Developing product level indicators to advance the nitrogen circular economy

Increasingly, circularity indicators for material, energy, and water systems guide circular economy design. While indicators for products made from recycled carbon-based materials are somewhat common, peer indicators for waste nitrogen-derived products are limited. It is important, however, to develop such indicators to guide emerging technologies that transform waste nitrogen into products. In this study, we summarize the nitrogen circularity indicator literature, emphasizing the agricultural and wastewater sectors. Next, we use the Material Circularity Indicator (MCI) developed by the Ellen MacArthur Foundation, to quantify the circularity of products made from waste nitrogen in swine manure. We considered four test cases using different technologies to recover nitrogen from the manure. Our analysis indicates that technologies that seem to increase circularity on the surface may not yield a substantial increase in MCI results. Finally, we discuss the strengths and weaknesses of using the MCI for product-level analysis and further developments.