Rheological Behavior of Wastewater Sludge Following Cationic Polyelectrolyte Flocculation

Abstract

The rheological characteristics of the wastewater sludge were investigated by using a Haake Rheostress RS 75 rheometer. The shear creep compliance experiments and the dynamic viscosity measurements were conducted. The shear creep compliance experiments indicate the addition of polymer coagulants to the sludge samples will form more rigid structures. The elastic solid-like behaviors were always observed in the samples with polymers. The Voigt model was successfully employed in modeling the viscoelastic retardation behavior of sludge samples in the shear creep compliance tests. Moreover, the dynamic viscosity curves of the sludge samples with/without polymer could be described by the power law model of Ostwald and de Waele at the medium shear rates, ca. 100–300 s⁻¹. Consequently, addition of polymer to the sludge tends to extend the applicable ranges of the shear rates for the power law model as well as to decrease the power law index.

Keywords:

• Flocculation
• Rheology
• Sludge
• Viscoelastic

ACKNOWLEDGEMENTS

The National Science Council of Taiwan, ROC, financially supported this work. The authors thank Professor S. B. Chen of the Department of Chemical and Environmental Engineering at the National University of Singapore for his generosity in letting us access his Haake Rheostress RS 75 rheometer.