Phosphorus recovery from sewage sludge via incineration with chlorine-based additives

Phosphorus (P) is an essential nutrient for all organisms, and the recovery of P from sewage sludge (SS) has been the focus of recent research. The effect of temperature and chlorine-based additives (MgCl2 and CaCl2) on P recovery and heavy metal (Cu, Zn, and Cr) removal during SS incineration were investigated. The results showed that temperature and chlorine-based additives increased the P fixation and improved the P-bioavailability. The fixation rate of P reached a maximum of 98.5% in SS using 3% Mg (MgCl2) at 900 degrees C and 97.8% in SS using 5%Ca (CaCl2) at 800 degrees C. Additionally, the mechanism of P associated with aluminum oxides/hydroxides (Al-P) transferring to that of magnesium oxides/hydroxides (Mg-P) and calcium oxides/hydroxides (Ca-P) was also investigated. The results indicated that Mg-3(PO4)(2) was formed via the reaction between AlPO4 and MgCl2 during incineration, which increased the P solubility in 2% citric acid. When AlPO4 was incinerated with CaCl2, Ca2PO4Cl which has a higher P-bioavailability than AlPO4 was formed. In addition, the mass fraction and leaching concentration of Cu and Zn in treated SS greatly decreased during SS incineration, while no reduction in Cr. These findings suggest that chlorine-based additives can be used to treat SS at high temperatures to obtain an ideal material for P-fertilizer production. (C) 2019 Published by Elsevier Ltd.