Abstract
The amount of excess sludge produced in municipal wastewater treatment plants in Japan is increasing every year as the urban population increases. The phosphorus in the excess sludge could be hopeful phosphorus resource since phosphate rock is being exhausted all over the world today. Japan imports much phosphorus from abroad every year but much of it is discharged out as excess sludge. Therefore, the solubilization process, one method of recovering phosphorus from the sludge, could be a promising solution. In this study, the subcritical water process, a new technology that solubilizes sludge under subcritical conditions, was applied before the phosphorus in the sludge was recovered with magnesium ammonium phosphate (MAP) process. As a result, the solubilization rate of excess sludge achieved was approximately 80%. In addition, about 94-97% of the phosphorus could be recovered.
