P-XTRACT®: Recovery of Phosphorus from Sewage Sludge

Recovery of Phosphorus

Phosphorus is an essential nutrient. Raw material sources with phosphorus deposits are limited and distributed among a small number of countries of origin, such as Russia, China and Morocco. Currently, it is believed that approximately 40% of the demand for phosphorus can be covered by thermal utilization of sewage sludge.

All substances previously removed from the wastewater are concentrated in the sewage sludge. Direct spreading of sewage sludge on agricultural land or landscaping would result in uncontrolled release of pollutants into the water cycle and thus into the food chain. In order to protect the natural cycle, the pollutants must first be safely removed.


P-XTRACT® is a thermal process for the recovery of phosphorus from phosphorus-containing fuels, such as sewage sludge. By adding certain (earth) alkali additives to the incineration process, heavy metals are depleted and the availability of the phosphorus for plants is increased. Subsequently, a high-quality fertilizer can be directly produced from the ashes and be spread regionally. This is our contribution to closing material cycles and conserving resources!

Regional recovery of phosphorus from sewage sludge ashes

Regional phosphorus recycling from sewage sludge ash - WEHRLE


P-XTRACT® is the extension of WEHRLE’s K3 Fluidized Bed Technology for sewage sludge designed to meet the legal requirements for the recovery of phosphorus, which will come into force for the first sewage treatment facilities in 2029. The distinguishing feature of the K3sludge Technology for the decentralized or regional mono-incineration of sewage sludge is the separation of the phosphorus ash in a temperature window of 700 – 750°C and thus at a point where most pollutants are still gaseous.

The special process conditions in the fluidized bed and the downstream hot gas cyclone for the separation of the flyable phosphorus-containing recyclable ashes give P-XTRACT® the following important process characteristics:

  • Achievement of recovery rate: more than 80% of the phosphorus can be recovered in form of ash fertilizer.
  • Elimination of pollutants: The addition of additives generates volatile heavy metal compounds in the ash, which are transferred to the gas phase due to the high process temperatures. Subsequently, the ash is already separated at temperatures of over 700°C in the hot gas cyclone, avoiding the precipitation of heavy metal compounds. Furthermore, the ash is almost free of dioxins and furans, since the temperature window of the De novo synthesis is not crossed. The volatile heavy metal compounds are safely removed in the downstream flue gas cleaning process.
  • Increased availability of phosphorus: The addition of additives generates new phosphorus phases, which are more available for plants than those of conventional sewage sludge mono-incineration processes.

Ash fertilizer from the incineration of sewage sludge
Ash fertilizer from sewage sludge incineration - WEHRLEAsh fertilizer from sewage sludge incineration - WEHRLEAsh fertilizer from sewage sludge incineration - WEHRLE


After years of development by WEHRLE, the Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) and the University of Freiburg, P-XTRACT® is ready for its first large-scale implementation. The European Union and the federal state of Baden-Württemberg are funding the project, also called P-XTRACT, for the construction of a pilot plant at the sewage treatment facility of AZV Staufener Bucht in Breisach-Grezhausen. The pilot plant is expected to treat 11,160 tOS/a of mechanically dewatered sewage sludge with a simultaneous high degree of energy self-sufficiency. Commissioning is planned for the end of 2022.

After the successful market launch, P-XTRACT® is available as add-on for future K3 plants for thermal utilization of sewage sludge or as retrofit.

The P-XTRACT project is funded by the European Union and the federal state of Baden-Württemberg. P-XTRACT® is a registered, protected word mark of WEHRLE-WERK AG.
The P-XTRACT<sup>®</sup> project is funded by the European Union and the State of Baden-Württemberg. P-XTRACT<sup>®</sup> is a registered, protected word mark of WEHRLE-WERK AG.