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a Dep. of Soil and Water Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, The Hebrew Univ. of Jerusalem, Rehovot 76-100, Israel
b Cooperative Inst. for Marine and Atmospheric Studies, Rosenstiel School of Marine and Atmospheric Sciences, Univ. of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149
* Corresponding author (Shenker{at}agri.huji.ac.il).
Received for publication May 3, 2007. Three chemicals—ferrous sulfate (FeSul), calcium oxide (CaO), and aluminum sulfate (alum)—were applied at different rates to stabilize P in fresh, anaerobically digested biosolids (FBS) obtained from an activated sewage treatment plant. A modified Hedley fractionation procedure was used to assess P forms in these sludge-borne materials and in a biosolids compost (BSC) prepared from the same FBS. Each biosolids material exhibited a unique pattern of P distribution among fractions. The most available P forms, namely: (i) water-soluble P (WSP); (ii) membrane-P; and (iii) NaHCO3–P, were stabilized by small rates of each of the chemicals; but the P transformation into more stable forms depended on the type of chemical added. The stabilized P forms were enhanced by high rates of CaO and FeSul, but were reduced by high rates of alum. The organic P (Po) in the first three fractions of the FeSul- and alum-stabilized biosolids was enhanced by the chemical addition, and Po transformation from NaOH-Po into NaHCO3–Po was found in calcium-stabilized biosolids. A positive relationship was found between NaHCO3–Po and the NaHCO3–extracted organic C in all chemically stabilized biosolids. One-step extraction by NaHCO3 or NaOH underestimated P extraction compared to the stepwise extraction. The reported results are consistent with solid-state P speciation reported earlier and contribute important information for optimizing biosolids stabilization to reduce P loss after incorporation in soils and for maximizing soil capacity to safely store pre-stabilized biosolids.
Abbreviations: alum, Al-sulfate BSC, biosolids compost Co, organic carbon FeSul, ferrous sulfate FBS, fresh dewatered anaerobically digested biosolids Pi, inorganic phosphorus Po, organic phosphorus WSP, water-soluble P
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