Behavior of fast and slow phosphorus release from sewage sludge–derived biochar amended with CaO

Liu, Qiang; Li, Jiayi; Fang, Zheng; Liu, Yangyang; Xu, Yunfeng; Ruan, Xiuxiu; Zhang, Xiaolei; Cao, Weimin

Behavior of fast and slow phosphorus release from sewage sludge–derived biochar amended with CaO

2021

The pyrolyzation of sewage sludge (SS) could efficiently transform inherent phosphorus (P) into bioavailable phosphate forms, which endows SS-derived biochar (SSB) the potential as a soil fertilizer. However, the details about the release behavior of P in SSB have not been systematically investigated. This study evaluated the fast and slow P releasing behaviors from SSB and CaO-amended SSB prepared under different pyrolysis temperature. The higher pyrolysis temperature and CaO addition could enhance the conversion of non-apatite inorganic phosphorus (NAIP) into more bioavailable apatite inorganic phosphorous (AP). Acidic and alkaline conditions were favorable for the fast release of P from SSB. Higher ionic strength condition gave greater releasing amounts of TP and the SO₄²⁻ facilitating a rapid release of TP than those for Cl⁻ and NO₃⁻. SSBs with CaO addition showed a much slower TP release than those without CaO both in fast release (24 h, with CaO: 0.05~0.4 mg TP g⁻¹ SSB, e.g., without CaO 0.5~5 mg TP g⁻¹ SSB) and slow release tests (21 days, with CaO: 1.2~4.1 mg TP g⁻¹ SSB, e.g., without CaO 1.8~5.7 mg TP g⁻¹ SSB). Ortho-P release was more remarkable for the SSB amended with CaO (~54% of TP), which was likely due to the formation of orthophosphate. The results of this study suggested that SSB prepared by high pyrolysis temperature and CaO addition had high potential as a slow P-releasing fertilizer for the soil.

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