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 Industrial ecology (IE) is the study of material and energy flows through industrial systems. The global industrial economy can be modelled as a network of industrial processes that extract resources from the Earth and transform those resource ...

or anthropogenic,

urban Urban means "related to a city". In that sense, the term may refer to: * Urban area, geographical area distinct from rural areas * Urban culture, the culture of towns and cities Urban may also refer to: General * Urban (name), a list of people ...

social Social organisms, including human(s), live collectively in interacting populations. This interaction is considered social whether they are aware of it or not, and whether the exchange is voluntary or not. Etymology The word "social" derives from ...

and

industrial metabolism Industrial metabolism is a concept to describe the material and energy turnover of industrial systems. It was proposed by Robert Ayres in analogy to the biological metabolism as "the whole integrated collection of physical processes that convert ra ...

. MFA is used to study material, substance, or product flows across different industrial sectors or within

ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syste ...

s. 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 The ''Journal of Industrial Ecology'' is a bimonthly peer-reviewed academic journal covering industrial ecology. It is published by Wiley-Blackwell on behalf of the Yale School of the Environment and is an official journal of the International So ...

'', '' Ecological Economics'', '' Environmental Science and Technology'', and ''Resources, Conservation, and Recycling''.

Methodology

Motivation

Human need A need is dissatisfaction at a point of time and in a given context. Needs are distinguished from wants. In the case of a need, a deficiency causes a clear adverse outcome: a dysfunction or death. In other words, a need is something required for a ...

s 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 In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to E ...

puts a previously unimportant waste flow,

carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...

, 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 The anthroposphere (sometimes also referred as the technosphere) is that part of the environment that is made or modified by humans for use in human activities and human habitats. It is one of the Earth's spheres. The term was first used by ninet ...

. 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 In physics, a mass balance, also called a material balance, is an application of conservation of mass to the analysis of physical systems. By accounting for material entering and leaving a system, mass flows can be identified which might have b ...

. 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 A chemical element is a species of atoms that have a given number of protons in their nuclei, including the pure substance consisting only of that species. Unlike chemical compounds, chemical elements cannot be broken down into simpler sub ...

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 In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...

. 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

is "a pure chemical substance consisting of one type of atom distinguished by its atomic number". * 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. MFASystem 3

Process balance

One of the main purposes of MFA is to quantify the

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...

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. MFAProcess1

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 An oil refinery or petroleum refinery is an industrial process plant where petroleum (crude oil) is transformed and refined into useful products such as gasoline (petrol), diesel fuel, asphalt base, fuel oils, heating oil, kerosene, lique ...

', 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 Industrial process data validation and reconciliation, or more briefly, process data reconciliation (PDR), is a technology that uses process information and mathematical methods in order to automatically ensure data validation and reconciliation by ...

, and the STAN-software offers basic reconciliation functionality that is suitable for many MFA application.

Examples of MFA 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 Material flow accounting (MFA) is the study of material flows on a national or regional scale. It is therefore sometimes also referred to as regional, national or economy-wide material flow analysis Material flow analysis (MFA), also referred to as ...

): 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 Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

and

waste Waste (or wastes) are unwanted or unusable materials. Waste is any substance discarded after primary use, or is worthless, defective and of no use. A by-product, by contrast is a joint product of relatively minor economic value. A waste prod ...

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 Life cycle assessment or LCA (also known as life cycle analysis) is a methodology for assessing environmental impacts associated with all the stages of the life cycle of a commercial product, process, or service. For instance, in the case o ...

, 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 Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (

), 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 ''The Limits to Growth'' (''LTG'') is a 1972 report that discussed the possibility of exponential economic and population growth with finite supply of resources, studied by computer simulation. The study used the World3 computer model to simula ...

'' 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), Brunner and Rechberger (2004), Baccini and Brunner (2012), and van der Voet et al. (2002). * Friedrich Schmidt-Bleek, who worked at the Wuppertal Institute, developed the MFA-related concept of Material Input Per Service unit (MIPS). * The

UNEP The United Nations Environment Programme (UNEP) is responsible for coordinating responses to environmental issues within the United Nations system. It was established by Maurice Strong, its first director, after the United Nations Conference on ...

Resource Panel was set up in 2007 by the United Nations Environment Program. In analogy to the Intergovernmental Panel on Climate Change (

IPCC The Intergovernmental Panel on Climate Change (IPCC) is an intergovernmental body of the United Nations. Its job is to advance scientific knowledge about climate change caused by human activities. The World Meteorological Organization (WMO) ...

) 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 System of Environmental-Economic Accounting (SEEA)System of Environmental-Economic Accounting 2012: Central Framework – final, official publication 2012, UN, EC, IMF, OECD and World Ban"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 The World Resources Forum (WRF) is a non-profit organisation for sharing knowledge about the economic, political, social and environmental implications of global resource use. WRF promotes resource productivity among researchers, policymaker ...

, a bi-annual international conference on material flow analysis and sustainable development. * MFA-IO is an approach to establish an MFA system of the whole economy using monetary and physical Input-Output tables. * The Sustainable Europe Research Institute (SERI) in Vienna, Austria, has developed a database called materialflows.net. * Dynamic MFA aims for long-term quantification of MFA systems and uses historic development patterns of physical stocks and flows to create robust scenarios for the years and decades to come. * Japan has developed into a hotspot for MFA research. The country has scarce mineral resources and therefore depends on imports of energy carriers, ores, and other raw materials. The Japanese government fosters research on material cycles and also inaugurated the 3-R concept.

Conducting a state-of-the-art MFA

A state-of-the-art MFA consists of the following steps: * Establish an explicit system definition: Specify the system boundary with geographical and temporal scope, processes (can contain stocks), and flows. Specify the material for which the system is to be quantified (product, substance, or indicator element). Make sure that each stock is associated with a process and that each flow connects one process to another. Flows can also begin or end outside the system boundary. * Define and name the system variables. The system variables include: All stocks within the processes, all flows between processes, and all flows coming from outside or going to outside the system boundaries. Sometimes, stocks are not considered and only the net stock changes are of interest. For each variable, it must be clear whether it is a stock or a flow, and this distinction needs to be reflected in the names and in the mathematical symbols chosen. * Quantify the system variables by linking them to literature, measurement, or modelled data. * Perform a mass balance check for all processes and the system as a whole. * Optional: Visualise your system by using the box-and-arrow scheme shown above or by using

Sankey diagram Sankey diagrams are a type of flow diagram in which the width of the arrows is proportional to the flow rate. Sankey diagrams can also visualize the energy accounts, material flow accounts on a regional or national level, and cost breakdowns. ...

s. * Document the MFA by reporting the explicit system definition along with the list of quantified system variables and the mass balance checks.

The difference between material and substance flow analysis

While the term 'substance' in 'substance flow analysis (SFA) always refers to chemical substances, the term 'material' in 'material flow analysis (MFA)' has a much wider scope. According to Brunner and Rechberger the term 'material' comprises substances AND goods, and the reason for this wide scope is the wish to apply MFA not only to chemical elements or substances but also to materials like steel, timber, or products like cars or buildings. It is thus possible to conduct an MFA for the passenger vehicle fleet by recording the vehicles entering and leaving the use phase.

Relation to other methods

MFA is complementary to the other core

methods

(LCA) and input-output (I/O) models. Some overlaps between the different methods exist as they all share the system approach and to some extent the mass balance principle. The methods mainly differ in purpose, scope, and data requirements. MFA studies often cover the entire cycle (mining, production, manufacturing, use, waste handling) of a certain substance within a given geographical boundary and time frame. Material stocks are explicit in MFA, which makes this method suitable for studies involving resource scarcity and recycling from old scrap. The common use of time series (dynamic modelling) and lifetime models makes MFA a suitable tool for assessing long-term trends in material use. * Compared to I/O analyses, the number of processes considered in MFA systems is usually much lower. On the other hand, mass balance ensures that flows of by-products or waste are not overlooked in MFA studies, whereas in I/O tables these flows are often not included due to their lack of economic value. Physical I/O models are much less common than economic tables. Material stocks are not covered by IO analysis, only the addition to stock can be included in form of capital accumulation. * Life cycle inventories record the demand for many different materials associated with individual products, whereas MFA studies typically focus on a single material used in many different products.

References

External links

CSIRO and UNEP Material Flow and Resource Productivity Database for Asia and the Pacific

materialflows.net
online portal for material flow data, providing access to material flow data sets on the national level * MFA is described in great detail and published on 166 pages in the first of four paper volumes co-edited with assistance from UNEP and in online form by th

Economy-wide Material Flow Analysis and Indicators

Material flow analysis in the context of environmental accounting

Online Material Flow Analysis Tool (OMAT)
online software to administer a Material Flow Analysis {{Systems science Environmental impact assessment Industrial ecology Environmental social science concepts