Forging a cohesive path: Integrating life cycle assessments of primary-origin phosphorus fertilizer production and secondary-origin recovery from municipal wastewater

Phosphorus (P) is an essential agricultural nutrient and its production as mineral P fertilizers from phosphate rock is well established. An alternative method involves recovering P from municipal wastewater treatment plants (WWTP) for reuse as fertilizer. Life cycle analysis (LCA) studies have been conducted to assess the environmental impacts associated with both processes. However, systematic comparisons of mineral and recovered P fertilizer production processes are scarce in the existing literature. In this review, we examine the goals, functional units, impact categories, and system boundaries of peer-reviewed LCAs for mineral P fertilizer production (n = 5), recovered P fertilizer production (n = 14), or both (n = 5). To enhance the overall impact and usefulness of these studies for policymaking, we propose a standardized approach for comparative P process studies, while emphasizing the need for simultaneously assessing the environmental effects of P fertilizer production and P recovery from WWTPs. We recommend including key impact categories that are relevant to both processes, such as eutrophication, acidification, global warming potential, soil and water pollution, resource use, and toxicity. Furthermore, adopting a functional unit of one kilogram of elemental P would facilitate better comparisons between LCAs. We also recommend standardized system boundaries that encompass the key aspects of each process.