Conference Topic: Renewable Energies and Sustainable Development SUPPLY CHAIN MANAGEMENT OF BIOMASS FOR ENERGY GENERATION: A CRITICAL ANALYSIS OF MAIN TRENDS

in managing supply chains, in particular, energy chains, such as Brazil, India, Russia and China, have not yet been addressed, at least, from the point of view of scientific research, to this bottleneck. Future research should involve managing the supply chain of energy biomass with sustainability issues, new technologies for conversion, storage and heat conservation. It is also recommended to use other databases to search, such as Scopus and Google Scholar, which include citations from sources other than the web of Science.


Introduction
Biomass is considered the most prevalent replacement of fossil fuels and is widely used in global energy production (Iacovidou, Hahladakis, Deans, Velis, & Purnell, 2017).In the power generation sector, biomass contributes to 9.7% of the total primary energy generation (Internacional Energy Agency [IEA], 2017); larger than the contribution of traditional and technically well-developed sources, e.g.nuclear (4.9%), hydropower failures in the connection links between the biomass feedstock sources and biorefineries due to spatial distribution and disaster impacts.They suggested that by increasing the reliability and improvement of the connections between the two facilities, supply chain costs can be considerably reduced.Jeong and Ramírez-Gómes (2018), who also supported this finding, applied a combined Multi-Criteria Decision Analysis (MCDA) and Fuzzy-MAcking Assessment Laboratory (F-DEMATEL) technique to identify suitable and favorable sites for biomass feedstock production and utilisation, using environmental, geophysical and socioeconomic criteria.The results of their analysis suggested that the ideal sites for biorefineries are near forests and in areas with low transport costs.The criteria that determined the sustainability of that particular biomass-to-energy supply chain management system were the plant cover, agricultural area, transportation cost and potential demand.This methodology can be used to verify suitable sites for biomass plants and decision-making in the private sector and at various levels of the government.
Regarding the safety of the residual biomass supply, Vacchiano, Berreti, Motta, and Mondino (2018) studied how to quantify the biomass required to design the location and size of the plants for energy and heat generation.The authors developed their research using an algorithm to measure available forest biomass using publicly accessible Landsat satellite images, regional forest inventory data, an artificial neural network (RNA) classifier using remote sensing information, the Improved Vegetation Index (EVI) and topography data.This combination resulted in a biomass forest map that reported the biomass available for bioenergy production from crop residues based on density of species-specific wood, biomass expansion factors, available volumes, forest accessibility and topography.Corcelli, Fiorentino, Vehmas, and Ulgiati (2018) used Life Cycle Analysis (LCA) as a research tool to study the use of energy generated in-situ from black liquor and residual biomass to support the demands of integrated pulp and paper mills and to reduce environmental burdens.Particularly, the partial generation of electricity and heat, by using waste within the system, leads to a remarkable reduction of impacts in all the categories investigated.
Regarding the production process, that is another important area for the efficient supply chain management, Vyhmeister et al. (2018) developed a study to analyse the challenge of selecting optimal technologies, especially when considering many available alternatives.These authors consider that selecting optimal production paths requires a shift from traditional material management practices to more sustainable practices.A case study was developed in which there were four target areas (efficiency, energy, economy and environment) evaluated by 21 pre-selected indicators as part of a multiobjective optimization problem of a biofuel production network consisting of four main elements: (1) raw materials management; (2) conversion technologies; (3) co-products modernization and (4) auxiliary sections for in-situ production of raw materials and utilities.The evaluation allowed identifying optimal networks, specific target areas with potential improvements and processing steps with great influence on the entire network performance.
In turn, Carleton and Backer (2018) argue that integrating the different interests of decision makers involved in a supply chain in an efficient and sustainable manner requires well-structured governance.It was researched the existing barriers to the development of bioenergy from the perspective of supply chain actors.The conducted interviews demonstrated the need to create subsidies, integrate bioenergy production with bio-based markets, correct poor coordination and lack of greater shared responsibility between state agencies, industry associations and non-profit organizations, resulting in a fragmented policy system.The authors proposed a set of measures to correct these points.
This review has demonstrated that the use of biomass and its residues to produce bioenergy require both a more efficient integration of the various links that make up a supply chain and a better improvement of each of these particular links.What happens is that the development of supply chain management is based on greater studies that seek innovation, competitiveness and greater environmental sustainability.
In this sense, to verify how the research is being developed and directed in this field, a bibliometric survey was held.This survey mapped the volume and diversity of publications carried out in the scope of Supply Chain Management in bioenergy to construct scientific maps from studies considered relevant.The aim of this was to demonstrate how scientific research is evolving in this area.

Methodology
Bibliometric method or analysis has emerged in the early twentieth century as a quantitative tool for evaluating the contribution of present studies in a research field and predicting their future research potential.That means bibliometric studies aim to demonstrate the direction of science in a certain field of knowledge (Gautam, 2017).Currently, this type of analysis is considered an established process of research evaluation, especially within the scientific and applied fields (Ellegaard & Wallin, 2015).
In this way, the present article is characterized as a retrospective and employs a bibliometric analysis of secondary data.This type of analysis generates relevant information for researchers who evaluate the evolution of scientific activity (Montero-Diaz, Cobo, Gutiérrez-Salcedo, Segado-Boj, & Herrera-Viedma, 2018) and that examinate bibliographic material from an objective, quantitative and qualitative perspective that is useful in the organization of information within a specific field (Albort-Morant & Ribeiro Soriano, 2016).
From a methodological point of view, bibliometric surveys can be understood as a systematic literature reviews through content analysis, where quantitative and qualitative aspects are analysed in their structure (descriptive research) and content criteria.A process model proposed by Mayring (2003) was adapted in our study.This contains the following four steps: (1) Collection and screening of data; (2) Descriptive analysis-it involves the processing of data based on, e.g. the number of publications per year, providing the background for later theoretical analyses; (3) Content analysis-it involves the analysis of data into peripheral, emerging and basic themes; (4) Material evaluation according to the relevant issues and interpretation of results.

Choice of Database
Thompson Reuters' Clarivate Analytics database, hereinafter referred to as Web of Science, was chosen as the main data source for gathering research outputs on the SCM of biomass-to-energy system.This database was chosen due to its widespread use and comprehensiveness: the tool has more than 50 thousand academic books, 12 thousand periodicals and 160 thousand congress annals.The Web of Science enables a multidisciplinary view of science and integrates all relevant sources for basic, applied research and technological innovation through patents, scientific content web sources, open access journals, conference proceedings and conferences.
The quality and quantity of biomass-to-energy SCM studies were assessed based on studies published within the last couple of decades.The keywords used to search in the database included the terms: "Biomass" and "Energy" and "Supply Chain Management".The field label used was "Topic" (TS) which selects words in the article title, abstract and keywords.The Boolean term "AND" was used to avoid overcollection of studies that might be irrelevant.Only English articles were researched given the innovative nature of this type of document, as well as its greater ease of disclosure due to the adopted language.
After selecting the technical parameters, the database searching was performed.Initially, the selected period was from 1991 to 2018.The year of 1991 was chosen because it was the period in which the indexation of the keywords in the articles occurred (Miguéis, Neves, Silva, Trindade, & Bernardes, 2013).However, publications that included the predefined characteristics were only found in year 2000.As a result, this year was selected as the starting point of the analysis, with 221 articles.

Software Used
Two tools were used in the analysis: the VOSviewer and the SciMAT.The VOSviewer is a free-access information technology program developed by Waltman and Van Eck (2012) to create, visualize and explore academic and scientific bibliometric maps, called term maps (Van Eck, Waltman, Dekker, & Van Den Berg, 2010).A term map is a two-dimensional map in which the occurrence frequency of a specific term is defined by the size of the label.For example, the larger the label, the higher the occurrence of the specific term.The distance between two terms can be interpreted as an indication of the relation of these terms based on the number of co-occurrences between them (Castillo-Vergara, Alvarez-Marin, & Placencio-Hidalgo, 2018).The analysis made in this program considers countries, most cited authors and keywords.The main advantage of this program is it focuses on the graphical representations of the data collected in a map, providing better insights on the purpose, scope and scale of the research conducted.This is particularly useful in viewing large datasets and facilitating interpretation (Cobo, López-Herrera, Herrera-Viedma, & Herrera, 2011;Dae-Hyun, Cho, Park, & Hong, 2016).The SciMAT tool developed by the University of Granada SECABA group is an open source software, created to carry out scientific mapping analysis in longitudinal structure.SciMAT allows the construction of scientific maps, as well as a better visualization of evolution within a scientific area (Cobo, López-Herrera, Herrera-Viedma, & Herrera, 2012).The system offers a diversity of resources that helps the researcher to conduct workflows that aid the mapping of science.The following flows were established for this research: the first one dedicated to the management of the knowledge base and its specificities, such as year and number of publications; the second dedicated to the analysis and mapping of science; and a third stream created to present the results and generated maps.The most highly cited article, i.e., "Miscanthus: European experience with a novel energy crop" by Lewandowski, Clifton-Brown, Scurlock, and Huisman (2000), analyses the use of miscanthus for bioenergy generation and current options for its production.This study presents replicable findings in other parts of the world, such as the United States.They concluded miscanthus possessed the technical capacity for heat generation, but limitations related to its high implantation cost and need for irrigation should be taken into account.
The second most highly cited article was from Eksioglu, Acharya, Leightley, and Arora (2009): "Analyzing the design and management of biomass-to-biorefinery supply chain", which discussed the logistical challenges of supplying biomass, especially corn and soybeans, for power generation.The study presented a mathematical model for projecting future aspects pertaining the supply chain management of biomass and its logistic implications in the biorefinery use, contemplating the processes involved in short, medium and long-term decision making. jas.ccsenet.
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The   In the last period analysed (2013 to October 2018), the focal themes detected were "Biomass", "Economy", "Emissions" and "Greenhouse gases".It is observed that the concerns are related to new inputs for energy production, such as forests (Bruckman et al., 2018;Simoes, Dinardi, & da Silva, 2018;Vacchiano et al., 2018).Although, in the period from 2007 to 2012, the forest residue had already occupied a prominent position among the publications.Only in this scope were nine publications, mainly associated to optimization research and mathematical modeling (Alam, Pulkki, Shahi, & Upadhyay, 2012;Kuhmaier & Stempfer, 2012).
Factors inherent to the definition of sustainability, i.e., the combination of economic, social and environmental aspects, were also highlighted in this last period (14 publications), with emphasis on articles dealing with the development and management of energy forests.Furthermore, most of the time, they are associated with optimization research and mathematical modeling, especially in European countries (England and Italy) and the United States and Canada.
Regarding the economic aspects, the use and productivity of the land (Tonini, Albizzati, & Astrup, 2018;Zhong et al., 2018), life cycle (Thakrar, Goodkind, Tessum, Marshall, & Hill, 2018) and energy efficiency (Garofalo, Campi, Vonella, & Mastrorilli, 2018) were explored.The environmental issue that was discussed by Ahmed and Sarkar (2018) and by Hansson and Hackl (2016) addresses aspects related to emission reduction and environmental conservation.Ahmed and Sarkar (2018) present the advantages of supply chain management for the production of second-generation biofuels by reducing the amount of CO 2 emission.Related to this theme, Bergendahl, Sarkis, and Timko (2018) carried out a research that can open a new field of study of Supply Chain Management, inserting elements such as water use management in the process.
Thus, according to the observed orientation of the publications analysed from 2000 to October 2018, some themes have been present since the beginning of the analysis.Studies on optimization and mathematical modeling, either biorefinery localization or input mapping for energy conversion, dominated the sample being present since its beginning, totalizing 49 articles or 22% of the publications, of which 23 were related to the use of energy forests.
The issue related to the analysis of GHG emissions has also been discussed since 2007.Until October 2018, 36 publications were devoted to the term (16%), which sought to study ways to reduce GHG emissions not only in the biofuel production process, but also throughout the supply chain, in order to make it environmentally and economically more sustainable.However, given that, there is still a lack of more multidimensional evaluation studies of the supply chain, there is a strong tendency to develop new studies and future publications on this topic, associating it with several issues such as environment, waste resources, emissions and management systems.
Thus, it is important to highlight that the key words selected: Biomass, Energy and Supply Chain Management are in line with the researched literature.Despite the diversity of the words, they have managed to bring together a range of scientific fields important for the development of science related to biomass, energy production and SCM.The research, therefore, by means of the chosen terms expands previous works that discuss the same subject, as for example, Seuring and Miller (2008), that they review literature on supply chain and the dimensions of the sustainable development, providing specific tendencies to the bioenergy sector.
The research also contributes in the methodological sense to works such as Gold and Seuring (2011), which through a literature review analyzed articles on bioenergy and supply chain management, concluding that the most important terms related to this theme are linked to aspects such as harvesting, collection, storage and transportation.This research, which used software algorithms to generate trends, showed that besides these issues, economic attributes, life cycle and land use, also concentrate a large part of the debate on the SCM.
For the moment, it is important to note that the trends identified do not occur in isolation.As demonstrated at the beginning of the study, the terms discussed here are transdisciplinary and cover several areas of research.There were also publications that dealt with several aspects at the same time, contributing to the engagement, training and extension of the study of the supply chain management of biomass for energy generation.

Final Considerations
The analysis demonstrated that biomass-to-energy SCM is a topic that has gained increased attention over the last six years.In spite of the fact that most research on energy generation from alternative sources focuses primarily on fuel production, engineering and biotechnology, there are groups of researchers, mainly in the United States, England and Italy that are focusing on exploring and assessing ways for making biomass-to-energy SCM to emerge as a promising option for contributing to the global energy matrix in the future.
The bibliometric analysis shows that the biomass-to-energy SCM is a global topic of concern.Countries (such as Brazil, India, Russia and China), which theoretically would have the greatest interest because of their availability of energy resources and continental dimensions, as well as greater difficulties in managing supply chains, have not shown an increasing interest yet (at least from a scientific research perspective.The multi-level stakeholders involved in the biomass-to-energy SCM will require evidence on the need of new approaches in this field, especially as reliance on fossil fuels will need to be reduced in the future.This evidence will need to be focused on the ability of these countries to ensure a constant supply of biomass for energy generation and to develop an economy of scale that will control and maintain the continuous production of bioenergy.
Consequently, future research should focus on identifying key strategic areas of research within the biomass-to-energy supply chain management where there are emerging issues of concern, such as sustainability, technology innovation, storage and heat conservation can set the pace for transformational change.Thus, gains in efficiency, competitiveness and compliance with environmental standards would contribute to the consolidation of the biomass energy sector in the global energy matrix. Figure

Table 2 .
and developed the studies are in the United States and England.Table2presents the 20 most cited publications on biomass-to-energy SMC out of a total of 221 articles identified on the topic.Most cited publications in the topic of biomass-to-energy SCM

Table 5 .
St   to 2006)did not held density or centrality in studies related to Supply Chain Management for energy generation, was consolidated as a focal theme from 2013.