Development of a method for phosphorus recovery from wastewaters

Abstract

As an irreplaceable element for all life on Earth, the supply of phosphorus (P) needs to be preserved. Since the natural inorganic resources are slowly depleting, one gazes upon secondary sources for P such as sewage sludge. By developing recovery processes for phosphorus from secondary sources we can respond to the ever-increasing consumption of phosphate fertilizers and ensure that future generations will have a secure food supply. In this thesis, a method for P recovery from post-precipitated sewage sludge is presented. The research has been part of the development of Helsinki Region Environmental Services’ RAVITA -process. The literature review describes the already existing technologies for P recovery and the general principles of the techniques used in the method development such as the design of experiments (DOE) and solvent extraction. The experimental section briefly defines the experimental procedures used in the original publications. In the results section first, the results from elemental analysis of the post-precipitated sludge are shown. The main components in the sludge are phosphorus and the metal used in precipitation in the production of the sludge. Trace metal concentrations in the post-precipitated sludge are below the average trace metal content of the sewage sludge in the EU. Then the findings from the optimization of the leaching procedure for post-precipitated sewage sludge are presented. Phosphoric acid was selected as leaching acid and the optimization was systematically implemented with the design of experiments procedure. Last the purification procedure for the obtained phosphoric acid solution was investigated. The precipitation metal is recovered from the phosphoric acid solution with solvent extraction.