Modern anaerobic digestion is receiving a new fillip within the framework of actual energy and environment context, and plays an increasing role for its abilities to further transform organic matter into biogas composed mainly of 50-75% methane, as thereby it also reduces the amount of final sludge solids for disposal whilst destroying most of the pathogens present in the sludge and limiting odour problems associated with residual matter. Anaerobic digestion thus optimises WwTP costs, its environmental footprint and is considered a major and essential part of a modern WwTP. The biogas can be easily used as a renewable energy source through the robust and established gas-engine technology such as combined heat-and-power units on site. Moreover, it is finding other applications such as vehicle fuel, substitute for natural gas and raw material in industrial processes for methane after purification and upgrading. The controlled production and exploitation of the biogas prevents methane from greenhouse gas emissions. As such, the anaerobic process for the sludge treatment and methane valorisation shifts then a sustainable paradigm from “treatment and disposal” to “beneficial utilisation” as well as “profitable endeavour”. While many efforts have being devoted to the application of anaerobic technologies worldwide, the research projects are still missing up to now on the core of an anaerobic process that is the reactor, in particular the sound understanding of various mechanisms involved in such a process to intensify the efficiency. Most of high rate upflow reactors, i.e. Upflow Anaerobic Sludge Blanket (UASB) reactor, Internal Circulation Anaerobic Reactor (ICAR) and Expanded Granular Sludge Blanket (EGSB) reactor, etc. have been leading anaerobic reactors in the world. As all multiphase reactors in Chemical and Environmental Engineering, these reactors are of very complex nature, particularly due to the coupling between the biochemical aspects and multiphase flows. While the biological mechanisms have been widely studied in the literature, the physical parameters and physico-chemical mechanisms involved in an anaerobic process were scarcely reported. It is widely recognized that except substrates and organic loading, hydrodynamic conditions are the most important operating parameter on the process efficiency in whatever upflow anaerobic reactors. This research project within the framework of ANR Blanc – NSF China aims at initiating an innovative process study on the fundamental understanding and thereafter intensification of the anaerobic sludge treatment and valorisation of biogas through a multiscale approach. Two main axes will be addressed in this project: (1) the behaviours of sludge granules will be exhaustively investigated from a hydrodynamic point of view between three phases in presence: sludge granules – biogas bubbles and water. Both physical and biological behaviours of a single granule in a microdevice will be linked to the global properties characterised in a 3D pilot at macroscale; (2) the mechanism and efficiency of methane generation will be studied from the nucleation of a microbubble at the surface of a granule until to the analyse of the biogas production issued from a 3D pilot at macroscale under various conditions. These works will be completed in a 2D pilot in presence of major interactions between three phases. Besides the hydrodynamic aspect considered with both advanced metrology such as Particle Image Velocimetry (PIV) at different scales and numerical simulation, complex rheological and biochemical characters of the sludge in the reactor will also be taken into account in this study. The perfect complementary partnership between our two teams allows us to proposing an original research program based on a multiscale approach to gain insight into several key fundamental mechanisms never investigated until now in the process of the anaerobic sludge treatment and valorisation of biogas.