Removal of phosphate from municipal sewage by high gradient magnetic separation

Abstract

The removal of phosphate from municipal sewage by high gradient magnetic separation using aluminium sulphate as precipitating agent and Fe₃O₄ as seeding material was studied. The effects of aluminium sulphate, Fe₃O₄, magnetic field intensity, pH value and flow-rate of sewage on phosphorus removal rate were investigated. The results show that addition of 200 mg/L Al₂(SO₄)₃ · 18H₂O and 300 mg/L Fe₃O₄, magnetic field intensity of 200 kA/m, pH value of 4.5 – 7.0 and flow-rate of 6.15 cm/s are both efficient and economic technical parameters for removal of phosphate. The pH value has a tremendous effect on the removal of phosphate. In the pH range of 4.5–7.0, more than 95% phosphate can be removed. Theoretical analysis indicates that the solubility of AIPO₄ is minimum at pH 4.0 – 7.0 and the electrostatic attractive force between AIPO₄ and Fe₃O₄ is maximum at pH 4.5 – 6.5.

Keywords

removal / phosphate / municipal sewage / high gradient magnetic separation