Evaluating phosphorus fluxes in Portugal: opportunities and limitations for the implementation of regional synergies between the wastewater and agricultural sectors

Portugal is deficient in phosphate fertilizers. However, it also hasa phosphorus (P) consumption chain with potential to promote sustainable management of P from waste. Creating a link between the waste and agricultural sectors supports a reduction in external dependence and promotes the circularity of a secondary raw material.

Gathering information about productive quantities, pollutant discharge points (PDPs), and P concentration in industrial activities, it is possible to infer the following: the food industry is concentrated in coastal urban areas like Lisbon and Porto, but contributes minimally to P losses in the form of waste (383 t/year); wastes from slaughterhouses, while rich in protein and suitable for biogas production, only contribute minimally to P resources (82 t/year); urban solid waste management is more structured, although with efforts in recycling and biogas production, its role in P recovery remains modest (1,35 kt/year); urban wastewater, however, shows the greatest potential for P recovery due to its widespread geographic distribution, and nutrient-rich sludge (7.3 kt of P). This highlights opportunities for P management, enhancing biofertilizer production.

Using the concept of Regional Resilience (RR) and Territorial Metabolism (TM), this work estimated agricultural demand for P fertilizer in mainland Portugal and P content in sewage sludge, from urban wastewaters, to partially replace the use of inorganic P fertilizers, at the municipal level. So far, Lisbon Metropolitan region appears to have the potential to reach 2,631.87 t/year of P recovered from wastewater, surpassing local agricultural demand (126.83 t/year). In the northern region, sewage sludge contains enough P to meet 25% of the region's fertilizer needs. In the Centro Litoral region, it is possible to meet 48% of the corresponding P needs. Opportunities for implementing synergy require accurate information on infrastructures, technology assessments corresponding to local characteristics, economic and environmental contributions, and compliance with legislative targets.