Heavy Metal Removal and Phosphorus Retention Using the Fenton Process for Sustainable Recycling of Anaerobically Digested Sewage Sludge

Abstract

Heavy metal removal from anaerobically digested sewage sludge and phosphorus (P) retention in the sludge were investigated through batch experiments using H₂O₂ and Fe₂(SO₄)₃ as the agents for oxidizing insoluble metallic compounds under acidic condition at pH 2.5. The addition of H₂O₂ to the sludge eluted Cd, Cu and Zn from the sludge more effectively than that of acid only. The initial concentrations of H₂O₂ required for the maximum elution efficiency were 1 g/L for Cd and Zn and 5 g/L for Cu. The addition of ferric ion (Fe(III)) also improved the elution efficiency of Cu. Ferric iron addition under the initial H₂O₂ concentration of 0.2 g/L gave rise to a more effective elution of Cu from the sludge than that in the absence of H₂O₂ or Fe(III). The addition of acid only or both acid and H₂O₂ caused the elution of P together with heavy metals. However, the addition of Fe(III) (1 g/L Fe) could retain P in the sludge, most of which was present as a slow-acting P fertilizer.