The Ash2Phos process can transform the sludge ash into a raw material for phosphorus extraction and thereby be a part of a circular solution for phosphorus management. The process consists of three steps: a first acidic step, a second alkaline step (where intermediate products are produced), and finally a conversion step where the intermediates are processed into final products.

The main inputs of the process are

• Ash from incinerated sewage sludge
• Acid (hydrochloric acid, HCl)
• Lime

The process consists of several successive chemical reactions that allow to separate elements of interest and detoxify the products. The mass balance of the process is favourable since most input chemicals become part of the products.

High concentration of phosphorus

Ash from mono-incinerated sewage sludge has high concentrations of phosphorus (7-10%), iron (10-15%), and aluminium (1.5-8%), but also contains unwanted heavy metals such as cadmium. The high content of metal has up until now created an obstacle for possible applications for the phosphate-rich ash.