Rheological Characterization of Anaerobic Sludge from Agricultural and Bio‐Waste Biogas Plants

Anaerobic sludges taken from 16 different biogas plants were analyzed with respect to their rheological characteristics. All sludges showed temperature‐dependent shear‐thinning behavior with viscosities from 900 – 6000 mPa s at 20 °C. Nevertheless, the liquid fraction of the anaerobic sludges also revealed temperature‐dependent, shear‐thinning behavior with viscosities well above water viscosity (2 – 40 mPa s at 20 °C). The rheological behavior of the liquid phase could be linked to organic fractions, i.e., proteins and polysaccharides. Shear‐thinning and temperature‐dependent behavior was modeled by the power‐law equation and the Arrhenius law, respectively.