4.1 Descriptive analysis
The present analysis consists of 416 papers published in the period from 2007 to 2020. As shown in Fig. 2, over the past five years the annual scientific production regarding the topics of CE and wastes has risen considerably. Various sources of information were considered, in which the scientific production trend began to emerge since 2016 and grown significantly between 2017 and 2020.
According to Prieto-Sandoval et al. (2018), the interest of the academic community grown considerably in 2003 after China had started promoting CE. In 2014, CE was included in the European Community Agenda, leading to a significant increase in scientific production during the following six years, mainly in the years of 2019 and 2020, in which 105 and 149 documents were published, respectively.
Even though Prieto-Sandoval et al. (2018) focused on CE and its relationship with the eco-innovation in the period 1969–2016, the findings in this study showed an incremental number of publications, in which 94% of them were condensed between the years from 2017 to 2020. This assertion evidences the evolution of scientific production and the progressive interest in CE, particularly over the last two years. A greater number of publications is observed in 2020, illustrating that CE theme gained importance, possibly as a consequence of COVID-19 disease declared global pandemic by the World Health Organization in March 2020 (World Health Organization 2020).
The obtained results evolution and scientific production growth over a 14-year period follows a second-degree polynomial function,
y = 1.7713x2 − 17.987x + 33.269 S1
in which the R2 value of 0.9215 represents a good fit between the regression line and the observed data.
The equation allows to build up a projection of the number of publications for the years 2030 and 2050. The former is linked to the year in which the United Nations established as a goal to attain the Sustainable Development Goals and their 169 targets defined in the 2030 Agenda, the new strategy adopted in 2015 aimed to administer the global development programs. The forgoing explains the turning point and rise in the number of publications related to sustained economic growth in that year, which implies sustainable production and consumption patterns.
The second of them, the year 2050, denotes the date on which the European Commission sets the target for achieving net-zero greenhouse gas emissions and decoupling economic growth from resource use by 2015 through the European Green Deal, which promotes a modern, resource efficient, and competitive economy (European Commission 2019).
The obtained results denote the interest of the global scientific community to accomplish with the international agreements, such as the 2030 Agenda, mainly the European Community countries facing the COVID-19 health emergency to confront the new waste challenges presented as a result of the pandemic.
On the other hand, the analysis revealed that, from the 416 examined documents, 72 countries have contributed to scientific production in the fields of CE and wastes in the period 2007–2020 (Fig. 3). The countries that stand out being in the top five are: Italy, which is the most productive country with 162 publications, followed by Spain (129), United Kingdom (123), China (115) and Brazil (78).
The analysis centered on the 20 countries with the world’s highest scientific production, of which 14 belong to the European Union, representing 70% of the total. It is worth noting that United Kingdom, even though it no longer belongs to the European Union since 31 January 2020, its contribution places it among the three countries with the highest number of publications.
In contrast, Germany and Japan have been pioneers in promoting CE through detailed policies (Geng et al. 2013). However, the European Union was who approved the action plans for their implementation in 2015 and proposed a monitoring framework (EC 2018).
Additionally, the European Commission launches the European Green Deal for the European Union and its citizens in 2019 as a developing strategy for promoting an equitable and prosperous society, with a modern, resource efficient and competitive economy, in which the goals for achieving net-zero greenhouse gas emissions and decoupling economic growth from resource use are set (European Commission 2019). The aforesaid clarifies the scientific interest of European countries involving this subject.
At present, green economy and decreasing atmospheric pollution rates are consolidated as key points for post-COVID recovery of cities (Pérez 2021). In this context, the European Green Deal emerges as an initiative for post-pandemic green recovery, aimed to promote a rehabilitation route based on a clean and circular economy that involves all its sectors for reaching an efficient use of resources, biodiversity recovery and the reduction of atmospheric pollution (European Commission 2021).
Compared with European countries, in the Americas, Brazil and the United States highlight with a production of 78 and 36 scientific papers, respectively. However, from a sample of 72 countries, Canada (18) and Mexico (13) ranked at the 22nd and 27th place, respectively. To these must be added the efforts of Chile (8), Colombia (5), Peru (4), Argentina and Ecuador (3 each), Costa Rica (2) and Bolivia (1). This information coincides with the recently launched C40 Mayors Agenda for a Green and Just Recovery; led by 40 mayors from all over the globe, it defines the steps to be followed to move towards an equitable recovery and a transition to a more sustainable economy in view of the COVID-19 pandemic (C40 cities 2021).
Among the cities joining the green and just recovery from the C40 Mayors Agenda, on the part of Latin America are Bogota, Colombia; Buenos Aires, Argentina; Curitiba, Salvador, Sao Paulo and Rio de Janeiro, Brazil; Guadalajara and Mexico City, Mexico; Lima, Peru; Medellin, Colombia; and Quito, Ecuador. North American cities from United States include Austin, Boston, Chicago, Houston, Los Angeles, Miami, New Orleans, New York, Philadelphia, Phoenix, Portland, San Francisco, Seattle, and Washington DC; while the participating cities from Canada are Montreal, Toronto, and Vancouver.
The aforesaid underlines the countries interest to encourage CE as an alternative for lowering material inputs, minimize waste generation, and decouple the use of natural resources from economic growth as the path for an equitable, green, and prosperous recovery towards a post-pandemic era. Nonetheless, results delineate the gaps that still exist between developed and developing countries in the subject.
The systematic review of literature emphasizes the academic interest of both countries and leading journals on CE and waste understandings with reference to the highest number of published papers (Table 1). Among these, the following stand out: Journal of Cleaner Production with 43 published articles; Resources, Conservation and Recycling (26) and Sustainability (Switzerland) (20). The journal Environmental Science and Pollution Research got the 13th position out of a universe of 20 journals, comprising five published articles and 47 citations.
The results coincide with the findings reported by Prieto-Sandoval et al. (2018) who, when attempting to establish a consensus of the CE concept, conducted a systematic literature review of leading journals, including the Journal of Cleaner Production, Journal of Industrial Chemistry, Resources, Conservation and Recycling, Journal of Environmental Technology and Journal of Sustainability.
It must be underlined that, although the research carried out by Prieto-Sandoval et al. (2018) is focused on eco-innovation, this paper analysis has approach on the topic of waste. Despite that, both analyses put in the first positions the leading journals in CE: Journal of Cleaner Production (Netherlands); Resources, Conservation and Recycling (Netherlands); and Sustainability (Switzerland); which revolve around the disciplines of business, management, accounting, economics, energy, sustainability, environmental sciences, politics, and law.
Table 1
Top 15 journals with the highest number of published articles on CE and waste (2007–2020)
No.
|
Source
|
Articles
|
H-Index
|
Total Citations
|
1
|
Journal of Cleaner Production
|
43
|
16
|
1134
|
2
|
Resources Conservation and Recycling
|
26
|
12
|
539
|
3
|
Sustainability (Switzerland)
|
20
|
9
|
246
|
4
|
Science of the Total Environment
|
18
|
9
|
202
|
5
|
Waste Management
|
18
|
8
|
212
|
6
|
Waste Management and Research
|
10
|
5
|
78
|
7
|
Bioresource Technology
|
9
|
7
|
381
|
8
|
Environmental Engineering and Management Journal
|
7
|
1
|
15
|
9
|
E3s Web of Conferences
|
6
|
2
|
7
|
10
|
Energies
|
6
|
2
|
9
|
11
|
Iop Conference Series: Earth and Environmental Science
|
6
|
1
|
6
|
12
|
Renewable and Sustainable Energy Reviews
|
6
|
4
|
63
|
13
|
Environmental Science and Pollution Research
|
5
|
4
|
47
|
14
|
International Multidisciplinary Scientific Geoconference Surveying Geology and Mining Ecology Management Sgem
|
5
|
0
|
0
|
15
|
Acs Sustainable Chemistry and Engineering
|
4
|
2
|
24
|
Source: Own elaboration based on Scopus database. |
On the contrary, the most frequently cited papers considered to have the greatest impact in the field of study were identified. Out of a total of 416 examined documents from 187 sources and 1406 authors, the 10 most cited papers were selected (Table 2).
Table 2
Most cited documents in the subject of CE and waste
Paper
|
Year
|
Source
|
Total Citations
|
TC per Year
|
Pan S-Y
|
2015
|
Journal of Cleaner Production
|
223
|
32
|
Malinauskaite J
|
2017
|
Energy
|
218
|
44
|
Nizami As
|
2017
|
Bioresource Technology
|
168
|
34
|
Lacy P
|
2016
|
Waste to Wealth: The Circular Economy Advant
|
161
|
27
|
Singh J
|
2016
|
Journal of Cleaner Production
|
146
|
24
|
Hu J
|
2011
|
Journal of Cleaner Production
|
141
|
13
|
Haupt M
|
2017
|
Journal of Industrial Ecology
|
99
|
20
|
Huysman S
|
2017
|
Resources Conservation and Recycling
|
98
|
20
|
Tisserant A
|
2017
|
Journal of Industrial Ecology
|
97
|
19
|
Liguori R
|
2016
|
Bioresource Technology
|
93
|
16
|
Source: Own elaboration based on Scopus database. |
The paper “Strategies on implementation of waste to energy (WTE) supply chain for circular economy system: a review” by Pan et al. (2015) had 223 citations in 2015. This document illustrates a portfolio of options for waste-to-energy technologies, such as combustion, gasification, and anaerobic digestion, for the purpose of achieving CE systems.
Alternatively, the study conducted by de Malinauskaite et al. (2017) performs a general review of the national systems for municipal waste management and the reconversion of waste into energy, under the perspective of CE in European countries. The authors recognize the calorific value of MSW, which implies its use as a “waste-to-energy” energy source, and its conversion into energy as a key factor to reach a CE that maintains the value of products, materials, and resources to market for as long as possible, minimizing waste and resource use. Given that CE is in the lead of the EU Agenda, Malinauskaite et al. (2017) concede that all UE Member States should transit to a smarter waste treatment with focus on CE approach in the context of waste policies.
Such paper examines EU policies implementation. Since WtE is traditionally linked to MSW management and organization, its approach considers the identification of distinct municipal waste management practices of the selected countries and their focus for adopting CE, as well as the extent to which WtE technologies have played any role in this matter.
In the third place, the paper “Waste biorefineries: enabling circular economies in developing countries” by Nizami et al. (2017) stands out with a total of 168 citations. This document highlights waste biorefineries as a choice for achieving CE in developing countries, where waste is valued as an encouraging energy source, that is to say as value-added products.
Once again, waste usage and energy generation from waste are among the most cited documents worldwide; thus, CE is placed as a solution to waste generation and emissions. The study performed by Loizia et al. (2018) stresses the relevance of implementing the CE model in food waste concerns, in which globally 1.3 billion t/year of foods are disposed of in landfills and contribute with 3.5–4.2 billion ton of CO2 equivalent. This paper is centered on the CE concept and the optimization and improvement of biogas production from an up-flow anaerobic sludge blanket reactor using food waste and natural minerals. The results lead to expect to use food waste in the existing anaerobic treatment plants, proposing a selective collection at source of this waste, its deviation from landfills and use as a secondary resource for energy recovery through a conversion towards a CE.
The aforementioned documents denote the importance of waste recovery, optimal use, reduction, and the need to implement waste treatment policies aimed to achieve a CE. In this sense, CE strategy defines its objectives towards the elimination, prevention, reuse, and recycling of materials, which must be achieved by 2030.
4.2 Conceptual and intellectual structure
The second analysis was focused on the conceptual structure through which the main themes and concepts were determined and deepened in the scientific research, achieving the identification of the network of keywords co-occurrence.
The search was accomplished through the filtering of results by the keywords that were most frequently presented in the abstract of the articles; a total of 25 terms were examined, from which the most relevant concepts (5) were: economy, circular, waste, management, and environment (Fig. 4).
The diameter of the circles represents the keywords frequency in the abstract, in which a largest diameter means the most researched topics; in this instance, the words economy, circular, waste, management, and environment were the most repeated keywords. At the same time, the thickness of the lines connecting the circles represents the strength of the relationship between two topics, as it is with the concepts of economy and circular, which are mightily linked, and these in turn with the topics of waste and management. The aforesaid due to the strong relationship between the reduction of waste generation and the cyclical use of resources.
From the strong relationship between circular economy and waste, the concepts of management, environmental, production, development, sustainable, and recycling are linked. The issue of waste production and management is a critical point when considering the implementation of CE policies, which are focused on promoting a shift in the production and consumption patterns, as proposed in the Sustainable Development Goal 12 of the 2030 Agenda (UN 2015).
This Goal aims to ensure sustainable consumption and production patterns, related to an efficient use of energy and resources, decrease environmental impact of the construction of infrastructure, improve access to basic services, and create green jobs, apart from generating greater profits derived from economic activities by reducing the use of resources, environmental degradation, and pollution. Simultaneously, people’s quality of life is improved through a systematic approach involving the cooperation of all the members of the supply chain (UN 2015). The relationship between CE and the production and management of wastes is strongly linked, as shown in Fig. 2, pointing that conceiving CE is not possible without considering a sustainable production that contributes to sustainable development.
The conceptual structure analysis also reveals a powerful linkage between CE and waste. According to Moraga et al. (2019), in their analysis of indicators to evaluate CE performance, it was found that most CE indicators from literature are focused on the preservation of materials, primarily on recycling, which is another of the most frequently found concepts. Although CE promotes recycling, it is not the only action to be considered. This evinces the need to explore various strategies, not only related to the preservation of materials but their functions, products, components, and energy, as stated by Moraga et al. (2019).
In addition, an analysis was conducted to determine the topics that have been trending over the last four years, considering the period of 2017–2020. It was observed that the main research topics have been fluctuating over time, including their frequency. In 2019, the topic of waste management was addressed more frequently (221), followed by recycling (190) and CE (168); whereas in 2020, the most trending topics were sustainable development and municipal solid waste (Table 3).
Table 3
Main research topics in the period of 2017–2020
2017
|
2018
|
2019
|
2020
|
Food industry (9)
|
Solid wastes (19)
|
Waste management (221)
|
Sustainable development (76)
|
Processes (7)
|
Industrial Ecology (16)
|
Recycling (190)
|
Municipal solid waste (68)
|
Developing countries (7)
|
Developing countries (14)
|
Circular Economy (168)
|
Solid waste (60)
|
Resource use (6)
|
Risk assessment (9)
|
Waste treatment (46)
Economics (45)
|
Economic aspects (52)
|
Source: Own elaboration based on Scopus database. |
The focus over the last years has been towards an integral insight, in which an evolution in the research of municipal solid waste and sustainable development towards a waste treatment policy have been noticed. This integral insight considered solid wastes and industrial ecology in 2018, whereas in 2019 it trended towards recycling and waste management. In the same year, the topic of CE was a spotlight among the research topics, while in 2020 the most frequent topics focused on sustainable development and municipal solid waste.
On the other hand, though the intellectual analysis, it was possible to identify schools of thought in the academic discourse. According to Beyhan and Cetindamar (2011), studies conducted by the same author constitute a body of knowledge and the authors who have related documents are cited together; thereby, authors network of co-citation is established.
Figure 5 shows 25 co-citation nodes representing the network of authors appearing together in the 25 selected articles from the database. Ghisellini, Wang, Zhang and the European Commission appear in the co-citation map as the authors with highest linkage to other authors, followed by Geissdoerfer and Kircherr, who are interpreted as the most influential authors.
The study performed by Ghisellini et al. (2016) is a baseline reference on CE, covering two decades of research in the literature review. The paper highlights its main characteristics and perspectives (origins, basic principles, advantages, disadvantages, models, and implementation at different global levels), hence its importance and co-citation frequency.
In contrast, Wang Y. excels for his contributions to the e-waste field, covering the ecological and health risk assessment for the spatial distribution of heavy metals in a CE park for e-wastes. His contribution contemplates the quantification of spatial flows of e-waste in China’s informal sector, the implications of China’s foreign waste ban on global CE, and the industrial symbiosis to achieve a CE through value-added materials reached through the design in the automobile industry (Han et al. 2018).
The work of Zhang et al. (2019) contributes to the waste issue and the need for considering the management of waste as a vision towards a CE with a zero-waste approach. Their analysis on the waste management barriers in China reveals the absence of regulatory pressures, environmental education, market pressures and demands to a smart waste management.
Conversely, the study performed by Geissdoerfer et al. (2017) is a baseline as it proposes CE as a new paradigm of sustainability that questions the relationship between both concepts, which is still unclear in the literature. The bibliometric analysis and snowballing techniques applied, served to establish the state of the art regarding CE and to identify the similarities, differences and relationships between CE and sustainability.
It must be noted that both Ghisellini's and Geissdoerfer's contributions have a central position on the map of sources of knowledge produced in the literature of European Union countries; the former was generated in Italy and Sweden, in collaboration with China, and the latter between United Kingdom and the Netherlands.
The European Commission highlights among the most co-cited authors. It is to be underlined that EU countries have a more advanced path in CE since the approval of their action plan for its implementation in 2015 and the application of their monitoring framework; thus, member countries of the European Union have had significant contributions to the knowledge production on the subject.