Phosphorus recovery from sewage sludge : Ideas for further studies to improve leaching

摘要: Development of methods to recover phosphorus will make handling sewage sludge moresustainable. In earlier studies incineration ash and SCWO-residues have been leached withacid base. Acid leaching gives a high degree recovery but releases besides phosphate alsothe main part other metals (including heavy metals). This large separation problem andgives complicated process technology. Leaching with base (NaOH) lower ofrecovery (up about 50 %) however less dissolution metals. When base, thecalcium content in the probably binds as calcium phosphate.To improve different possibilities can be studied such use two-step leachingprocess. first step acid dissolves magnesium. Treating leachate withsulphuric acid, sulphate (gypsum) is precipitated phosphoric obtained.Remaining or SCWO-residual product afterwards treated by alkaline leaching. Anotheralternative study at anaerobic conditions. Since ferrous iron(II) moresoluble than ferric iron(III) more easily dissolved metalcontamination lower.