Characterization of Phosphorus Species in Biosolids and Manures Using XANES Spectroscopy

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Abstract
Identification of the chemical P species in biosolids or manures will improve our understanding of the long‐term potential for P loss when these materials are land applied. The objectives of this study were to determine the P species in dairy manures, poultry litters, and biosolids using X‐ray absorption near‐edge structure (XANES) spectroscopy and to determine if chemical fractionation techniques can provide useful information when interpreted based on the results of more definitive P speciation studies. Our XANES fitting results indicated that the predominant forms of P in organic P sources included hydroxylapatite, PO4 sorbed to Al hydroxides, and phytic acid in lime‐stabilized biosolids and manures; hydroxylapatite, PO4 sorbed on ferrihydrite, and phytic acid in lime‐ and Fe‐treated biosolids; and PO4 sorbed on ferrihydrite, hydroxylapatite, β‐tricalcium phosphate (β‐TCP), and often PO4 sorbed to Al hydroxides in Fe‐treated and digested biosolids. Strong relationships existed between the proportions of XANES PO4 sorbed to Al hydroxides and NH4Cl‐ + NH4F‐extractable P, XANES PO4 sorbed to ferrihydrite + phytic acid and NaOH‐extractable P, and XANES hydroxylapatite + β‐TCP and dithionite–citrate–bicarbonate (DCB)‐ + H2SO4‐extractable P (r2 = 0.67 [P = 0.01], 0.78 [P = 0.01], and 0.89 [P = 0.001], respectively). Our XANES fitting results can be used to make predictions about long‐term solubility of P when biosolids and manures are land applied. Fractionation techniques indicate that there are differences in the forms of P in these materials but should be interpreted based on P speciation data obtained using more advanced analytical tools.
Funding Information
  • U.S. Department of Energy, Division of Materials Science and Division of Chemical Services