Waste not, want not
"One man gathers what another man spills." What is waste to one person is treasure to another. This same notion is the basis for industrial ecology, a framework for understanding material and energy flows through the economy. Developed in the late 1980s and early 1990s, the industrial ecology framework examines economic systems through the lens of biological ecosystems.
As defined by Graedel, Allenby and Linhart, "The concept of industrial ecology is one in which economic systems are viewed not in isolation from their surrounding systems, but in concert with them. As applied to industrial operations, it requires a systems view in which one seeks to optimize the total materials cycle from virgin material, to finished material, to component, to product, to waste product and to ultimate disposal. Factors to be optimized include resources, energy and capital."
In other words, industrial ecology integrates economic processes so that the wastes and byproducts of one industry become the feedstock of the next, thereby using the fewest possible virgin resources and generating the fewest environmental impacts for a given economic output. Achieving this integration requires implementation of a variety of environmental concepts - pollution prevention, recycling, life cycle analysis and design for environment.
Finding the links
Using industrial ecology as a conceptual model, opportunities to link manufacturing processes can be identified. The premier example of a highly integrated set of industries cited in the literature is the Kalundborg, Denmark industrial park. Since it has been described extensively elsewhere, it will not be discussed further here.
A simple example is the relationship between co-located petrochemical facilities and refineries. In many of these complexes, byproduct streams that have little or no value in one facility can be used to make useful products in the other. For example, the gas from one refinery's light ends recovery unit, which was historically fed to the plant fuel systems, was rerouted to an idle olefins recovery unit. There, the relatively low ethylene and propylene (less than 30 percent) concentrations were recovered as high-value products, ethane and propane were recovered as feedstocks to olefin production units, heavier compounds were sent to gasoline blending and residual components were sent to the clean fuel system.
While this example is relatively linear, since most of the recovered materials were either incorporated into plastic products or used as fuels, it represents one step toward more integrated industrial processes.
Another example of process integration that spans a broader range of industrial activity is the materials flow of chemicals used by the printed wiring board (PWB) industry to etch copper. As a rule, the copper in spent etchants is recovered because of its relatively high market value and concentrations (greater than 1 pound per gallon).
In one elegant process, alkaline ammoniacal etchants are supplied to PWB manufacturers, where they are used to etch patterns on PWBs. Spent etchant is then sent back to the chemical supplier, where the copper is extracted with an organic solvent to create a copper-rich organic layer and copper-lean aqueous solution.
The aqueous phase is regenerated by the addition of ammonia and other additives to create fresh etchant. The organic layer is treated with sulfuric acid to remove the copper from the organic solvent.
Regenerated solvent is fed back into the process, and the copper in the aqueous stream is recovered as copper sulfate pentahydrate via crystallization, or as copper metal via electrowining. Copper sulfate recovered by this process can be used to manufacture other copper-based chemicals, or used directly in a number of applications, including wood preservatives and algaecide.
The application of industrial ecology is not restricted to the manufacturing sector. As an example, methane gas generated during refuse decomposition at a closed municipal landfill can be used to power an electric generator rather than vented to the environment or burned in a flare. In this way, materials that were once wasted can be integrated back into the economy, reducing the need for virgin resources. In addition, incentives for this type of process may include reduced air permitting requirements and revenue from the sale of the generated electricity.
Currently, there are no regulations that explicitly encourage industrial ecology; however, implementing industrial ecology requires the use of some techniques that are explicitly covered in the regulations. Primary among these is the Resource Conservation and Recovery Act (RCRA), which regulates materials identified as solid waste, that includes hazardous and nonhazardous waste.
For example, in the etchant process described above, saturated etchant would generally be considered a solid waste under RCRA because it meets the definition of a "spent material." In this particular case, however, RCRA provides an exclusion from solid waste regulation for secondary materials that are reclaimed and returned to the original process in which they were generated. The spent etchant is eligible for this exemption, provided several specific conditions are met.
This is an example of how the U.S. Environmental Protection Agency (EPA) provides an incentive to practice the principles of industrial ecology. By exempting specific waste streams as solid, and sometimes as hazardous, waste, the regulatory burden for managing these streams is reduced. This reduction of management burden can be particularly significant if an exclusion such as this changes a waste generator from large quantity status to either small quantity status or conditionally exempt status and results in relaxed regulatory requirements.
Other regulatory incentives include precious metals recovery as described in 40 Code of Federal Regulations (CFR) Part 266 Subpart F.
One potential barrier for those attempting to incorporate the principles of industrial ecology into their operation is that the implemented process may be interpreted as what EPA has described as "sham recycling." In a general sense, EPA's determination rests on whether or not the secondary material being recycled can be considered a commodity.
Practices considered by EPA to be sham recycling include processing waste materials that are ineffective or only marginally effective for the claimed use; using waste material in quantities exceeding the amount required for the process; not implementing provisions to prevent loss of the waste material; using waste material containing significant levels of contamination as feedstock when commercially available substitutes are contaminant free; and not adequately documenting waste material usage.
The above examples illustrate the promise industrial ecology holds and highlight some key implementation points. The impetus for developing these processes was not environmental, but economic. In the etchant example, the value of the copper in the spent etchant was recognized before the significant push for waste reduction.
For etchant suppliers, copper recovery can be a significant source of revenue and, therefore, is key to the alkaline ammonia business and not just an environmentally advantageous thing to do. Similarly, recovering olefins from fuel gas and electrical energy from landfill gas was driven by the revenues these processes generate. Thus, by focusing on the potential value of byproducts or waste streams, opportunities for recovery may be more readily recognized.
Another attribute of the etchant process is its integration of at least three different industries: the PWB industry, the etchant supplier and the copper sulfate users. The link between the copper source - the PWB industry - and the copper sulfate user - e.g., the wood preservative industry - is the etchant supplier.
For this particular process to succeed, etchant suppliers must be familiar with the byproducts and feedstocks of at least two different industries. There is value in understanding the potential use of the wastes and byproducts of one industry in another sector. This information is especially useful for byproducts with lower values, since there may be fewer beneficial uses for these materials. To encourage this information sharing, government and other organizations operate materials exchanges, which attempt to create markets for byproducts, off-spec product and wastes.
The promise of a truly integrated economy - where the only raw inputs are labor and energy - is far from being achieved, and likely never will be. However, as we begin to understand economic activity in the context of biological ecosystems, we can better learn how to integrate our materials and energy cycles. There are opportunities in a variety of industries, and we are beginning to build the resource web links that will sustain our standard of living with minimal environmental impact. By creating and strengthening these links, we will develop stronger and healthier industrial and biological ecosystems. Then we may truly leave only footprints.
For more information
Frosch, R.A. 1995. "Industrial Ecology," Environment, December 1996, v37n10, pp. 16-24, 34-37.
Graedel, T.E. and B.R. Allenby. 1995. Industrial Ecology.
Grann, H., "The Industrial Symbiosis at Kalunborg,
Denmark," paper presented at the National Academy of Engineering's Conference on Industrial Ecology, Irvine, Calif., May 9-13, 1994.
Malloy, Lawrence T. 1997. "Getting Ready for the Next Millennium," Environmental Protection, July 1997, pp. 28-31.
The Journal of Industrial Ecology, MIT Press.
California Materials Exchange (CalMAX), http://www.ciwmb.ca.gov/calmax/
Links to other industrial ecology sites:
Indigo Development - Sustainable Development Division of RPP International, www.indigodev.com/Links.html
National Pollution Prevention Center for Higher Education, www.umich.edu/~nppcpub/resources/ResLists/Ind.Ec.html
Resources for industrial ecology and its promotion:
U.S. Department of Energy Center for Sustainable Business, www.sustainable.doe.gov/business/indeco.htm
This article originally appeared in the 05/01/1999 issue of Environmental Protection.