Acidification and alkali precipitation for phosphorus recovery from municipal digested sludge

Municipal digested sludge (MDS) has considerable phosphorus content that is between 1% and 15% in dry matter and it is a potential source for phosphorus recovery. A high amount of MDS is generated from sewage treatment plants in large cities and has many environmental concerns with its organic and inorganic constituents. In this study, phosphorus was recovered by precipitation with Ca(OH)₂ and NaOH. Acid pretreatment was applied to MDS with H₂SO₄ and 58.7% of phosphorus was extracted from the solid phase to the liquid phase at pH 2. Up to 99% of dissolved phosphorus in the liquid phase was recovered with Ca(OH)₂ and NaOH. Almost similar phosphorus precipitation rates were achieved with both bases but higher phosphorus contents (17% as P₂O₅) in precipitates were obtained by NaOH. The product obtained in this study can serve as a high-quality raw material substitute for the low-grade phosphate rocks (<15% P₂O₅) commonly utilized in the phosphate industry. Furthermore, this research presents a practical, environmentally friendly and cost-effective approach for sustainable sludge management and phosphorus production.