Phosphate Removal from Municipal Wastewater with Low Lime Dosage

The potential use of lime in the pre-treatment of municipal wastewater before the biological process was investigated. The aim of this work was to develop an equilibrium model for predicting optimal treatment conditions to assure satisfactory P removal efficiency and to minimize carbonate precipitation, that causes high lime dosage and excessive sludge production. Model calibration was performed with the results of lime addition tests to actual sewage. The proposed equilibrium model for lime addition to municipal wastewater assumes phosphate and carbonate solubility controlled by metastable Ca4H(PO4)3 and amorphous CaCO3, respectively. Model predictions suggest that lime addition up to pH 9 may assure efficient removal of phosphorus and prevent carbonate precipitation, even in wastewater with high alkalinity content.