pH dependent phosphorus release from waste activated sludge: contributions of phosphorus speciation

• P release and speciation study from WAS were performed at pH = 2–11.
• SMT protocol was used for P speciation release tests from WAS.
• Release percentages of P fractions are made clear at different pHs.
• MINTEQ was used to simulate the phosphate and metal ions release.

For phosphorus (P) recovery from waste activated sludge (WAS), the most important step is to release P into the solution, which is greatly dependent on the pH of the solution. The contributions of different P speciation to P release amount from WAS as well as P release kinetics were investigated at different pHs, with the Standards Measurements and Testing (SMT) protocol being used for P fractions tests. The results showed that the total P in the solid (TP(s)) release percentages were 36.2% and 12.4% at pH = 2.0 and pH = 11.0, respectively. P speciation and fractions study made clear that the released P comes mainly from dissolving of inorganic P (IP) under acid condition, but from non-apatite inorganic P (NAIP) and organic P (OP) under alkaline condition. Simulation study using Visual MINTEQ indicated that the P release amount came from the experimental results is unanimous.