2.1. Industrial Symbiosis Case Studies
shows the schematic overview of a company’s production process with the corresponding input and output resource flows, which already indicate the points of contact for IS activities, leading to economic, environmental, and social benefits. It was derived from the analyzed IS case studies to extract and abstract the points of contact for IS possibilities.
A smeltery in China recovered raw materials out of gaseous waste/aerosol, sludge/mud, and solid waste by filtering, extracting, concentrating, and compressing the resources out of each waste stream (Yuan and Shi 2009
). The Guitang Group in China approached a disposal problem by using their sludge as the calcium carbonate feedstock for a new cement plant while reducing residual and waste flows (Zhu et al. 2008
Furthermore, IS activities can lead to the buildup of IS networks not only across different supply chains, but also along the supply chain of one industry. For example, Yang and Feng
) investigated the Chinese IS of the Nanning Sugar Industry, which incorporated affiliated companies centered around their core business of sugar production to (re-)process the residual and waste flows of the mother company (Yang and Feng 2008
). Enterprises of cane farming, paper, alcohol, health products, and the cement industry were all located at the upstream or the downstream of the main sugar production, extending their own core business to an entire IS supply chain (Yang and Feng 2008
). These IS activities led to various environmental, social, and economic benefits; for example, reduced costs, pollution controlling fees and environmental impacts, new jobs, and innovation for advanced business models were created, and the supply of raw materials and material quality were ensured (Yang and Feng 2008
). Additionally, a sugar company in the Ulsan Industrial Park in South Korea had similar experiences by expanding the company’s own collection of downstream companies, generating new revenues (Park et al. 2008
). With the utilization of almost all residual and waste flows of sugar production, a better product quality was achieved, as well as reduced environmental emissions and disposal costs (Park et al. 2008
2.3. Quantitative Indicator System
shows the guiding framework for the sustainability performance of an IS system; its content and approach design is oriented to the three types of knowledge (system, transformative, and normative knowledge), which have their roots in the fields of transdisciplinarity and sustainability sciences (Lang et al. 2012
). From this (normative) sustainability perspective, the IS entities could envision a desired future state of their IS systems; this could be, for example, a “zero waste”, “zero emission,” or “CO2-neutral” park, or that the IP pursues to align its business performance to the science-based targets (SBT)1
). After investigating the status quo of the system under consideration, possible future scenarios could be developed with the method of scenario planning (beginning from the actual state). In accordance with the defined goals or pursued sustainability trajectory, scenarios of optimally utilized IS systems can be developed. Once the desired future vision is defined, various transformation pathways from the desired future to the actual state can be elaborated with the method of backcasting (planning possible measures/milestones backward, which then will be operated forward). This process can include all share- and stakeholders.
By setting up a sustainability (key performance) indicator system which is in line with the quantifiable goals, the progress of the IS system can be continuously tracked and monitored. If an overarching organizational unit or a core team of the IS system is established, it could control and push the IS performance towards the trajectory of circular economy and sustainable development. Defining the (sustainability) goal of the IS system is crucial in order to arrange the approach and transformative pathways (corresponding suitable IS measures) in a targeted manner.
A general guiding systematic approach can support the development process of an indicator system:
1. What is the overall purpose of the IS system?
An example of an answer could be: To contribute to sustainable development and circular economy.
2. According to which (gradual) goals and criteria should the IS system be aligned?
This could be, for example, a target orientation towards a “zero waste”, “zero emission”, “CO2-neutral”, or SBT park.
3. What are requirements of the IS system?
One possible answer could be: The essential requirements of an IS system can be summarized briefly: (1) Optimize/maximize the social and economic benefit, (2) minimize environmental burden, and (3) operate as a resilient and adaptive system. Thus, the overall sustainability contribution of an IS system can be assessed as an increase in resource productivity and efficiency, with positive social impacts and a continuously well-operating system.
4. What should be measured?
As already displayed in Figure 1
, inputs of financial, human, and environmental (material, water, energy, land use) resources are required, and simultaneously, outputs of economic, social, and environmental impacts are generated. Each category of input- and output-related resources and impacts can be measured by specific indicators.
5. How should these be measured?
In such a systematic framework, input-related indicators—addressing financial, human, and environmental resource properties—and output-related indicators—addressing economic, social, and environmental impact categories—can be developed.
Once the IP sets its quantitative indicator system, a base year shall be chosen and measured so that a time series can be tracked for each indicator. Then, a balance sheet can be implemented, in which the absolute and relative change values in relation to the values of the base year of each individual indicator can be recorded. This approach enables goal-directed IS management, while the continuous improvement processes and the yearly progresses of the IS system can be traced by the indicator time series (referenced to a base year). If necessary, measures can be taken if the performance does not correspond to the desired progress. It is recommended to define an overarching target for the entire IP and a respective roadmap with quantifiable targets and milestones to ensure a goal-oriented IS management.
On the basis of the systematics developed, the indicators were derived and further developed in line for the IS performance measurement. The following general, environmental, economic, and social indicator sets do not claim to be exhaustive, but should be successively extended and derived from common methods and standards to facilitate a systematic approach and data collection/analysis. They represent example systems that can be adapted according to the specific target orientation of each IS system, which is defined by the IP itself, since the objectives and priorities are set by the respective members of the industrial estate.
An IS general indicator system was developed for the aspects of IS structure, IS activity, IS knowledge transfer, IS system resilience, and adaptability (Table 2
). It can be set up in order to generate an overview of the current state and activity level of the IS system and to get a glimpse of where the journey can go in terms of IS (sustainability) performance. The special indicators are resilience and system adaptability. Valenzuela-Venegas et al.
) developed a resilience indicator which is based on two sub-indicators: The network connectivity index and flow adaptability index. The network connectivity index considers the number of connections among the entities while evaluating the minimum and maximum number of connections, in order to measure the endurance of the entire network system against possible disruptive events (e.g., loss of an entity) (Valenzuela-Venegas et al. 2018
). The flow adaptability index quantifies the necessary (material) flows and the capacities of the entities to compensate a disruption in the system (e.g., fluctuating material flows) (Valenzuela-Venegas et al. 2018
shows an IS environmental indicator system, specialized to the performance of IS cascading loops/systems (resources, emissions, etc. saved through IS activities). It differentiates input- and output-related indicators. While most of the presented indicators are easier to understand, the following two require further explanation:
Generally, energy consists of two parts: Exergy and anergy. Exergy is the part of the total energy of a system that is actually usable and can do work, anergy is the total opposite. The general relationship between exergy and the material life cycle involves high-exergy resources (low entropy) being extracted from the environment, processed and consumed by the economy, and returned to the environment as low-exergy materials, i.e., waste (high entropy) (Seager and Theis 2002
). So, over the phases of the entire life cycle, exergy is reduced, while the share of anergy and entropy increases; i.e., in order to keep a system at a certain level, new usable energy must be supplied and consumed “from outside” again and again.
Emergy is an expression of all of the past work performed by the environment, economy, and society in the entire process chain to generate a product or service (incl. all of the energy consumed in direct and indirect transformations). Due to the incorporation of all previous work and services, an emergy sustainability index is a single comprehensive, aggregated indicator, and can represent the sustainability performance of the system under consideration (Sun et al. 2016
). By studying the Shenyang Economic and Technological Development Zone (SETDZ) in China, Geng et al.
) found out that emergy indicators are not all-encompassing measures of environmental and economic performances, but are appropriate to indicate the overall performance of one IP, especially when these are complemented with other methods and respective indicators. For example, the emergy indicator of relative emergy savings (RES) can be defined as the ratio of avoided inputs through all of the IS activities to total emergy inputs without related IS activities (Geng et al. 2014
). Furthermore, this indicator can be extended to consider the entire life cycles of products and services.
shows an IS economic indicator system. The input- and output-related indicators generally address cost savings achieved through IS activities. While most of the presented indicators are simple to understand, the following two require further explanation:
A resource productivity indicator (RP) can reflect the interlinked relation between economic growth and specific material consumption, indicating the circular economy performance of an IS system (Wen and Meng 2015
The Emdollar value of total emergy savings (ETS) represents the economic benefits gained by IS activities (Geng et al. 2014
shows an IS social indicator system. These indicators mainly address non-material IS exchanges, whereof the employees of the IP can benefit socially by establishing joint utility and infrastructure projects of kindergarten, mensa, canteen, cafeteria, or cross-company organized mobility.