Investigating the Steady-State Rheological Properties of Activated Sewage Sludge for Effective Post-Treatment

Abstract

Pipeline transportation has become an effective way to transport sludge from wastewater treatment plants due to its high transportation efficiency, low operating cost, and low environmental pollution. Before designing and optimizing the sludge-conveying pipeline, it is first necessary to analyze the rheological properties of the sludge. In this paper, activated sludge with varying volume concentrations (Cw) of 2.38%, 3.94%, and 5.39% was used as the research object. Under three temperature (T) conditions of 293 K, 298 K, and 303 K, the sludge concentration and temperature were investigated, and based on the results, a rheological model of activated sludge was established. The experimental results indicated that the upward and downward paths of the shear stress change curve were generally similar but did not overlap, and a hysteresis loop was formed between the two due to the characteristics of sludge shear thinning. The limiting viscosity of sludge with different concentrations increased with the increase in sludge concentration. This phenomenon was caused by the differences in the internal flocculent network structure of sludge with different concentrations and the different fluid flow effects. At different shear rates, the shear stress and sludge viscosity in the experiment decreased with the increase in temperature. The stability of the test sludge was weakened with the increase in temperature. Additionally, the viscosity of sludge decreased with the increase in shear rate and then stabilized, exhibiting shear thinning characteristics. The above rheological properties were described using the Bingham and Herschel–Bulkley models.