DEPOLECO

The project will develop new concepts for catalytic degradation of organic contaminants in groundwaters at neutral pH with air as sole oxidant. It responds to the increasingly obvious need to develop eco-compatible and long-term effective methods for in-situ cleaning up of soils and groundwaters. Recent proofs-of-concepts from our team and others show that deleterious side-effects and limitations of current advanced oxidation processes based on strong oxidants could be overcome. This could be done by exploiting the intrinsic ability of natural Fe(II)-minerals present in soils and sediments to produce Recative Oxygen Species (ROS) and to degrade organic molecules in the presence of airborne O2 in darkness. Up-scaling such a concept to complex field sites requires a three-step strategy able to unravel the reactivity, selectivity and applicability of specific natural and geo-inspired Fe(II)-catalysts, which will be addressed through three dedicated work-packages. Task 1 (Reactivity) will quantify the ability of waterlogged natural soils and aquifers sediments as well as of synthetic geo-inspired nanoparticles to produce ROS and other reactive species upon air oxidation. Indeed, finely divided (high surface area) Fe(II)-rich minerals from soils/sediments, especially Fe(II)-clays and Fe(II)-sulfides, are formed or regenerated during waterlogging periods because of anaerobic microbial respiration of Fe(III) and sulfate and are susceptible to produce ROS when exposed to air when the soil/sediment returns to dry conditions. The role of such genuine soils/sediments mineral in ROS production upon natural redox cycling, and potential subsequent pollutant degradation is largely unexplored. Beyond investigating the natural ability of genuine soil minerals to produce ROS, we will also synthesize reactive geo-inspired Fe(II)-substrates that will be used to amend the soils/sediments in order to improve ROS production and pollutant degradation. Task 2 (Selectivity) will evaluate the capacity of the geo-inspired Fe(II)-substrates synthesized in Task 1, to degrade the contaminants adsorbed to their surface, by directly measuring the kinetics of these degradation reactions (Fig. 5). We will focus on Fe(II)-rich phyllosilicates and Fe-sulfides nanoparticles, analogous to soil/sediment minerals, but optimized for presenting hydrophobic surfaces, very-high surface-area, and redox active Fe(II)-surface sites. These synthetic substrates will thus be designed to potentially degrade a wide variety of non-polar molecules including high priority pesticides and will be further tested as soil amendments in Task 3. Task 3 (Applicability) will monitor the degradation of organic pollutants in batch/mesocosms experiments that will be conducted on contaminated soils and sediments, with or without addition of synthetic Fe(II)-substrates. Understanding the pollutant degradation mechanisms and improving their efficiency will particularly rely on identifying and quantifying the degradation products of the targeted pollutants Three model molecules belonging to contrasted classes of pollutants (quinone antibiotics, phenylurea herbicides, and PAHs) will be especially targeted, with the aim to give novel mechanistic bases to implement eco-compatible in-situ remediation of contaminated groundwaters, for a large panel of high-priority contaminants. The project will thus set the fundamental bases for a wide range of future ecofriendly applications, especially designed for decontaminating soils and groundwaters. Indeed, it will directly address the ability of natural soils/sediments, genuine or amended with reactive substrates, to degrade organic contaminants upon redox cycling. This unique approach will yield unprecedented clues for evaluating the natural resilience of natural environments with respect to organic contaminants and for designing long-term in situ remediation methods based on eco-compatible amendments.