Beschreibung:
<jats:p>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) NaHCO<jats:sub>3</jats:sub>–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 (P<jats:sub>o</jats:sub>) in the first three fractions of the FeSul‐ and alum‐stabilized biosolids was enhanced by the chemical addition, and P<jats:sub>o</jats:sub> transformation from NaOH‐P<jats:sub>o</jats:sub> into NaHCO<jats:sub>3</jats:sub>–P<jats:sub>o</jats:sub> was found in calcium‐stabilized biosolids. A positive relationship was found between NaHCO<jats:sub>3</jats:sub>–P<jats:sub>o</jats:sub> and the NaHCO<jats:sub>3</jats:sub>–extracted organic C in all chemically stabilized biosolids. One‐step extraction by NaHCO<jats:sub>3</jats:sub> 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.</jats:p>