Enhancing waste activated sludge dewaterability by reducing interaction energy of sludge flocs

Abstract

How to efficiently improve waste activated sludge (WAS) dewaterability is a common challenge in WAS treatment and management throughout world. The interaction energy of sludge flocs is of great importance for sludge dewaterability. In this study, the relationship among the repulsive force of sludge flocs, hydrophilic/hydrophobic characteristics of sludge flocs, and sludge dewaterability have been quantitatively and qualitatively investigated based on extended Derjaguin-Landau-Verwey-Overbeek theory for the first time. The energy barrier of sludge flocs has good correlations with sludge dewaterability (p < 0.05). Trivalent cations (Al³⁺ and Fe³⁺) and Fenton's reagent reduced the interfacial free energy (ΔG) from 9.4 mJ/m² of raw sludge to -34.2 (Al³⁺), -60.5 (Fe³⁺), and -63.2 (Fenton) mJ/m², respectively, indicating that the hydrophilic surfaces of the sludge flocs converted to hydrophobic (△G < 0), and decreasing Lewis acid-base interaction energy (W_AB) of sludge flocs. In addition, most of the trivalent cations (Al³⁺ and Fe³⁺) were attached to sludge flocs, leading to neutralize negative charges and mitigate electrostatic interaction energy (W_R) of sludge flocs. The reduction of W_AB and W_R eliminated energy barrier of sludge flocs and repulsive force between sludge flocs. In comparison, monovalent (Na⁺ and K⁺) and bivalent (Ca²⁺ and Mn²⁺) cations cannot completely change the hydrophilic surface characteristic and negative charge of sludge flocs. The existed energy barrier prevented sludge flocs to agglomerate with each other, thus resulting in a worse dewaterability. This study illustrated that reducing interaction energy of sludge flocs played a critical role to improve sludge dewaterability.

Keywords: Cations; Dewaterability; Energy barrier; Extended DLVO theory; Waste activated sludge.