 × 10 3 Mg per month.

| GIS-based model
For the good organization of each identified variable, sugarcane and forestry area maps as well as municipality borders were added to the GIS system as a layer. To estimate the residue (straw from sugarcane and residues from eucalyptus) amounts per municipality and per mass center buffer approach, the layer areas and borders were overlaid. A calculation of the residue amount and energy resources, such as for the electric energy (EE) and ethanol, was performed. The last step considered the evaluation comparison between the demand and consumption for EE and ethanol ( Figure 3).

| Estimates of potential energy generation (PEG)
Evaluating the technical potential of decentralized energy production by SS and EFR depends on having a consistent database, which begins with the quantification of their availability. The agronomic requisites for soil conservation and the EFR and SS gravimetric compositions are essential variables for energy exploitation studies.
Notably, the heterogeneity of SS and EFRs makes it difficult to select a technological route for energy exploitation, to ensure compatibility with the evaluated residues. This characteristic provides multiple possibilities for chemical technologies that can be used to exploit a specific residue. The primary interest in this study was to evaluate the energetic potential from the lower calorific values (LCVs) individually for two agricultural residues without emphasizing the relevance of one technology in relation to the other. Then, the technological biochemical route was chosen to estimate the energy from SS and EFRs. This process is based on the enzymatic decomposition of organic matter by microbes via codigestion to produce biogas and subsequently generate electrical energy. 50 Biochemical conversion processes are recommended for residues with a high percentage of biodegradable organic material and high-humidity content.

From SS
The technical potential of generating energy from SS was estimated by considering the technological route of anaerobic digestion via codigestion with vinasse. Vinasse was identified because there is a series of sugarcane and ethanol mills around the ARC (Figure 2). According to Viana, 51 the average monthly LCV of SS (June to October) is 17 584.52 MJ Mg -1 . To estimate the electric energy generation, the following energetic indicator was used, and it considers the availability of SS and LCV.

From EFR
The inventory and definition of EFR represent the study basis for evaluating the EFR potential for energy generation. During industrial wood processing from tree seeding to the tree harvest, a high percentage of organic matter is usually generated. Common sense dictates that residues are the remains that occur from harvest processing, and they are not incorporated into the final product. 52,53 The LCVs are very similar among the bark and stalks. 49,54,55 Thus, in this study, an average value of 17 165.84 MJ Mg -1 was used for the dry base, according to Foelkel. 49 The final PGE considered the total eucalyptus residue availability as well as the average LCV.

From SS
The use of biomass as a raw material for new products opens up the possibility of producing energy and biofuels as bioethanol. The amount of ethanol that can be produced can be assessed by multiplying the sugarcane straw availability by the indicator, which is 287 L Mg -1 of straw. 56 Sugarcane straw, which is the aerial part of the plant (dry and green leaves and tops) except for the industrially treated stalks, is basically made up of cellulose (40%), hemicelluloses (30%) and lignin (25%). 55 Nevertheless, according to Santos et al, studies performed with in natura sugarcane straw have displayed a composition of 38% cellulose, 29% hemicelluloses and 24% lignin. The ash content is typically two to four times higher compared with sugarcane bagasse. This amount can vary depending on the material collection site, weather conditions, vegetative development stage, and cultivar. An understanding of the structural complexity of the lignocellulosic materials requires knowledge of the physicochemical properties of each of their cell wall components to determine the exact energy potential.

From EFR
In terms of chemical composition, the plant cell wall of eucalyptus is made of cellulose, hemicellulose, and lignin. Many studies related to the manipulation of lignin biosynthesis have been conducted. 57,58 There is strong interest in this field due to the possibility of producing plants that are more appropriate for the delignification processes used to produce cellulose as well as the new industry of converting biomass to turn lignified biomass into bioethanol. 59 Producing bioethanol from residual lignocellulose has great environmental appeal if the emissions of CO 2 into the atmosphere are compensated for by the absorption of the gas during new plant biomass development. Brazil has special conditions if we consider the lignocellulosic residues from the forestry sector, because the residual biomasses are available in a reasonably clean form and in large amounts. 60 Bragatto 61 and Matsushita et al 62 showed the technical potential of bioethanol production from EFRs. In their studies, evaluations were performed on the residue chemical compositions, total soluble carbohydrate extraction mechanisms, acid and alkaline pretreatment processes, enzymatic hydrolysis, and a comparative analysis with sugarcane bagasse. The ethanol production process from soluble sugars is considered 1G fuel, and it does not involve breaking the cell wall. The bioethanol production per hectare is 1600 liters per hectare, according to 1G routes. 61 The ethanol consumption data ( Table 2) were compared with the ethanol amounts calculated from the available residue production with an evaluation of the demands and consumption and, thus, the deficits and surplus figures for the region.

| Spatial distribution of crop residue areas based on a mass center approach
The municipalities were grouped according to a spatial clustering standard on the residue availability for sugarcane and eucalyptus. For this reason, the methodology was based on the availability of the total residues in the ARC per real occupied area as follows: 1. Identify the major producers of residues based on the available statistical and georeferenced information; 2. Characterize the possible spatial structure of those municipalities in terms of residue availability.
An analysis of the potential residue production (sugarcane and forestry) in the ARC was performed by median center (mass center) approach. This method is an iterative procedure first used by Kuhn and Kuenne (1962) 63 and refined by Burt and Barber. 64 At each step (t) in the algorithm, a candidate median center is found (X t , Y t ) and then optimized until it | 2295 ROMERO Et al.
represents the location that minimizes the Euclidean distance d to all the features (i) in the dataset (Equation 1).
This approach allows the user to reach the best results while considering the true location of the planted areas, whether eucalyptus or sugarcane, instead of using aggregated values, such as the statistics from the municipalities. Figure 4 shows the distribution of residues per ARC municipality for sugarcane and forestry according to the described methodology. The sugarcane residues were more available in the central-western to northern regions. Regarding eucalyptus, however, the residues were distributed in the centraleastern to northern regions. The map shows a clear overlap of the residue availability, which operationally aids their exploitation.

| RESULTS
The points in red ( Figure 4A), green ( Figure 4B) and blue ( Figure 4C) are the centers of mass (CM) related to both crops/plantations (sugarcane-S and eucalyptus-E), sugarcane, and eucalyptus (T), respectively. This approach allows the user to identify the best place where a residue processing mill could be placed.
From the CM T , in red, buffers were generated to analyze the data. It was considered only a CM because the difference from the sugarcane CM S and eucalyptus CM E was the minimum (± 23 km).
Sugarcane residues are available from April until December. However, they can provide 100% of the EE but only up to 85% of the ethanol needs of the ARC, when considering a buffer of 90 km ( Figure 5C, 5). However, despite providing only 18% of the EE for ARC needs (buffer 75 km; Figure 5A), the eucalyptus residues can supply energy during the entire year, including time outside of the sugarcane harvest period. In terms of ethanol (buffer 75 km; Figure 5B), the production only supplies the alcohol needed by the ARC. During the other part of the year (April to December), the eucalyptus can be added, increasing the potential energy supply.
Tables 3 and 4 discriminate between the production area and net residue availability for sugarcane and eucalyptus per municipality, respectively. The following analysis will consider the net residue availability around the buffer built from CM T , that is, using sugarcane and eucalyptus, as mentioned previously.
(1) Using a buffer of 75 km to generate EE (107 658 TJ year -1 ) ( Figure 6A) as well as a buffer of 50 km for ethanol consumption (1852 ML year -1 ) ( Figure 6B) would be enough to meet the needs of the ARC. Some scenarios could be configured:

F I G U R E 4
1. For a buffer of 45 km, the residue availability will provide EE to the seven highest consuming municipalities in the ARC ( Figure 7A), while in the same buffer zone, the ethanol consumption needs can be met for eight municipalities ( Figure 7B), and six of those municipalities are the same as the highest consumers of both ethanol and EE. 2. For a buffer of 30 km, the residue availability can meet the needs of three municipalities, which include the biggest consumers in EE ( Figure 8A), or two municipalities regarding the ethanol consumption needs ( Figure 8B).

| Consumption and demand balance: electricity analysis by municipality
By comparing the information in Table 1 with that in Table  7 for the study area as a whole, the consumption of EE was 93 260.63 TJ year -1 , whereas the EE generated from the residues could reach 170 382.54 TJ year -1 . The difference between these numbers is almost 55%; that is, the generated EE supplies all the consumption. Figure 9 shows the spatial distribution of the municipalities that have a positive balance (the generation of EE is higher than the consumption) and the municipalities in which the balance is negative (the generation of EE is lower than the consumption).
However, by comparing Tables 1 and 7, it is possible to list the 10 municipalities that have higher positive balances of EE and the ten with negative balances (Table 8).
With the leftover electricity on one side (positive balance of 64 543.80 TJ), it is possible to supply the consumption of the ten major consumers (negative balance of 36 789.92 TJ);

ROMERO Et al.
that is, approximately 60% more energy is generated. The top 8 consumer municipalities (46 146.85 TJ) have figures ( Table 1) that reach almost as high as the consumption of the remaining 82 (47 114.56 TJ). This result shows that both scenarios can be analyzed in terms of public policies. One of the scenarios is aimed at addressing the 8 major consumers, and the other scenario aims at compensating for the remaining 82 municipalities.

| Consumption and demand balance: ethanol analysis by municipality
Regarding the residues for bioethanol production, there is a positive balance of 4 × 10 9 L after discounting the needs of each one of the municipalities. This figure can supply the needs of those that, through their production-consumption cycle, produced negative figures (1 × 10 9 L). Thus, the region would be ethanol self-sufficient when only considering the sugarcane residues and the forestry residues. The region that has intense agriculture also produces residues from annual crops of soybeans, wheat, and beans, which have not been considered in this study. Table 9 shows the ten municipalities with a positive balance (generation greater than consumption), and they can supply 3 710.54 ML, which is a threefold deficit from that presented by all the municipalities (31). These 31 municipalities have presented a deficit of −965.99 ML, as noted in Table 10. In fact, only one municipality, MG, could supply the deficit from 31 municipalities. In terms of public politics, as in the case of ethanol, the map ( Figure 10) provides clear information for more direct action, allowing for a better focus on this matter.

| DISCUSSION
Sustainability is important in the context of the bioeconomy or the transition to a bioeconomy, and the time variable and the spatial variable are very important (van Eijck and Romijn, 2008). 65 Thus, the aim of this study was to contribute tools that may help to reach this goal. The results showed the efficiency of the spatial analysis, and, in this case, the local to regional ranges. Thus, we are on the correct path for residue profits to occur at the local level, and we offer a more appropriate basis for the transition to a bioeconomy as a "local node, global network" Bulkeley. 66 Furthermore, the results are in accordance with the Brazil iNDC (2014) 6 primarily concerning GHG mitigation, in implementing policies and measures to adapt to climate change and South-South initiatives, and in cooperation with other developing countries in areas such as biofuel capacity building, low carbon, and resilient agriculture.
Despite the ARC being located in a region with a wellbuilt infrastructure, including an energy sector, it has suffered constant variation regarding the hydric conditions that impact electric power generation. 13,15,67 Some of the needs of the reservoirs that feed the ARC are shared by other important macro regions of São Paulo. This issue causes difficulties in choosing priorities. 68 The same authors who described the factors that caused the water scarcity in the São Paulo region suggested that the number of days required to produce treated water was increased over the operational limits. Therefore, the amount of water available to customers decreased.  Furthermore, this type of situation became more susceptible to extreme climatic events, such as the crises during the summers of 2013/2014 (high temperatures and lack of rain). At this point, new alternatives should be explored to minimize future impacts. 5 Although our discussion did not focus on social matters, the results may be used to promote greater justice regarding energy access because the spatial analysis describes the local higher or lower residue availability, and as a result, the availability of energy (electric and ethanol) in accordance with some analyses that have had a local/social focus, such as the work of Damgaard et al 69 We predict that this work will support greater social justice due to the decentralization of biogas generation; however, this goal will require public policies that lead energy companies to take more actions locally. Forbord et al 70 reinforced the idea that public policies are fundamental to the development of bioenergy at the local and regional levels in cases analyzed in Norway.
The focus of this study was to create conditions for public agents to analyze the energy issue from another perspective in addition to just looking at values. This viewpoint allows for the organization of new policies to consider the residue   72 is that energy and food do not compete; by contrast, they can be complementary in terms of land use, public investments in innovations, technology and rural extension, the promotion of stable prices, and the encouragement of local production.

| CONCLUSIONS
This study focused on estimating the potential for electric energy generation and ethanol production by addressing agricultural residues while considering the spatial analysis. The spatial analysis has shown to be very effective in identifying areas that have agricultural residues, their availability for use as nonfossil fuels and for replacing nonfossil fuels for electrical energy. The balance between the possibility of using those residues to produce electricity and ethanol and their demand in the ARC has allowed us to identify possible ways to exploit that energy, either to feed major consumers (in smaller numbers) or to supply minor consumers (in greater number). Moreover, we explored the synergy by considering the availability of residues (sugarcane and eucalyptus) that could be added to the annual crop residues (not considered in this study) and other important sources of residues to create a more stable set of possibilities for energy generation. This type of initiative will be reflected in hydric (human

Ranking Municipalities
Generation -consumption surplus of bioethanol (ML year −1 )   consumption x agriculture use) and environmental questions (carbon balance and climate change). In a country with great resources, such as Brazil, this example has demonstrated the benefits of transitioning an economy based on fossil fuels to a bioeconomy. Furthermore, solutions can occur on a local/regional level more than on a national level. Thus, the use of tools for spatial analysis, such as the use of satellite images and geographic information systems, provides great efficiency.