Rheological characterization of sludge in divided granular-like and pasty states using a granular rheometer

Abstract

Structural changes during sludge treatments impact flowability and raise severe technical issues. In this study, the sludge consistency is analysed using the thread rolling test.Transition from pasty to granular-like material occurs at a total solid (TS) content of 43 wt. %. A granular rheometer is used to characterize sludge's flowability over a wide range of TS content. The typical powder-like behaviour is recorded whatever the TS contents. All the shear stresses/consolidations curves exhibit a linear increase, highlighting the contribution of frictional interactions. Fitting the Mohr-Coulomb failure criterion to these curves emphasizes a substantial rise of frictional interactions from 43 wt.%. Flow functions are determined from the Mohr's circle stress analysis. According to the classification of powder flowability, sludge behaviour is analogous to that of very cohesive powders for 25.5 < TS < 43 wt.% while for lower and higher TS contents, the material behaves like cohesive powders.