Biological nitrogen recirculation to food protein – A review

Nitrogen is a part of a complex cycle with transformative reactions being not only an essential element for living organisms, but also facilitating negative environmental impacts as eutrophication and climate change. To reduce the negative environmental impacts, closing the nitrogen loop, reducing inputs of fossil-based synthetic nitrogen fertilizers, and returning nitrogen-rich material and waste streams back into the food system are essential. This review investigates the potential of nitrogen transformation technologies to return nitrogen to food systems from existing material streams, levelling the imbalances of the nitrogen cycle. Review of both conventional and biotechnological pathways for nitrogen recovery, as well as of legal aspects and safety issues uncovers the knowledge gaps, potentials, and barriers for making nitrogen circular in a food system context. Further a few technologies aiming the recirculation of the nitrogen disclosed as a basis for potential industrial scale up and implementation.