Phosphorus Recovery from Bio Feedstock using the Improved Hard Process

by Bhavish Patel (presenting author)1, Mohamed Tarik1, Tobias Borgmeyer2, Albert Schuler1, Christian Ludwig1,2

1: Bioenergy and Catalysis Laboratory (LBK), Energy and Environment Research Division (ENE), Paul Scherrer Institut (PSI), Switzerland; 2: Environmental Engineering Institute (IIE), School of Architecture, Civil and Environmental Engineering (ENAC), École polytechnique fédérale de Lausanne (EPFL), Switzerland


Phosphorus (P) is an essential element used for growth by both plants and animals. Renewable P was once obtained by Guano droppings, but due to disproportionate demand it is now mined, predominantly from North Africa. Its main use (>90%) is in the agricultural industry where it is estimated that over 1 billion tonnes has been lost into the environment since 1950. An alternative for P does not exists, nor can it be produced synthetically. Thus, the recovery of P and directing it back into the loop is essential to prevent the depletion of this finite resource.

Some high-volume sources of P include sewage sludge, slaughterhouse bones and waste agricultural residues. The recovery of P from such sources can typically be achieved via acid-based extraction, also called the wet processing route. However, in view of cost competitiveness, P recovered from these feedstocks for use as fertilizer may not be fully feasible and supported. Therefore, this work focuses on the production of high purity P for application in the chemicals industry obtained via thermal processing which is suited for low to medium P content feedstocks.

One such process is the Improved Hard Process (IHP) where P containing feedstock is treated at temperatures of up to 1400°C in the presence of a reducing agent, Carbon, and an additive, Silicon Dioxide. Thus, in this work the results from the treatment of organic feedstocks including Raw Sewage Sludge, Incinerated Sewage Sludge Ash as well as Animal Bones will be presented for the first time. Furthermore, experiments to decipher the optimum Feedstock:C:SiO2 will also be deciphered.