Present phosphorus (P) recovery technologies mainly contain P recovery from sludge liquor or ash. These types of technologies are suitable for large wastewater treatment plants (WWTPs) with enhanced biological phosphorus removal (EBPR), digestion and/or incineration. In Finland and other Nordic countries, strict P discharge limits require chemical precipitation, thus EBPR alone is not sufficient. Ammonium recovery from wastewater, on the other hand, is not so often discussed. However, recovery from WWTP reject waters would decrease the energy demand of ammonium synthesis by Haber-Bosh technology and the energy demand of the WWTP's biological process. Helsinki Region Environmental Services Authority (HSY) has developed a new process called RAVITA whereby P and nitrogen recovery are combined in order to produce phosphoric acid (H3PO4) and ammonium phosphate (NH4)3PO4. Furthermore, in this process metal salt used in precipitation is recovered. The research was carried out on pilot (1,000 population equivalent) and laboratory scales. The objectives of this article are to explain the principles of the RAVITA process and give the first results of processing and production of chemical sludge.

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