 nothing is lost, nothing is created, everything is transformed. This sentence from Lavoisier, a 18th century French chemist, summarizes the law of conservation of mass. In other words, for any system close to all transfers of matter and energy, the mass of the system must remain the same constant over time as the system mass cannot change, so quantity can either be added or removed. This mass balance principle sits at the heart of material flow analysis and as you all see is essential for measuring material flows, their associated environmental impacts and this can be done at the scale of companies, cities, regions or even countries. This accounting technique is essential to know because it sits at the heart of topics such as circular economy, climate change policies, urban metabolism, donut economics, life cycle assessment and much more. Hi, I'm Aristide from Metabolism of Cities and in this video you will learn what material flow analysis is, how it is being used through some examples, as well what are the insights you can extract from such an analysis. With all that being said, let's dive deeper and let me illustrate what material flow or MFA is by showing some slides. The first question you might be asking yourself is what is material flow analysis? According to Bruner and Rechberger, material flow analysis is a systematic assessment of the flows and stocks of materials within a space defined in space and time, so if we look at this system over here, we have drawn some system boundaries and we're looking at everything that enters the system in terms of flows, stays within the system in terms of stocks, but also moves between processes. Now I have to unpack this because there are many concepts that I have just introduced and that are important to be further elaborated. For instance, I talked about system boundaries. What is a system boundary? Well, an MFA system or a material flow system is this combination of a couple of things. First of all, the material flows, so the arrows you have here in the diagram of the stocks, so whatever stays within your system for more than a year, let's say, and the processes that are the subsystem of your system, if you will. Here I have the box P and the box C and these are, let's say, production and consumption. So you have imports going to production, from production goes to consumption, from consumption we have exports, but also perhaps recycling that goes back to production. So you have your processes, the boxes, the flows, the arrows and the stocks which are flows that stay within your system for more than your defined time boundary. Now what is your time boundary or your system boundary? The system boundary is this dotted lines box around everything. So this system boundary is, let's say, a boundary that you define of what is measured, what is included in your system and what is excluded from your system. You define the system boundary both in space and time. So for instance here, if you see, I said that the system boundary is EU28, well now 27, and it dates for 2018. So that's the year of reference I'm looking at. You could choose a country, a city or even some virtual limits such as a company which can be spread around the globe because of course not all operations are carried out in the same country. It can also be a household. Now that we've defined what is an MFA system, let's define what is a process. So if you remember in the previous graph of these boxes, the production on the one hand, the consumption on the other. So to very define what a process is, you have to think of it, it's a transformation or a storage of a flow from one state to another. So for instance, a wastewater treatment plan, so it receives wastewater, it's takes all of the phosphorus and the nitrogen out of it, let's say, and then it releases it back to a stream or a river or something like that. The same thing with a waste-sineration process, it receives let's say municipal solid waste, it burns it, it produces once again vapor that transforms into electricity and then on the other hand you have ashes and other downgraded materials that you would want to landfill at the end of it. So that is a process. Now how about stocks? We said that we have processes, flows and stocks. Stocks is, as I mentioned, more or less a flow that does not move for the period of time that you're looking at your system. So for instance if I'm doing a material flow analysis for one year, for a country, a stock is whatever doesn't move for more than a year. So this can be a car, this can be a house, this can be your computer or your phone, you're looking at it. So it's any type of reservoir or buffer, material buffer that stays within your system for more than a certain quantity of time. And these stocks can remain constant over time, they can increase or decrease. So increase whenever we do constructions for instance, new constructions, new homes, new infrastructures, buying durable goods and on the other hand it can also decrease or deplete. So for instance it can, we can demolish, we can mine or we can throw to waste. And as you can see here in the image we have flows entering our system, so the 10 tons per year, another 5 tons going out and because of the material balance we need to have 5 tons that stay within our system. And these are added to our stock, which is already 750 tons for that year. On the flip side we can have a depletion of stock, so the stock gets smaller and smaller. And so this time we have 5 tons entering our system, 5 tons being released from our stock, such as waste, and then exit our system we have the 5 entering plus the 5 exiting from our stock adding to 10 tons per year. So stocks can be of too nature, they can be natural and man-made stocks or anthropogenic stocks. So the natural or geogenic stocks, well of course it can be a query that you can get gravel, you can get sand, but you can also get metal ores, you can get oil, gas, many other primary or raw materials. You can also get surface water or groundwater. So these are let's say the natural stocks and their concentration of course may vary, so we can have very concentrated stocks and the more we use them the less concentrated it gets, so the more money we need to put and the more energy we need to put in order to extract these ores or these raw materials. So that's why we're discussing more and more about anthropogenic stocks, man-made stocks, or material urban stocks. So as you can see in the image of course this can be buildings, infrastructures, wires, so metals, it can be non-metallic minerals, so the bricks, the concrete, the sand, the gravel, it can be metals, it can be plastics, it can be wood, it can be many different things that we include in our territory for more than a year. Of course a man-made stock does not mean that we can use it as we want, it has to be technically feasible, it has to be economically feasible as well in order to facilitate the reuse of materials from the man-made stock. So we've discussed about the system boundary, the processes, the stocks, and now finally the flows. Well the flows are materials and materials can be of different nature, it can be substances, molecules, it can be goods or services that flow from one process to another. So it can be from a mine to a manufacturing plant to a household or to let's say a supermarket and then to a waste collection process and then to a waste treatment process. You have different processes or different boxes and then you have arrows that link them through materials. In general we measure that with a unit of mass, so it can be tons, it can be kilograms, it can be kilotons sometimes or thousands of tons, sometimes gigatons so billion of tons and this is per year of course because that's the the interval of time that we're looking at our system boundary. So Brunner and Rechberger in their in their book called Practical Handbook of Material Flow Analysis they also differentiate two things. First of all they say that a flow entering a process is an input, a flow exiting a process is an output, but also you can have imports and exports so meaning things that come from outside of your system boundary and go outside of your system boundary. So if we have here Switzerland as a system boundary whatever comes from outside of Switzerland into Switzerland that's an import and then what leaves Switzerland is an export but then if you have a process here let's say agriculture well this is both an import and an input but if from agriculture it goes to households directly then that's just an input it's not an import it's just a you know a jargon or a terminology that that they think is important to to underline you know in practice it doesn't it doesn't have much of implications. So we've seen what are the different components of a material flow analysis we're looking at a system boundary we have to draw a system boundary geographically and in time we have to define what are the processes that we're looking at and therefore what are the flows the stocks that are interlinking these processes and then once we have all of this we can start doing a material flow analysis. In a different video we have already explained some of these steps of a material flow analysis but if I have if I have to go quickly through them you have five main steps whenever you're doing a material flow analysis. First of all you define your system as I mentioned so you have to define first of all what is the question that you're trying to answer because any material flow analysis you do it to answer a question because anyone can decide an arbitrary let's say sets and subsets of processes that you want to include in your system right after all it's up to you to decide what you want to include and exclude however we generally include everything needed in order to answer a question so for instance what would be the impact of recycling in let's say a glass consumption within a country how would it reduce imports exports and waste if we recycled more that's a defined question based on that we will have a system that well a system boundary so space and time but also a selection of processes and flows that reflect that can help us answer that question once we have this system definition step two is you collect the flows and stocks needed to do a material flow balance right in some cases you have some uncertainties right over there you can look at reports into estimates and all of that and whenever you don't have estimations or characterizations via technical reports or academic literature you can calculate these by general equations so because you know that your system needs to be in balance per process you need to have an equality between what comes in what goes out and what stays in your stock so you have a bunch of equations if you manage to solve them then you have your your system that is balanced once you do that you then illustrate your material flow analysis by what we call a sankey diagram and we have two videos explaining what is a sankey diagram but also how to make one so i'll refer to them in the description below but also you can find them on our youtube channel once you have illustrated your flows you can start interpreting your material flow analysis what does it mean what is the main source of flows where do they come from what is the relationship between what we extract locally and what we import are we import dependent country or an export dependent country are most of our emissions due to local production or because we import stuff that have associated environmental effects elsewhere so over there you start interpreting your results your quantities and in step five you can start doing recommendations in order to optimize or change your system that goes back to step one which is the problem definition for instance the example of a glass recycling well what can we do to optimize the system should we increase recycling should we change waste regulations where do we act within this system diagram and these are the five main steps for doing an MFA but to summarize why we do a material flow analysis well material flow analysis is a very powerful tool because it can help us detect early harmful and useful material accumulations within our system so for instance there is a lot of metals or heavy metals that are accumulated in water reservoirs there is a lot of lead for instance in painting and we need to change the type of painting because we can predict how much lead is going to is going to accumulate in in our homes we can also start identifying the need of action so if we know that there is an early detection of toxic materials then we can start saying okay we should develop policies for resource waste and environmental policy management another way to do it is to evaluate the effectiveness of current and planned measures so let's say that your city your country or your company develops policies or measures in order to decrease your environmental impact or your footprint let's say well by doing a material flow analysis you can test this you can make scenarios saying okay let's imagine that we increase 10% of recycling in our company where would that what would that change how much would we reduce flows elsewhere and what would be the environmental effect associated to this finally one of the purposes of doing a material flow analysis is to design new type of products and have them ecologically optimized products processes as well so over there you can start thinking okay i want this function from a product a service or a process what is the best way i could materially energy energy and water optimize it in terms of flows this is typically one of the use cases of material flow analysis now let me give you a theoretical example just before a practical example and then we're going to wrap this up so here we have an example of this famous example of glass recycling so over here we have two processes production and consumption we have four flows this one the import going to production the sale going from production to consumption the the waste going from consumption being exported outside of the city and then you have recycling going from consumption back to production and depending on if you want your system to be static or dynamic you also take into account the change rate of your stocks so over here if the the stock of the production increases or decreases the stock of the consumption increases or decrease this is typically one easy way to to make a material flow diagram with your system boundary your processes over here your flows four main flows and then your stock if it's increased or decreased let me now show you a real real life example where you can see how how this has been done so not too long ago we collaborated on on working on the London footprint and over there we looked at Greater London so the metropolitan area of London and we looked at the mass of food flows entering exiting and being transformed within the metropolitan area of London what can we see here so for instance we have one two three four five six seven eight different processes and we have flows connecting them right going inside and out of them and here in in red we see the greenhouse gas emissions I'll omit them just for a moment let's focus on the green parts on the green flows so we see for instance that we have a number of flows that go to to manufacturing and some of them are imported or most of them should I say and some of them are locally harvested from manufacturing or producing locally you have some parts that are waste over here or losses and the main the majority of it going to to processing to retail sorry wholesale and retail from there some of them are exported and most of them are consumed either within households or in in restaurants canteens and other places and finally from the consumption of these flows they go to waste and either they're they're waste they're collected locally or they're redistributed to to other parties and then from waste collection they're treated by different by different means of waste treatment so this is a synthetic image of the the food footprint of London what does it tell us it tells us that of course most of of flows that are needed for the consumption of food in London are imported and some of them or half of them are imported locally from other you know UK regions other are and the other half is important from the rest of the EU and the world that's one bit we also see that there is losses in your system here and there we also see that the majority of food is consumed locally and we see that the majority of of waste is treated in incineration so over here it's a quick synthetic overview of how a system works in this case it's a city but it could be a country it can be a company and it helps you in in one glance to understand what are the proportions and what we should be doing within the system so for instance here we could say we need to absolutely reduce the imported food flows by increasing local production in order to increase the resilience of the system in order to decrease let's say the greenhouse gas emissions emitted to the imports in order to better control the the quality of the jobs from people working in agriculture and and and other stuff we could also start thinking okay we need to have more jobs in in manufacturing right or in processing so it really helps us to have a look for instance over here we could say there is a lot of loss or food waste going from wholesale and retail we should work on this one as well it really helps you very rapidly to to think about solutions once you see the entire picture we could also say well perhaps it's it's a nonsense to have incineration because we're burning you know water in a sense most of the organic mass within food waste is water so we're heating up water perhaps we could compost it and reuse it back to local production here perhaps we could make biogas and then use it for energy etc etc so all of these synthetic material flow analysis helps you to to better understand how a system works better understand what what are your levers of of action and of change but also to identify where should we change anything what are the main sectors what are the main actors that i should activate in order to change my system so if i have to synthesize what we have learned first of all material flow analysis is an essential analytical tools that helps us to have a systemic analysis for cities companies economic sectors to reduce their environmental effect and their footprint now if you have any questions comments or if you would like any other videos please leave them down below in the comments and we will see you in the next video cheers