Degradation of organic pollutants in groundwaters: new ecocompatible routes without strong oxidants (DEPOLECO) – DEPOLECO

ask 1 (Reactivity) will quantify the ability of Fe(II) minerals in soils/sediments to produce ROS and other reactive species upon oxidation by air. Indeed, Fe(II)-rich clays and Fe(II) sulfides are formed or regenerated during periods of waterlogging via anaerobic microbial respiration and are likely to produce ROS when exposed to air. air during the dry period. The role of these natural redox cycles on the degradation of organic pollutants is largely unexplored. We will extend this approach, initiated on natural minerals rich in Fe(II), to geo-inspired substrates analogous to soil minerals, synthesized to target a wide range of organic pollutants.
Task 2 (selectivity) will assess the ability of these geo-inspired Fe(II) substrates to degrade contaminants adsorbed on their surface, by directly measuring the kinetics of these degradation reactions. We will focus on Fe(II)-rich phyllosilicates and Fe sulfide nanoparticles, analogous to soil/sediment minerals, but optimized to exhibit hydrophobic surfaces, very high specific surface area and surface Fe(II) sites. reagents. These synthetic substrates will therefore be designed to potentially degrade a wide variety of non-polar molecules, including high priority pesticides, and will then be tested as soil/water table amendments in Task 3.
Task 3 (Applicability) will measure the degradation of organic pollutants in batch/mesocosm experiments that will be conducted on contaminated soils and sediments, with or without the addition of synthetic Fe(II) substrates. Understanding the mechanisms of pollutant degradation and improving their efficiency will be based in particular on the identification and quantification of the degradation products of the targeted pollutants. Three model molecules belonging to contrasting classes of pollutants (quinone antibiotics, phenylurea herbicides and PAHs) will be particularly targeted, with the aim of providing new mechanistic bases for implementing an eco-compatible in situ remediation of contaminated groundwater.

The work carried out partly concerned WP1, with the synthesis of geo-inspired substrates and the study of their ability to produce reactive species, in particular radicals, during oxidation by air with O2 as the only oxidant. These initial results were the subject of an article published in 2023.

This work is continuing within the framework of two ongoing theses. The project will thus lay the fundamental foundations for a wide range of future ecological applications, specially designed for a wide range of high priority contaminants. Indeed, it will directly address the ability of natural soils/sediments, authentic or modified with reactive substrates, to degrade these organic contaminants during natural redox cycles. This unique approach will provide unprecedented clues to assess the natural resilience of natural environments to organic contaminants and to design long-term in situ remediation methods based on eco-compatible amendments.

Morin G., Averseng F., Carrier X., Le Pape P., Du Y., HongE Y., Bourbon E., Sportelli G., A. Da Silva T., Mezzetti A., Baya C., Allard T., Brest J., Rouelle M. (2023) Phosphate Boosts Nonhydroxyl Radical Species Production upon Air Oxidation of Magnetite and Iron Sulfides at Neutral pH. Journal of Physcical Chemistry C 127, 9650-9662

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.