Rheological Properties of Municipal Sewage Sludge: Dependency on Solid Concentration and Temperature

Building centralized sludge treatment plants are a beneficial way to properly treat dewatered sludge from wastewater treatment plants, in which excess sludge haven’t been treated properly. Thus, as the directly control parameter in municipal sludge treatment process, sludge rheological data are required for optimized design and operating in pumping and mixing. The main objective of this study was to investigate the rheology of municipal wastewater sludge, especially the different rheological behaviour for sludge from sludge treatment process-stream with or without anaerobic digestion. Besides, the dependency of sludge rheology on solid concentration and temperature and the predictive capability of rheological models were also investigated. The results revealed that the sludge samples showed shear-thinning and thixotropic characteristics. It was found that, irrespective of the existence of anaerobic digestion, sludge samples all performed a qualitatively same rheological behaviour, while they quantitatively behaved differently. It was also proved that both solid concentration and temperature effected sludge rheology critically. The best correlation between limit viscosity or the value of sludge thixotropy and solids concentration were determined by regression analysis. In this study, the Ostwald de Vaele model fits the experimental data best.