Thixotropic behaviour of thickened sewage sludge

Abstract

The aim of the work is a description of the rheological behaviour of thickened sewage sludge. The sample of thickened sludge was collected from the wastewater treatment plant, where pressure flotation unit is used for a process of thickening. The value of dry matter of collected sample was 3.52%. Subsequently the sample was diluted and the rheological properties of individual samples were obtained. Several types of rheological tests were used for the determination of the sample. At first the hysteresis loop test was performed. The next test was focused on the time-dependency, i.e. measurement of dependence of dynamic viscosity on the time at constant shear rate. Further dependence dynamic viscosity on the temperature was performed. Then the activation energy was obtained from measured values. Finally, the hysteresis areas were counted and measured values were evaluated with use of Herschel-Bulkley mathematical model.

Rheological characteristics of municipal thickened excess activated sludge (TEAS): impacts of pH, temperature, solid concentration and polymer dose

“…Thickened activated sludge, a product of the thickening process, is a very complicated colloidal material which is composed of organic and inorganic particles. The organic part of thickened sludge we studied consists of bacteria such as Pseudomonas, Flavobacterium, Acinetobacter, Achromobacter, Actinobacteria, but also protozoa and micromycetes, while the organic matter consists mainly of solid particles of sand [3]. The rheological and flow behaviour during the thickening of this complicated non-Newtonian pseudo-plastic fluid needs to be intensively investigated so as to optimize the performance of the thickening process, minimize the cost of polymer consumption and achieve maximum possible increase in total solid concentration of thickened activated sludge for efficient performance of the anaerobic digesters.…”

Evaluation of efficiency of technologies for wastewater sludge hygienisation

“…The thickened sludge is a very complicated colloidal system, which is composed of organic and inorganic particles. Thickened sewage sludge has the similar rheological properties as activated sewage sludge or digested sewage sludge (Trávníček, Junga 2014).…”

UQ eSpace

“…Complexities include yield values, which require a certain threshold of stress below which no flow occurs, and variable functions of shear rate, where shear stress increases at a nonconstant rate with shear rate (Figure 3, left). (Cao, et al, 2016) Municipal sludge rheology is well studied, with the conclusions that shear rate and shear stress relation can be described as a yield pseudoplastic (also Bingham pseudoplastic, Herschel-Bulkley) (Hong, et al, 2016) (Cao, et al, 2016) (Baudez, et al, 2011) (Trávníček & Junga, 2014). Specifically, sludge is characterised by yield stress ( ), the shear stress below which fluid resists flow.…”

“…Another important phenomenon that characterises municipal waste sludge rheology is thixotropy (Cao, et al, 2016) (Trávníček & Junga, 2014). Thixotropy is the change in sludge rheology due to exposure to shear over time.…”

“…Creek (Kealy, 2007) digested sludge shows decrease of both yield and increase of stress with increasing temperature. The effect of temperature on rheology can be quantified and modelled as a part of viscosity, where viscosity is linked to temperature by the Arrhenius law (Trávníček & Junga, 2014).…”