Identification of the rheological properties of mechanically dewatered sewage sludge from uniaxial compression tests
Résumé
Sewage sludge is one of the largest by-product recovered in a municipal wastewater treatment plant. Thickening, conditioning and mechanical dewatering are necessary treatments to remove the moisture, which reduces the volume, improves the handling, facilitates the storage and decreases the transport costs for further valorization. However, sludge processing, reuse and disposal are complex technical problems in the field of wastewater treatment. In particular, the complex transition between solid and fluid states is challenging in terms of pumping, land spreading and drying (Baudez 1998). Therefore, the characterization of rheological behavior of mechanically dewatered sewage sludge is essential to optimize the processing design.
Few publications are devoted to the characterization of pasty sludge having total solid content (TS) higher than 15%. Indeed, classical methods are not suitable for the determination of the rheological properties of these highly concentrated sludges. However, literature shows that conventional uniaxial compression tests are widely used in various fields of research for characterizing similar pasty, gelatinous or solid-like materials.
In this work, we have developed an entire methodology - from experiment through modelling and on to simulation - to describe the deformation and flow of a mechanically dewatered sewage sludge (i.e. at TS around 20%) under a given mechanical load. This methodology is carried out by implementing uniaxial compression, so that it can be applied to sludge behaving as a soft solid with TS between the liquid limit (evaluated by a slump test, as adapted by Baudez (2002) to ensure that the sludge sample can not flow under its own weight by gravity) and the plastic limit (ASTM D 4318 to ensure that it can be considered as a continuous medium).