Closing the phosphorus loop Recovery, recycling and sustainable design

Phosphorus is a fundamental element in both living systems and modern industry. Its essential role in agriculture – particularly as fertilizer – has made society critically dependent on phosphate rock, a finite and geopolitically concentrated resource. At the same time, phosphorus mismanagement and its linear use contribute to serious environmental problems, such as eutrophication. These two converging challenges – resource depletion and ecological impact – highlight the need for more sustainable, circular approaches to phosphorus use and chemical design. This dissertation investigates the associated underlying issues and how to address them through an interdisciplinary lens rooted in environmental-, analytical- and synthetic chemistry. Contributions to phosphate recovery and recycling from waste streams – particularly human urine – are made by using legislative frameworks to show that recovered materials such as struvite are safe to use, even when sourced from polluted material. Using a different sustainability angle, the safe-and-sustainable design of organophosphate flame retardants is also investigated. Based on a developed framework using quantitative structure-activity relationships, alternative chemical structures are proposed in silico, synthesized and investigated, yielding promising targets with enhanced flame retardant capability and improved environmental profiles. Finally, an outlook is offered on using redox-neutral chemistry to enable fine P-chemical synthesis using inorganic, ideally recovered phosphate salts. All in all, this dissertation addresses key challenges in closing the anthropogenic phosphorus ´cycle´ and helps transition toward a modern, circular phosphorus economy that is safer and more resilient.