title: A uniaxial cyclic compression method for characterizing the rheological and textural behaviors of mechanically dewatered sewage sludge.
abstract: The mechanically dewatered sewage sludge with total solid content around 20% on a weight basis is very similar to yield stress fluid, its complex transition between solid and fluid states is not perfectly reversible and especially challenging in terms of pumping, land spreading and drying. To characterize the rheological and textural properties of highly concentrated sludge, a specific methodology based on uniaxial single and cyclic compression tests is developed. Three types of sludge samples (fresh original, fresh premixed and aged original ones) are extruded into cylinders and pressed between two parallel plates using a material testing machine. In single compression, the bioyield point beyond which the sludge fractures is around 7.3 kPa with true strain equal to 0.21. The cyclic compression tests reveal that the sludge behaves as a viscoelastic body when the true strain is smaller than 0.05 and as a visco-elasto-plastic once exceeding the yield stress. The elastic module is around 78 kPa; the viscosity is deduced, in the order of magnitude 104-105Pa·s and the yield stress is estimated about 4 kPa. In the unloading phase, the sludge behaves again as a viscoelastic body with clear hysteresis. With the increase of compression speed, the viscosity declines, which confirms that the sludge is a shear-thinning material. The yield stress and the bioyield increase with compression speed, but it does not induce extra internal damage in the samples since the resilience and the cohesiveness are unaltered. The reliability and sensitivity of the method is justified by highlighting the changes of sludge behavior due to aging and premixing effects: both decrease the strain energy density, but do aggravate the adhesiveness of the sludge; the aging makes the sludge less cohesive, while the premixing does not modify its cohesiveness. In spite of changes in test conditions, the elastic module of sludge samples remains unchanged.
authors.affiliation: Université de Toulouse; Mines Albi, CNRS; Centre RAPSODEE, Campus Jarlard, F-81013 Albi, France.
authors.forename: Fenglin
authors.initials: F
authors.lastname: Liang
authors.affiliation: Université de Toulouse; Mines Albi, CNRS; Centre RAPSODEE, Campus Jarlard, F-81013 Albi, France.
authors.forename: Martial
authors.initials: M
authors.lastname: Sauceau
authors.affiliation: Université de Toulouse; CNRS, Mines Albi, INSA, UPS, ISAE-SUPAERO; ICA (Institut Clément Ader); Campus Jarlard, F-81013 Albi, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Dusserre
authors.affiliation: Université de Toulouse; Mines Albi, CNRS; Centre RAPSODEE, Campus Jarlard, F-81013 Albi, France. Electronic address: Patricia.Arlabosse@mines-albi.fr.
authors.forename: Patricia
authors.initials: P
authors.lastname: Arlabosse
mesh_terms: D011312:Pressure; D015203:Reproducibility of Results; D012212:Rheology; D012722:Sewage; D014783:Viscosity
chemical_list: D012722:Sewage
keywords: Aging; Premixing; Rheology; Sewage sludge; Texture; Visco-elasto-plastic; Yield