Material Flow Challenges in Industrial Ecosystems

Materials Transactions, Vol. 43, No. 3 (2002) pp. 364 to 367 Special Issue on Environmentally Benign Manufacturing and Material Processing toward Dematerialization c 2002 The Japan Institute of Metals

Bert Bras ∗

Georgia Institute of Technology, Atlanta, GA 30332-0405, USA

In Industrial Ecology the core idea is to ﬁnd symbiotic relationships where waste material from one company is being used by other companies and industrial ecosystems are created. Although the idea is simple, fundamental challenges exist related to the quality of the material, stability of the system, etc. A core question is how to assess of the “goodness” of such a system. In this paper, it is shown how ecological input-output analysis metrics can be used to analyze ﬂows.

(Received October 22, 2001; Accepted December 27, 2001) Keywords: materials, industrial ecology, ﬂow analysis, recycling

1. Industrial Ecology pollution prevention efforts are mapped that most often focus on elimination of pollutants from existing products and pro- The term “Industrial Ecology” was popularized by an ar- cess technologies-the temporal scope is on the order of man- ticle by Frosch and Gallopoulos1) in which the idea of an ufacturing process and the organizational scope is usually the industrial ecosystem is introduced to take advantage of the manufacturing group. analogs to biological ecosystems. They note that this ecosys- In industrial ecology, a much larger scope of concerns is tem would ideally be closed: “a chuck of steel could poten- applicable. As shown in Fig. 1, industrial ecology encom- tially show up one year in a tin can, the next year in an auto- passes pollution prevention and life-cycle engineering (LCE) mobile, and 10 years later in the skeleton of a building.” For type approaches. While LCE type approaches are limited to this closed system to exist, any waste from one part of the a single product from a single manufacturer, the concern of ecosystem must be used as input to another part of the sys- industrial ecology ranges over many products (with different tem. Using this idea, waste from one manufacturing process life cycles) from multiple manufacturers over a larger time does not have a negative impact on the environment if it can scale. be used as input to another process. The complexity of Industrial Ecology is illustrated in 2. Ecological Thinking in Industry Fig. 1, which compares the environmental and organizational scales of environmental protection approaches.2) The verti- A few industrial ecosystems exist or are in the making, cal scale indicates the scope of organizational concern, rang- but they are rather the exception than the rule. In general, ing from the manufacturing facility at the origin, through a the Europeans and the Japanese have progressed further than group of X manufacturers to society as a whole. The hor- the U.S. beyond the lower left corner and are moving to- izontal scale indicates the corresponding length of the time wards industrial ecology.3) Specifically, 1) product take back scale, ranging from the time during the manufacturing pro- and recycling are actively pursued to avoid landfill disposal, cess, through the product lifecycle, to the span of civiliza- 2) life-cycle analyses are performed to reduce environmental tion. The scales are not linear but indicate important distinc- impact over the entire product life, and 3) strong collabora- tions between approaches. In the lower left corner, traditional tions between stakeholders (suppliers, recyclers, governmen- tal bodies, etc.) are established. All these activities can be viewed as a move towards industrial ecology. Certain companies are clearly evolving beyond “business as usual” and can be viewed as “thinking outside the box”. At Interface Flooring Systems, a multinational textile company headed by Ray C. Anderson who is a strong proponent of sustainable development, the approach is centered on “quantification, qualification, symbiosis”. This means that once a waste streams’ amounts have been defined (quantification) and their severity assessed (qualification), an attempt is made not just to reduce it, but to find an outlet that can actually use the waste as a feedstock. These outlets can be other industries, and a symbiotic industrial ecosystem (as promoted by industrial ecology) can be obtained. However, this symbiotic approach can also take place more Fig. 1 Classification of environmental impact reduction approaches.2) directly with Nature. Interface Flooring is using natural materials for some of its carpet products, e.g., animal hair and recently corn based fibers.3) Similarly, DaimlerChrysler is us- ∗E-mail: [email protected] Material Flow Challenges in Industrial Ecosystems 365 ing natural reinforcing fibers (flax or sisal, depending on loca- 4. Analyzing Material Flows tion) instead of glass fibers in some of its polymer composite components because these natural fibers can be more easily A more significant challenge is to assess the “goodness” of decomposed, both when recycling production scrap and also industrial ecosystems. It is interesting to note that the Kalund- at the end of the useful life of the vehicle.3) borg, Denmark, industrial ecosystem came about through serendipity and not through carefully planned up-front design. 3. Challenges The State of Georgia in the US tries to actively link companies with waste-streams to potential users of those wastes. How- Although the pursuit of industrial ecosystems offers many ever, how does a policy maker, or anybody else, know that a advantages, the paradigm shift of viewing groups of industries system is “good”? And how can we best improve industrial and even Nature as a large interconnected system does pose ecosystems? For this, fundamental understanding and metrics some problems and fundamental challenges. are needed that allow stakeholders in industrial ecosystems to make better decisions regarding the material flows. 3.1 Feedstock material quality Both Interface and DaimlerChrysler noted that an entirely 4.1 Traditional metrics new supply chain had to be set-up. For example, Daimler- Some favor assessments that use monetary metrics. How- Chrysler had to ensure a consistent crop quality, which even ever, money represents a reverse flow to energy and material meant redesigning farming equipment, and developing qual- flows in that it flows out of cities, farms, companies, etc. in ity control systems to deal with unavoidable variations in the exchange for resources that flow in. Unlike energy, money natural fiber “manufacturing” process, such as the amount circulates. Unfortunately, money enters the picture only when of rainfall. Another example is efforts by Archer Daniels a natural resource is converted in manufactured goods or hu- Midland in identifying a use for waste flyash (similar to ce- man services, and no price is put on the work of Nature that ment) generated by their fluidized bed coal combustion sys- sustains the whole resource. This has caused many to real- tem. The fluidized bed system successfully decreases air pol- ize that money is an artificial concept that is insufficient to lution, but the chemical composition of the waste flyash de- capture what happens in the physical world. pends in turn on the composition of the coal, which varies Frequently, metrics like recycled content and recovery rates greatly. As a result, the flyash is unsuitable for many appli- are used to quantify the level of cycling of materials in a sys- cations. In essence, the same manufacturing process quality tem. Recycled content is formally defined as. control systems that have only recently been embraced by in- recycled inputs dividual manufacturers will need to be embraced on a much Recycled content = . (1) total production inputs larger scale. The higher the recycled content, the greater the material 3.2 Ecosystem stability cycling in a system. Recycled content is used by the auto in- Given that the quality of the materials can be guaranteed, dustry and pulp and paper companies to indicate the percent there is a fundamental issues of material supply and flow. of a new product composed of recycled materials. The recov- Kalundborg, Denmark, is often cited as a long-standing, suc- ery rate is mathematically defined as. cessful industrial ecosystem. However, few know that two material recovered after consumption Recovery rate = . of the Kalundborg companies also had facilities in Savannah, total material consumption Georgia (USA) and there no symbiotic relationship was estab- (2) lished. The reasons are unknown, but it does point out to the issue of ecosystem stability. In (natural) ecology, two types Recovery rate is used by trade associations such as the Alu- of ecosystem stability are considered: minum Association, and the United States Geological Survey • Resistance stability which indicates the ability of an uses a similar metric (percent recycled) to indicate the degree ecosystem to resist perturbations and maintain its struc- of recycling of different metals. ture and function intact. • Resilience stability which indicates the ability to recover 4.2 Analyzing flow characteristics using ecological when the system is disrupted by a perturbation. input-output mathematics In an industrial ecosystem, resistance stability is needed to However, a different approach, namely, Ecological Input- withstand fluctuations in material supplies or demands. Most Output Analysis, can be used to assess the cycling of materi- 5) successful individual companies are able to withstand mar- als. This approach rooted in natural ecology principles has ket and resource fluctuations. However, a small perturbation also been used in economics, and provides some interesting in material supply in a network of connected companies may new ways of assessing and analyzing material flows in indus- cause a ripple and oscillatory effect to the point that the net- trial ecosystems. Among others, Input/Output analysis traces work is damaged. Resilience stability from individual mem- flows forwards from inflows and backwards from outflows; bers of the ecosystem is then needed to recover. Interestingly, supports structural and dependency analyses; includes a range growing evidence from natural ecology suggests that these of usefull flow metrics for assessing the amount of (material) two kinds of stability may be mutually exclusive, or at least, cycling, the influence of indirect flows, the connectedness of it may be difficult to develop both at the same time.4) a system, the total flow, flow path lengths, etc. Two primary input-output cycling metrics are Return- cycling Efficiency and Cycling Index. Return cycling effi- 366 B. Bras ciency, REk, is defined for each process Hk as the percentage of throughflow Tk that has already been through process Hk at least once; that is, it is the percent of flows at a given process that are cycled. A return cycling efficiency of zero character- izes a situation in which all flows through a process only pass through once while a value of one indicates a closed system in which all flows are completely cycled. Because REk represents the proportion of throughflow Tk attributable to cycled flows, the product of REk and Tk is equal to the amount of cycled flow at process Hk. Furthermore, the amount of cycled flows in the system can be defined as: n Fig. 2 Industrial ecosystem and material flows. TSTc = REk · Tk. (3) k=1 Table 1 Metric values for comparison. while the total flows in the system are defined as: Metric Value n Recycled content 0.375 TST = Tk. (4) Recovery rate 0.5 k=1 RE1 0.367 A cycling index (CI) for a system of flows is defined as RE2 0.367 the percent of total system throughflow (TST) that is cycled RE3 0.326 RE4 0.367 (TSTc). REp 0.367 TST CI = c . (5) REc 0.326 TST CI 0.358 The cycling index is unitless and ranges from zero (i.e., zero cycled flows) to one (i.e., a completely closed system). processing (e.g., making steel sheets), H1, production (e.g. Two additional cycling metrics that are particularized for producing a product from steel sheets), H2, and recycling, H4. 5) industrial material flows are introduced. REc and REp are There are extraction wastes, production wastes, and wastes called the consumption and production cycling efficiencies, from consumers discarding old products. Within the system, = , ... , respectively. With the set of processes Hu, u 1 m, material flows from material processing to production to con- representing all consumptive processes and the set of pro- sumption to recycling and finally back to material processing = ... , cesses Hp, p 1 g representing all industrial produc- to enter the cycle again. Some material wastes from production processes, REc and REp are defined as follows: tion proceed directly to recycling. The resulting metric values m are shown in Table 1. REuTu The values for recycled content and recovery rate are cal- = u=1 . culated using eqs. (1) and (2). Clearly the value for REp is REc m (6) not equal to that of recycled content and the value of REc is Tu not equal to that of recovery rate (nor are the traditional met- u=1 rics equal to any of the individual REi values). Several other g examples of industrial systems in which input-output cycling REpTp metrics differ from traditional metrics for measuring material p=1 cycling are in.5) RE = . (7) p g For systems without as significant of indirect effects (i.e., Tp systems that have less alternate paths for materials to flow p=1 through) the traditional metrics and several of the input-

As REc increases, the cycling of material through con- output flow metrics are similar if not the same. For a sys- sumptive uses increases while, as REp increases, the cycling tem with more complex path structures, on the other hand, of material through industrial processes increases. In general, the traditional metrics are shown to not fully handle the di- an increase in CI is desirable from an environmental perspec- rect and indirect paths of flows through the system. For more tive. More is being done with less virgin inputs. A more complex systems, indirect flows have a greater effect on the specific goal is to increase REc while decreasing REp (unless amount of material cycling at specific processes, resulting in increase in REp is due to increased new scrap recovery). Such return cycling efficiencies that are not equivalent to the tradi- a goal encourages the efficient return of material to consump- tional metrics. The input-output flow metrics, therefore, are tion while discouraging excessive material cycling in indus- more generally applicable than the traditional metrics. Recy- trial processes. cled content and recovery rate do not necessarily represent the To compare the Input-Output Analysis with traditional percent of material that is cycled in a system or in a particular metrics, consider the system shown in Fig. 2. It is based process of a system and, therefore, do not truly measure mate- on the Type II industrial ecosystem model.6) The numbers are rial cycling. And material cycling is foundational in industrial hypothetical. Virgin material enters the system in material ecosystems. Material Flow Challenges in Industrial Ecosystems 367

5. Conclusions 2) B. Bras: “Incorporating Environmental Issues in Product Realization,” Industry and Environment 20, (1997) 7Ð13. 3) WTEC, Environmentally Benign Manufacturing, (WTEC Panel Report, Industrial ecosystems offer significant advantages, but sig- Baltimore, MD, Loyola College, 2001). nificant and fundamental challenges exist, such as material 4) E. Odum: Basic Ecology, (Holt-Saunders International, 1983). quality control, stability issues, and assessment metrics. Tra- 5) R. Bailey: Input-Output Analysis: An Approach for Modeling Industrial ditional metrics may not be sufficient and scientific findings Material Flows, (Georgia Institute of Technology, Atlanta, GA, 2000). 6) T. E. Graedel and B. R. Allenby: Industrial Ecology, (Englewood Cliff, and tools from Natural Ecology, such as Input-Output Analy- New Jersey: Prentice Hall, 1995). sis can help, and are needed, as shown by the results.

REFERENCES

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