Investigation of the fluid circulation and the macro-mixing process in a stirred model fermenter of non-Newtonian liquid was conducted by the comparative use of flow following sensor particles, ERT and CFD. Average fluid circulation times were estimated from (i) the measured vertical position of the sensor particle, (ii) the fluctuating ERT signals of single ERT planes and (iii) the simulated dispersed phase. The estimated average circulation times of all the three methods are comparable for the two investigated impeller positions. Furthermore, axial residence profiles of the sensor particles were extracted, which reveal the impact of the impeller configuration to the axial mixing homogeneity. Moreover, the results confirm the conclusions about the effect of the off-bottom clearance of the impeller derived by Reinecke et al. (2012) in a 1000 L pilot fermenter. The excellent detectability of the particles and the consistent results confirm the feasibility of the combined method for further investigation of the complex flows in biogas fermenters. (C) 2016 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.