Sequential electrodialytic recovery of phosphorus from low-temperature gasification ashes of chemically precipitated sewage sludge

Raimon Parés Viader, Pernille Erland Jensen, Lisbeth M. Ottosen, Jesper Ahrenfeldt, Henrik Hauggaard-Nielsen

Research output: Contribution to journalJournal article


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.
Original languageEnglish
JournalWaste Management
Pages (from-to)211-218
Number of pages7
Publication statusPublished - 2017


  • Electrodialysis
  • Heavy metals
  • Low-temperature gasification
  • phosphorous
  • Sewage sludge ash

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