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.

Broader Impact in Science and Technology: Materials with low thermal conductivity at high temperature are crucial to the development of higher energy efficiency engines for power generation and transport. New results indicate that there is the prospect of discovering materials with much lower thermal conductivities than existing ceramics and that the mechanisms of thermal conductivity may be radically different from the conventional phonon scattering picture in simple crystalline materials. This project addresses the challenge of identifying compounds having even lower thermal conductivity with an emphasis on layered crystal structures with strongly anisotropic thermal conductivity. We believe that the project will have broad impact on technology through improved heat management materials and impact the science of materials through fundamental advances in understanding thermal conductivity in complex crystal structures.Intellectual Merit: Apart from the important discovery aspects, we believe the merit of our proposal lies in our integrated, collaborative approach to the identifying candidate materials from an enormous number of oxide compounds and an understanding how anisotropic thermal conductivity is related to crystal structure anisotropy. The aim of our integrated experimental and simulation program is to go beyond an intuition-based Edisonian approach to a more systematic approach to the discovery of materials. The basis of the approach is to combine state-of-the art simulations with both traditional synthesis and processing of ceramics together with combinatorial approaches exploring compositional variations to provide a more rapid discovery path. The initial emphasis is on complex, fluorite-derived structures and perovskite-related layered structures that have very low and/or strongly anisotropic thermal conductivities. Layered crystal structures, such as the perovskites, provide the opportunity to investigate whether the layers can impede perpendicular thermal transport at the atomic level as well as facilitating both the thermal-transport properties and other important performance criteria.