Insights into Cetyl Trimethyl Ammonium Bromide Improving Dewaterability of Anaerobically Fermented Sludge

Abstract

Cetyl trimethyl ammonium bromide (CTAB), as a promising sludge dewatering conditioner, its underlying dewatering mechanism has not been deeply understood so far. This study therefore aims to fully investigate how CTAB improves sludge dewaterability. Experimental results showed that capillary suction time, specific resistance to filtration, the water content of anaerobically fermented sludge (AFS) cake and bound water content respectively decreased from 164.1 ± 10.7 s, 1.90 ± 0.05×10 12 m/kg, 97.36 ± 0.12%, and 1.39 ± 0.03 mg/g DS to 32.1 ± 1.4 s, 0.18 ± 0.01×10 12 m/kg, 70.55 ± 0.21%, and 0.30 ± 0.01 mg/g DS under 75 mg/g TSS CTAB conditioning. Mechanism revelations showed that CTAB conditioning neutralized the negative charges on EPS surface and reduced repulsive force between sludge flocs, improved the hydrophobicity of sludge cells, and damaged the outer membrane of sludge cells. The presence of CTAB also decreased the concentrations of [[EQUATION]] , humic acid, and proteins in the liquid phase through electrostatic attractive or hydrophobic interactions. All these CTAB-caused variations in either sludge cells and liquid phase caused increases in rigid settable solids proportion and the relative hydrophobicity but decreases in the small particles proportion, turbidity of filtrate, and viscosity of AFS, thereby enhancing AFS dewaterability. The findings deepen our understanding of CTAB affecting sludge dewatering and also may guide engineers to exploit promising strategies to facilitate sludge dewatering in the future.

Keywords: Anaerobic fermentation, fermented sludge, sludge dewatering, surface energy, cetyl trimethyl ammonium bromide