Influence of fluid flow on chemical reactions under water-unsaturated conditions – INFLOW

INFLOW assembles an interdisciplinary team at the interface between chemistry, fluid mechanics and Earth sciences to explore how multiphase flows of water and air control the chemical reactivity at mineral surfaces in unsaturated porous media. These dynamics play a central role in the transport and degradation of contaminants in soils, which constitute highly heterogeneous and dynamic reactors. While reactive transport properties are generally characterized in saturated conditions, it is unknown how different levels of water saturations alter reaction kinetics. To address these scientific challenges, INFLOW will combine comprehensive experimental investigations of molecular mechanisms at mineral/water interfaces (WP1) with pore-scale imaging of transport and reaction rates using emerging microfluidic techniques (WP2). These experimental data will feed the development of a new modelling framework for upscaling reactive transport dynamics in unsaturated porous media (WP3), integrating reaction rates and thermodynamic parameters, as well as transport dynamics in multiphase flows.
A key challenge is to bridge the gap between the molecular scale chemical processes and physical processes (e.g. multiphase flow and dispersion/diffusion in porous media). The coupling of modern in situ interfacial chemistry measurements and emerging microfluidics techniques offer a unique opportunity to unlock this major scientific question. INFLOW will tackle this issue by focusing on the case of antibiotic agents widely used in human and veterinary medicine. Recently, quinolones and other antibacterial agents have emerged as aqueous micropollutants in surface waters, groundwater and soils. Their transport and mobility in the environment are strongly related to the nature and relative abundance of the mineral phases, e.g. Fe-oxyhydroxides, commonly found in the Earth’s near-surface environment. Although redox transformation of these compounds is key to their environmental and engineered degradation, the underlying reaction mechanisms remain elusive. In particular, the surface speciation of antibiotics and their molecular transformation on mineral surfaces is unclear. In addition, much of knowledge that currently exists concerns the reactivity of environmental mineral surfaces in suspension or slurry systems, and under equilibrium conditions. Therefore, it is unknown how unsaturated flow dynamics influence these interfacial processes and likely drive non-equilibrium reactions.
Our research hypotheses are: (i) multiphase flow of water and air in porous media induces strong macroscopic heterogeneities in water content and flow velocities, thus controlling solute residence times and exposure to reactive surfaces; (ii) at the pore-scale, the induced enhanced concentration gradients lead to breakdown of the complete pore-scale mixing assumption of conventional reactive transport models; (iii) unsaturated flow dynamics likely have a major impact on the fate of organic compounds bound to mineral surfaces. To test these hypotheses, INFLOW will combine novel experimental investigations (WP1 and WP2) with advanced numerical and theoretical modeling (WP3). This multidisciplinary approach will provide a unique dataset from the molecular scale to the porous media scale. INFLOW is the first project to develop a multi-scale and interdisciplinary methodology linking molecular mechanisms of chemical reactions with multiphase flow dynamics in porous media, hence opening a broad range of environmental applications.