1. Introduction
In ecology, the concept of symbiosis describes a closed and often long-term interaction between two or more different biological species. This long-term association may, but does not necessarily, benefit both participants. Symbiotic relationships take place naturally in an ecosystem (different communities of living organisms in association with inorganic environmental components). Since 1989, academic literature has shed light on the fact that industry bears a resemblance to natural ecosystems [
1], thus closing loops in the industrial socio-ecosystem means the integration of cascading uses, by-product synergies, pooling services and consolidated waste management in an effort of reconciliation with natural ecosystems, even though there are obvious differences from natural ecosystems [
2,
3,
4]. In recent years, there has been a small but compelling set of studies into the role of Industrial symbiosis stakeholders, such as corporations, SMEs, business associations, anchor tenants and governmental agencies, which has provided enough evidence to recognize the advantages of industrial symbiosis integration in a social ecological dimension [
5,
6,
7,
8,
9]. Although many studies have focused on industrial symbiosis (IS), most of them focus only on eco-efficiency [
10], performance assessments [
11] and technical exchange potential using chemical engineering [
12]. From the best of our knowledge no significant study has been made into the spatial proximity analysis in the industrial ecosystems. Therefore, the authors accept the challenge to operationalize a systemic approach of social ecological dimension in the industrial symbiosis, through the engagement of applied, social and business management sciences to cope with the spatial proximity analysis of an industrial ecosystem [
13,
14]. Thus, industrial symbiosis is built towards a common understanding of system dynamics governance in the industrial network, analysed from a broader geographical perspective [
15,
16,
17].
In this paper, we define industrial symbiosis (IS) as an organizational strategy, which is a sub-field of industrial ecology, considering firms as organized organisms. This metaphor proposes a social innovation where industry entails a semi-closed ecosystem in which material and energy flows should be reincorporated in the system by a circular logic. However, it does not mean that inter-firm actions do not concern individual firms. On the contrary, individual firms must integrate IE in the individual project of their company to allow communication and interdependency as members of the system. Thus, we think of industrial symbiosis as a social innovation strategy, based on the ability to transform global society into one that makes better use of materials. In doing this, we are assuming that social innovations in industry could be triggered by metaphors, which make us think out of the box. In that sense, we are going beyond the definition proposed by Chertow [
18], who highlights the technical and biophysical aspects. We are convinced that the human dimension is essential for the understanding of industrial symbiosis as a social process, based on ecological, political, cultural and economic aspects. Although Industrial ecology already claims that the social dimension integration improves the theoretical conceptualization of industrial ecosystems dynamics as evidenced by the French school studies on Territorial industrial ecology [
19] then simply Territorial ecology [
20]. Indeed, this paper aims to contribute with the discussion about the advantages of using geographical systems dynamic approach to embed complexity in the social analysis of industrial symbiosis, [
21], enabling a vision beyond firms’ individual actions in the search for eco-efficiency.
1.1. Industrial Symbiosis
Inspired by the previous iconic studies of industrial symbiosis, we identify two main drivers in the analytical process of industrial symbiosis, as mechanisms that steer the sustainable transition of industry. First, the internal firms’ production assessment looking for the economic viability window in the intersection between costs reduction coming from efficiency [
22] and the valorisation of by-product improving the technical and economic productivity resulting from the cooperative synergies. Where any disruption or reduction in economic benefits may be sufficient to interrupt the symbiotic flow or, in the worst case, force the departure of a firm from the network [
8]. The second driver concerns the broader social sphere aiming to understand and develop the stakeholder coordination within the industrial symbiosis. It is within this second mechanism that we can take advantage of a comparative analysis of the geographical proximity issue [
16] in industrial symbiosis.
The current debate highlights the circular economy (CE) addressed in our conceptual framework, which proposes to derive strategies for a shift from a linear to a circular industrial structure [
14,
15,
23]. The circular economy is understood in this paper as the extension of value and utility of product, therefore production and consumption wastes are used as secondary resources, providing solutions and co-benefits to a range of economic and environmental issues [
4,
23]. There are four sources of value creation for the circular economy identified in the literature: 1. The power of the inner circles (the long-lasting durability of products and services), 2. The power of circling longer (the available options of refurbishing, remanufacturing, repairing and reuse of a product or material), 3. The power of cascade use (to diversify reuse along the value chain), 4. The power of pure inputs (biodegradability, uncontaminated materials and the efficiency of collection and redistribution). Looking at industrial symbiosis as an organizational strategy in the quest of social innovation, we take it to be embedded in the Industrial Ecology field, because it is interested in inter-firm relationships, mainly based on cooperation, highlighting the relationship with the biosphere and using ecological ecosystem dynamics as a metaphor. When evoking industrial symbiosis in the paper, we consider it as one of the axes of circular economy, an axe that focus their efforts in the inter-firm relationship strategies, therefore we can assume that industrial symbiosis puts into practice some circular economy principles. However, despite the growing interest in the industrial symbiosis examples the question of how these circular principles work in practice remains unanswered. More discussion about the biophysical and social influence of stakeholders in the industrial ecosystem is required. Which stakeholders? Which motivations? Which values govern the system’s structure?
1.2. Dunkirk, Industrial Ecosystem Analysis
The aim of this study, based on results obtained in Dunkirk, is to test the territorial embeddedness of the industrial symbiosis, considered as a social innovative strategy, looking deeper into the systemic proximity understanding of this socio ecological dynamic. To measure geographical proximity, defined as space and relationship distance [
24], it seems to be essential to assume that conditions other than the by-product exchange define the geographical location, because by definition, the by-product production firms are multifunctional. Multifunctional firms have functions other than by-product exchange, which usually plays an ancillary role. Therefore, the by-product exchange perspective does not influence
a priori their location in the territory, establishing a geographical proximity between production and consumption, which is different from monofunctional production [
24]. In the multifunctional firms the by-product synergies depend on primary production processes, leading to a direct relationship in which the greater the final production, the more by-products are generated. Thus, a feedback loop is identified in the production side, since the higher the efficiency in reducing waste, the lower the number of by-products available to be shared. The stakeholder relationship network has already been considered in the literature [
3,
25] but not through a geographical systems dynamic perspective, which would allow us to better understand the mechanisms, motivations and values in the industrial symbiosis for the sake of sustainability, understood in this study simply as the time endurance of this institutional cooperation mechanism.
The Dunkirk case study provides an excellent base for investigation in a developed country, with an existing and available academic literature about the territorial embeddedness of this industrial symbiosis [
12,
15,
16,
17,
24,
26,
27,
28,
29]. Dunkirk encompasses some features that also seem to facilitate the connections between stakeholders and the collaboration in the network, such as the seaport location and the facilitator role played by the local public authority.
The method for evaluating territorial embeddedness in the industrial symbiosis, underlines the key drivers for each stakeholder’s behavioural patterns [
30], triggering the systems dynamic approach through a Causal Loop Diagram (CLD), with a coherent narrative string to demonstrate if in the Dunkirk industrial symbiosis territories influence and are influenced by, the industrial system. We analyse the interactive behaviour, cooperation, institutional productive capacity, organizational strategies and by-product flow exchanges, which allow us to understand the qualitative nature of such interdependences. Through this study, we provide relevant insights to answer, what are the key drivers that we need to influence to guarantee the essential functions in the industrial symbiosis? The geographical proximity methodology utilized contributes to the complex understanding of social industrial ecosystems, disentangling human motivational causality. In this study, we frame the Dunkirk IS’s motivational causality, identified as the economic/political drivers related to the industrial ecosystem structure, the conflicts of interest, game theory, learning process; institutional pathways and idiosyncrasy belong to this social process.
Figure 1, illustrates how the geographical system dynamics approach takes place in the industrial symbiosis, utilizing a common theoretical ground that encompass complexity theory, stakeholders and ecosystems theory, including analytical tools that allow the internalization of complexity in the business and public policies decision-making process. In trying to get a better understanding of the industrial system, an over-simplification of structure would miss some of the properties of the system, because the system’s complexity cannot be ignored. In addition, when the ecosystem metaphor is applied to industrial systems, we demonstrate the analytical benefits for the understanding of industrial symbiosis. The industrial ecosystem theory gives room to incorporate complexity into the diversity of industrial stakeholders, supplying them with tools to manage the conflict between different and sometimes contradictory values and interests [
24,
26,
27].
This paper has five sections: In
Section 2 we define the theoretical framework for our analysis. Industrial symbiosis is embedded in complexity theory, economic geography theory and ecosystems theory. In
Section 3, we introduce system dynamics as a methodology to identify the drivers and leverage points of the industrial symbiosis. The results of the study are analysed using Causal Loop Diagrams (CLD). In
Section 4, we discuss the geographical proximity of the Dunkirk industrial symbiosis analysis. Finally, we end the paper with concluding remarks.
3. Methodology
System dynamics is a methodology developed for the study of complex non-linear problems emanating from systems behaviour, able to incorporate, remove or change the structural mechanisms between actors and their idle periods. The publication of books like
Industrial Dynamics [
41],
Urban Dynamics [
42] and
Limits to growth [
43] gave birth to a tradition in the use of system dynamics to study complex issues, incorporating concepts such as retroactive flows and stock variables to the academic research on social systems within an evolutionary framework approach [
41]. According to Forrester, J. [
42] four features characterize system dynamics when modelling behaviour: 1. a boundary is drawn around the system, 2. retroaction generates ties of structural elements within the boundaries, 3. level variables represent accumulations within the feedback, 4. velocity variables (flow) represent the activity within flows streams.
The Causal Loop Diagram (CLD) developed in this paper for the Dunkirk industrial symbiosis, introduces the concept of feedback loops for key social drivers. A geographical proximity perspective needs to be integrated into the system dynamics approach to cope with behaviour patterns, stakeholder’s causal relationships, resources allocation decisions and environmental thresholds which influence future decisions, shaping the social industrial system depicted in the CLD. The system dynamics method addresses complex issues depicting the consequences of stakeholder’s behaviours and agreements that may seem counterintuitive in the model. For example, the disruption of one loop like “private resources for innovation” can result in a reinforcing effect (positive polarity) in the “Emerging technology variable” or a balancing effect (negative polarity) in “Eco-efficiency technology” which counteracts or resists the direction of the original flow. The data used in this paper comes from primary and secondary sources. The secondary sources of information include the entire set of scientific papers and reports published in English and French regarding the industrial symbiosis from 1990 to now, gathering different perspectives and addressing different research questions. Besides, as primary sources engaged in this study, we include a set of interviews conducted with expert analysts and researchers that are involved in the organizational process and know in detail the local industry to corroborate the information obtained in the literature.
CLD’s are an intermediary step between system conceptualization and the development of a quantitative simulation model. CLD ‘s may be used as an analytical tool in their own right. In this respect, this study does not extend to a numerical assessment of geographical industrial ecosystems, thereby excluding the model test and simulation of scenarios in qualitative terms; instead, it focuses on problem identification, identification of behavioural patterns and policy design and testing. Once the model is developed and the necessary data gathered, the next rational step in the analysis would be the integration of quantitative assessments to test the validity of the models through simulations.
For the case study, we used data from publicly available sources, interviews, site visits and collaborations with local organizations. Publicly available sources consist of 17 academic papers and reports in English and in French about the Dunkirk industrial symbiosis experience, encompassing different perspectives and addressing different questions. We then cross-validated the publicly available data obtained from the literature analysis presented in the Annex 1 Materials by interviewing some consultants who have repeatedly met with stakeholder of the industrial symbiosis.
The geographical system dynamics approach composed by three previously mentioned theoretical sources: complexity theory, stakeholder theory and ecosystems theory. It is important to provide theoretical foundations for a methodology which, from the best of our knowledge, has never been used in previous research studies, in order to give clarity to the arguments supporting this methodological choice. The geographical system dynamics method tries to integrate the differences while identifying the common features, to ensure their ability to represent territorial mental models, thus one of the main contributions of CLDs is the identification of key drivers able to cause large-scale changes in the system from small adjustments, a kind of multiplier effect. Even when parallel visions coexist in the understanding of the industrial ecosystem in Dunkirk, the coincidences’ identification could contribute to draw up agreements and collective trajectories; therefore, system analysis gives access to structural and long-term simulations of the public policy interventions. The causal variables showed in the CLD offer two categories: 1. The industrial by-product valorisation, and, 2. The pooling of services as innovative strategy in the industrial symbiosis. The previous differentiation follows purposes, seeking to provide clarity to the loops but interlinkages are present in the full diagram depicted in
Section 4.1. We designate variable titles by quotation marks in the text. In CLDs, the arrows indicate the causal relationships between the variables. These relationships can have a positive or negative sign. A positive sign implies that variable X connects with variable Y and they move in the same direction (an increase in X leads to an increase in Y and a decrease in X leads to a decrease in Y). A negative relationship implies that the variables move in opposite directions (an increase in X leads to a reduction in Y and a reduction in X leads to an increase in Y. The feedback can both reinforce and balance (marked as R and B in the diagram).
5. Discussion
The explanatory pathways leading to industrial symbiosis in Dunkirk can be explored through a geographical proximity analysis, using the six geographical dimensions [
37] shaped by the CLD analysis (
Table 2). In the Dunkirk industrial ecosystem, proposed interventions rank relatively high according to the literature reviewed and the experts interviewed. Some of the recurrent obstacles that the Dunkirk industrial symbiosis needs to tackle to achieve sustainability include technical, economic, informational, organizational, infrastructural and legislative problems [
44,
45].
Industrial ecology analyses social relationships, characterized by irreversible and dissipative flows in time and space, this circular understanding of systems is consistent with our understanding of industrial symbiosis, open dynamic systems [
42], stakeholder theory [
46] and complex adaptive theory [
47]. Therefore, industrial symbiosis as a social innovative strategy embedded in Industrial ecology should be able to inspire the sustainability paradigm shift in industry at the local scale [
48]. In this study, we frame the socio-economic approach with the theoretical assumption that position dialectic logic at the heart of industrial symbiosis’s sustainability [
36]: cooperation/competition, efficiency/resilience, local/global and autonomy/authority, coming from a coherent theoretical framework. In addition, other relevant insights stress the centralized/de-centralized governance in the symbiosis dynamic: anchor-tenant relationship or scavengers’ symbiosis dynamic [
7,
18].
Location: the territorial scale produces institutions’ representations referring to social structures according to our models. At the local level (microsocial), the governance mechanisms are decided and applied by social actors, who at the same time are regulated by those same mechanisms [
49]. This analysis shows that lack of communication within stakeholders represents one of the main hindrances to the industrial symbiosis, even when the
Absolute geographical location that separates the actors is short. The symbiosis takes place within a perimeter of 17km around the industrial zone, along the coast boarder, starting from the town of
Saint Georges sur l’Aa to the port of Dunkirk [
50], with an average distance of 2–3 km between collaborative firms. From the
Relative location perspective, the collaboration principle acts on the inter-firm relationships (network members) encouraging them to extend their boundaries thanks to the communication and transport investment in the search for external partner integration (suppliers, customers, municipality, etc.). Industrial symbiosis implementation is determined by several factors, such as the nature of the activities, the history, location, coordination willingness and the existing organizational structure of industrial symbiosis stakeholders [
51].
Landscape: The Dunkirk industrial symbiosis is based on electricity, steelmaking slag, heat, scrap, acid waste, refractory brick exchanges and pooling services coordinated by ECOPAL. Electricity production through a residual steam and public heating network have public acceptance, however the increase in steelmaking slag and scrap and increases in wastewater and sewage sludge could face legitimacy problems with regard to the environmental impacts of these activities in the territory. Large-scale infrastructure interventions are likely to cause protests, because of the negative public image of disposal problems. In the industrial symbiosis, the potential scale-up of the public urban heating network might result in landscape changes in the town, due to the industrial strip that surrounds the city, triggering competition with other forms of land use.
Territoriality: The territory of the Dunkirk IS has a decentralized structure (low centralization), as the valorisation of by-product is individually handled by the firms, which produce each by-product independently. The industrial by-product valorisation entails relatively low connectivity and high contiguity, because firms exchange by-products locally. The municipality of Dunkirk is involved in the public heating network and the sewage treatment project, which increases connectivity while decreasing contiguity. Contiguity is high when the raw materials and inputs used in the production process come from the Dunkirk area and low when they are transported over long distances to be integrated into the production process. Industrial symbiosis is an organizational strategy, which fosters contiguity in the geographical dimension of the supply chain. Since the steel and construction industries are essential in the Dunkirk industrial ecosystem, both sectors have a big potential to be strategically embedded in the territory, closing supply and demand loops, supported by emerging technologies and investments as shown in the CLD (balancing feedback B3,
Figure 3). The governance structure in Dunkirk encompasses very few stakeholders and is therefore dependent on a small and centralized set of by-products, triggering some structural problems because of the low ubiquity (understood as the number of firms that produce and consume each waste exchanged within the IS) and low diversity of by-products and the small number of firms that produce and consume.
Scaling: Industrial symbiosis is a multi-scale phenomenon—from the microscale of individual firms to the mesoscale of industrial ecosystems. When we talk about industrial ecosystems, we do not ignore the role played by the individual firms, on the contrary we attempt to stress the role of concepts like industrial symbiosis, that provide socially warranted meaning to individual actions, therefore defining how individual firms perceive problems and link them to the potential solutions. Some of the problems that need to be addressed collectively, if firms want to tackle them, are for example water source allocations, by-products synergies, environmental problems, employee qualifications and energy alternatives. At the same time, firms are also involved in global market dynamics, because their final products are usually sold in international markets. Thus, industrial symbiosis should be able to integrate global (large-scale cycles) and local (small-scale cycles), which in the long term is an attempt to balance geographic imbalances by closing global raw materials cycles imported at Dunkirk. This means that the Dunkirk IS seeks to reduce its outside dependence on raw materials and energy through the by-product valorisation and the by-product reincorporation in the industrial ecosystem cycles. From the perspective of the geographical system dynamics approach, we assume that the transitional de-globalization process, usually takes place in the Dunkirk IS case study, without causing shortage related problems (i.e., the transport of low economic value materials is unfeasible due to costs and carbon emissions) but providing an opportunity to supply inflow demand through locally produced by-products. These results cannot be generalized to other industrial symbiosis experiences with different geographical and social environments but it sheds light on an interesting topic that is rarely discussed in the academic Industrial ecology literature.
Spatial differentiation and uneven development: The spatial differentiation of the Dunkirk industrial symbiosis is closely related to location and scaling, since processes of convergence and differentiation find expression in proximities and economies of scale. Spatial differentiation [
37] reveals the rework of established patterns, that is, Housing concentration is defined by industrial ecosystems, which provides job opportunities. Regarding uneven development, the current supply sources of the Dunkirk IS are geographically disparate, according to Dunkirk trade balance [
52]. With big deficits in carbon oil, waste oil and other raw materials, while at the same time being a global provider of steel, construction, energy, agriculture machinery and inputs for the car and pharmaceutical manufacturing industries.
Spatial embeddedness and path dependency: The current eco-efficiency technology, which has a functional infrastructure to develop “end-of-pipe” solutions, influences and paves the way for the future political and institutional pathways to follow. The highly centralized technological investments and the few opportunities for emerging technologies, hinder the industrial by-product valorisation and the pooling services in the industrial symbiosis strategy. Implementing eco-efficiency strategies based on centralized systems therefore reproduces the lock-ins concerning the socio-ecological industrial ecosystem. Infrastructural decisions for the future induce the path dependencies in Dunkirk, including the political choices of new mono-incineration plants that influence the expected scenarios of the industrial ecosystem for stakeholders and decision-makers.
6. Conclusions
The conceptualization of governance in IS is not simple to understand and internalize because of the complexity involved in the ecosystem and the stakeholders’ conflicts of interest. The success of the IS is mainly related to the governance quest which is the balance between the autonomy/authority, cooperation/competition strategies engaged through local/global scales. The governance [
53] encompasses ecological, cultural, political and economic embeddedness of actors and the means of governance become crucial to enhance the self-organization. The territorial approach of industrial symbiosis encourage its emergence and sustainability, thus assuring redundancy for key functions. In this study, the functional understanding gains relevance in the Dunkirk industrial symbiosis, when analysing the causal loops through a complex adaptive method for social industrial ecosystems.
Systems analysis is a methodology which aims to improve the understanding of human motivational causality and the network interactions, including the economic and political contextual drivers in the industrial ecosystem, inquiring into stakeholders’ behavioural patterns, conflicts of interests, values and motivations. In the literature review, academics define industrial symbiosis as a social innovation which goes beyond the positive scientific approach, we attempt to recognize its standardized dimension, referring to human intentionality and the aim of improving industry. If well steered, industrial symbiosis has the potential to improve innovation and resilience in industry, encouraging industrial ecosystem development, providing a scientific structure to deal with the social intentionality in a systemic way, based on the multiplicity of values, diversity of interests and stakeholder preferences. Looking to make a geographical analysis of industrial symbiosis with a theoretical framework, we draw up six geographical dimensions to improve the systemic understanding able to drive this approach towards a dynamic science [
49].
There have been many structurally complex studies of industrial symbiosis at the micro-level but few equivalent studies at the micro- or meso-level looking at the behaviour of actors and its institutions, determined by the social private/public structure.
This study is not exempt from criticisms related to the research method in terms of robustness and validity; the ideas expressed by the experts during the interviews and gathered from the literature review are not directly transferable to industrial symbiosis. The comparability of results with other studies and the generalization of conclusions is debatable; however, the originality of this method can contribute to the understanding of the role of territory in the industrial symbiosis strategy in the search for sustainability. The originality of the geographic system dynamics is based on the richness of references and qualitative information collected, structured in a systemic and reproducible method.