Variation in phosphorus speciation of sewage sludge throughout three wastewater treatment plants: Determined by sequential extraction combined with microscopy, NMR spectroscopy, and powder X-ray diffraction

Qian Wang, Chitra S. Raju, Nina Almind-Jørgensen, Mikkel Laustrup, Kasper Reitzel, Ulla Gro Nielsen*

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The variation in phosphorus (P) speciation of sewage sludge throughout three wastewater treatment plants (WWTPs) was obtained by combining sequential P extraction with optical and scanning electron microscopy (SEM), chemical analyses, powder X-ray diffraction (PXRD), and 27Al and 31P nuclear magnetic resonance (NMR) spectroscopy. The WWTPs combine chemical P removal (CPR) and enhanced biological P removal (EBPR) and were compared to understand the effect of iron (Fe) dosing with and without codosing of aluminum (Al) and thermal hydrolysis on the P speciation. 31P NMR showed comparable inorganic orthophosphate (ortho-P, 53-60% of total P) and organophosphate (organic-P, 37-45%) in primary sludge, whereas polyphosphate (poly-P, 23-44%) from poly-P accumulating organisms (PAOs) was mainly observed in the secondary sludge. Inorganic ortho-P (90-98%) dominated after anaerobic digestion, which degraded poly-P and most organic-P. The inorganic ortho-P was mainly Fe bound P (Fe-P), especially after anaerobic digestion (71%). Codosing of Fe and Al led to two comparable fractions: Fe-P (38%) and P sorbed on amorphous Al (hydr)oxides (38%). Vivianite was identified in all samples by microscopy and chemical extraction but was PXRD amorphous in 12 out of 17 samples. Thus, vivianite may be more common in sewage sludge than previously known.

Original languageEnglish
JournalEnvironmental Science and Technology
Volume56
Issue number12
Pages (from-to)8975-8983
ISSN0013-936X
DOIs
Publication statusPublished - 21. Jun 2022

Keywords

  • P and Al NMR
  • analytical chemistry
  • chemical P removal
  • P recovery
  • phosphorus speciation
  • vivianite

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