Shear and solid-liquid separation behaviour of anaerobic digested sludge across a broad range of solids concentrations for CFD modelling

In this work, the shear properties of an anaerobic sludge were measured from 0.4 to 12.5 vol%, which corresponds to the solids concentrations seen in lagoons. The sludge showed Newtonian behaviour at 0.4 vol% and Herschel-Bulkley yield stress fluid behaviour for higher concentrations ranging from 0.5 to 12 vol%. We compared multiple approaches to determine relationships between the model fitting parameters of consistency, <i>k</i>, flow index, <i>n</i>, and shear yield stress, <i>t</i><i>_y</i> with solids volume fraction <i>f</i>.The solid-liquid separation properties were measured from sedimentation and filtration experiments to obtain compressibility and permeability properties across all the above-mentioned concentrations, enabling development of hindered velocity sedimentation curves.