Calcination Technology for Manufacturing Mineral Fertilizer Using CaO-Enriched Sewage Sludge Ash



A calcination technology was developed to directly convert sewage sludge ash (SSA) to mineral fertilizer. SSA samples, having a wide range of P2O5 content (15.6–36.0 mass%), were collected from ten different wastewater treatment plants. CaCO3 was added to SSA samples to adjust their CaO content to 45 mass%. The CaO-enriched SSA samples were then heated in an electric furnace at temperatures of 1250 or 1300 °C for 10 min. This could increase the citric acid solubility of P2O5 to 80–99%, regardless of the P2O5 content of SSA tested. In addition, approximately 75–97% of SiO2 in SSA became soluble in 0.5 M HCl after being subjected to calcination. The high citric acid solubility of P2O5 and HCl solubility of SiO2 in calcined products were attributable to the generation of silicocarnotite (Ca5[(SiO4)(PO4)](PO4)) and gehlenite (Ca2Al2SiO7), respectively. The levels of toxic heavy metals such as Cr, Ni, As, Cd, and Hg in the calcined product were below their regulation levels for calcined sludge fertilizer in Japan. The calcination of CaO-enriched SSA is potentially a useful option to increase the solubility of P2O5 and SiO2, thereby improving their plant availability, regardless of the P2O5 and SiO2 contents of SSA.


Sewage sludge ash Calcium carbonate Calcination Citric acid-soluble P2O5 


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© Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.Central Research LaboratoryTaiheiyo Cement CorporationChibaJapan

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