Phosphorus Recovery from Sewage Sludge Ash: Chemical Processing and Granulation for Sustainable Fertiliser Production

The recovery of phosphorus from sewage sludge and sewage sludge ash (SSA) is a crucial step toward achieving sustainable resource management and closing nutrient cycles. This manuscript provides a comprehensive overview of current technologies for phosphorus recovery, focusing on both chemical and thermochemical processes, including acid leaching, struvite precipitation, and high-temperature treatments. Special attention is given to industrially implemented approaches such as the KomPhos, PHOS4green (GLATT/SERAPLANT), AshDec, and RecoPhos processes. The discussion addresses the technical, environmental, and economic aspects of each method, highlighting their advantages, limitations, and regulatory challenges. Economic evaluation criteria such as investment and operating costs, potential revenue, and environmental impacts are also examined. Additionally, the paper presents illustrative process flow diagrams and evaluates the prospects for large-scale implementation. By integrating technological innovation with sustainability goals, phosphorus recovery from SSA emerges as a vital strategy for reducing dependency on imported phosphate rock and promoting circular economy practices.