Closing the micronutrient loop: recovering and redirecting trace elements from food supply chains for a circular and nutrition-secure future.

Micronutrient deficiencies remain a major issue in the lives of billions of people worldwide. Meanwhile, significant losses occur along the food chain for many important micronutrient trace elements, which further compounds this global nutrition problem. The micronutrient stream of iron, zinc, selenium, copper and others are lost in agriculture residues, food processing by-products, retail waste, wastewater and post-consumer organic wastes. These deficiencies do not only lower nutritional efficiency, but also lead to environmental degradation and resource depletion. In response, approaches to the circular economy that focus on nutrient recovery and reuse are coming from the research realm as promising strategies to increase sustainability and nutrition security. This review compares and discusses the micronutrient losses from all stages of the food system and the technologies available to recover trace elements from organic waste streams. Recovery methods such as biological, physicochemical, thermal and hybrid processes are critically discussed with respect to recovery efficiency, scalability and environmental performance. The review also reveals significant safety concerns for nutrient recycling, such as toxic metal contamination, pathogens, pharmaceutical residues, and regulatory constraints. Reintegration options for recovered micronutrients into food systems are also discussed, such as crop biofortification, food fortification, nutraceutical production and animal feed applications. Furthermore, the impact of micronutrient circularity on nutrition, environment and economy is evaluated within the context of sustainable food systems and circular bioeconomy frameworks. The findings of this review confirm that the micronutrient loop can help simultaneously address the food waste, finite resource, and nutrition security challenges globally. But there are considerable technological, regulatory harmonization and consumer acceptance issues that will need to be resolved before this can be widely adopted.