Phosphorus recovery from digested sewage sludge as MAP by the help of metal ion separation

This study was designed to solve metal ion influence problem on phosphorus recovery from digested sewage sludge as MAP. The experimental steps were proceeded to maximize MAP production and its quality. Used experimental steps were: (a) Acidic dissolution of phosphorus, (b) Removal of metal ions from phosphorus rich water phase, (c) Recovery of phosphorus as MAP, (d) Separation of MAP. All digested sewage sludge samples were taken from Stuttgart University sewage treatment plant for research and education (LFKW). Four different forms of LFKW digested sewage sludge were used as feeding sample. These were: original digested sludge, diluted digested sludge, centrifuged digested sludge and incinerated digested sludge. A Donnan membrane unit having a Nafion 117 (DuPont) cation exchange membrane was used to remove metal ions from the samples used. Highest metal ion removal efficiencies, which were 98%, 97%, and 80% for Al, Ca and Fe ions, respectively, were obtained from incinerated digested sludge run. Incinerated digested sludge run was used as preliminary step for MAP production and high quality MAP was produced. Produced MAP fulfils all requirements related with Düngemittelverordnung 2003 and it could be used as a fertilizer in Germany.