Abstract :
[en] The North West Europe (NWE) Interreg Phos4You (P4Y) project addresses the phosphorus (P) challenge. P is a nutrient essential for all living organisms. Though it is a finite resource on earth, P is largely wasted today. The EU acknowledged this by adding phosphate rock to its list of critical raw materials in 2014. There is a need to boost the use of secondary raw P. The project addresses rural, urban and port areas in NWE. P is needed in rural areas as fertilizer or feed additive (often produced in port areas). P is transferred within food to urban areas where 82% of NWE-citizens live in (World Bank, 2015), and wasted there, via sewage and waste. P4Y specifically targets recovery from municipal waste water treatment plants.
In 2015 NWE imported 100% of its mineral P-needs. 45% of the demand could be supplied by circular economy. The project will exploit the recovery potential of P in municipal sewage water (113,000 t/y P), estimated to cover 26% of the mineral P-demand in NWE. To achieve this change, P4Y supports 44 enterprises by producing demonstrators in real life conditions of 6 P-recovery technologies for municipal sewage water.
One of these new technologies for P recovery will be developed at ULiège. The novelty of this process is that it treats directly the raw sludge instead of ashes obtained from incineration, as encountered in many processes. The idea is to directly leach the sludge with acids and to remove the solid residue. Afterwards, the aqueous liquor is purified thanks to an organic extraction to remove the heavy metals. Finally, the phosphorus is precipitated in calcium salts.
For the development of this process one key issue is to find the optimal water content at which sludge will be leached. Indeed, the water present in the sludge will dilute the acid and reduce the leaching capacity while increasing the consumption of raw acids. On another side, a dried sludge has other properties such as wettability or porosity developed during the drying. However, dry sludge may need an additional grinding step and request other technologies to handle the so formed powder.
The first leaching tests performed on sludge with different levels of dryness obtained by a combination of dewatering and convective drying are running. The influence of the drying step on the whole P recovery process will be illustrated during the presentation.
