Phosphorus Recovery in Sewage Sludge by Electrokinetic Based Technologies: A Multivariate and Circular Economy View

Phosphorus (P) is essential to all life being and a key ingredient in fertilizers to sustain high crop yields. It is an indispensable nutrient for food production and in a world of 9 billion people by 2050, securing sufficient P will be critical for future food security. Phosphorus has no substitute, but can be continually reused, being an example of a critical resource that could be utilized more efficiently in a circular economy to support sustainable growth and decrease pollution sources. Electrokinetically based technologies can be effective and viable options for P recovery from sewage sludge. In this work, chemometrics was used to develop a multivariate model based on 13 previously reported electrodialytic experiments (ED) of sewage sludge. The model predicted P recovery based on the experimental variable: cell design, time, current density and sewage sludge properties. The model showed that the cell design, current density and time highly influenced P recovery. Accounting the best recovery percentage achieved in the studies used for the model, 70% in 3 days using 0.21 mA/cm², ED technology has the potential to recover 280,000 tP/y of the total P in the sewage sludge. A strengths, weaknesses, opportunities, and threats analysis of EK technology for P recovery was also performed and several advantages were identified. For example, depending of the reactor design, the installation of whole electrokinetic treatment system may be adapted to the current wastewater treatment plants reactors decreasing the installation costs. One of the main identified threats to P recovery technologies is the lack of EU-level phosphorus legislation. But the presence of cost-effective alternatives to increase its recovery could be a driver towards an effective political/socio-economical implementation.