From waste to resource - recycling sewage sludge ash into phosphate-rich plant fertilizer

The Phos4plant project aims to investigate a new process for producing a mineral fertilizer from sewage sludge ash. The potential of leaching the phosphorus from the ash using organic acids produced by microorganisms is being investigated. The soluble phosphorus compounds are electrochemically precipitated in a further process step to produce mineral fertilizer. The aim of the project is to optimize the leaching and precipitation in order to achieve the highest possible phosphorus to (undesirable) heavy metal ratio and consequently to obtain a fertilizer with low contamination. The quality of the fertilizer should be able to meet the approval requirements (as a fertilizer; Fertilizer Ordinance). The project is accompanied by a profitability and life cycle analysis, which compares the current processes and the extraction of mineral fertilizer from decomposition and shows the potential of a circular economy, regional fertilizer production from sewage sludge ash.