Release of phosphorus from ash produced by incinerating waste activated sludge from enhanced biological phosphorus removal

A technical problem involved in the phosphorus removal using the enhanced biological phosphorus removal (EBPR) process is disposal of the phosphorus rich waste sludge. There are possibilities that any phosphorus in the disposed sludge would release to water environment. If the release occurs, it will nullify the efforts made in wastewater treatment. This paper reports results of a preliminary study made to examine the fate of phosphorus in the ash is produced by incinerating waste sludge from a laboratory unit of the EBPR process. A large part of phosphorus in the ash released in a relatively short time. Most of the phosphorus released at a normal temperature was apparently polyphosphate. The release was very fast at a high temperature. The finding suggests that hot water elutriation could be used as a means of recovering phosphorus from the ash. It was also suggested that the release could be prevented by adding an appropriate amount of iron to the sludge to be incinerated. The released phosphorus was susceptible to precipitation by metals, especially iron.