SYMBIOSIS

Industrial symbiosis is part of a new field called industrial ecology. Industrial ecology is principally concerned with the flow of materials and energy through systems at different scales, from products to factories and up to national and global levels. Industrial symbiosis focuses on these flows through networks of businesses and other organizations in local and regional economies as a means of approaching ecologically sustainable industrial development. Industrial symbiosis engages traditionally separate industries in a collective approach to competitive advantage involving physical exchange of materials, energy, water, and/or by-products. The keys to industrial symbiosis are collaboration and the synergistic possibilities offered by geographic proximity.

Introduction
The term ‘industrial symbiosis’ was coined in the small municipality of Kalundborg, Denmark, where a well-developed network of dense firm interactions was encountered. The primary partners in Kalundborg, including an oil refinery, a power station, a gypsum board facility, and a pharmaceutical company, share ground water, surface water, wastewater, steam, and fuel, and they also exchange a variety of by-products that become feedstocks in other processes. High levels of environmental and economic efficiency have been achieved, leading to many other less tangible benefits involving personnel, equipment, and information sharing. Many other examples of industrial symbiosis exist around the world and illustrate how the concept is applied.
This article describes the nature of the industrial symbiosis in Kalundborg. Then, it discusses the many elements of industrial symbiosis such as energy and water cascading, cogeneration, and materials exchange. It also examines tools such as input/output matching, stakeholder processes, and materials tracking. Then, the article discusses how industrial symbiosis is a useful umbrella term because it can describe exchanges across entities regardless of whether they are colocated, located near one another but not contiguous, or located within a broader spatial area such as regionally. It also examines technical and regulatory considerations that have come into play in various locations and that can facilitate or inhibit industrial symbiosis. Finally, it considers future directions with regard to industrial symbiosis based on historical and current experience.

Definition of industrial symbiosis and related
The term ’symbiosis’ builds on the notion of biological symbiotic relationships in nature where at least two otherwise unrelated species exchange materials, energy, or information in a mutually beneficial manner, with the specific type of symbiosis known as mutualism. So, too, industrial symbiosis consists of place-based exchanges among different entities that yield a collective benefit greater than the sum of individual benefits that could be achieved by acting alone. Such collaboration can also foster social values among the participants that can extend to surrounding neighborhoods. As described in what follows, the symbioses need not occur within the strict boundaries of a park, despite the popular use of the term ‘eco-industrial park’ to describe organizations engaging in exchanges.
At the same time interest began to develop in industrial symbiosis and eco-industrial parks, a number of other parallel tracks advanced that might be construed, broadly, as green development. These include residential, commercial, industrial, and community development as captured in terms such as sustainable architecture, green buildings, sustainable communities, and smart growth. Eco-industrial development or sustainable industrial development narrows down the possibilities to refer predominantly to industrial and commercial activities. Cooperating businesses that include a materials/water/energy exchange component qualify the activity as industrial symbiosis. The materials exchange component has also been referred to as a by-product exchange, by-product synergy, or waste exchange and may also be referred to as an industrial recycling network.
As with the term ‘industrial park’, the term ‘eco-industrial park’ refers to eco-industrial development on a particular plot of real estate. An eco-industrial park may include many ecologically desirable goals, including mechanisms to reduce overall environmental impact, conserve materials and energy, and foster cooperative approaches to resource efficiency and environmental management. The terms ‘industrial estate’ and ‘eco-industrial estate’ are more commonly used in Asia and can include communities of workers who live in or near the group of businesses constituting the industrial estate. Gunther Pauli popularized a similar notion , zero-emissions parks, to emphasize the drive toward sustainable industrial development. The agricultural community has found that while traditional agriculture incorporated cyclical reuse of by-products, industrial agriculture became much more linear, consuming materials and disposing of wastes. Therefore, many zero-emissions researchers describe integrated biosystems in which at least two biological subsystems are part of an integrated process to reduce emissions and reuse agricultural by-products.
Some writers refer to eco-industrial networks to capture a broad range of environmental and economic activities among businesses. Just as economic clusters have come to mean a group of businesses that are sectorally related by the products they make and use, such as the furniture cluster in central North Carolina in th USA, the term ‘eco-industrial clusters’ is sometimes used to describe environmental interactions among firms in the same or related industries. Industrial complexes of sectorally-related firms have been successful for the past several decades in overall pollution reduction in industries such as pulp and paper, sugarcane, textiles, and plastics.

Although materials and energy exchanges have been a significant part of industry for centuries, focus on environmental attributes is much more recent. In a foundational 1989 article on industrial ecology, Frosch and Gallopoulos described the underlying notion of an ‘‘industrial ecosystem’’ in which ‘‘the consumption of energy and materials is optimized and the effluents of one process may serve as the raw materials for another process.’’ Others have extended the ecosystem metaphor to see related industrial activities as a food web and to interpret the roles of various scrap and remanufacturing businesses as the scavengers and decomposers of these systems.
In any multidisciplinary field such as industrial ecology, there are strands from many disciplines and paths of research that are the antecedents of current understanding. Industrial symbiosis was not popularized, however, until the first articles and analyses of the industrial region in Kalundborg were published during the early 1990s. One origin of industrial symbiosis is from the chemical industry, which embeds an intrinsic value chain of materials as they are degraded. Other terms discussed previously originate in ecology, agricultural studies, engineering, and/or business economics. Cogeneration and utility sharing have been justified on engineering, environmental, and economic grounds. Indeed, private industry sees cost efficiency as a driving factor in stimulating these relationships, whereas city planners, economic development experts, and real estate developers also emphasize land use, social and environmental aspects, and the synergies that can arise from colocation. Van Berkel summarized three types of synergies that help to characterize trends emerging in different types of symbiosis network: (1) synergies across the supply chain, (2) synergies from shared use of utilities, and (3) synergies from local use of by-products. As new projects are formed and old projects evolve, more common definitions will emerge.