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.