A scalable index for quantifying circularity of bioeconomy systems

Increasing resource demands and efforts to mitigate anthropogenic impacts have thrust circular bioeconomy into the spotlight. However, there currently lacks a metric to provide singular quantification of circularity. This study showed development of a Circularity Index (CI) with value between 0 (completely linear) and 1 (completely circular) to quantify circularity of resource flows at different system scales, identify weak links in value-chains, and determine tradeoffs in the system. This study describes 1) CI for systems containing consumable, renewable, and recovered resources; 2) CI application for two examples: nitrogen in a corn-soybean farm and energy in the U.S. food and agricultural system. CI showed that nitrogen circularity increased from 0.687 to 0.860 through implementation of renewable fertilizer from manure compared to synthetic fertilizer. CI also demonstrated improved energy circularity in the U.S. food and agricultural system, increasing from 0.179 to 0.843 when integrating food-energy-water systems via hydrothermal liquefaction and nutrient recycling.