Material flow analysis (MFA), also referred to as substance flow analysis (SFA), is an analytical method to quantify flows and stocks of materials or substances in a well-defined system. MFA is an important tool to study the bio-physical aspects of human activity on different spatial and temporal scales. It is considered a core method of industrial ecology or anthropogenic, urban, social and industrial metabolism. MFA is used to study material, substance, or product flows across different industrial sectors or within ecosystems. MFA can also be applied to a single industrial installation, for example, for tracking nutrient flows through a waste water treatment plant. When combined with an assessment of the costs associated with material flows this business-oriented application of MFA is called material flow cost accounting. MFA is an important tool to study the circular economy and to devise material flow management. Since the 1990s, the number of publications related to material flow analysis has grown steadily. Peer-reviewed journals that publish MFA-related work include the Journal of Industrial Ecology, Ecological Economics, Environmental Science and Technology, and Resources, Conservation, and Recycling.
Methodology
Motivation
Human needs such as shelter, food, transport, or communication require materials like wood, starch, sugar, iron and steel, copper, or semiconductors. As society develops and economic activity expands, material production, use, and disposal increase to a level where unwanted impacts on environment and society cannot be neglected anymore, neither locally nor globally. Material flows are at the core of local environmental problems such as leaching from landfills or oil spills. Rising concern about global warming puts a previously unimportant waste flow, carbon dioxide, on top of the political and scientific agenda. The gradual shift from primary material production to urban mining in developed countries requires a detailed assessment of in-use and obsolete stocks of materials within human society. Scientists, industries, government bodies, and NGOs therefore need a tool that complements economic accounting and modelling. They need a systematic method to keep track of and display stocks and flows of the materials entering, staying within, and leaving the different processes in the anthroposphere. Material flow analysis is such a method.
Basic principles MFA is based on two fundamental and well-established scientific principles, the systems approach and mass balance.Marina Fischer-Kowalski, The Intellectual History of Materials Flow Analysis, Part I, 1860-1970, Journal of Industrial Ecology 2(1), 1998, pp 61-78, .Marina Fischer-Kowalski, The Intellectual History of Materials Flow Analysis, Part II, 1970-1998, Journal of Industrial Ecology 2(4), 1998, pp 107-136, . The system definition is the starting point of every MFA study.
System definition
An MFA system is a model of an industrial plant, an industrial sector or a region of concern. The level of detail of the system model is chosen to fit the purpose of the study. An MFA system always consists of the system boundary, one or more processes, material flows between processes, and stocks of materials within processes. Physical exchange between the system and its environment happens via flows that cross the system boundary. Contrary to the preconceived notion that a system represents a specific industrial installation, systems and processes in MFA can represent much larger and more abstract entities as long as they are well-defined. The explicit system definition helps the practitioner to locate the available quantitative information in the system, either as stocks within certain processes or as flows between processes. An MFA system description can be refined by disaggregating processes or simplified by aggregating processes.
Next to specifying the arrangement of processes, stocks, and flows in the system definition, the practitioner also needs to indicate the scale and the indicator element or material of the system studied. The spatial scale describes the geographic entity that is covered by the system. A system representing a certain industrial sector can be applied to the USA, China, certain world regions, or the world as a whole. The temporal scale describes the point in time or the time span for which the system is quantified. The indicator element or material of the system is the physical entity that is measured and for which the mass balance holds. As the name says, an indicator element is a certain chemical element such as cadmium or a substance such as CO2. In general, a material or a product can also be used as indicator as long as a process balance can be established for it. Examples of more general indicators are goods such as passenger cars, materials like steel, or other physical quantities such as energy.
MFA requires practitioners to make precise use of the terms 'material', 'substance', or 'good', as laid out, for example, in chapter 2.1 of Brunner and Rechberger, one of the main references for the MFA method.
A chemical element is "a pure chemical substance consisting of one type of atom distinguished by its atomic number".IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "chemical element". A substance is "any (chemical) element or compound composed of uniform units. All substances are characterised by a unique and identical constitution and are thus homogeneous." From chapter 2.1.1 in Brunner&Rechberger. A good is defined as "economic entity of matter with a positive or negative economic value. Goods are made up of one or several substances". From chapter 2.1.2 in Brunner and Rechberger. The term material in MFA "serves as an umbrella term for both substances and goods". From chapter 2.1.3 in Brunner&Rechberger.
Process balance
One of the main purposes of MFA is to quantify the metabolism of the elements of the system. Unlike economic accounting, MFA also covers non-economic waste flows, emissions to the environment, and non-market natural resources.
The process balance is a first order physical principle that turns MFA into a powerful accounting and analysis tool. The nature of the processes in the system determine which balances apply. For a process 'oil refinery', for example, one can establish a mass balance for each chemical element, while this is not possible for a nuclear power station. A car manufacturing plant respects the balance for steel, but a steel mill does not.
When quantifying MFA systems either by measurements or from statistical data, mass and other process balances have to be checked to ensure the correctness of the quantification and to reveal possible data inconsistencies or even misconceptions in the system such as the omission of a flow or a process. Conflicting information can be reconciled using data validation and reconciliation, and the STAN-software offers basic reconciliation functionality that is suitable for many MFA application.
Examples of applications on different spatial and temporal scales
MFA studies are conducted on various spatial and temporal scales and for a variety of elements, substances, and goods. They cover a wide range of process chains and material cycles. Several examples:
MFA on a national or regional scale (also referred to as material flow accounting): In this type of study, the material exchanges between an economy and the natural environment are analyzed. Several indicators are calculated in order to assess the level of resource intensity of the system. Corporate material flow analysis, or MFA along an industrial supply chain involves a number of companies: The goal of material flow analysis within a company is to quantify and then optimize the production processes so that materials and energy are used more efficiently manner, e.g., by recycling and waste reduction. Companies can use the results obtained by Material Flow Cost Accounting to reduce their operational costs and improve environmental performance. In the life cycle of a product: The life cycle inventory, whose compilation is at the core of life cycle assessment, follows the MFA methodology as it is based on an explicit system definition and process balances.
Historical development
Mass balance or the conservation of matter has been postulated already in ancient Greece, and it was introduced into modern chemistry by Antoine Lavoisier (cf. chapter 2.1.3 in Brunner&Rechberger,), from where it found its way to chemical engineering and finally to environmental science. Other seminal contributions were made by Sanctorius and Theodor Weyl. Dennis Meadows made a wide audience aware of the physical foundation of the economy when he co-authored the bestseller Limits to Growth in 1971. Meadows et al. based their predictions on an analysis of resource stocks; see in the glossary of environmental science. The methodology of MFA was developed during the 1980s and 1990s. Development happened simultaneously in different research groups. Central publications on the MFA methodology include Baccini and Bader (1996),Baccini and Bader 1996, 'Regionaler Stoffhaushalt' (Regional metabolism), Spektrum Akademischer Verlag, Heidelberg (Germany), Brunner and Rechberger (2004), Baccini and Brunner (2012),Baccini P. & Brunner P.H. (2012). Metabolism of the Anthroposphere, Analysis, Evaluation, Design. 2nd Edition, The MIT Press, Cambridge, MA. and van der Voet et al. (2002).'Predicting future emissions based on characteristics of stocks', Ecological Economics, 2002, 41(2), 223-234. Friedrich Schmidt-Bleek, who worked at the Wuppertal Institute, developed the MFA-related concept of Material Input Per Service unit (MIPS). Stefan Bringezu specified this concept in economy-wide material flow analysis, as screening tool for product life-cycle assessment within a cross-scale framework. He defined indicators such as Total Material Requirement (formerly Total Material Input) and Raw Material Input, which are used to quantify the Material Footprint of products, infrastructures and countries. The UNEP Resource Panel was set up in 2007 by the United Nations Environment Program. In analogy to the Intergovernmental Panel on Climate Change (IPCC) it brings together experts from many disciplines and institutions to review the current state of research on societal metabolism and to communicate the latest findings to policymakers and stakeholders.
Recent development MFA concepts have been or are being incorporated in national accounts in several countries and regions such as the EU and Japan. MFA is also used in the System of Integrated Environmental and Economic Accounting. Several international conferences or other meetings provide a platform for researchers and policymakers to meet and exchange results and ideas, including the World Resources Forum, a bi-annual international conference on material flow analysis and sustainable development. Waste Input-Output (WIO)-MFA is an approach designed to establish a comprehensive MFA system for the entire economy. This is achieved by utilizing monetary Input-Output (IO) tables and incorporating physical information related to material inputs. The method seamlessly integrates MFA with Input-Output models, offering a straightforward means to transform monetary flows within an Input-Output table into distinct physical flows categorized by materials. WIO-MFA serves as an illustrative example of MFA based on economic Input-Output analysis. The Sustainable Europe Research Institute (SERI) in Vienna, Austria, has developed a database called material flows.net.