Computational Fluid Dynamics Simulations Were Used to Study the Effect of Bottom Configuration and a Hanging Baffle on the Mixing Inside a Gas-Lift Digester Filled with Non-Newtonian Sludge. the Navier-Stokes and Continuity Equations Were Solved Numerically using Commercially Available Finite Element Method-Based Solver. the Results from This Simulation Were Found to Be in Good Agreement with Previously Reported Experimental Findings. at a Gas Recirculation Rate of 84.96 L/h, the Poorly Mixed Zones Inside a Flat Bottom Digester Were About 33.6% of the Digester Volume, While in the Case of Digesters with 25° and 45° Conical Bottoms Poorly Mixed Zones Were About 31.9% and 29.6%, Respectively. the Power Law Viscosity Index, N, Did Not Have a Significant Effect on the Mixing Pattern under the Conditions Studied. Introduction of a Hanging Baffle in Combination with a 45° Hopper Bottom Resulted in Reduction of the Poorly Mixed Zone by a Factor of Three Compared to a Flat Bottom Without Baffle Configuration. Although the Introduction of a Hanging Baffle Was Able to Significantly Reduce the Size of the Poorly Mixed Zones Inside a Gas-Lift Digester, Further Optimization of the Digester Geometry May Lead to Additional Improvements. © 2007 Elsevier Ltd. All Rights Reserved.