Only at 600 ☌ P-CA and available P were affected by the temperature, where the P-CA increased and available P decreased. The P-NAC content reached a maximum (79% of TP) at 300 ☌ and then declined at higher temperatures. Nevertheless, the solubility of biochar-P in the extractants presented different trends with temperature. The total P content increased with pyrolysis temperature (≥300 ☌). Higher pyrolysis temperature resulted in increased pH, BET surface area, pore volume, ash, fixed carbon, Ca, Mg and Zn contents, as well as formation of stable Ca minerals (calcite and oxalate). Physicochemical properties and extractable P were strongly affected by pyrolysis temperature. Available phosphorus content was extracted using 2% citric acid (P-CA), neutral ammonium citrate + water (P-NAC) and Mehlich 1 solution (0.0125 mol L −1 H 2SO 4 + 0.050 mol L −1 HCl). Additionally, the relationships between extractable P and physicochemical properties were evaluated for SSB obtained over a wide range of temperatures (200 ☌ 300 ☌ 500 ☌ and 600 ☌). In the present study we evaluated P solubility and bioavailability using different chemical extractants. This hinders the prediction of P bioavailability. However, SSB presents a diversity of P compounds, mainly in mineral forms with different degrees of chemical stability. Sewage sludge-derived biochar (SSB) is a phosphorus (P) source with potential to replace soluble P fertilizers.
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