Waste-to-Energy: Multi-Criteria Decision Analysis for Sustainability Assessment and Ranking

Waste-to-Energy: Multi-criteria Decision Analysis for Sustainability Assessment and Ranking offers a comprehensive view of the technologies and processes for energy generation as a path for waste treatment, presenting all the necessary information and tools for selecting the most sustainable waste-to-energy solution under varying conditions. The book combines methods such as lifecycle assessment, sustainability assessment, multi-criteria decision-making, and multi-objective optimization modes. In addition, it provides an overview of waste-to-energy feedstocks, technologies and implementation, then goes on to investigate the critical factors and key enablers that influence the sustainable development of the waste-to-energy industry.

The book proposes several decision-making methods for the ranking and selection of waste-to-energy scenarios under different levels of certainty and information availability, including multi-criteria, multi-actor and multi-attribute methods. Finally, the book employs lifecycle tools that allow the assessment of economic, environmental and social sustainability of waste-to-energy systems.

• Explores existing and state-of-the-art waste to energy technologies and systems, as well as their feedstock requirements
• Presents a wide perspective of sustainability issues of waste-to-energy technologies, also discussing critical influential factors or key enablers for promoting the sustainable development of waste-to-energy solutions
• Provides multi-dimensional decision-making techniques for choosing the most suitable and sustainable waste-to-energy technologies for different scenarios

• Language: English
• Publisher: Academic Press
• Release date: May 12, 2020
• ISBN: 9780128166130

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China

Chapter 1

An overview of waste-to-energy: feedstocks, technologies and implementations

Lu Sun¹,², Wenjing Liu³, Minoru Fujii¹, Zhaoling Li¹, Jingzheng Ren⁴ and Yi Dou¹,⁵,    ¹Center for Social and Environmental Systems Research, National Institute for Environmental Studies, Tsukuba, Japan,    ²Department of Environment Systems, Graduate School of Frontier Sciences, The University of Tokyo, Chiba, Japan,    ³School of Environment and Natural Resources, Renmin University of China, Beijing, P.R. China,    ⁴Department of Industrial and Systems Engineering, Hong Kong Polytechnic University, Hong Kong Special Administrative Region, P.R. China,    ⁵The University of Tokyo, Tokyo, Japan

Abstract

Waste-to-energy (WtE) is a key issue of a waste management system. From the perspective of the energy system, WtE will contribute to the development of a low-carbon society. However, due to the lack of reviews of the historical and evolutionary aspects, studies related to WtE have not been comprehensively summarized from either a quantitative or qualitative perspective. This study applied bibliometric analysis to review the research features and trends of WtE study. Results showed that seven productive countries, including the United States and China, have made great contributions to the WtE studies. In terms of research methods, life cycle assessment is the most popular method. The main research fields focus on greenhouse gas emissions, environmental impact, and energy technology innovations. The research topics showed that improve energy recovery efficiency and climate change impacts have received increasing attention in WtE research. This chapter provides a comprehensive review of WtE research and quantifies the research networks and key information.

Keywords

Network analysis; waste-to-energy; research trend; BibExcel

1.1 Introduction

Waste management is an essential aspect in city development, and has become a hot issue in developing countries. The most common methods used for waste treatment are landfilling, composting, recycling, mechanical–biological treatment, and waste-to-energy (WtE) (Psomopoulos et al., 2009). Energy recovery from waste is an essential part of waste management (Astrup et al., 2015; Yu and Chau, 2009), and numerous researchers have studied WtE technologies, including system design and evaluation (Chen et al., 2012; Grosso et al., 2010). During the past decades, the WtE technology has undergone rapid development, and there are a lot of studies that have focused on nonthermal technologies, such as anaerobic digestion and fermentation, and thermal treatment methods, such as gasification and waste incineration. The conditions in developing and developed countries are different due to their different waste management conditions and policies. In the developed countries, such as Europe and Japan, the promotion of waste recycling is the first priority, and WtE projects in these countries are decreasing year by year. However, in developing countries, such as China, the number of WtE plants are increasingly significantly. WtE technologies can improve waste management in the fast-growing cities of developing and emerging countries (Zhang et al., 2007). Considering the recent awareness of global climate change, many governments have enacted policies regarding the release of greenhouse gas (GHG) emissions into the environment. Also, many policies that promote investment in renewable energy technologies (Demirbaş, 2001), including WtE technology, have been put into place (Cheng and Hu, 2010).

WtE research covers a varied scope of disposal strategies for treatment residues, emissions reduction, technology application (Chen and Christensen, 2010; Stehlík, 2009), etc. However, since the lack of a WtE review of the historical and evolutionary aspects, studies related to WtE have not been comprehensively reviewed from either a quantitative or qualitative perspective. Although some reviews have summarized the widely used technologies and evaluation methods, very few studies have summarized the existing studies at a global level. A comprehensive integrative review provides insights into what contents have been covered and the new trends of this research field. Moreover, since the existing studies focus on the typical technology assessment or case study analysis, there are very few studies reviewing WtE from the perspectives of historical research features and trends.

Under such circumstances, this study aims to gain insights into the overall WtE research field, and summarize the major findings, contributions, and further directions of WtE research based on bibliometric analysis, including (1) the publication characteristics, such as journal, subject category, citation, and reference; (2) the cooperation and contribution of different countries/territories and authors; (3) keyword analysis to identify the research aspects and the development trends of WtE research; and finally (4) based on the above results, revealing the research fronts and hot topics in the future. The whole chapter is organized as follows. After this introduction section, the methodology and data sources are described in Section 1.2. Section 1.3 presents the main results and discusses research results. Finally, Section 1.4 draws research conclusions.

1.2 Methodology and date sources

1.2.1 Bibliometric analysis and visualization tools

Bibliometric analysis is a method to quantitatively assess the characteristics of academic literature by statistical methods, such as evaluation of the patterns of authors, journals, countries, and institutes in a specific fields (Chen et al., 2016). Besides, it also can examine the knowledge structure and development of research fields based on the analysis of related publications, such as keywords analysis (Kam et al., 2007). Moreover, the development of visual techniques can illustrate the results of bibliometric analysis in a more intuitive way.

Currently, there are more than 10 kinds of literature mapping software, and each software has its own advantages. BibExcel is an indispensable tool for the conversion and treatment of bibliographic data. It also contains an abundance of routines for creating different types of bibliometric analyses. BibExcel can conduct bibliometric analysis, citation analysis, and can produce net-files for coauthorships, cocitations, and then convert these for further analysis and visualization with Pajek or Gephi. Bibliometrics has been applied to many scientific fields (Gao et al., 2016; Ghafouri et al., 2014; Vargas and de Souza Vanz, 2014). Network analysis is used to evaluate various relationships among interacting units (Venkatraman and Newman-Wolfe, 1994). Network analysis is used in literature reviews by establishing nodes that may be represented by research papers, keywords, countries, institutions, or authors. Arcs, which are relationships, such as collaborations and influences of these nodes, can also be evaluated. Network analysis requires a network exploration tool with high-quality layout algorithms, data filtering, clustering, statistics, and annotation (Bastian et al., 2009). In addition, two visualization software were used for visual analysis: Gephi is an open-source and user-friendly platform, it is the leading visualization and exploration software for all kinds of graphs and networks; CiteSpace is a software that can provide functions to visualize and analyze trends and patterns of scientific literature (Chen, 2004).

The community detection method is applied to identify influential research networks. Community detection in networks is one of the most popular topics of modern network science. Communities, or clusters, are usually groups of vertices having higher probability of being connected to each other than to members of other groups, though other patterns are possible. Detecting communities is of great importance in sociology, biology, and other research fields, disciplines where systems are often represented as graphs (Fortunato, 2010). Community detection can describe the quality of the communities, as measured by the modularity (Blondel et al., 2008). The advantages of community detection are that it can determine research networks by graph clustering, node expression, and generalized community discovery. The analysis flow chart for the literature review in this study is shown in Fig. 1.1. More details on these methods and tools are detailed in the following subsections.

Figure 1.1 Flow chart for the systematic literature analysis.

1.2.2 Data sources and processing

The original data included in this study were derived from the Web of Science (WoS) database. This database collected 2546 publications with the keywords waste-to-energy (OR waste-to-energy) and management system as a theme (including title keywords, keywords in abstract, author keywords and keywords plus) from 2006 to 2016. To clarify the data type, we selected article in the document types option and English in the languages option for further analysis in this paper. The original date was selected on September 21, 2017. Firstly, we imported the original data downloaded from WoS into BibExcel, and completed preliminary statistical analysis, cooccurrence analysis, and coword analysis. Then, the resulting net-files about the connections between countries/territories, authors, and keywords were imported to Gephi for visualization.

1.3 Results

1.3.1 Publication characteristics

1.3.1.1 Primary analyses of the selected publications

Fig. 1.2 shows the top five productive journals and the number of annual publications. The results show that the annual WtE-related publications gradually increased from 2006 to 2016. The amount increased from 69 in 2006 to 451 in 2016, increasing by 654% over 11 years. Such a large increase means that WtE-related research have received more and more attention. The WtE-related publications were published in more than 2000 different journals from 2006 to 2016. Fig. 1.2 lists the top five most productive journals.

Figure 1.2 The performance of the WtE-related articles from 2006 to 2016. (Impact factor based on the year 2017). WtE, Waste-to-energy.

Journal of Cleaner Production is the most popular journal in this research field, publishing 158 papers in total between 2006 and 2016. Especially after 2013, it become the journal that annually published the most articles. Waste Management was also a productive journal with 153 papers in the research period, and the publications increased steadily annually and reached their peak in 2015. In addition, Renewable & Sustainable Energy Reviews’ had the lowest number of annual publications of the top five most productive journals, but it had the highest impact factor in 2017 (IF=8.050), followed by the Journal of Cleaner Production (IF=5.715), Waste Management (IF=4.030), Resources Conservation and Recycling (IF=3.313), and Waste Management & Research (IF=1.803). Moreover, these top journals account for 20.19% of the total publications. Other than the journals listed in Fig. 1.2, the International Journal of Life Cycle Assessment (52), Applied Energy (49), Energy (42), and Journal of Environmental Management (33) also published a number of related articles. Comprehensively, Journal of Cleaner Production, Waste Management, and Renewable & Sustainable Energy Reviews are the most influential journals in the WtE research field.

The 2546 publications cover 147 subject categories in WoS. Environmental Sciences (982), Engineering, Environmental (771), Energy & Fuels (530), Green & Sustainable Science & Technology (358), and Engineering, Electrical, & Electronic (229) are the top five subject categories. Other subject categories are shown in Fig. 1.3, and indicate that WtE research has been developed in a wide range of fields.

Figure 1.3 Subject categories of WtE-related publications during 2006–16. WtE, Waste-to-energy.

1.3.1.2 The most frequently cited articles

Citations can reflect the influence of an article, and annual citations can provide more intuitive information. Among 2546 publications, only 32 papers (1.26%) were cited more than 100 times, and 773 papers (30.36%) were cited 10–99 times. Table 1.1 lists the top 15 most cited articles (Arena, 2012; Bianzino et al., 2012; Brennan and Owende, 2010; Cherubini et al., 2009a; Ekvall et al., 2007; Fritzmann et al., 2007; Holm-Nielsen et al., 2009; Hopewell et al., 2009; Horbach et al., 2012; Martins et al., 2010; Masoso and Grobler, 2010; Ortiz et al., 2009; Pöschl et al., 2010; Roberts et al., 2010; Wang and Oliveira, 2006), and includes the characteristics, such as the total citations, annual citations, article titles, author names, publication years, and journal titles.

Table 1.1

aR: Rank of the annual citations.

The top three ranks of citations and annual citation’s ranking are the same. The most highly cited article is titled Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and coproducts, authored by L. Brennan and P. Owende and published in Renewable and Sustainable Energy Reviews in 2010, with 1349 citations and 192.71 annual citations. This study reviewed the technologies underpinning microalgae-to-biofuels systems and forecast that microalgae-derived biofuels can substitute fossil fuels, which indicates that renewable energy, such as biofuels production, is becoming more and more popular in WtE research. The second-most cited is State-of-the-art of reverse osmosis desalination, authored by C. Fritzmann et al. in 2007, which was cited 640 and 64 times per year. This study discussed the current practices of waste management and disposal as well as new trends such as the use of hybrid plants. This article has an emphasis on technical features and applications in desalination, which is more practical and reflects the application of technology in WtE research. The paper with third highest number of citations (414) and annual citations (51.75) is titled The future of anaerobic digestion and biogas utilization, which was published in Bioresource Technology in 2009. This study discussed the anaerobic digestion of animal manure and slurries and offered several benefits by improving their fertilizer qualities, reducing odors and pathogens, and producing biogas. This study provides a way to solve major environmental and veterinary problems of the animal production and organic waste management sectors.

Citation analysis indicates that research on WtE has typically focused on environmental impact assessment and biogas production systems (Dagnall et al., 2000; Wei et al., 2009). A major concern over the past two decades has been waste management systems, treatment technologies, and sustainability evaluation.

1.3.2 The characteristics of different countries/territories

1.3.2.1 The contributions of different countries/territories

The distribution of WtE-related publications cover 99 countries, which indicates the research on WtE is a global scientific field. Table 1.2 shows the top 10 most productive countries with more than 70 publications in total. The United States (453) is the most productive country, followed by China (310), Italy (249), the United Kingdom (163), Spain (144), Canada (124), Germany (102), Sweden (91), Australia (83), and Demark (77). The United States was the most productive country every year during 2006–20. In 2016 China surpassed the United States to became the No.1 productive country, indicating its increasing attention to WtE research. Apart from total publications of a country, h-index also an important index to reflect the influence of a country. Table 1.2 lists the top 10 most influential countries, including the number of publications, all citations of one country, and h-index. It is clear that the United States is the leader in this research field. The United States is not only the most productive country, but also the most influential country. Italy, China, and Denmark also have a high h-index, especially Denmark, although the number of total publications is low (No. 10), it has a higher h-index (No. 4), which indicates that Denmark has a higher research capacity.

Table 1.2

TP, The number of publications and rank; TC, all citations of one country and rank.

aR: Rank of the annual citations.

1.3.2.2 The contributions of different institutions

In total 312 unique academic institutions published on this topic from 2006 to 2016. The Technical University of Denmark (59 publications), the Chinese Academy of Sciences (48 publications), University of Regina (39 publications), Beijing Normal University (33 publications), and Polytechnic University of Milano (25 publications) were the top five most productive institutions (Table 1.3). The h-index results show that the Technical University of Denmark, the Chinese Academy of Sciences, and Beijing Normal University are the top three academic institutions.

Table 1.3

TP, The number of publications; TC, all citations of one institution and rank.

aR: Rank of the h-index.

1.3.3 Coauthorship analysis

Fig. 1.4 presents a scattered network of the WtE research field. The top 453 most productive scholars, who range from 2 to 51 publications, are selected. There are eight main distinct clusters in the cocitation network. The different clusters are shown by different colors, the same color indicates the same cluster and the thicker the lines connecting scholars, the more cooperation between them.

Figure 1.4 Network of coauthorship. Note: The authors have more than five WtE publications.

Cluster 1 is led by Huang GH, Li Y, and Cai Y from the Beijing Normal University, who cooperated more than 15 times with each other. This cluster’s focus was on linear programming models development of urban solid waste management system, in order to address the possible effects of energy prices on the identified waste management policies. The second cluster includes 20 researchers and is led by T. Christensen and A. Damgaard, originally from the Technical University of Denmark. Their studies highlight the environmental impact assessment and energy recovery of WtE technologies. The third cluster includes organic waste treatment, bioenergy systems, and mainly focuses on European countries. Cluster 3 has eight of the most influential authors and is led by X. Gabarrell and J. Rieradevall from Universitat Autònoma de Barcelona.

G.H. Huang, T.H. Christensen, Y.P. Cai, Y.P. Li, and A. Damgaard are the most productive and influential scholars. The most collaborative scholar is professor G.H. Huang, originally from the University of Regina, Canada, but who is now working at Beijing Normal University. His publications appear mostly with Y.P. Li, who also now works at Beijing Normal University, and their work has an emphasis on multistage programming theory and methods under uncertainty conditions of water and waste management systems. Professor T. Christensen and A. Damgaard are the most influential scholars on the development of life cycle assessment (LCA) models for the assessment of complex solid waste systems. They are the main developers of the EASEWASTE and EASETECH models developed at DTU Environment.

Coauthorship analysis results shows that the cooperation of scholars has a regional orientation; they tend to cooperate with scholars in their own country, where the number of cooperation times is much higher than with foreign scholars. However, scholars being active in international communication and cooperation, especially in information and experience sharing, is vital for the development of WtE research.

1.3.4 Research hotspots

1.3.4.1 Keywords analysis

To make the analysis more reasonable and accurate, the first step is pretreatment of the original data. Similar keywords are regarded as one keyword, for example, LCA, municipal solid waste (MSW), and so on. Therefore a total of 6171 keywords were obtained for further analysis. 5058 (81.94%) keywords only appear once, while 85 (1.38%) keywords appear more than 10 times. In this study, the period of 2006–16 was divided into three stages (2006–09, 2010–13, and 2014–16), aiming to present the trend of WtE-related researches in a more intuitive manner. By integrating the top 10 most frequent keywords of each stage, 15 keywords were selected. Fig. 1.5 shows the top 15 most frequent keywords during different years. Life cycle assessment is the most frequently keyword in each stage, and in total appears 329 times, followed by Waste management 154 times, MSW 136 times, Sustainability 111 times, and GHG 99 times.

Figure 1.5 The top 15 frequency keywords.

Keywords information in one publication may include objectives, methods, and purposes. To further identify the information, we selected the keywords which appeared over 10 times, and finally, 101 keywords and 1159 connections (keywords occur simultaneously) were selected. Fig. 1.6 shows the frequency of keywords co-occurrence in the same publication. The overall objectives are relevant to waste management and WtE technologies. Types of waste include solid waste, organic waste, sewage sludge, and wastewater. WtE technologies typically focused on incineration, anaerobic digestion, composting, and gasification. Topics appearing together are of great relevance or complementarity, for example, LCA as the most important tool showed up with waste management and sustainability most frequently; anaerobic digestion as the common method or compared with, appeared with biogas, incineration, and composting most frequently.

Figure 1.6 The network of the frequently used keywords.

1.3.4.2 Research prospects

In terms of research methods, LCA is the most popular method. LCA has become an important tool in waste management, studying the environmental aspects and potential impacts throughout a product’s life from raw material acquisition through production, use, and disposal (Finnveden et al., 2005). LCA can identify the actual environmental effects of emissions and wastes, it is widely used to compare the environmental impacts of WtE treatment options (Shie et al., 2011), and the results can provide an overview of the environmental aspects of different waste management strategies and scientific support for sustainable waste management (Cherubini et al., 2009a). It has been used to evaluate a variety of aspects in WtE systems, including GHG emissions (Cherubini et al., 2009b), energy performances (Cherubini et al., 2008; Sun et al., 2018), circular economy (Pan et al., 2015), and impact on global warming (Lausselet et al., 2017).

Input–output analysis (IO analysis) has become more and more popular in WtE studies (Dias De Oliveira et al., 2005; Rocco et al., 2017). IO analysis is more popular when scholars focus on footprint analyses (Li et al., 2018). IO analysis can take into account indirect carbon emissions from upstream industrial sectors (Weidema et al., 2008). An integrated LCA and IO analysis (Hybrid LCA) has received more attention, the major advantage is that it can address not only direct CO2 emissions from various waste treatment processes but also indirect emissions from upstream activities, for example, the evaluation of the use of energy or materials, which is commonly not considered in most LCA-based models (Maalouf and El-Fadel, 2018).

Other methods such as cost–benefit analysis (Oliveira and Rosa, 2003) and analytic hierarchy process (AHP) are utilized in the literature (Donnellan et al., 2015). Each method has its advantages and limitations and is discussed in the relevant literature. After a review of current WtE research methods, there are four categories, those based on cost–benefit analysis, those based on life cycle analysis, IO analysis, and those based on the use of a multi-criteria technique such as AHP (Karagiannidis and Perkoulidis, 2009; Morrissey and Browne, 2004).

The main WtE research topics (Fig. 1.7) include GHG emissions reduction (McKay, 2002; Porteous, 2001), residues treatment (Sabbas et al., 2003), energy technology innovations (Chen and Christensen, 2010; Stehlík, 2009) and. Improving the efficiency of energy recovery is a key issue in WtE studies, and scholars tend to study this from two perspectives, either technology-based (Bosmans et al., 2013; Ionescu et al., 2013; Stehlík, 2009) or system improvement–based (Demirbas, 2011; Fujii et al., 2012; Ohnishi et al., 2018). The most recent studies focused on technology innovations (Ramos et al., 2018; Ryan and Daim, 2017). In recent years, climate change has received more attention in modern waste management, and it is crucial to understand the role of WtE with respect to potential contributions to CO2 emissions and savings (Bogner et al., 2008; Christensen et al., 2015). Besides the main research topics, circular economy (Hu et al., 2011), industrial symbiosis (Costa et al., 2010; Geng et al., 2009), and sustainability indicators (Chong et al., 2016) also appeared amongst the popular keywords. Furthermore, scholars in these studies sought to identify aspects of WtE technologies in developing countries (Tan et al., 2015), especially in the Asia–Pacific region (Demaria and Schindler, 2016; Tan et al., 2015; Zhao et al., 2016).

Figure 1.7 Research hotspots and trends.

1.4 Discussion

Waste treatment plays a key role in society. WtE is important in solid waste treatment because it can significantly reducing waste volume and recover energy. The development of WtE technology and systems play a significant role in improving waste treatment and the implementation of sustainable development strategies. Through the review and summary of the development of WtE research over the past 20 years, the visual analysis method can help researchers grasp the research frontiers and hot issues in this field, and exploring the potential improvement of research in this field, in order to further develop future study.

Research in WtE is a fast developing area which combines theories and technologies in several different areas. The total number of papers in this field significantly increased over 2006–16, from 69 papers to 451 papers per year. Moreover, citation analysis indicates that research on WtE has typically focused on environmental impact assessment and biogas production system. The United States is leading in WtE research, it has the most publications, the highest citation frequency, and the highest h-index. Apart from China, the developed countries account for most of the outputs and show more international cooperation. The authors’ network cooccurrence analysis shows that scholars tend to cooperate with scholars in their own country, but also scholars are active in international communication and cooperation, which plays a constructive role in promoting global WtE research.

WtE research has moved toward a variety of topics and a multiplicity of methods. The early WtE system evaluation researches were based on the theory of LCA, especially the development of environmental indicators. With the application of different methods in different fields and systems, scholars have gradually applied multiapproach methods to assess energy recovery efficiency, environmental impacts, and decision-making for WtE system. The results from the keywords analysis show the cross-application of various methods in recent years, and methods such as IO analysis, cost–benefit analysis, and AHP have become the foci of WtE research. The hot topics analysis results showed that GHG emissions reduction, residues treatment, and energy technology innovations are the main topics. Improving the efficiency of energy recovery and climate change impact analysis have received increasing attention in WtE research.

There are still some limitations in the research methods of this study. Firstly, this study doesn't cover all the WtE studies from 1996 to 2016. This is due to the use of WtE as a keyword for search, and some articles that do not use this keyword may have been omitted. In addition, due to the limitations of the WoS database itself, some related articles may not have been covered, resulting in incomplete analysis of its