Exploring industrial symbiosis for circular economy: investigating and comparing the anatomy and development strategies in Italy

Purpose – The purpose of this paper is to investigate the most recurrent variables characterizing the collaborative relationships of industrial symbiosis (IS) (hereinafter also referred to as “ anatomic ” variables) established in the attempt to adopt circular economy (CE) by collecting evidence from a rich empirical set of implementation cases in Italy. Design/methodology/approach – The current literature on IS was reviewed, and a content analysis was performed to identify and define the “ anatomic ” variables affecting its adoption in the circular economy. We followed a multiple-case study methodology investigating 50 cases of IS in Italy and performed a content analysis of the “ anatomic ” variables characterizing each case. Findings – This research proposes the “ anatomic ” variables (i.e. industrial sectors involved, public actors involvement, governmental support, facilitator involvement and geographical proximity) explaining the cases of IS in the circular economy. Each “ anatomic ” variable is discussed at length based on the empirical evidence collected,withaparticularreferencetothe impactonthedifferentdevelopmentstrategies(i.e. “ bottom-up ” and “ top-down ” ) in the cases observed. Originality/value – Current literature on IS focuses on a sub-set of variables characterizing collaboration in IS. This researchbuilds on extant literature to definea new framework offive purposeful “ anatomic ” variables definingISinthecirculareconomy.Moreover,wealsocollectanddiscussabroadvarietyofempiricalevidence inwhatisastillunder-investigatedcontext(i.e.Italy).


Introduction
Industrial symbiosis (IS) is one of the main applications of the circular economy (CE) paradigm at the meso-level and it implies a close, symbiotic collaboration between the companies involved (Chertow and Ehrenfeld, 2012;Fraccascia et al., 2021a;Herczeg et al., 2018;Neves et al., 2020).
The IS concept originates from biology where symbiosis is defined as "an association of dissimilar organisms in a mutually beneficial relationship" (Schwarz and Steininger, 1997, p. 49).IS stems from that concept applied to the industrial context and refers to the Industrial symbiosis for circular economy engagement of "traditionally separate entities in a collective approach to competitive advantage involving physical exchange of materials, energy, water, and by-products" (Chertow, 2000, p. 314).Even if rooted in Industrial Ecology, IS is strictly connected to CE (see, e.g.Fraccascia et al., 2021b).Indeed, the IS paradigm aims to (1) value wastes and byproducts, and (2) close the loop between resources, materials, and products.In this view, materials, utilities, and by-products that are produced as an output from a process in a company can be introduced as an input in other processes either in the same company or in other ones.Materials, utilities, and by-products exchange is a fundamental practice in the implementation of the IS paradigm and calls for close collaboration between the different companies that are part of the IS (Chertow, 2000;Herczeg et al., 2018;Neves et al., 2020).In order to spot and exploit potential latent synergies (i.e. to understand how to value materials, utilities, and by-products formerly considered as waste), collaboration and knowledge sharing among different companies and stakeholders are key enablers for creating symbiotic collaborations (Chertow and Ehrenfeld, 2012;Mortensen and Kørnøv, 2019).The IS paradigm is thus a collaborative CE paradigm, where different companies jointly collaborate to value materials, utilities, and by-products, formerly disposed because considered as waste, with the ultimate objective of closing resources loops (Agudo et al., 2023;Chertow and Ehrenfeld, 2012;Chertow, 2000;Fraccascia, 2019;Herczeg et al., 2018;Neves et al., 2020).
The extant literature on IS has dealt with either specific IS cases (Oughton et al., 2022;Patala et al., 2020) or multiple case studies (Uusikartano et al., 2022).Past studies argued conceptual frameworks (Baldassarre et al., 2019;Boons et al., 2017), also aimed at identifying drivers and barriers to the implementation of the IS paradigm (Domenech et al., 2019;Herczeg et al., 2018).Scholars pointed out the benefits stemming from the IS paradigm adoption and performance assessment (Agudo et al., 2023;Fraccascia, 2019;Fraccascia et al., 2021a).Past reviews of the extant literature (Mortensen and Kørnøv, 2019;Neves et al., 2020;Schl€ uter et al., 2022) grounded this research field, also proposing a research agenda for those interested in IS.
Extant literature gives a comprehensive overview of the IS concept.Nonetheless, we believe that the variables characterizing the application of IS paradigms could be further investigated.In particular, previous research focuses on (1) analyzing single variables impacting on collaboration dynamics in IS paradigm (see, e.g.Patala et al., 2020), (2) analyzing the relationship between the development of IS and a small batch of these variables (see, e.g.Uusikartano et al., 2022) and (3) analyzing a small batch of these variables (see, e.g.Domenech et al., 2019, who explore the key characteristics of IS networks in Europe investigating, for instance, the geographical distribution and the network size).Accordingly, current literature on IS focuses on a sub-set of variables characterizing collaboration and the development of IS.An overview and empirical analysis of the several variables characterizing collaboration in IS most recurrent and rooted in extant literature deserves more academic research, as well as the relationship between these variables and the development of IS.We aim to tackle this research gap and offer (1) an overview of the most recurrent variables characterizing the collaboration in IS, (2) an empirical analysis of these variables in order to further advance current understanding about IS (Oughton et al., 2022) and (3) understand if these variables depend on the chosen development strategy of the IS implementation case.We are aware this research should be, on the one hand, context-specific to capture the delicate intertwined relationship among the different variables that characterize IS paradigms, and, on the other hand, based on empirical data (Ahmad et al., 2023;Neves et al., 2020).
Against this background, our study aims at advancing both theory and practice of IS by (1) investigating the key variables that characterize the IS paradigm, (2) the dependence of these key variables on the IS development strategy and (3) gathering empirical evidence about such key variables in the context of IS cases in Italy.Our unit of analysis is thus represented by IS cases in Italy.The choice of Italy as the research locus is based on the need to focus on a homogeneous context, before moving to larger areas (such as the European MD geographical area), and on a context with an advanced development level of CE principles (in accordance, e.g. with Maranesi and De Giovanni (2020) and Susur et al. (2019)).The generalizability of our results to other empirical contexts will be discussed in the last Section of this manuscript, also in terms of limitations.
This manuscript is organized as follows.Section 2 illustrates the state-of-the-art about IS, describing the factors that characterize this CE collaborative paradigm.Section 3 describes the methods and materials used for this study.Section 4 reports the main findings.Section 5 discusses the main findings and the main contributions of this study, also illustrating the limitations as well as the opportunities for future research.

Circular economy
The CE has gained momentum both among researchers and practitioners leading to a debate covering different domains, such as strategic, operational and technology management (Centobelli et al., 2020).The CE addresses the current "Linear Economy"called also the "take-make-dispose" paradigm-which has led to resource depletion and pollution in recent decades.The CE is an alternative paradigm for the economy that fosters environmental sustainability (Baldassarre et al., 2019;Boons et al., 2017;Chiaroni et al., 2021).Environmental sustainability is also one of the priorities of policy makers, who introduced, for instance, dedicated reporting schemes (Paolone et al., 2020(Paolone et al., , 2021)).While Linear Economy is based on an open cycle of resources, CE aims at closing this loop through the skillful combination of technological cycles and managerial practices (Bocken et al., 2016;Centobelli et al., 2020;Su et al., 2013).The adoption of CE has been investigated at different levels.The first level is the micro-level.The micro-level refers to the application of the CE paradigm by the single company, which aims to transition from a linear to the CE in its production systems through different circular management practices.The second level is the meso-level.The meso-level refers to the application of the CE paradigm by a network of companies (business ecosystem), in which the companies involved cooperate to apply CE principles jointly within the network by leveraging latent synergies among the production processes.The third and last level is the macro-level.The macro-level refers to the application of CE on a larger scale, i.e. city, province, region, and nationwide; it requires a paradigmatic shift from the Linear to the CE not only in the industrial sector but also in all other sectors and the social and cultural system (Aarikka-Stenroos et al., 2022;Franz o et al., 2021;Ghisellini et al., 2016;Merli et al., 2018).

Industrial symbiosis
The literature about IS is rooted in Industrial Ecology, where it was first investigated starting from the late 1980s driven by concerns about the environmental sustainability of the mainstream industrial system (Frosch and Gallopoulos, 1989).Industrial Ecology aimed thus at reducing the impact on the environment by considering industrial systems as an ecosystem, where wastes from an industrial process could be considered as raw materials for another industrial process to close the resources loop (Ehrenfeld and Gertler, 1997;Frosch and Gallopoulos, 1989).It is worth mentioning that, even though the IS concept stems from biology and is rooted in Industrial Ecology, the IS concept is strictly linked to CE for three main reasons.First, IS represents one of the main application of CE at meso-level (see, e.g.Ghisellini et al., 2016).Second, there are several contributions (see, e.g.Bocken et al., 2016;Homrich et al., 2018;Merli et al., 2018) that address IS as one of the strategies to implement circular business model for closing the loop.Third and last, IS is a paradigm through which CE principles could be practically implemented (see, e.g.Domenech et al., 2019).

Industrial symbiosis for circular economy
The concept of IS leverages symbiotic collaboration and linkages among different companies to close the loop (Ehrenfeld and Gertler, 1997).These symbiotic collaborations and linkages represent key characteristics of Eco-Industrial Parks, defined as companies located close to one another "that form partnerships to exchange resources to increase resource utilization and reduce environmental impact" (Dai et al., 2022)."Close proximity" is thus a key characteristic of Eco-Industrial Parks (Chertow, 2000;Côt e and Cohen-Rosenthal, 1998;Dai et al., 2022).Besides, Eco-Industrial Parks can originate either from the ex-post application of Eco-Industrial Parks characteristics to already existing Industrial Parks or from the ex ante planning and design of Industrial Park according to Eco-Industrial Parks characteristics (Chertow, 2000;Susur et al., 2019).IS and Eco-Industrial Parks are strictly related (Bai et al., 2014;Chertow, 2000;Neves et al., 2020).IS principles are applied in Eco-Industrial Parks.The symbiotic relationship between the companies involved in an Eco-Industrial Park enable to value by-products and thus to close-the-loop (Bai et al., 2014;Neves et al., 2020).Close geographical proximity among the involved companies was initially considered a "hallmark" to apply IS (Chertow, 2000;Ehrenfeld and Gertler, 1997).However, geographical proximity was no more considered a milestone criterion with the late advancement of literature (Lombardi and Laybourn, 2012).
From a development strategy perspective, two main avenues for the foundation of IS implementation cases can be distinguished between self-organizing cases and facilitated cases.Self-organized cases are characterized by spontaneous agreements among the involved organizations, among the operating actors that will exchange resources.Conversely, facilitated cases are characterized by the presence of an organization (private or public) in charge of managing and facilitating (officially, disclosing it, or unofficially, without disclosing it) the implementation of IS (Bellantuono et al., 2017;Côt e and Cohen-Rosenthal, 1998;Dai et al., 2022).
We label these two development strategies as "bottom-up", referring to self-organizing cases, and "top-down", referring to facilitated cases (following Dai et al., 2022).

Identifying the variables characterizing collaboration in industrial symbiosis
To implement IS, by-products, materials, and utilities produced as output of a production process should be available to be valued and reintroduced as input into another production process.IS leads thus to environmental benefits, by closing the resources loop.Symbiotic exchanges represent the sufficient and necessary condition to implement IS.Symbiotic exchanges are needed to convert an output considered as waste into a valuable input.Besides, symbiotic exchanges are sufficient to identify an IS case.However, it should be noted that to implement symbiotic exchanges the different companies involved in IS have to collaborate.Collaboration among the companies involved in IS is a necessary condition for the implementation of symbiotic exchanges and thus IS.Collaboration enables symbiotic exchanges because it fosters the relationship among different actors.Nonetheless, collaboration between different companies does not qualify an IS case.Symbiotic exchanges can be quite complex in nature and involving different sectors.Indeed, different industrial sectors often collaborate in IS cases to benefit from the possibility to use the output of one industrial sector as an input of another industrial sector.Thus, formerly considered industrial wastes are valued as input into other industrial processes (Chertow and Ehrenfeld, 2012;Mortensen and Kørnøv, 2019;Neves et al., 2020;Oughton et al., 2022).
Collaboration can be also characterized by the geographical proximity among the set of companies involved in IS (as already highlighted in previous Sections) (Chertow and Ehrenfeld, 2012;Jensen, 2016;Jensen et al., 2011;Shi et al., 2010;Velenturf and Jensen, 2016).
Different actors, other than companies, can collaborate in IS.On the one hand, these actors include public actors.They refer to the involvement of public entities such as municipalities and public-owned consortia.Public actors can support the collaboration of the organization MD involved in the implementation of IS by doing, e.g.managerial and administrative activities (Chertow and Ehrenfeld, 2012;Mortensen and Kørnøv, 2019;Uusikartano et al., 2022).
On the other hand, these actors include facilitators.It refers to a non-public actor [1] which supports the collaboration among the organizations involved in the IS implementation case.Accordingly, for instance, a facilitator could be represented by a university involved in the emergence of IS in order to assess its feasibility and support the organizations in the actual implementation of IS (Patala et al., 2020;Schl€ uter et al., 2022;Walls and Paquin, 2015).
Collaboration could also be supported through an economic support.Governmental support (e.g.incentives) could support the collaboration among different actors by providing the needed financial support.Governmental support differs from the involvement of public actor.The former refers to incentives, supporting schemes providing economic support to the involved organizations.The latter refers to the involvement of a public entity (e.g. a municipality) in the IS implementation case (Chertow and Ehrenfeld, 2012;Herczeg et al., 2018;Mortensen and Kørnøv, 2019).
Table 1 reports thus the most recurrent variables characterizing collaboration in IS, which have been identified by reviewing extant academic literature.Table 1 describes these variables-that we label as "anatomic" variables-that must be considered while analyzing cases of implementation of IS.By "anatomic" variables we mean the variables characterizing the collaboration in Industrial Symbiosis.Therefore, they are key variables.However, we named them "anatomic" variables to emphasize that these variables influence the way actors collaborate, thus the way collaboration "lives".This list of variables will constitute the theoretical framework for our empirical investigation in the specific context of Italy.It refers to the geographical distance among the companies involved in each Industrial Symbiosis implementation case.In particular, if the involved companies are located within a radius distance of around 30 km (a value reported as the average reference distance by Jensen, 2016;Jensen et al., 2011;Shi et al., 2010), then geographical proximity is validated

Industrial symbiosis for circular economy
Materials and methods A narrative literature review was performed (Fan et al., 2022).We started from a small batch of articles on IS by main contributing authors (e.g.Chertow M. R., Lombardi D. R., Neves A.).Both backwards and forward snowball sampling methods were then applied to review literature on IS.Thanks to the narrative literature review it was possible, on the one side, to define the concept of IS and, on the other side, to identify the variables that characterize the collaborative relationship in IS, hereinafter referred to as "anatomic" variables.Through the narrative literature review, we gathered the articles dealing with collaboration in IS (see, e.g.Chertow and Ehrenfeld, 2012;Domenech et al., 2019;Mortensen and Kørnøv, 2019;Patala et al., 2020;Uusikartano et al., 2022).A content analysis (Weber, 1990) was performed on the collected articles to triangulate and cluster the information provided by different articles.We identified the variables characterizing collaboration, either explicitly mentioned or implicitly mentioned through the analysis performed by the articles' authors.We did not aim to collect all the variables characterizing IS.We put major emphasis on the variables more related to the collaborative relationship among different actors in IS implementation cases.Accordingly, we focused on inter-firm collaboration dynamics.We adopted an exploratory approach.We did a convenient selection of the variables most recurrent in extant literature to include the variables characterizing collaboration most rooted in IS literature.For instance, we excluded from our analysis the variables with no impact on collaboration, such as the capital-intensiveness of the considered sector, the innovative level of the considered company, the availability of skilled workforce.We identified five different variables characterizing collaboration in IS.Lastly, we labeled those variables as "anatomic" variables.
We considered both academic and empirical sources of evidence to identify the most relevant cases of IS implementation in Italy.We qualify an IS implementation case as a collaboration between at least two different entities (or at least two different business units belonging to the same company, considering big companies) that perform symbiotic exchanges between each other.
First, we reviewed current academic literature by applying both an unsystematic and a systematic search strategy (Fan et al., 2022;Kraus et al., 2022).As for the unsystematic search, we started from a small number of contributions on IS and we applied both backwards and forward snowball sampling methods to gather IS implementation cases in the Italian context, of which extant literature already gives evidence.As for the systematic search, we selected the Scopus database given its broad coverage of journals on CE, industrial ecology, and IS topics.We selected the keywords of IS or eco-industrial park* and Ital* (not to miss relevant contributions) collecting more than 60 articles which were then manually filtered by reviewing, first, titles and abstracts, and second, full texts to include only contributions that were relevant to our objectives.To filter the retrieved articles, we applied both exclusion and inclusion criteria.We excluded articles with only a theoretical perspective on the IS concept, with only a technical, engineering focus.Conversely, we included articles providing realworld cases of implementation of IS in Italy, providing not only technical information on industrial process but also managerial information about the actors involved and the collaboration dynamics in the implementation case.We gathered evidence of 13 IS implementation cases in Italy through the unsystematic search strategy and of 16 cases through the systematic search strategy.We thus gathered information on 29 IS implementation cases in Italy though both search strategies.
Second, to enlarge this sample and collect more evidence on the practical implementation of IS in Italy, we also considered two empirical sources providing information on the application of the IS paradigm in Italy.The first empirical source refers to the Symbiosis Users Network (SUN), which is the first Italian network on IS, involving almost 40 partners representing industrial, governmental and research entities.The second empirical source refers to the Italian Chambers of Commerce, which promote the knowledge sharing of virtuous cases and best practices referring to the IS paradigm in Italy.Overall, we gathered MD evidence of 27 IS implementation cases in Italy.Thereafter, we removed duplicates of which we already gathered evidence through academic sources.We thus gathered evidence of 21 additional IS implementation cases in Italy.
Combining and triangulating the academic and empirical sources enabled us to gather evidence of 50 IS implementation cases in Italy.Figure 1 presents a schematic representation of the IS cases retrieved from academic and empirical sources.
Thereafter, we implemented a multiple-case study research design for collecting evidence about the variables included in our theoretical framework (Eisenhardt, 1989).Each IS implementation case was analyzed through secondary sources of information and data (e.g.academic articles, companies' websites, sectorial reports, and press releases).Professional full-text journal databases, such as LexisNexis, were used to support our research.We collected and analyzed an overall of about 150 sources among academic articles, companies' websites, sectorial reports and almost press releases.
Table 2 provides an overview of the different secondary sources analyzed and distinguishes between "top-down" and "bottom-up" IS implementation cases.The information retrieved from the different sources was then clustered and triangulated through content analysis (Weber, 1990).Hence, we collected relevant information on the "anatomic" variables characterizing the identified IS implementation cases in Italy (refer to Table 1).A particular focus is deserved by the "anatomic" variable referring to geographical proximity.In particular, the precise geographical location of the headquarters of the companies involved in each IS implementation case has been determined through Google Maps and Google Earth applications.Only if the headquarters of the involved companies were located within a radius equal or lower than 30 km (considered as the average reference distance), then geographic proximity was validated.

Industrial symbiosis for circular economy
Table 3 presents a preliminary synoptic overview of the retrieved IS implementation cases in Italy in terms of (1) total number of involved companies, (2) number of companies involved in the same case, (3) total number of involved sectors, (4) number of sectors involved in the same case, and (4) the breakdown by geographical area.In Table 3 we reported contextual information for the whole sample of IS implementation cases, for "bottom-up" cases, referring to self-organizing cases, and for "top-down" cases, referring to facilitated cases.
Data show that the majority of IS implementation cases in Italy refer to "bottom-up" cases, i.e. to self-organizing cases sprouting from spontaneous initiatives."Bottom-up" IS implementation cases account for 70% of the total cases, whereas "top-down" cases for the remaining 30%.Even though the number of IS implementation cases in Italy is higher for the "bottom-up" cases, the "top-down" cases involve a larger number of companies.Indeed, "top-down" cases involve more than one thousand companies, whereas "bottom-up" cases involve more than one hundred companies.The total IS implementation cases in Italy involve therefore more than one thousand and one hundred companies.The majority of cases involve between two and four different companies, which are close to each other (this insight is consistent with what reported, e.g. by Domenech et al. (2019), who posit that local networks involve a smaller number of companies).The 27% of "top-down" cases involve more than one hundred companies, whereas none of "bottom-up" cases involve more than one hundred companies.Lastly, 3% "bottom-up" cases involve one single company, which implements IS practices internally, i.e. exchanges are implemented between different business units of the same company.

MD
The distribution of the total IS implementation cases seems rather even throughout the Italian peninsula, with the Northern, Central and Southern areas accounting for 36%, 30 and 34% respectively.The distribution of the "bottom-up" IS implementation cases shows a prevalence of Southern Italy accounting for 43% of the total.Conversely, the distribution of the "top-down" IS implementation cases is rather uneven in favor of Northern Italy, accounting for 60% of the total.Annex provides contextual information, "anatomic" variables and development strategy and a brief description for each of the 50 IS implementation cases in Italy.

Findings
In the following sections, we report evidence about the "anatomic" variables characterizing the collaborative relationship of IS implementation cases in Italy, considering first each "anatomic" variable separately, and then the most occurrent "anatomic" variable in the two development strategies.

"Anatomic" variables of industrial symbiosis implementation cases in Italy
Table 4 presents a synoptic overview of the "anatomic" variables for the retrieved IS implementation cases in Italy.In Table 4 we reported the "anatomic" variables for the whole sample of IS implementation cases, for "bottom-up" cases and for "top-down" cases.
In the following paragraphs, each "anatomic" variable is considered separately and analyzed for total, "bottom-up" and "top-down" IS implementation cases in Italy.(ISTAT, 2009)."Bottom-up" cases involve all but one (i.e.electricity sector) industrial sectors; similarly, "top-down" involve all but one (i.e.wholesale and retail trade sector) industrial sectors.The manufacturing sector, which refers to the transformation of materials into final products, is the main sector involved, respectively accounting for 52%, 55 and 45% of the total, "bottom-up" and "top-down" IS implementation cases.Among the manufacturing sectors, the main ones are the food and beverage sector and the chemical sector.The second most important sector is the one referring to water supply, sewerage, waste management, and remediation activities, respectively accounting for 20%, 18 and 26% of the total, "bottom-up" and "top-down" IS implementation cases.The sector referring to professional, scientific, and technical activities is the third most involved sector accounting respectively for 8%, 5 and 15% of the total, "bottom-up" and "top-down" IS implementation cases.The other sectors being involved (i.e.(1) agriculture, fishing, and forestry, (2) construction, (3) education, (4) wholesale and retail trade, (5) electricity) account for less than 10% of total, "bottom-up" and "top-down" IS implementation cases.The relevance of the manufacturing sector and of the sector referring to water supply, sewerage, waste management and remediation activities emerged also in Neves et al. (2020).Besides, we report also the relevance of the sector referring to professional, scientific and technical activities, whereas Neves et al. (2020) did not considered this sector as a main one in favor of electricity and agriculture sector.We mention, for instance, an interesting case, in which the sector referring to professional, scientific, and technical activities was involved together with the food and beverage sector.This example shows the role of collaboration between different actors to value resources and close the loop.Different manufacturing companies active in the food and beverage sector were looking for the possibility to value the by-products produced as outputs of their production processes.A company operating professional, scientific and technical activities was involved to assess different options to value those by-products from a technical and economic feasibility perspective.The possibility to value those by-products in the bio-fuels industry was identified among the most attractive ones.The possibility to involve a company operating in the bio-fuels industry pulled the companies operating in the food and beverage sector to choose this outlet.
Public actors' involvement.The involvement of a public actor refers to the involvement of public entities such as municipalities, public education and research entities, and publicowned consortia.Public actors are not involved in the majority of total and "bottom-up" IS implementation cases in Italy.60% of the total and 74% of "bottom-up" IS implementation cases in Italy do not involve any public actor.Conversely, the majority of "top-down" IS implementation cases in Italy involve public actors (i.e.73% of total cases).The involvement of public actors has been considered crucial in IS, especially in facilitating the emergence of "top-down" cases (see, e.g.Uusikartano et al., 2022), in line with findings reported in Table 4.The involvement of public actors is relevant, for example, in district heating cases.In these cases, by-products of the manufacturing sector are valued to produce heat, which must be distributed across the buildings of the close municipality.Thus, public actors are involved in these cases to support the development of the district heating pipeline, easing the bureaucratic process to the development of the pipeline.For instance, in one of the retrieved cases the public actor was involved to value the wood processing wastes produced by a company operating near a city in Northern Italy.The collaboration between the company and the public actor enabled to unfold the possibility to use the wood processing wastes to fuel the local district heating network and thus provide heat to several residents of the nearby city.

MD
Governmental support.Governmental support refers to the availability of support schemes, incentives, investment funds or other supporting mechanisms aimed to support the companies involved in the IS implementation cases from an economic perspective.The large majority of total, "bottom-up" and "top-down" IS implementation cases in Italy have not benefited from governmental support.There was no governmental support respectively, in 84%, 83 and 87% of the total, "bottom-up" and "top-down" IS implementation cases in Italy.Governmental support has been identified as a relevant driver on which to act to promote the adoption of both CE and IS.Moreover, the governmental support should be consistently designed by the governmental entities operating at different geographical scale (Neves et al., 2020).Even though governmental support is not much developed in the specific Italian context, it could be leveraged to raise companies' awareness of IS advantages (Herczeg et al., 2018;Mortensen and Kørnøv, 2019) and thus support further development of this paradigm in Italy.Even though governmental support is not widespread in the IS implementation cases in Italy, it should be mentioned that it could represent a trigger to implement the IS paradigm.The availability of supporting and incentive schemes could be the lever through which the diffusion of the IS paradigm can be promoted even among more skeptical companies, and especially among companies who lack the financial resources to implement the IS paradigm.This last point holds particularly true for start-ups.For instance, governmental support was crucial for a start-up operating in the chemical sector, which developed a prototype to value an olive oil by-product.Through governmental support, the start-up was able to further develop the prototype, collect the olive oil by-product from different local agricultural companies and extract valuable organic molecules from it.
Facilitator involvement.The involvement of a facilitator refers to the involvement of an entity acting as coordinator of the IS network, managing the relationship among all the involved companies.A facilitator is involved in the majority of "top-down" cases (i.e.73% of total "top-down" cases).The facilitator has therefore a fundamental role in "top-down" cases (coherently to Patala et al., 2020).Considering "bottom-up" cases, a facilitator is involved in the 23% of total "bottom-up" cases.Regarding the role performed by the facilitator, it acts mostly (i.e. in over 90% of the cases) as the managerial and/or technical coordinator supporting and engaging all the different companies and stakeholders involved in the case.Moreover, this managerial and/or technical coordinator role is mostly performed by professionals or education institution (i.e. in over 70% of the cases).For instance, a successful implementation of IS principles was driven by the technical and managerial coordinator role performed by an education institution.A steel mill was looking for a way to value one of the by-products coming from its production process.The local university was involved in order to assess the technical feasibility of valuing those by-products and find possible outlets in which they could be reintroduced as input.The technical feasibility study validated the possibility to value those by-products and to introduce them as an input for the cement production process.The university then supported the steel mill by contacting several companies belonging to the cement industry and by engaging them in this symbiotic exchange.In this case, the facilitator was represented by an education institution, and it coordinated the actual implementation of symbiotic exchanges from both a technical and managerial perspective.To conclude, the facilitator's role in supporting the managerial and/or technical coordination activities is a driver to increase the number of companies involved in the same case.Indeed, the majority of "top-down" cases involve a facilitator, and almost 30% of "top-down" cases involve in the same case more than one hundred companies, suggesting that there may exist a connection between facilitator involvement and the number of companies involved.

Industrial symbiosis for circular economy
Geographical proximity.The relevance of geographical proximity was initially considered as fundamental in the seminal contribution by Chertow (2000) and then questioned over time (see, e.g.Lombardi and Laybourn, 2012).Our findings confirm the paramount relevance of geographical proximity.Indeed, the large majority of total, "bottom-up" and "top-down" IS implementation cases in Italy involve companies with geographical proximity (i.e. the involved companies are within an average radius of 30 km, identified as a reference distance value, e.g. by Jensen, 2016).Respectively, 72%, 69 and 80% of the total, "bottom-up" and "topdown" IS implementation cases in Italy involve companies with geographical proximity.For instance, geographical proximity is relevant in IS cases involving companies operating in the agricultural sector.Local agricultural companies involved in IS implementation cases in Italy are mainly small and medium size companies.In these cases, an innovative company found a new way to value the agricultural by-products, but it needs a constant and steady flow of agricultural by-products.Therefore, by-products coming from different agricultural companies must be grouped to collect enough quantities.Being geographically close could be a relevant lever to reduce managerial complexity in agricultural by-products handling and transportation.A quite interesting counter case shows that the need for geographical proximity might be overcome by new digital technologies, such as networking platforms.Platforms have been acknowledged also as a risk-mitigation tool (Caporuscio et al., 2023).For instance, a textile networking platform connects companies operating in the collection and sorting of used garments with tailors and designers.Through the networking platform used garments are collected, sorted through the adoption of Artificial Intelligence, and then distributed to a network of more than twenty tailors and designers distributed across the whole country, who make them wearable again.
The "anatomy" of industrial symbiosis implementation cases in Italy This Section summarizes the "anatomy" of IS implementation cases in Italy.In Section 2, we presented the two development strategies for IS, namely, "bottom-up" and "top-down".We focus here on these two development strategies to investigate whether a certain "anatomic" variable is more occurrent when a specific development strategy is followed.Thereafter, we try to investigate the rationale behind the prevalence of that "anatomic" variable under a specific development strategy.We aim thus to identify the most relevant "anatomic" variables to be pursued when following a specific development strategy.
Figure 2 shows the most and the least occurrent value for each analyzed "anatomic" variable for "bottom-up" and "top-down" IS implementation cases in Italy.The most occurrent variable is defined as the value of the "anatomic" variable with the maximum occurrence value.The least occurrent variable is defined as the value of the "anatomic" variable with the minimum occurrence value.
Given the most and least occurrent "anatomic" variables reported in Figure 2, it is possible to group them in two clusters.The first cluster refers to development-dependent variables.These variables vary depending on the development strategy of the IS implementation cases in Italy (i.e."bottom-up" and "top-down").Public actors' and facilitators' involvement are development-dependent variables.Most of the sole "top-down" IS implementation cases in Italy meet these two variables.The involvement of a facilitator or a public actor is thus relevant in the implementation of "top-down" cases given that these two actors could support the development of the IS implementation cases.Indeed, the involvement of a facilitator or a public actor makes it easier to involve a larger number of companies in "top-down" IS implementation cases in Italy.The facilitator and/or the public actor (depending on the peculiarities of each case) act as a coordinator and can more easily engage a larger number of companies handling the managerial complexity (without any managerial burden for the companies involved in the practical implementation of IS).Besides, the facilitator and/or the MD public actor raise awareness of IS' benefits and build trust between the different companies involved in the IS paradigm (consistently with Patala et al. (2020) and Uusikartano et al. (2022)).For instance, the involvement of public-owned consortia could facilitate the implementation of IS by easing the administrative burden for the companies involved, which could thus focus on the activities enabling to implement symbiotic exchanges.
The second cluster refers to development-independent "anatomic" variables.These variables do not vary depending on the development strategy of the IS implementation cases in Italy (i.e."bottom-up" and "top-down").The industrial sector, governmental support and geographical proximity belong to this group of variables.Companies involved in IS implementation cases in Italy are characterized by geographical proximity, which emerges as a key characteristics (consistently with Chertow, 2000) of IS implementation cases in Italy regardless of the development strategy.The low level of governmental support does not provide clear incentives to companies willing to implement IS principles.This result could be affected by the low level of development of national policies on IS (coherently to Neves et al., 2020).Indeed, the regulatory framework was only recently updated with the new National Strategy for CE (Ministero della Transizione Ecologica, 2022).Neither the low governmental support nor the unclear regulatory framework indicate effective ways through which to implement IS to the Italian companies.Consequently, most of Italian IS implementation cases involve the same sector (i.e. the manufacturing sector) and companies characterized by geographical proximity, which self-organize, and implement IS principles.

Key contributions
This article's contributions to extant literature in the field of CE and IS are threefold: (1) we improve characterizing IS by proposing a set of variables to describe the anatomy of IS, (2) we gathered a rich evidence of IS implementation cases in Italy and we characterized the gathered cases with respect to the "anatomic" variables (3) we discussed the relationship between the "anatomic" variables and the development strategies (top-down and bottom-up) of IS cases.
From the academic research point of view, we further advance the debate about the application of CE at meso level focusing on IS.We provide a research framework, which  Industrial symbiosis for circular economy analyzes the "anatomic" variables characterizing collaboration in IS.This analysis could be the starting point to dig deeper into the application of CE at meso level enabled by collaboration.The "anatomic" variables offer an answer to the quest for additional research argued by Ahmad et al. (2023), Neves et al. (2020).Moreover, these "anatomic" variables have been analyzed with reference to a particular and rich empirical context.
We distinguished these "anatomic" variables in two clusters: development-depend and development-independent variables.The development-dependent variables are represented by public actors' involvement and facilitator involvement.We identified these two "anatomic" variables as development-dependent variables because most of the sole "top-down" IS implementation cases in Italy meet these two variables.The role of a facilitator and/or a public actor was found important, especially for "top-down" cases, by handling managerial complexity and promoting awareness and trust among the involved companies (merging what stems from Patala et al., 2020, with Uusikartano et al., 2022).
The development-dependent variables are represented by industrial sectors involved, governmental support and geographical proximity.We identified these three "anatomic" variables as development-independent variables because they do not vary between "top-down" and "bottom-up" development strategies of the IS implementation cases in Italy.Through this empiric analysis of the "anatomic" variables, we first of all validated the paramount relevance of the manufacturing sector, involved in the majority of Italian cases (consistently with what reported by Neves et al., 2020).Our empirical findings highlight the low level of governmental support for IS in Italy, suggesting policymakers a lever on which to act to promote the deployment of IS among Italian companiesthe recent National Strategy for CE (Ministero della Transizione Ecologica, 2022) could be an important keystone in the governmental support path.At the same time, we highlighted policy makers have a potential role in (1) easing the bureaucratic and administrative procedures connected with IS implementation (e.g. with specific norms on secondary raw materials usage) and (2) providing incentive schemes to companies willing to implement IS but lacking proper financial means (e.g.start-ups).Lastly, empirical evidence reports the importance of geographical proximity among the involved companies.Indeed, even if the minority of Italian cases involve companies with no geographical proximity, this "anatomic" variable is still nowadays a paramount variable in IS confirming the seminal definition by Chertow (2000), in contrast with Lombardi and Laybourn (2012).
Implications for scholars, managers, and policy makers We believe that this article presents relevant implications for researchers, practitioners, and policy makers.From an academic standpoint, we strengthen the paramount role of collaborative relationship to implement CE at meso level, with reference to IS implementation.Besides we posit that the collaborative relationship can be characterized by five "anatomic" variables whose values differ based on the development strategy of the IS implementation.From a managerial standpoint, this article can represent a practical guideline for managers looking for how to implement IS.For instance, managers can grasp from this article the most relevant industrial sectors to be involved to implement IS.From a policy maker standpoint, this article represents a call for action.Indeed, we posit that governmental support is not yet fully developed to support properly the development of IS.Therefore, we suggest policy makers to focus on IS supporting schemes to promote the deployment of IS.

Limitations
Our contributions should be interpreted in the light of their limitations.The first limit refers to the application of our theoretical framework to a single Country, and this limits the generalizability of results.Even though we argue that the framework can be generalizable to other socio-technical contexts, the occurrence of the "anatomic variables" could significantly MD differ from Country to Country.Besides, the distribution of the overall IS cases is rather even throughout the Italian peninsula.However, the "bottom-up" cases and the "top-down" cases are more focused, respectively, on Southern and Northern Italy.This uneven distribution of "bottom-up" and "top-down" cases could represent a further limitation to the generalizability of results and an avenue for future research.In this view, we call for future research to identify and compare the values of the "anatomic" variables characterizing the IS paradigm in other geographical areas (i.e.other countries and/or larger areas such as the European Union).
Moreover, a sample of geographical areas at different development stages of their IS paradigm could be compared to better capture the potential relative relevance that the variables might assume at different stages.In this view, we argue for further longitudinal investigations of IS paradigms.The observation over time of the "anatomic" variables in both "bottom-up" and "top-down" IS implementation cases can unveil what variables-and, consequently, what policies and incentives-should be prioritized to facilitate the growth and sustainability over time of the cases of IS.Finally, there could have been an interpretation bias in analyzing the extant literature to identify the "anatomic" variables and design the theoretical framework that collects the main characteristics of an IS paradigm.In this view, further academic research should confirm or deny our list of "anatomic" variables, also based on empirical evidence from other Countries.

Future research avenues
Future avenues for future research emerge by broadening the scope of our work.First, a deeper investigation into the relationships among the micro, meso and macro implementation levels of CE could be performed.Indeed, a single company (i.e.micro-level) could be active at a national scale (i.e.macro-level) but also at a continent or global level.In the same way, a network of companies could involve companies operating in the same country or beyond, in different continents.Therefore, the boundaries to distinguish among micro, meso and macro level could be further investigated to advance a clearer definition of the different implementation levels of CE.Second, a deeper investigation into the relationships between the companies' headquarters geographical distance and IS implementation could be performed.The "anatomic" variable referring to geographical proximity deserves additional research efforts, for instance further studies could focus on (1) confirming or questioning the reference average distance and (2) on performing sensitivity analysis on the reference average distance.Third, the role of unofficial facilitators was not investigated in this article.In particular, unofficial facilitators refer to stakeholders who, even though not formally recognized and appointed as facilitators, actually perform such role (Schl€ uter et al., 2022).Therefore, a deeper investigation into the "anatomic" variable referring to the facilitator's involvement distinguishing between official and unofficial facilitators could deserve further academic research.Fourth, we considered two development strategies (i.e."top-down" and "bottom-up").However, these two strategies are not dichotomic and mixed approaches are applicable even though not investigated in this paper.Further studies could thus tackle mixed approaches by focusing, for instance, on those in which bottom-up development is facilitated through top-down methods.Fifth and last, we selected the "anatomic" variables as the ones most recurrent in IS literature.Accordingly, further research could focus on broadening the set of "anatomic" variables to be considered.
Despite the above limitations, we argue that our study could contribute to a better understanding of the IS phenomenon as an emerging paradigm for a sustainable future.

Figure 2 .
Figure 2. The most and least occurrent "anatomic" variables of "bottomup" and "top-down" industrial symbiosis implementation cases in Italy

Table 1 .
Definition Industrial sectors involved.Eight different industrial sectors are involved in the total IS implementation cases in Italy.The industrial sectors are classified following the Italian ATECO classification

Table A1 .
Note1.Facilitators could be not only non-public actors but also public actors in geographical contexts other than Italy.