Electrodialytic extraction of phosphorus from ash of low-temperature gasification of sewage sludge

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

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Low-temperature gasification allows the production of energy from biomass with high contents of low melting point compounds, like sewage sludge, and the recycling of the nutrients as P from the resulting ashes as renewable fertiliser. Major drawbacks are, however, the presence of heavy metals and the low plant-availability of Al- and Fe- phosphate compounds in the gasification ashes. In the present research, the feasibility of a 2-compartment electrodialytic (ED) setup for P separation from Al, Fe and heavy metals in two different low-temperature gasification ashes was investigated. One ash was from gasification of sewage sludge where P was precipitated with Fe and Al salts, from which it was possible to extract up to 26% of the P. The other ash was from co-gasification of a mixture of biologically precipitated sewage sludge and wheat straw pellets. More promising results were obtained with this ash, as up to 90% of the P was extracted from the ashes. For both ashes, P was extracted by ED in acidic aqueous solutions with ratios of Fe, Al and each heavy metal to P considerably below the values found in the initial ashes. Therefore, the 2-compartment ED cell technology was proved as possible method to separate Al, Fe and heavy metals from P for low-temperature gasification ashes
Translated title of the contributionElektrolytisk ekstraktion af fosfor fra lav-temperatur forgasningsaske produceret på spildevandsslam
Original languageEnglish
JournalElectrochimica Acta
Pages (from-to)100-108
Publication statusPublished - 2015


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

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