Impact of calcination temperature, organic additive percentages, and testing temperature on the rheological behaviour of dried sewage sludge

The main objective of the present work is to evaluate the influence of calcination pretreatment (600–1,000°C), organic additive incorporation (4% methocel, 4% amijel, and 8% starch), and testing temperature (20–60°C) on the rheological flow behaviour of dried sewage sludge and sewage sludge ashes. Besides, the dependency of sludge systems rheology on total solid content (4–15%) and methocel percentage (3–6%) was also evaluated. Furthermore, characterization techniques such as thermal gravimetric analysis-differential scanning calorimetry, X-ray fluorescence, X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscopy were employed to investigate, respectively, the thermal decomposition, the chemical composition, the structural variations, the specific surface area, the surface morphology, and microstructure of sludges. The analysis of rheological characteristics according to best-fitting rheological models such as Herschel–Bulkley, Ostwald–de Waele, Cross, and Carreau models revealed that the yield stress ( ) and infinite apparent viscosity ( ) increase with an increase in TS or methocel percentage and decrease with increasing calcination or testing temperature. The strong impact of testing temperature concerning the reduction of the viscosity involves high activation energy ( ). This last criterion was used to compare the inter-particle strength of sludge systems.