Concretization of Preparation Conditions for Phosphorus Fertilizer using a Sewage Sludge Ash-melting Process and Applicability Evaluation on Full-scale Agricultural Fields

The depletion of mineral phosphate as a resource is of great concern. Seeing as incinerated sewage sludge ash contains the same level of phosphorus as that of mineral phosphate, there is a possibility the ash can actually be used as a substitute. This research is aimed at clarifying the composition range of incinerated ash from sewage sludge, whereby slag fertilizer of the appropriate quality is obtained using a melting process. In addition, the safe application of the generated slag fertilizer on agricultural fields is also examined. To examine how the quality of slag fertilizer will be influenced by differences in ash composition, it was produced out of model ash. Findings showed that the slag fertilizer satisfied quality standards when the ash is composed of : 17wt% or more phosphoric acid, 15wt% or more magnesia oxide, and 40wt% or more alkali. It was also confirmed that slag fertilizer of the appropriate quality can be produced from incinerated ash at disposal stations, as long as the ash composition can be adjusted to satisfy the above-mentioned values. After the safety of heavy metals found in the slag fertilizer was examined through a content test, it was confirmed that the lead and chrome amounts satisfy values regulated by the Fertilizer Control Order. Upon analysis of crops where the slag fertilizer was applied, it was determined that lead, cadmium, and chrome amounts are below the accepted maximum limits stated in the Food Sanitation Law. This research indicates that the slag fertilizer can be applied to soils.