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Low-temperature-steam activation of phosphorus in biochar derived from enhanced biological phosphorus removal (EBPR) sludge
- Qian, Tingting, Wang, Li, Le, Chencheng, Zhou, Yan
- Water research 2019 v.161 pp. 202-210
- adsorption, biochar, calcium, environmental factors, ionic strength, pH, phosphorus, phosphorus fertilizers, pyrophosphates, sludge, soil, temperature
- The property and release behavior of phosphorus in biochar derived from enhanced biological phosphorus removal sludge (EBPR sludge) were investigated. A low-temperature-steam (LTS) activation method was developed to increase the P availability in the biochar. The results demonstrate that the P content in the biochar is comparable to that in typical P fertilizers. The biochar contained a considerable portion of fast-release P. Polyphosphates (poly-P) were the predominant P species in the biochar. LTS greatly improved P availability in biochar produced at 700 °C by hydrolyzing insoluble poly-P to soluble pyro-P and ortho-P. In addition, the presence of Ca2+ could greatly reduce the P-release from biochar produced at lower temperature, e.g. 400 °C, due to that Ca2+ could facilitate the precipitation/adsorption of orthophosohates/pyrophosphates released from the low temperature biochars. Such phenomena was not observed with high temperature biochar, as the soluble poly-P released from 700 °C biochar could complex with Ca2+ rather than precipitated with it. Other environmental conditions, i.e., environmental pH, ionic strength of the soil porewater, and presence of low-molecular-weight acid, only had minor or negligible effects on the P-release of most studied biochars. This study concludes that LTS-activated-700 °C biochar could be a promising P fertilizer given its high, rapid, and unaffected P-release under various environmentally relevant conditions.