Abstract
The concentrations of the main and hazardous components of 26 sewage sludge ashes collected from 14 incineration facilities were determined in order to evaluate the practicality of making phosphate fertilizer from sewage sludge ash. Results indicated that sewage sludge ash is one practical source for making fused phosphate fertilizer. However, due to the high concentrations of hazardous components in the sewage sludge ashes, a fusing process for sewage sludge ashes was needed to remove the hazardous components from them.
Two sewage sludge ashes with appropriate amounts of additives (MgO and CaO) were subjected to fusing processes in an electric resistance furnace, and then crushed by immediate water-cooling. The fused phosphate fertilizer made from the two sewage sludge ashes had high solubilities of over 95% for P2O5 and MgO in citric acid. The mol ratios of P2O5, MgO, and CaO in the fused phosphate fertilizer were comparable to those of commercial fused phosphate fertilizers (P2O5:MgO:CaO=1:2.5-3.5:2.5-3.5). In addition, except for copper, the concentrations of hazardous components in the fused phosphate fertilizer were lower than that before the fusing processes and lower than the Japanese standard values.
