Membrane bioreactors (MBRs) are widely used in wastewater treatment processes. However, membrane fouling mitigation remains challenging. Several strategies have been developed industrially to enhance MBR productivity, including coarse bubble aeration. The way such aeration participates in hydrodynamic patterns is an important research topic given its major contribution to the energy costs of such facilities. The methods currently used for hydrodynamic characterization suffer from several drawbacks, mainly due to the system’s complexity. Consequently, there is a need for a nonintrusive method that could be employed in reactors with complex internal geometry and in the presence of activated sludge. This article presents the evaluation and adaptation of the electrical resistivity tomography (ERT) to gain insights into hydrodynamic conditions and to determine how bubbles are distributed within membrane bioreactors in different aeration conditions. An approach used by geophysicists was adapted to a semi-industrial MBR: a numerical procedure was used to validate ERT’s ability to recover precise information in a complex geometry such as MBR membrane tank. Experiments were conducted in a semi-industrial membrane bioreactor with clear water and activated sludge. The resulting images were analyzed in terms of bubble dispersion over a section of the pilot. Heterogeneities were detected in all configurations studied in numerical simulations, although the results also emphasize the diffuse character of gas distribution obtained with the ERT method. Experimental results highlight how gas distribution is mainly localized inside membrane modules and its homogeneity over the module depends on activated sludge rheological properties and air flow rate. MBR operation could be optimized by considering the operating conditions which provide efficient gas distribution over the membrane module obtained at a scale representative of industrial reactors.