Temperature effect on shear flow and thixotropic behavior of residual sludge from wastewater treatment plant

The temperature and shear rate effects on rheological behavior of residual sludge from wastewater treatment plant was investigated in this work. The model of Herschel–Bulkley was used to fit the shear rate dependence of the shear stress. The temperature increase induced not only an increase in the yield stress and the flow index of sludge but also a decrease of the consistency index of sludge. The temperature dependence of limit viscosity at high shear rate of the residual sludge was fitted by an Arrhenius equation. For constant shear rate applied on the sludge at 20 °C a thixotropic behavior was observed and analyzed using a modified model of Herschel–Bulkley in which a structural parameter λ was included in order to account for the time-dependent effect.