top of page

Material Flow Analysis (Part 2)

Studying urban food systems: results of the material flow study

Plant Chicago’s mission is to develop circular economies, but that term can be difficult to define. While there are certain principles of a circular economy, such as recapturing “waste” nutrients, materials and energy, reducing ownership and using more services, using only renewable energy, minimizing energy inputs, and no longer sourcing virgin materials… there is actually no set definition for the circular economy! Furthermore, there is no established way to measure circularity (yet!). Plant Chicago has set out on an ambitious project to start measuring the circular economy at the facility scale.

During the spring of 2016, graduate student Eva Chance (INRA, the French National Institute for Agricultural Research) and undergraduate student Julia Noberto (University of Illinois Chicago) conducted a material flow analysis between all of the businesses co-located at The Plant. This marks the first attempt to measure all of the materials flowing in and out of the facility, as well as between the different food businesses co-located at The Plant.

The study was done with thirteen distinct businesses located in The Plant, including the non-profit Plant Chicago and the for-profit owner of the building, Bubbly Dynamics. The aim was to take a snapshot of all the circular systems operating and developing at The Plant. Participating businesses were asked to share their material and electricity flows for the months of March, April and May 2016.  Businesses had to estimate, measure, and go through their paperwork to recall every material that went through their business during that time. The material flow data, which included water and electricity flows, was collected and used to create Sankey diagrams for every business.


Figure 1: Sankey diagram of Plant Chicago’s demonstration growing operations, the indoor aquaponics farm and mushroom lab (units in lbs)

Sankey diagrams represent all the flows going through a system with arrow thickness proportional to the flow they represent. All the businesses participating in the study have their own diagram and can be found in the final report (link found at the end of this blog). At the time of the study, Plant Chicago had two major research spaces: the indoor farm and the mushroom lab. Like all agricultural systems, the largest input and output is water (by weight). The Sankey diagram example above shows the amount of water used to grow the plants in the aquaponics farm as well as the mushrooms from inoculation to finished product (inputs). It also shows the “waste” water (outputs) from both operations.

You may notice that the system looks unbalanced, with more outputs than inputs. This has to do with the fact that the study was just a snapshot of time, and that some outputs are reflective of inputs that took place before the beginning of March. As such, it’s difficult to draw conclusions on specific inefficiencies in production. It is, however, a valuable tool for visualizing certain realities of growing food.

Using the above diagram, for example, we can see that there is a great deal of water needed to grow plants and mushrooms. “Closed-loop” systems such as aquaponics are often over 90% more efficient with water use compared to in-ground agriculture, but the material flow analysis demonstrates that a significant amount of water  gets “lost” in the growing process. While Plant Chicago’s aquaponics farm is designed to continually recirculate water and nutrients, water is removed from the system due to transpiration from the plants as well as evaporation from the surface of fish tanks.

Mushroom operations, however, have a lot more potential for recapturing water used in the production process. Unlike growing plants, the majority of water loss does not come from transpiration and evaporation, but through the inoculation process, which requires that the growing medium is either pasteurized or sterilized. Both sterilization and pasteurization processes use a lot of water, but that water output could serve as an input for either indoor or outdoor growing as it is still in liquid form, and is nutrient-rich and pathogen-free.


Figure 2: Qualitative flows representing the free materials exchanges between the tenants of The Plant.

The diagram above illustrates the circular flows at The Plant during the study period; showing the web of interactions of the actual and potential free exchanges between the different tenants. For example, the spent grains produced by the brewery are central to many projects, including the planned anaerobic digester project.

During the 3 months of this study, of all the materials flowing through the system:

42% were reused on site (primarily spent brewers grain) 31% went to the landfill 26% were used in goods sent off site

While it’s encouraging to discover that the majority of materials are being reused or made into goods (and not going to a landfill), it’s important to remember that this is a just a snapshot of time. In order to get a comprehensive look at all of the materials flowing through the businesses at The Plant, we would need an entire year worth of data to account for seasonality in material flows.

Plant Chicago is using this study to guide future research projects. Since the two largest material flows are water and spent grain, Plant Chicago research for the next year will focus primarily on the potential uses of these two materials between businesses co-located at The Plant. We’re also partnering with the Illinois Institute of Technology to build on Eva’s work and devise an ongoing system to monitor material flows between businesses. If we are able to measure materials flowing through the building, we can start measuring both the environmental and economic impact that circular systems can produce!!

For more information about the whole study and material flows for the rest of the system in The Plant, including the diagrams, you can look at Eva’s master thesis here.


bottom of page