Circularity Index Offers Roadmap for a Sustainable Future

Researchers at the University of Illinois Urbana-Champaign have developed a Circularity Index, providing a comprehensive tool for measuring circularity in bioeconomic systems. Their study, published in Resources, Conservation, and Recycling, outlines the methodology and demonstrates its application through two case studies: a corn/soybean farming operation and the entire US food and agriculture system.

As the world confronts the challenges of mitigating climate change and meeting the needs of a growing population, the emphasis on creating circular economies for sustainable production is intensifying. However, to effectively assess these strategies and their impacts, reliable metrics are essential.

“The traditional economic system is linear – we produce, distribute, use, and dispose of products. To increase sustainability, we need to develop a circular economy. Rather than just using natural resources, we must recover, reuse, and recycle waste materials,” notes Yuanhui Zhang, Study Lead Author and 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 U. of I.

Circular bioeconomy has become a hot topic in research, but most studies are merely descriptive and there’s no way to measure impacts. To move the technology forward, we need measurements to quantify effects, establish benchmarks, compare approaches, and identify weak spots.

Yuanhui Zhang, Study Lead Author and Professor, University of Illinois Urbana-Champaign

The researchers introduced a comprehensive guide to the Circularity Index (CI), which measures circularity on a scale from 0 to 1. A score of zero indicates a fully linear system, while a score of one represents a completely circular system. The CI evaluates eight categories: take, make, distribute, use, dispose, recover, remake, and reuse. The index is calculated by inputting data into each of these categories.

Zhang and his team demonstrated the application of the CI through two case studies. The first study focused on nitrogen cycling in a corn-soybean farm in the Midwestern United States over an eight-year period. They compared the effects of two fertilizer treatments—urea and manure—by inputting production and output data. The CI calculations revealed a value of 0.687 for urea and 0.86 for manure, indicating that manure fertilizer contributes to a more circular economy.

In the second case study, the team analyzed the US food and agriculture system, particularly focusing on energy consumption. Using national data from the USDA, EPA, and DOE, they compared the current system with a model based on the Environment-Enhancing Food Energy and Water System (EE-FEWS) framework, which emphasizes the recovery, remaking, and reuse of organic waste. Their findings showed that the current system has a CI of 0.179, while the EE-FEWS approach could achieve a CI of 0.84.

Our current production system relies primarily on fossil fuel, with some use of solar and wind energy. But there is very little recovery of biowaste. If we recover food waste and manure and turn it into energy and fertilizer, we can recycle it back to the agricultural systems it originates from. Employing the EE-FEWS framework would greatly improve circularity of the US bioeconomy.

Yuanhui Zhang, Study Lead Author and Professor, University of Illinois Urbana-Champaign

The CI is a versatile method that can be applied to various resource types and systems based on the area of interest. It can measure both mineral resources, like carbon or nitrogen, and non-mineral resources, such as water or energy. The CI is adaptable to different scales, from individual processes or farms to entire industry sectors, national economies, or even the global economy.

We know it’s important to reduce fossil fuel use, increase renewable resources, and minimize our water consumption. But to do so effectively, we need to know how much and what the weak links and tradeoffs are. The CI provides a single number that allows you to establish a baseline, compare systems, and determine best strategies for action.

Yuanhui Zhang, Study Lead Author and Professor, University of Illinois Urbana-Champaign

The CI can act as a valuable indicator for supporting policy initiatives, including the United Nations’ Sustainable Development Goals. Additionally, it holds commercial potential, allowing food companies to showcase their production circularity to consumers.

Journal Reference:

Zhang, Y., et al. (2024). A scalable index for quantifying circularity of bioeconomy systems. Resources Conservation and Recycling. doi.org/10.1016/j.resconrec.2024.107821.