PASCH - Recovery of plant nutrients, especially phosphorus from ash of sewage sludge 

The aim of the interdisciplinary research and development project is the design and examination of a process for nutrient recovery from sewage sludge ash. Particularly, the phosphorus is to be recovered for plant nutrition. 

Within a first stage, techniques are investigated which are appropriate to create an ash fraction with higher phosphate concentration than found in the raw ash. Afterwards, the part of the ash that is rich in phosphorous enters a chemical or biological leaching. Thus, the phosphorus becomes dissolved. Prior the precipitation of the phosphorus as plant-available nutrient, metals and heavy metals must become removed from this leachate.

In cooperation with the project “PhoBe” extensive examination of the plant availability of the phosphorous contained in the product and of the innocuousness of the generated mineral fertiliser is carried out. 

Several disposal and recycling options for sewage sludge and ash are analysed by a life cycle assessment. The project will be closed with a preliminary conceptual design of the developed process for industrial scale which will allow an estimation of the annual phosphate recovery costs.