Improving agricultural spreading of pasty sewage sludge by using rheological analysis: model experiments

Abstract

Agricultural reuse of pasty sewage sludge is analyzed in the mechanical viewpoint. We first present a new concept of rheological characterisation, which shows that these materials present a dual behavior with both viscoelastic solid-like and viscous liquid-like parts. The abrupt transition occurs at a critical shear stress, which is of importance to study the spreading. On a rotating disk, the material flows abruptly only when the critical shear stress is reached. We finally show that in a dimensionless form, the spreading starts always at a critical point, which can be easily determined independently.