In the attached link there is the article, by Donatello and Cheeseman (2013), where there is the list of different studied methods for recovering material and recycling ISSA (Incinerate Sewage Sludge Ashes).
They have been studied experimentally. I would be glad to know any full scale example and industrial application.
http://www.sciencedirect.com/science/article/pii/S0956053X13002559