Recovery of Phosphorus From Dried Sewage Sludge for Fertilizer Formulations

Phosphorus (P) is an indispensable nutrient in agriculture. The PULSE process (Phosphorus University of Liège Sludge Extraction) was developed to recover P from sewage sludge. One challenge with sewage sludge from municipal wastewater treatment plants is the high concentrations of iron, aluminum and heavy metals. Reactive extraction was used to remove these. The PULSE process was operated on pilot-plant scale at three different sites with different sludges. In order to account for the differences between the sludges, the operating parameters were optimized for the respective properties of the sludge using simulations that allow accounting for the equilibria of speciation in the aqueous phase, the reactive equilibria during extraction, and the equilibria describing precipitation. In particular, the simulation allows to consider different models for the non-ideality of electrolyte solutions of up to concentrated systems.
It was shown that by combining detailed modeling and lab-scale experiments, it is possible to optimize the PULSE process to account for differences in sludge from different wastewater treatment plants. The results show that the optimized parameters result in an excellent recycled P material suitable for use as a fertilizer component.