Schwertmannite-based heterogeneous Fenton for enhancing sludge dewaterability over a wide pH range

Abstract

Fe-based Fenton technology is commonly used to enhance sludge dewaterability, but it requires subsequent neutralization, resulting in excessive chemical consumption. In this study, we investigated the feasibility of using schwertmannite-composited Fe₃O₄ (Sch/Fe₃O₄) as a heterogeneous Fenton catalyst to enhance sludge dewaterability without the need for pH adjustment. A high reduction efficiency of sludge specific resistance to filtration (94.4%), moisture content (11.4%) and bound water (45.5%) after Sch/Fe₃O₄ +H₂O₂ treatment at initial pH 7.5 were obtained, suggesting that Sch/Fe₃O₄ +H₂O₂ posed good dehydration performance without any acidification. SO₄^2- and H⁺ generation in Sch/Fe₃O₄ system played an important role in sludge pH decrease, which facilitated sludge cell lysis, intracellular water release, and provided a suitable pH for Fenton reaction. Reactive species (•OH, •O₂^-, and ¹O₂) from Sch/Fe₃O₄ +H₂O₂ could effectively destroy sludge EPS, releasing more bound water. Additionally, the negatively charged compounds were neutralized by dissolved Fe²⁺/Fe³⁺. Sch/Fe₃O₄, as a skeleton builder, rearranged the dissociative sludge flocs to improve the incompressibility and permeability of sludge cake. Finally, sludge treated with Sch/Fe₃O₄ +H₂O₂ achieved organic matters reserve, heavy metals reduction, further benefiting the final disposal.

Keywords: Heterogeneous Fenton; SO(4)(2-); Schwertmannite; Sludge dewatering.