Phosphorus is essential for food production, but its current management is inefficient, environmentally harmful and heavily dependent on finite, geopolitically concentrated phosphate rock. At the same time, substantial secondary and legacy phosphorus resources in manure, industrial wastes, wastewater, food-chain residues and soils remain underused, and less than 1%of secondary phosphorus is recycled globally. This work investigates how wastewater-based phosphorus recycling can be implemented as a reliable fertiliser source for crop production in the European Union by assessing its technical, regulatory and economic readiness and its capacity to substitute mineral inputs while maintaining environmental and agronomic safety. First, a global synthesis of secondary and legacy phosphorus resources and a barrier analysis show that manure, mining and fertiliser industry wastes, wastewater and food waste already account for phosphorus flows comparable to current fertiliser demand, while accumulated stocks in soils and sediments exceed it. Yet recycling is constrained by interacting technological, logistical, economic, regulatory and social barriers, highlighting the need for integrated, transdisciplinary approaches that align stakeholder functions and requirements with the properties of recycled products. Second, wastewater-derived fertilisers in Denmark, Germany and Spain are screened against EU and national legislation and agronomic boundary conditions. Only five out of 22identified technologies fully comply across all three countries, but these compliant routes could meet around 9–22% of wheat, barley and rye phosphorus requirements at national level, with higher contributions in specific regions. The analysis underscores that wastewater recycling is aspatially heterogeneous but non-negligible lever for reducing mineral fertiliser dependence and sewage sludge use. Third, an integrated environmental–economic framework is developed for Spain to compare continued sewage sludge application with struvite, vivianite and calcium phosphate recovered from wastewater. Using data from almost 28,000 agricultural plots, heavy metal accumulation over 50- and 100-year horizons is simulated and combined with a cost–benefit analysis that internalizes environmental externalities, including soil remediation and foregone production. The results indicate that continued sludge use can lead to widespread exceedances of zinc, copper and cadmium limits, particularly in alkaline soils, whereas substitution with advanced recycled products substantially reduces these risks. When externalities are included, advanced recycling routes become economically competitive with, and in some cases preferable to, the baseline, even if direct financial returns remain modest. Overall, the present work shows that wastewater-derived fertilisers are not a universal solution, but when their properties are matched to regulatory, agronomic and economic requirements, they can form a robust component of a diversified, circular phosphorus strategy for European agriculture.
Juan Serrano (Sun,) studied this question.