Phosphorus recovery from sewage sludge by an electrokinetic process

As population keeps growing, it becomes important to guarantee the supply of staple foods, being necessary to assure good level of nutrients in the soil. Phosphorus (P) is a macronutrient indispensable for plants growth and a non-renewable resource, as phosphorites are estimated to be able to supply P for the next ca. 80 years. Additionally, the quality of this raw material has deteriorated due to contamination, which has increased processing costs of mineral P fertilizers. The recovery of nutrients, like P, from secondary resources urges.
Waste streams as sewage sludge (SS) and sewage sludge ash (SSA) may contain contaminants or unwanted elements regarding specific applications, but they also contain secondary resources of high value (e.g. elements with fertilizer value).
The incineration of SS is an highly used technique, namely in the Northern part of Europe. With SS incineration, the matrix volume will be significantly reduced and, at the same time, organic contaminants (such as PCB, PAH, …) will be thermally destructed.
However, heavy metals still remain in the ashes and, to “re-use” them as fertilizer, inorganic contaminants should be removed. Electrokinetic transport process (EK) can be an option to promote metal removal from SSA, allowing its potential re-use in agriculture or, followed by a next treatment step, phosphorous could be extensively removed from SSA matrix and further recovered in an electrolyte compartment.