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The Greening of Industrial Ecosystems The Greening of Industrial Ecosystems. 1994. Pp. 69-89. Washington, DC: National Academy Press. Wastes as Raw Materials DAVID T. ALLEN and NASRIN BEHMANESH Postconsumer waste, industrial scrap, and unwanted by-products from manufacturing operations should not be viewed as wastes. Rather, they are raw materials that are often significantly underused. One of the research challenges of the emerging discipline of industrial ecology will be to identify productive uses for materials that are currently regarded as wastes, and one of the first steps in meeting this challenge will be to understand the nature of industrial and postconsumer wastes. More than 12 billion tons of industrial waste (wet basis) are generated annually in the United States (Allen and Jain, 1992; U.S. Environmental Protection Agency [EPA], 1988a,b). Municipal solid waste, which includes postconsumer wastes, is generated at a rate of 0.2 billion tons per year (EPA, 1990). When these material flows are compared with the annual output of 0.3 billion tons per year of the top 50 commodity chemicals (Chemical and Engineering News, June 28, 1993), it is apparent that wastes should not be ignored as a potential resource. While these comparisons between waste mass and the mass of commodity products make apparent the magnitude of industrial wastes, considering mass flows alone can be somewhat misleading. The extent to which industrial wastes could serve as raw materials depends not only on the mass of the waste stream, but also on the concentration of resources in the wastes. As shown in Figure 1, the value of a resource is proportional to the level of dilution at which it is present in the raw material. Resources that are present at very low concentration can be recovered only at high cost, while resources present at high concentration can be recovered economically. The primary goals of this paper will be to evaluate the flow rates and concentrations of valuable resources in waste streams and to determine the
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The Greening of Industrial Ecosystems FIGURE 1 The Sherwood plot: Selling prices of materials correlate with their degree of dilution in the initial matrix from which they are being separated. Note that the horizontal axis shows increasing dilution, or decreasing concentration, in the initial matrix. SOURCE: National Research Council (1987). extent to which materials currently regarded as wastes might be used as raw materials. We will begin with a brief examination of the total quantities of material circulating through the waste cycles. We will then focus on a series of metals, tracking their flows as wastes and comparing the waste mass and concentration level of recycled wastes, discarded wastes, and virgin raw materials. OVERVIEW OF INDUSTRIAL AND POSTCONSUMER WASTE GENERATION AND MANAGEMENT Mapping the flows of more than 12 billion tons of industrial and postconsumer waste is a challenging task. Part of the challenge is integrating information from many diverse sources of data. For example, more than a dozen national sources of data on industrial wastes are available (Eisenhauer and Cordes, 1992), but each covers only a portion of industrial waste generation. Each was collected over a different time period and each considers a different subset of waste generators. Despite these difficulties, each of the data sources provides a unique perspective on industrial waste streams and can be useful. The main focus in this paper will be on just a few of these inventories, most notably the National Hazardous Waste Survey and, to a much lesser extent, the Toxic Release Inventory and
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The Greening of Industrial Ecosystems the biennial survey of waste generators collected under the Resource Conservation and Recovery Act (RCRA). The Toxic Release Inventory (TRI) (EPA, 1991), collected annually under the Superfund Amendments and Reauthorization Act (SARA), Title III, provides data on the emission profiles of more than 300 chemical species. While the TRI data are useful for profiling the releases of specific chemicals, they provide little information on the total waste stream. In contrast, the biennial survey of generators and the biennial survey of treatment, storage, and disposal facilities collected under the RCRA provide data on total waste mass but little data beyond loosely defined waste categories on the composition of the waste streams. A hybrid data base of information collected by Research Triangle Institute for the Environmental Protection Agency under RCRA (EPA, 1988c) combines some of the best features of both the TRI and the RCRA biennial survey. This data base, which is called the National Hazardous Waste Survey, combines detailed data on waste composition and data on bulk waste stream properties. It has two basic components, a generator Survey focusing on waste characterization and a survey of treatment, storage, disposal, and recycling (TSDR) facilities focusing on waste treatment and disposal. The flow diagram of Figure 2 was prepared using the TSDR section of the survey and some data on air emissions from the TRI. It shows the flow patterns and approximate flow rates of industrial hazardous waste streams. All waste streams regulated under RCRA are included; also included are some wastes exempt from the RCRA regulations and some hazardous wastes managed in units exempt from RCRA permitting requirements. The total mass flow rate of all streams represented in the National Hazardous Waste Survey is approximately 0.75 billion tons per year and the total mass of releases and off-site transfers reported through the TRI totals 0.003 billion tons per year. Therefore the data represent only about 5-10 percent of the total flow rate of industrial wastes. Even though just a small fraction of industrial wastes is represented, the excluded wastes are primarily from a limited group of industries: mining, pulp and paper manufacturing, electrical power generation, and petroleum production. So, the National Hazardous Waste Survey can begin to provide a picture of the flow rates and compositions of waste streams. It is far from comprehensive and omits some major sectors of the economy that generate substantial wastes, but it represents some of the best information available on waste stream composition. Figure 2 reports the flow rates of hazardous waste streams generated by U.S. industry in 1986, the only year for which the survey data are available. As indicated in Figure 2, a small fraction of solvent, metal, and other wastes, less than 1 percent of total waste mass generated, flows through recycling loops. The total mass involved in recycling is about 5 million tons per year (mt/yr). The largest single stream in terms of total mass flow, nearly 720 mt/yr (more than 90 percent of the total waste flow), is hazardous wastewater. Most of this stream is water with a small percentage of nonaqueous contaminants; hence the mass of the chemically hazardous component of this stream is within an order of magnitude of the
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The Greening of Industrial Ecosystems FIGURE 2 Flow of industrial hazardous wastes in treatment operations (1986 data in millions of tons per year). components being recycled. A third set of waste streams, about 4 mt/yr, is sent to various thermal treatment technologies which include direct incineration, fuel blending, and reuse as fuel. While an examination of total waste flows is a necessary first step in assessing the use of waste streams as raw materials, total mass is not a good indicator of the potential value of waste streams. Instead, the concentration and mass flow rates of valuable resources in the waste streams will be the most important evaluation criteria. Unfortunately, reliable composition data are not generally available for waste streams, so it is not always possible to evaluate the potential for recycling. One set of materials for which waste composition data are available is metals. The National Hazardous Waste Survey contains data on the flow rates of the 16 metals listed in CFR 261, Appendix VIII (Resource Conservation and Recovery Act, Subtitle C, Sections 3001-3013, 42 U.S.C., Sections 6921-6934  and Supplement IV ). The next two sections will review the mass flow rates and concentration distributions of selected metals in industrial waste streams.
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The Greening of Industrial Ecosystems FLOWS OF SELECTED METALS IN INDUSTRIAL WASTES As a first step in evaluating the potential of industrial wastes for use as raw materials, we will consider the flows of three metals—cadmium, chromium, and lead. Figures 3,4, and 5 report the amount of cadmium, chromium, and lead sent to major industrial waste management operations. For cadmium and chromium, only a small fraction of the material is recovered. In the case of cadmium, approximately 1,300 out-of a possible 16,000 tons were sent to recovery operations in 1986. In contrast, a major portion of lead generated as industrial wastes (106,000 out of 189,000 tons) is sent to metal recovery. Recycling is feasible for many lead-containing streams because an efficient collection and reprocessing system is in place for used automotive storage batteries. With such extensive recycling of lead, it should come as no surprise that secondary nonferrous metal processing (Standard Industrial Classification [SIC] code 3341), which is largely lead battery recycling, is the dominant source of lead wastes (Figure 6). The flows of cadmium, chromium, and lead in industrial hazardous wastes, FIGURE 3 Flow of cadmium in hazardous waste treatment operations in 1986 (tons per year).
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The Greening of Industrial Ecosystems FIGURE 4 Flow of chromium in hazardous waste treatment operations in 1986 (tons per year). illustrated in Figures 2-5, cannot be considered in isolation. They are merely a part, albeit a major part, of the total waste stream flow. A second major component of waste stream flows is municipal solid waste. The total mass flow of municipal solid waste is approximately 0.2 billion tons per year, which is considerably less than the total flow of industrial hazardous wastes (0.75 billion tons per year) and total industrial wastes (12 billion tons per year). Simple tonnage comparisons can be misleading, however. To assess the potential value of industrial hazardous waste and municipal solid wastes as sources of raw materials, it is necessary to compare the flows of specific materials. For example, according to the U.S. EPA (1989), the dominant contributor to lead in the municipal solid waste (MSW) stream is storage batteries. Depending on rates of recycling, batteries contribute between 100,000 and 150,000 tons per year of lead to MSW. Recent data (EPA, 1989) indicate a 90 percent rate of recycling, resulting in 100,000 tons of waste out of the 800,000 tons of lead in used batteries. Other sources of lead in the MSW stream include consumer electronics (estimated to be 60,000 tons), glass and ceramics (8,000 tons), plastics (4,000 tons), metals such as soldered cans
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The Greening of Industrial Ecosystems FIGURE 5 Flow of lead in hazardous waste treatment operations in 1986 (tons per year). (1,000 tons) and pigments (1,000 tons). None of these other sources of waste result in any significant degree of lead recycling, largely because of the low concentrations of lead in the products. Analysis of these waste management data represents a first step in performing studies in industrial ecology. The next step is to integrate waste generation data with production data. Coupling the waste flow data for lead presented above with the data on lead production and consumption presented in Table 1 yields the lead flow diagram shown in Figure 7. Lead is used at a rate of roughly 1.2 million tons per year. Most is consumed in the production of lead storage batteries and these batteries are eventually retired. Roughly 90 percent of these used batteries are recycled, so the net loss of lead through battery disposal is about 100,000 tons. Other sources of lead in MSW total roughly 70,000 tons per year. Industrial hazardous wastes are another Sink for lead. Of the 189,000 tons of lead in hazardous wastes, roughly 53,000 tons are sent to disposal. The remainder is recycled, but the recycling of both hazardous and battery wastes generates roughly 100,000 tons of lead waste. Comparing the total flow of lead with the amount of lead
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The Greening of Industrial Ecosystems FIGURE 6 Industrial sources of cadmium, chromium. and lead wastes.
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The Greening of Industrial Ecosystems TABLE 1 Production and Consumption of Lead, 1986 and 1989 Amount, 1986a (metric tons) Percent, 1986a Amount, 1989b (metric tons) Percent, 1989b Production Mine production 340,000 411,000 Secondary lead 615,000 809,000 Consumption Metal products 146,000 12.7 170,000 13.3 Storage batteries 854,000 77.9 1,012,000 78.9 Other oxides 69,000 5.0 58,000 4.5 Miscellaneous (including gasoline additives) 55,000 4.4 43,000 3.3 TOTAL 1,124,000 100.0 1,283,000 100.00 a U.S. Department of the Interior (1988). b U.S. Department of the Interior (1991). FIGURE 7 Simplified model of the industrial ecology of lead (amounts in tons per year).
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The Greening of Industrial Ecosystems eventually requiring disposal, we see that lead is reprocessed at about 75 percent efficiency: If this efficiency is to be improved, then the streams that are currently reaching disposal must find productive use. Overall recycling efficiency could be improved by increasing the collection of lead batteries above 90 percent, by improving the efficiency of secondary lead smelting, and by targeting for recycling industrial waste streams from nonbattery operations. Figure 8 compares some of the waste streams currently requiring disposal with those currently being recycled. Examination of Figure 8 reveals that more concentrated waste streams are more likely to be recycled than waste streams with low lead concentration. Although the decision whether or not to reclaim a metal from a waste stream is complex, it is in essence an economic question. Accordingly, it depends not only on the value of the recycled material, but to a significant extent on concentration. DILUTION DETERMINES RECYCLABILITY As in the case of lead, the concentration at which recycling of other materials in the waste stream becomes cost-effective depends on the value of the raw material (see Figure 9). The Sherwood diagram (Figure 1) showed that whereas materials such as gold and radium can be recovered from raw materials that are quite dilute in the resource, materials such as copper can be recovered economically only from relatively rich ores. Given the price, it is therefore possible to estimate the concentration at which materials can be recovered. By comparing metal prices, minimum economically recoverable concentration (from the Sherwood diagram), and data on the concentration distributions of metals in waste streams (Figure 9), it is possible to estimate what fraction of metals in hazardous waste streams can be recycled. These estimates are reported in Table 2 and indicate that metals in hazardous wastes are underutilized. This could be because only waste streams with very high metal concentrations are recovered or because only a small fraction of potential recyclers at all feasible concentration levels recover metals. Figure 10 is an attempt to differentiate between these two cases. To develop Figure 10, the concentration distribution of metals in recycled waste streams was examined. The concentration below which only 10 percent of the metal recycling took place was assumed to be a lower bound for economic metal recovery from the waste. This concentration was then plotted, together with the 1986 metal price (recall that the waste data are from 1986) to generate Figure 10. Also plotted on Figure 10 is the Sherwood diagram for virgin materials. Comparison of the Sherwood plot for virgin materials and the waste concentration data
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The Greening of Industrial Ecosystems FIGURE 8 Concentration distributions of lead in waste streams undergoing recycling and concentration distributions of lead in all industrial hazardous waste streams (1986). The concentration below which only 10 percent of recycling takes place is noted.
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The Greening of Industrial Ecosystems TABLE 2 Percentage of Total Metal Loadings That Can Be Recovered Economically (derived from Sherwood Plot) from Industrial Hazardous Waste Streams Metal Minimum Concentration Recoverable, from Sherwood Plot (mass fraction) Percent of Metal Theoretically Recoverable (%) Percent Recycled in 1986 (%) Sb 0.00405 74-87 32 As 0.00015 98-99 3 Ba 0.0015 95-98 4 Be 0.012 54-84 31 Cd 0.0048 82-97 7 Cr 0.0012 68-89 8 Cu 0.0022 85-92 10 Pb 0.074 84-95 56 Hg 0.00012 99 41 Ni 0.0066 100 0.1 Se 0.0002 93-95 16 Ag 0.000035 99-100 1 TI 0.00004 97-99 1 v 0.0002 74-98 1 Zn 0.0012 96-98 13 reveals that most metals in waste streams are recycled only at high concentrations. The concentration of resources in recycled wastes is generally higher than for virgin materials, indicating significant disincentives to make use of waste. Figures 9 and 10 demonstrate that there are many opportunities for increased recycling. SUMMARY Compositions and sources of recycled waste streams can be examined and opportunities for improving recycling efficiencies can be explored. Unfortunately, these analyses rely extensively on a single data base of industrial waste, the National Hazardous Waste Survey. This collection of data, which is the only comprehensive and detailed source of information on the composition of industrial hazardous waste streams, was based on wastes generated during 1986 and is already somewhat outdated. The data are also restricted to wastes classified as hazardous under the provisions of the Resource Conservation and Recovery Act. The lack of current, comprehensive, and reliable data on waste composition remains a serious barrier to studies in industrial ecology. If the limitations of available data are understood, however, it is possible to
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The Greening of Industrial Ecosystems FIGURE 9 Concentration distribution of recycled metals and the concentration distributions of metals in all industrial hazardous waste streams (1986 data). The concentration below which only 10 percent of recycling takes place is noted for each metal.
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The Greening of Industrial Ecosystems FIGURE 10 The Sherwood plot for waste streams. The minimum concentration of metal wastes undergoing recycling (see Figures 8 and 9) is plotted against metal price. The Sherwood plot for virgin materials is provided by comparison. Points lying above the Sherwood plot indicate that the metals in the waste streams are underused, that is, waste streams undergoing disposal are richer than typical virgin materials. Points lying below the Sherwood plot indicate that the waste streams are vigorously recycled. examine the industrial ecology of some metals. The results reveal that the concentrations of metal resources in many waste streams that are currently undergoing disposal are higher than for typical virgin resources. Thus, extensive waste trading could significantly reduce the quantity of waste requiring disposal. ACKNOWLEDGMENT This work was supported by the University of California Toxic Substances Research and Teaching Program. REFERENCES Allen, D. T., and R. Jain, eds. 1992. Special issue on industrial waste generation and management. Hazardous Waste and Hazardous Materials 9(1):1-111. Eisenhauer, J., and Cordes, R. 1992. Industrial waste databases: A simple roadmap. Hazardous Waste and Hazardous Materials 9(1): 1-19. National Research Council. 1987. Separation and Purification: Critical Needs and Opportunities. Washington, D.C.: National Academy Press.
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The Greening of Industrial Ecosystems U.S. Department of the Interior. 1988. Minerals Yearbook: 1986, Metals and Minerals, Volume 1. Washington, D.C.: U.S. Government Printing Office. U.S. Department of the Interior. 1991. Minerals Yearbook: 1989, Metals and Minerals, Volume 1. Washington, D.C.: U.S. Government Printing Office. U.S. Environmental Protection Agency. 1988a. Report to Congress: Solid Waste Disposal in the United States, Volume 1, EPA 530-SW-88-011. U.S. Environmental Protection Agency. 1988b. Report to Congress: Solid Waste Disposal in the United States, Volume 2, EPA 530-SW-88-011B. U.S. Environmental Protection Agency. 1988c. 1986 National Survey of Hazardous Waste Treatment, Storage, Disposal and Recycling Facilities, EPA/530-SW-88-035. U.S. Environmental Protection Agency. 1989. Characterization of Products Containing Lead and Cadmium in Municipal Solid Waste in the United States, 1970 to 2000, EPA/530-SW-89-015A. U.S. Environmental Protection Agency. 1990. Characterization of Municipal Solid Waste in the United States: 1990 Update, EPA 530-SW-90-042. U.S. Environmental Protection Agency. 1991. Toxics in the Community, EPA 560/ 4-91/014.
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