Electrodialytic Separation of Phosphorus and Heavy Metals from Two Types of Sewage Sludge Ash

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During sewage sludge incineration phosphorus (P) is retained in the ash in a form not directly available to plants. As P is a sparse resource, it is important to develop techniques for recovery of P from incinerated sewage sludge ashes (ISSA). Heavy metals are concentrated in ISSA and separation of P and heavy metals is required. The present work is an experimental screening of a new combination of acid extraction and electrodialysis–electrodialytic separation (EDS) for simultaneous P recovery and removal of heavy metals. Experiments were conducted with two different ashes; rich in Fe or Al. The separation method was best suited for the Fe-rich ash, where it was possible to separate P into one processing solution, heavy metals (Cu, Zn, Ni, Pb) into another, keeping the ash suspended in a third solution (which though still contained P after 1 week of EDS). For the Al rich ash, the separation was not similarly encouraging. The high release of Al during the extraction influenced the speciation of P and negatively charged P complexes were not prevailing. On the contrary to Al, the Fe containing ash particles were insoluble so Fe did not interfere with P speciation and separation after extraction.
Original languageEnglish
JournalSeparation Science and Technology
Issue number12
Pages (from-to)1910-1920
Number of pages11
Publication statusPublished - 2014


  • Phosphorous
  • Urban mining
  • Heavy metals
  • Sewage sludge ash
  • Electrokinetics
  • Electrodialysis

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