In the face of climate change challenges and the need for resources for our growing population, there is a rising interest in creating circular economies to promote sustainable production practices. However, to assess these strategies and their consequences, reliable metrics are essential. Researchers from the University of Illinois Urbana-Champaign have introduced a Circularity Index that offers a thorough approach to measuring circularity within bioeconomic systems. Their recent paper details this method and showcases it through two case studies: a corn and soybean farming operation, and the entire U.S. food and agriculture system.
“Traditionally, our economic model is linear: we produce, distribute, utilize, and then discard products. To enhance sustainability, we should aim for a circular economy where we not only utilize natural resources but also recover, reuse, and recycle materials,” explained lead researcher Yuanhui Zhang, a professor in the Department of Agricultural and Biological Engineering (ABE), part of the College of Agricultural, Consumer and Environmental Sciences and The Grainger College of Engineering at the University of Illinois.
“The concept of a circular bioeconomy is gaining traction in research, yet most findings are simply descriptive, lacking in measurable impacts. To advance this technology, we require effective metrics to assess effects, create benchmarks, draw comparisons, and pinpoint vulnerabilities,” he added.
The researchers present a detailed breakdown of the Circularity Index (CI) in their paper, which rates circularity on a scale from 0 (entirely linear) to 1 (entirely circular). This index encompasses eight categories: take, make, distribute, use, dispose, recover, remake, and reuse. The CI is calculated by inputting available data into these categories.
Zhang and his colleagues illustrate the CI’s application through two case studies. The first study analyzes nitrogen cycling in a corn-soybean farm located in the Midwestern United States. The team inputs production and output data over an 8-year span and assesses the impacts of two fertilizer types: urea and manure. The CI values calculated are 0.687 for urea and 0.86 for manure, suggesting that manure fertilizer contributes to a more circular economy.
The second case study focuses on the U.S. food and agriculture sector and concentrates on energy consumption. Using national data from the USDA, EPA, and DOE, they compare the current system to an alternative based on the Environment-Enhancing Food Energy and Water System (EE-FEWS) framework, which emphasizes the recovery, remaking, and reusing of organic waste. The existing system was assessed with a CI of 0.179, while the EE-FEWS approach could elevate it to 0.84.
“Currently, our production system is heavily reliant on fossil fuels, with some integration of solar and wind energy. However, we hardly recover biowaste. By processing food waste and manure into energy and fertilizer, we can recycle these back into the agricultural systems where they originated. Adopting the EE-FEWS framework could significantly boost the circularity of the U.S. bioeconomy,” Zhang elaborated.
The CI is a versatile method that can be adapted for various resource types and systems, depending on the area of focus. These resources can be minerals, like carbon or nitrogen, or non-minerals, such as water or energy. The systems can range from a single process or farm up to an entire industry sector, national economy, or even the global economy.
“We recognize the importance of cutting down fossil fuel consumption, increasing renewable resources, and reducing water use. However, to achieve these goals efficiently, we must understand the specifics, including weak links and trade-offs. The CI provides a single metric that enables baseline establishment, system comparisons, and the identification of optimal action strategies,” Zhang stated.
The CI can act as a valuable indicator to support policy efforts like the United Nations’ Sustainable Development Goals. Additionally, it holds potential commercial benefits; for example, food companies can use it to showcase their production circularity to consumers.
