Approaches for Quantifying the Metabolism of Physical Economies: Part I: Methodological Overview

This article is the first of a two-part series that describes and compares the essential features of nine existing "physical economy" approaches for quantifying the material demands of the human economy upon the natural environment. A range of material flow analysis (MFA) and related techniques is assessed and compared in terms of several major dimensions. These include the system boundary identification for material flow sources, extents, and the key socioinstitutional entities containing relevant driving forces, as well as the nature and detailing of system components and flow interconnections, and the comprehensiveness and types of flows and materials covered.
Shared conceptual themes of a new wave of physical economy approaches are described with a brief overview of the potential applications of this broad family of methodologies. The evolving and somewhat controversial nature of the characteristics and role that define MFA is examined. This review suggests the need to specify whether MFA is a general metabolic flow measurement procedure that can be applied from micro to macrolevels of economic activity, or a more specific methodology aimed primarily at economy-wide analyses that "map" the material relations between society and nature. Some alternative options for classifying MFA are introduced for discussion before a more detailed comparative summary of the key methodological features of each approach in the second part of this two-part article.
The review is presented (1) as a reference and resource for the increasing number of policy makers and practitioners involved in industrial ecology and the evaluation of the material basis of economies and the formulation of eco-efficiency strategies, and (2) to provoke discussion and ongoing dialogue to clarify the many existing areas of discordance in environmental accounting related to material flows, and help consolidate the methodological basis and application of MFA.     

Maintenance and Expansion: Modeling Material Stocks and Flows for Residential Buildings and Transportation Networks in the EU25

Material stocks are an important part of the social metabolism. Owing to long service lifetimes of stocks, they not only shape resource flows during construction, but also during use, maintenance, and at the end of their useful lifetime. This makes them an important topic for sustainable development. In this work, a model of stocks and flows for nonmetallic minerals in residential buildings, roads, and railways in the EU25, from 2004 to 2009 is presented. The changing material composition of the stock is modeled using a typology of 72 residential buildings, four road and two railway types, throughout the EU25. This allows for estimating the amounts of materials in in‐use stocks of residential buildings and transportation networks, as well as input and output flows. We compare the magnitude of material demands for expansion versus those for maintenance of existing stock. Then, recycling potentials are quantitatively explored by comparing the magnitude of estimated input, waste, and recycling flows from 2004 to 2009 and in a business‐as‐usual scenario for 2020. Thereby, we assess the potential impacts of the European Waste Framework Directive, which strives for a significant increase in recycling. We find that in the EU25, consisting of highly industrialized countries, a large share of material inputs are directed at maintaining existing stocks. Proper management of existing transportation networks and residential buildings is therefore crucial for the future size of flows of nonmetallic minerals.     

Global Phosphorus Flows in the Industrial Economy From a Production Perspective

Human activity has quadrupled the mobilization of phosphorus (P), a nonrenewable resource that is not fully recycled biologically or industrially. P is accumulated in both water and solid waste due to fertilizer application and industrial, agricultural, and animal P consumption. This paper characterizes the industrial flows, which, although smaller than the agricultural and animal flows, are an important phosphorus source contributing to the pollution of surface waters. We present the quantification of the network of flows as constrained by mass balances of the global annual metabolism of phosphorus, based on global consumption for 2004, all of which eventually ends up as waste and in the soil and water systems. We find that on a yearly basis, 18.9 million metric tons (MMT) of P is produced, of which close to 75% goes to fertilizer and the rest to industrial and others uses. Phosphoric acid is the precursor for many of the intermediate and end uses of phosphate compounds described in this study and accounts for almost 80% of all P consumed. Eventually, all of the P goes to waste: 18.5 MMT ends up in the soil as solid waste, and 1.32 MMT is emissions to air and water. Besides quantifying P flows through our economy, we also consider some possible measures that could be taken to increase the degree of recovery and optimization of this resource and others that are closely related, such as the recovery of sulfur from gypsum and wastewater (sludge), and fluorine from wet phosphoric acid production.     

An Analysis of Stocks and Flows Associated with Water Consumption in Indian Households

The focus of urban water system metabolism studies has, by and large, been restricted to what comes under the domain of the urban water utilities: water treatment and supply, and wastewater collection, treatment, and disposal. The material and energy flows both necessitated and facilitated by the supply of treated water to households—the water demand subsystem—are by no means negligible. This article studies the key flows into households associated with water consumption and the environmental impacts related to the same for India as a whole. Electricity consumption in washing machines and water heaters contributes the most to almost all the 13 environmental impact categories considered. This is easily explained by the fossil fuel heaviness of the Indian mix (>60%). Soaps contribute the most to terrestrial eco‐toxicity and malodorous air. In India, on a national scale, all the environmental impact categories deserve attention. The absolute consumption of electricity, soaps, and detergents, and the demand for home appliances will increase in the years to come.     

Tracking Construction Material over Space and Time: Prospective and Geo‐referenced Modeling of Building Stocks and Construction Material Flows

Construction material plays an increasingly important role in the environmental impacts of buildings. In order to investigate impacts of materials on a building level, we present a bottom‐up building stock model that uses three‐dimensional and geo‐referenced building data to determine volumetric information of material stocks in Swiss residential buildings. We used a probabilistic modeling approach to calculate future material flows for the individual buildings. We investigated six scenarios with different assumptions concerning per‐capita floor area, building stock turnover, and construction material. The Swiss building stock will undergo important structural changes by 2035. While this will lead to a reduced number in new constructions, material flows will increase. Total material inflow decreases by almost half while outflows double. In 2055, the total amount of material in‐ and outflows are almost equal, which represents an important opportunity to close construction material cycles. Total environmental impacts due to production and disposal of construction material remain relatively stable over time. The cumulated impact is slightly reduced for the wood‐based scenario. The scenario with more insulation material leads to slightly higher material‐related emissions. An increase in per‐capita floor area or material turnover will lead to a considerable increase in impacts. The new modeling approach overcomes the limitations of previous bottom‐up building models and allows for investigating building material flows and stocks in space and time. This supports the development of tailored strategies to reduce the material footprint and environmental impacts of buildings and settlements.     

Dynamic Modeling of In‐Use Cement Stocks in the United States

A dynamic substance‐flow model is developed to characterize the stocks and flows of cement utilized during the 20th century in the United States, using the generic cement life cycle as a systems boundary. The motivation for estimating historical inventories of cement stocks and flows is to provide accurate estimates of contemporary cement in‐use stocks in U.S. infrastructure and future discards to relevant stakeholders in U.S. infrastructure, such as the federal and state highway administrators, departments of transportation, public and private utilities, and the construction and cement industries. Such information will assist in planning future rehabilitation projects and better life cycle management of infrastructure systems. In the present policy environment of climate negotiations, estimates of in‐use cement infrastructure can provide insights about to what extent built environment can act as a carbon sink over its lifetime. The rate of addition of new stock, its composition, and the repair of existing stock are key determinants of infrastructure sustainability. Based upon a probability of failure approach, a dynamic stock and flow model was developed utilizing three statistical lifetime distributions—Weibull, gamma, and lognormal—for each cement end‐use. The model‐derived estimate of the “in‐use” cement stocks in the United States is in the range of 4.2 to 4.4 billion metric tons (gigatonnes, Gt). This indicates that 82% to 87% of cement utilized during the last century is still in use. On a per capita basis, this is equivalent to 14.3 to 15.0 tonnes of in‐use cement stock per person. The in‐use cement stock per capita has doubled over the last 50 years, although the rate of growth has slowed.     

城市物质流分析框架及其指标体系构建

借鉴国内外物质流分析的研究成果,结合我国城市物质代谢特点,建立了城市物质流分析的框架及指标体系。该框架以城市社会经济系统物质通量的变化为核心,增加了对城市社会经济系统可持续能力的考察以及对城市和区域循环经济贡献的关注。论文识别了城市物质流分析中系统边界界定等关键问题,并提出了解决方法;指标体系在借鉴国家层面物质流分析指标体系的基础上,注重对城市经济系统内部循环及不同城市经济系统间的物质循环的考察,增加了再生资源输入量、内部资源回收量、可回收废物输出量、新鲜水输入量、中水回用量等指标,用于表征城市可持续发展的能力及实践成果。     

The Waste Input-Output Approach to Materials Flow Analysis

Abstract: A general analytical model of materials flow analysis (MFA) incorporating physical waste input-output is proposed that is fully consistent with the mass balance principle. Exploiting the triangular nature of the matrix of input coefficients, which is obtained by rearranging the ordering of sectors according to degrees of fabrication, the material composition matrix is derived, which gives the material composition of products. A formal mathematical definition of materials (or the objects, the flow of which is to be accounted for by MFA) is also introduced, which excludes the occurrence of double accounting in economy-wide MFAs involving diverse inputs. By using the model, monetary input-output (IO) tables can easily be converted into a physical material flow account (or physical input-output tables [PIOT]) of an arbitrary number of materials, and the material composition of a product can be decomposed into its input origin. The first point represents substantial saving in the otherwise prohibitive cost that is associated with independent compilation of PIOT. The proposed methodology is applied to Japanese IO data for the flow of 11 base metals and their scrap (available as e-supplement on the JIE Web site).     

Applying Ecological Input-Output Flow Analysis to Material Flows in Industrial Systems: Part I: Tracing Flows

Input-output mathematics, which allows a modeler to fully consider direct and indirect relationships among conserved flows in a system, has a long history in economics with prominent use dating to Leontief in the 1930s. Nearly all previous industrial applications of input-output analysis have been grounded in the monetary flows of an economy. Here however, because of the central nature of physical flows in the environmental impact of industry, we consider physical flows to be a fundamental component of an industrial economy. Hence, we propose an input-output based approach for modeling physical flows in industry independent of their monetary implications.
In this first part of a two-part article, a framework for using input-output mathematics to model material and energy flows is constructed from a foundation laid by previous research in nutrient and energy cycling in natural ecosystems. The mathematics of input-output flow analysis is presented from an ecological perspective, culminating in two core capabilities: tracing of flows with environs (investigated in this article) and characterizing system behavior with flow metrics (presented in the second article). We assert that environ analysis is an effective means for tracing flows through industrial systems while fully considering direct and indirect flow paths. We explore material flows of aluminum and five other metals in depth using environ analysis in this article.     

Dynamic Models of Fixed Capital Stocks and Their Application in Industrial Ecology

Industrial assets or fixed capital stocks are at the core of the transition to a low‐carbon economy. They represent substantial accumulations of capital, bulk materials, and critical metals. Their lifetime determines the potential for material recycling and how fast they can be replaced by new, more efficient facilities. Their efficiency determines the coupling between useful output and energy and material throughput. A sound understanding of the economic and physical properties of fixed capital stocks is essential to anticipating the long‐term environmental and economic consequences of the new energy future. We identify substantial overlap in the way stocks are modeled in national accounting, dynamic material flow analysis, dynamic input‐output (I/O) analysis, and life cycle assessment (LCA) and we merge these concepts into a common framework for modeling fixed capital stocks. We demonstrate the usefulness of the framework for simultaneous accounting of capital and material stocks and for consequential LCA. We apply the framework to design a demand‐driven dynamic I/O model with dynamic capital stocks, and we synthesize both the marginal and attributional matrix of technical coefficients (A‐matrix) from detailed process inventories of fixed assets of different age cohorts and technologies. The stock modeling framework allows researchers to identify and exploit synergies between different model families under the umbrella of socioeconomic metabolism.     

Material and Energy Flows and Environmental Impacts of the Internet in Switzerland

The Internet leads to material and energy consumption as well as various environmental impacts on both the regional and global scale. Yet, assessments of the Internet's energy consumption and resulting greenhouse gas emissions are still rare, and assessments of material flows and further environmental impacts are virtually non‐existent. This article investigates material flows, the direct energy consumption during the use phase, as well as environmental impacts linked to the service, “Internet in Switzerland.” In our model, the service, Internet in Switzerland, is divided into various Internet participant categories. All devices used to access or provide Internet services are merged in a limited number of equipment families and, as such, included in an inventory of the existing infrastructure (stock). Based on this inventory, a material flow analysis (MFA) is performed, which includes the current stock as well as flows resulting from growth and disposal. The direct energy consumption for the operation of the infrastructure is quantified. Environmental impacts are calculated with a life cycle assessment approach, using the ecoinvent database and the software, SimaPro, applying four different methods. The MFA results in a 2009 stock of 98,100 tonnes. Approximately 4,130 gigawatt hours per year, or 7% of the total Swiss electricity consumption, were used in 2009 to operate the Swiss infrastructure. The environmental impacts caused during the production and use phases vary significantly depending on the assessment method chosen. The disposal phase had mainly positive impacts as a result of material recovery.     

Cadmium Flows Caused by the Worldwide Production of Primary Zinc Metal

Material flows of the economic cycle can contain toxic substances, which enter the economy as impurities in raw materials or are intentionally added as minor or even main constituents during the manufacture of industrial or consumer goods. Cadmium, predominantly associated with zinc minerals, is a by-product of the primary zinc production. Cadmium is generated when zinc is extracted from zinc ores and concentrates, an intermediate product resulting from flotation processing after the zinc ore has been mined and milled. Information on the amount of cadmium generated from zinc extraction is rarely published. In this article, we assess generation and fate of cadmium accumulating worldwide in the production of primary zinc from ores and concentrates. Model calculations for the beginning of the 21st century show that annually about 30,000 tonnes of cadmium were generated, but only approximately 16,000 tonnes were converted to primary cadmium metal, key material for the production of other cadmium compounds (e.g., cadmium oxide), and cadmium-containing goods (e.g., nickel−cadmium batteries). Hence, about 14,000 tonnes of cadmium must have been transferred somewhere else. The fate of about 5,500 tonnes can be plausibly explained, but it is difficult to determine what happens to the rest.     

降水量变化对蒙古栎落叶分解过程的间接影响

分析了在4种不同降水量条件下蒙古栎叶凋落物基质质量的变化,并应用分解袋法研究其凋落物在蒙古栎次生林内的分解过程.结果表明：与对照相比,降水量减少条件下,蒙古栎叶凋落物的初始N、P、K浓度显著升高,初始木质素浓度显著降低,凋落物分解速率大,N、P、K矿化率高,N和P固持时间缩短;降水量增加情况下,其凋落物初始N浓度显著降低、木质素浓度显著升高,N、P、K矿化率低,N和P固持时间延长.4种类型叶片凋落物的质量损失过程均符合指数降解模型,分解速率可以由凋落物木质素/N来预测.相关性分析显示,木质素浓度高、N浓度低的两种凋落物的分解速率与N浓度相关性最大;而木质素浓度低、N浓度高的两种凋落物的分解速率与木质素浓度相关性最大.说明降水量的变化显著地改变了蒙古栎叶凋落物的基质质量,进而间接地改变了凋落物的分解过程.     

Materials Flows in Finland: Resource Use in a Small Open Economy

In this article, the development of natural resource use in Finland during the period 1970-1997 is analyzed. In measuring natural resource use, the concept of total material requirement (TMR) is applied. The focus is on the linkages of resource use with the changing structures of the economy. The linkages are studied using input-output analysis.
Using input-output analysis, the TMR is further partitioned into resources used for domestic final use or for total material consumption (TMC) and total material requirement of exports (TME). The analysis shows that TMR has the problem of double accounting: if the TMRs of all countries of the world are summed, then international trade would be accounted for twice in the world TMR, once in imports and once in exports of each country.
The TMC concept does not have this kind of defect. In a small, open economy like that of Finland, where the share of foreign trade is large, the difference between the TMR and the TMC is also large. We show that by 1997, the TME comprised about half of Finland's TMR and that the growth of the TMR over the study period has been due to the TME only as the TMC has stayed rather constant.     

Applying Ecological Input-Output Flow Analysis to Material Flows in Industrial Systems

This article, continuing with the themes of the companion article, expounds the capabilities of input-output techniques as applied to material flows in industrial systems. Material flows are the primary focus because of their role in directly linking natural and industrial systems and thereby being fundamental components of environmental issues in industrial economies. The specific topic in this article concerns several material flow metrics used to characterize system behavior that are derived from the ecological development of input-output techniques; most notable of these metrics are several measures of material cycling and a measure of the number of processes visited by material while in a system. These metrics are shown to be useful in analyzing the state of material flow systems. Further-more, the metrics are shown to be a central link in connecting input-output flow analysis to synthesis (i.e., the process of using measurements of system behavior to design changes to that system). By connecting the flow metrics to both environmental objectives and controllable aspects of flow models, changes to existing flow systems are synthesized to generate improved system behavior. To bring this pair of articles to a close, several limitations of input-output flow analysis are summarized with the goal of stimulating further interest and research.     

Approaches for Quantifying the Metabolism of Physical Economies: A Comparative Survey: Part II: Review of Individual Approaches

This article is the second of a two-part series that describes and compares the essential features of nine "physical economy" approaches for mapping and quantifying the material demands of the human economy upon the natural environ-ment. These approaches are critical tools in the design and implementation of industrial ecology strategies for greater eco-efficiency and reduced environmental impacts of human economic activity. Part I of the series provided an overview, meth-odological classification, and comparison of a selected set of major materials flow analysis (MFA) and related techniques. This sequel includes a convenient reference and overview of the major metabolism measurement approaches in the form of a more detailed summary of the key specific analytical and other features of the approaches introduced in part I. The surveyed physical economy related environmental analysis ap-proaches include total material requirement and output mod-els, bulk MFA (IFF (Department of Social Ecology, Institute for Interdiscplinary Studies of Austrian Universities) material flow balance model variant), physical input-output tables, substance flow analysis, ecological footprint analysis, environmental space, material intensity per unit service, life-cycle assessment (LCA), the sustainable process index, and company-level MFA.     

Unified Materials Information System (UMIS): An Integrated Material Stocks and Flows Data Structure

Modern society depends on the use of many diverse materials. Effectively managing these materials is becoming increasingly important and complex, from the analysis of supply chains, to quantifying their environmental impacts, to understanding future resource availability. Material stocks and flows data enable such analyses, but currently exist mainly as discrete packages, with highly varied type, scope, and structure. These factors constitute a powerful barrier to holistic integration and thus universal analysis of existing and yet to be published material stocks and flows data. We present the Unified Materials Information System (UMIS) to overcome this barrier by enabling material stocks and flows data to be comprehensively integrated across space, time, materials, and data type independent of their disaggregation, without loss of information, and avoiding double counting. UMIS can therefore be applied to structure diverse material stocks and flows data and their metadata across material systems analysis methods such as material flow analysis (MFA), input‐output analysis, and life cycle assessment. UMIS uniquely labels and visualizes processes and flows in UMIS diagrams; therefore, material stocks and flows data visualized in UMIS diagrams can be individually referenced in databases and computational models. Applications of UMIS to restructure existing material stocks and flows data represented by block flow diagrams, system dynamics diagrams, Sankey diagrams, matrices, and derived using the economy‐wide MFA classification system are presented to exemplify use. UMIS advances the capabilities with which complex quantitative material systems analysis, archiving, and computation of material stocks and flows data can be performed.     

Food Consumption and Nutrient Flows: Nitrogen in Sweden Since the 1870s

Changes in food consumption and related processes have a significant impact on the flow of nitrogen in the environment. This study identifies both flows within the system and emissions to the hydrosphere and atmosphere. A case study of an average inhabitant of the city of Linköping, Sweden, covers the years 1870, 1900, 1950, and 2000 and includes changes in food consumption and processing, agricultural production, and organic waste handling practices. Emissions to the hydrosphere from organic waste handling increased from 0.57 kilograms of nitrogen per capita per year (kg N/cap per year) to 3.1 kg N/cap per year, whereas the total flow of nitrogen to waste deposits grew from a negligible amount to 1.7 kg N/cap per year. The largest flow of nitrogen during the entire period came from fodder. The input of chemical fertilizer rose gradually to a high level of 15 kg N/cap per year in the year 2000. The total load per capita disposed of to the environment decreased during these 130 years by about 30%.     

Assessment of the Industrial Tomato Processing Water Energy Nexus: A Case Study at a Processing Facility

Increased demand for water and energy and growing recognition of environmental issues motivate awareness of how these resources are used in industry. Industrial tomato processing consumes substantial quantities of both water and energy. To understand how these resources are used in tomato processing and what opportunities exist for improving efficiency, a water energy nexus (WEN) assessment was conducted that accounted for the various ways energy becomes embedded in water during processing by motors, pumps, fans, and boilers. The WEN assessment was conducted at an industrial tomato processing facility that processed 265 metric tonnes of fruit per hour to develop a map of water and associated energy use at each processing step. A total of 1.29 billion kilograms (kg) of water were used for the processing season, with 870 million kg routed to flumes. The analysis identified the thermal energy used to generate steam for the various heat exchangers and evaporators used during processing as the greatest source of embedded energy in process water (778,000 gigajoules per season). The electrical energy embedded in the process water totaled 4.4 million kilowatt‐hours per season, over 80% of which was attributed to pumping. Moreover, the data were used to identify opportunities to improve efficiency by adjusting water loads on equipment and developing strategies for water and energy conservation and recovery. The baseline water and energy use data provided by the WEN assessment can enable additional modeling to assess resource efficiency measures and the life cycle impact of processed tomato products.     

Global Rare Earth In‐Use Stocks in NdFeB Permanent Magnets

The rare earth elements are indispensible in modern technology, especially in the applications of permanent magnets. Very little quantitative information is available on rare earth elements used in permanent magnets, however. This study looks back to 1983, when neodymium‐iron‐boron (NdFeB) permanent magnets were first manufactured, and reaches to 2007, when the market of permanent magnets was well developed. We draw on the historical data on permanent magnets from China, Japan, the United States, and Europe to provide the first estimates of global in‐use stocks for four rare earth elements—praseodymium (Pr), neodymium (Nd), terbium (Tb), and dysprosium (Dy)—in NdFeB permanent magnets. In‐use stocks amount to 62.6 gigagrams (Gg) Nd, 15.7 Gg Pr, 15.7 Gg Dy, and 3.1 Gg Tb; these stocks, if efficiently recycled, could provide a valuable supplement to geological stocks as they are almost four times the 2007 annual extraction rate of the individual elements.