Phosphorus recycling from secondary materials like sewage sludge ashes offers an interesting alternative to imported mineral phosphates. However, a separation of P from the bulk ash is normally required, due to its low plant availability and the presence of heavy metals. More than 80% of P was recovered from incineration sewage sludge ashes in the past using a two-compartment electrodialytic cell. In contrast, the recovery was below 30% for ashes from low-temperature gasification using the same setup, due to the high presence of Al- and Fe(III)-P bindings. In the present study, an electrodialytic process combining sequentially a pair of two-compartment cells allowed a recovery of up to 70% of phosphorus from these ashes. The use of a second cell, where the ashes were treated in an alkaline pH, allowed the P solubilisation from aluminium and ferric phosphates and its separation from most metals as they became insoluble. Furthermore, the ratio of Al, Fe, Mg and most heavy metals to P was comparable to wet process phosphoric acid. Therefore, this sequential process was found to be suitable to recycle P and potentially use it in the production of common fertilizers like diammonium phosphate.
- Heavy metals
- Low-temperature gasification
- Sewage sludge ash
Parés Viader, R., Erland Jensen, P., Ottosen, L. M., Ahrenfeldt, J., & Hauggaard-Nielsen, H. (2017). Sequential electrodialytic recovery of phosphorus from low-temperature gasification ashes of chemically precipitated sewage sludge. Waste Management, 60, 211-218. https://doi.org/10.1016/j.wasman.2016.11.030