Characterization of Phosphorus Species in Biosolids and Manures Using XANES Spectroscopy

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 (r ² = 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. Copyright © 2006. American Society of Agronomy, Crop Science Society of America, Soil Science Society . ASA, CSSA, SSSA