Rheological characteristics of an anaerobically digested rye and maize silage mixture: Impact of solid concentration and particle size on rheological properties

Abstract

This study investigates the rheological properties of rye and maize silage digestate from an industrial digester. In addition to the usual flow mode, oscillatory measurements were performed to highlight the visco-elastic characteristic of the digestate. Regardless of total solid (TS) content and solids size, results showed a shear-thinning behavior with a yield stress of the digestate, which was modelled by a Herschel-Bulkley equation. Furthermore, reducing the solids size by roughly a factor of 10 led to a 35-fold decrease in the viscosity at 20 s−1 for digestate with 8% of TS, which could improve the efficiency of mixing in digesters. On the other hand, the apparent viscosity of the digestate increases with increasing TS, which corresponded to a rise in cohesive energy. Equations linking rheological parameters and TS were provided. These models can be use in Computational Fluid Dynamics studies for a better modeling of the hydrodynamics within digesters.