The Evaluation of Sewage Sludge Incinerator Ash and Recovered Phosphorus Compound for Material Recycle

Abstract

To effectively use sewer system resources, reducing phosphorus content in incinerator ash was carried out in order to improve the quality of the ash when used as raw material for cement. The phosphorus removed from the ash is recovered as calcium phosphate. From the result measured the constituent of incinerator ash before and after the alkali elution, it was proved that phosphorus is eluted by 46% in an alkali solution. Although the mass of the ash after the elution decreased 14%, this was proved to be attributed to that phosphorus and aluminum can be selectively eluted to the solution. The phosphorus compound recovered as calcium phosphate contains phosphorus by 12%, and is 100% citric-acid soluble. With respect to toxic heavy metals specified by the Fertilizer Control Law, the contents of Cd and As were within the specifications, while Ni, Cr, Pb and Hg were not detected using the available chemical analyses. When the phosphorus compound was used as fertilizer, it was confirmed that the recovered compound is harmless to plant matter and there was no accumulation of heavy metals in crops. The contents of Mn and Zn were lower than crops grown using marketed fertilizer (superphosphate of lime and fused phosphate). Using an eggplants, the same effect as fertilizer was acquired with a quantity of recovered compound equal to half the amount of superphosphate of lime and fused phosphate. It was confirmed that the number of crops and crop yields can be increased by using a greater quantity of the recovered compound.