In this study, we examined the efficiency of mixing due to liquid jets in a model anaerobic digester. Xanthan Gum Keltrol T (XGKT) solution which is transparent and has similar rheological characteristics to those of digested sludge was selected as the model Experiments were carried out using 0.15 and 0.4 wt% XGKT solutions. Four different liquid jet orientations were used in a cylindrical vessel, namely vertical-downward, vertical-upward, tangential 45 upward and tangential 45 downward. A decolourisation method involving an acid-base reaction was used for flow visualisation. A fluorescent dye was used as the tracer to observe the mixing patterns in the vessel. Video images of flow visualisation experiments were analysed to investigate the changes in the volume of well-mixed regions as a function of mixing time. The results from flow visualization were compared with those from both computational flow dynamics (CFD) simulations and electrical resistance tomography (ERT). Results showed that well mixed region volume decreases with increasing liquid apparent viscosity. Complete mixing was achieved in 0.15 wt% XGKT solution, which has rheology similar to that of digested sludge with 2.3% solids, with all four different jet arrangements. For 0.4 wt% XGKT solution, which has rheology similar to that of digested sludge with 5% solids, mixing efficiency with jet arrangement changes in the following order: upward > 45 degrees upward >45 degrees downward > downward jet arrangement. The results suggested that we can use transparent materials to study rheological behaviours of sludge and visualize the dynamics of mixing. Results from both ERT and CFD agreed well with those from flow visualization experiments. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.