Ifsttar PhD subject

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Title : Transport and retention of fluorinated pollutants in soils: small scale experiments, magnetic resonance imaging and computer simulations

Main host Laboratory - Referent Advisor   -

Director of the main host Laboratory   -

PhD Speciality Transport réactif en milieu poreux

Axis of the performance contract 3 - COP2017 - Planning and protecting regions

Main location Nantes

Doctoral affiliation UNIVERSITE DE NANTES

PhD school EGAAL - Ecologie, Géosciences, Agronomie et Alimentation

Planned PhD supervisor RUBAN Véronique  -    -

Planned financing Contrat doctoral  - Ifsttar

Abstract

The transport of pollutants in soils depends on many factors: advection with the flow of water that infiltrates in the soil, retention of pollutants on the solid surfaces, molecular diffusion, etc. Numerous models have been proposed to predict the transport of various organic pollutants within soils. These models are generally based on the determination of the partition coefficient of the contaminant between the water and the soil. However, an accurate prediction of pollutant transport also requires some local information on the processes governing the transfer. Obtaining this kind of data remains a challenge, but magnetic resonance imaging (MRI) has emerged in the last few years as a viable solution [1][2][3].

The aim of this research project is to investigate the transport of perfluorinated alkylated substances (PFAS) in different porous media of increasing complexity: bead packings, sands, soil aggregates and intact soils. PFAS are a family of molecules used in different applications and their dissemination in the environment is highly scrutinized since a few years [4]. The production of a few PFAS has even been stopped in Europe and in North America in 2015, but some of them are still synthetized [5][6]. The PhD student will have to study the transport of a PFAS in porous media by various experimental and numerical means. On the experimental side, he/she will perform breakthrough experiments (a rather classical kind of experiment when one wants to determine a partition coefficient) and ¹⁹F MRI (a PFAS molecule contains fluorine nuclei that can be detected by ¹⁹F MRI). A preliminary step in this direction has already been undertaken by two members of the supervision team of this PhD project [3] by ¹⁹F nuclear magnetic resonance (NMR) relaxometry, which we now plan to combine with ¹⁹F MRI. MRI provides a wealth of data that often cannot be fully exploited in a simple way. This is why the experimental results will be completed by some computer simulations of the breakthrough and MRI experiments. This modelling part will be based i) on Virtual Soil (a numerical tool developed by INRA that can simulate one-dimensional transport in soils, https://www6.inra.fr/vsoil) and ii) on a small-scale three-dimensional transport model in order to assess the importance of the radial gradients of concentration that may arise because of entrance effects or due to the relatively small length over diameter ratio of the samples that will be imaged by ¹⁹F MRI.

The main goals of the PhD student will be: i) to investigate the influence of different porous media on transport and retention properties of a PFAS; ii) to study the dynamics of the transfer of a PFAS within the porous media; iii) to simulate the experimental data with different transport models, to select the most appropriate one and to infer the values of the parameters characterizing the transport of a PFAS within different porous media (from bead packings to intact soils).

Keywords : soil; pollutant; perfluorinated compound; retention; transport; breakthrough curve; MRI (magnetic resonance imaging); computer simulation

Main host Laboratory - Referent Advisor	-
Director of the main host Laboratory	-
PhD Speciality	Transport réactif en milieu poreux
Axis of the performance contract	3 - COP2017 - Planning and protecting regions
Main location	Nantes
Doctoral affiliation	UNIVERSITE DE NANTES
PhD school	EGAAL - Ecologie, Géosciences, Agronomie et Alimentation
Planned PhD supervisor	RUBAN Véronique - -
Planned financing	Contrat doctoral - Ifsttar
Abstract The transport of pollutants in soils depends on many factors: advection with the flow of water that infiltrates in the soil, retention of pollutants on the solid surfaces, molecular diffusion, etc. Numerous models have been proposed to predict the transport of various organic pollutants within soils. These models are generally based on the determination of the partition coefficient of the contaminant between the water and the soil. However, an accurate prediction of pollutant transport also requires some local information on the processes governing the transfer. Obtaining this kind of data remains a challenge, but magnetic resonance imaging (MRI) has emerged in the last few years as a viable solution [1][2][3]. The aim of this research project is to investigate the transport of perfluorinated alkylated substances (PFAS) in different porous media of increasing complexity: bead packings, sands, soil aggregates and intact soils. PFAS are a family of molecules used in different applications and their dissemination in the environment is highly scrutinized since a few years [4]. The production of a few PFAS has even been stopped in Europe and in North America in 2015, but some of them are still synthetized [5][6]. The PhD student will have to study the transport of a PFAS in porous media by various experimental and numerical means. On the experimental side, he/she will perform breakthrough experiments (a rather classical kind of experiment when one wants to determine a partition coefficient) and ¹⁹F MRI (a PFAS molecule contains fluorine nuclei that can be detected by ¹⁹F MRI). A preliminary step in this direction has already been undertaken by two members of the supervision team of this PhD project [3] by ¹⁹F nuclear magnetic resonance (NMR) relaxometry, which we now plan to combine with ¹⁹F MRI. MRI provides a wealth of data that often cannot be fully exploited in a simple way. This is why the experimental results will be completed by some computer simulations of the breakthrough and MRI experiments. This modelling part will be based i) on Virtual Soil (a numerical tool developed by INRA that can simulate one-dimensional transport in soils, https://www6.inra.fr/vsoil) and ii) on a small-scale three-dimensional transport model in order to assess the importance of the radial gradients of concentration that may arise because of entrance effects or due to the relatively small length over diameter ratio of the samples that will be imaged by ¹⁹F MRI. The main goals of the PhD student will be: i) to investigate the influence of different porous media on transport and retention properties of a PFAS; ii) to study the dynamics of the transfer of a PFAS within the porous media; iii) to simulate the experimental data with different transport models, to select the most appropriate one and to infer the values of the parameters characterizing the transport of a PFAS within different porous media (from bead packings to intact soils).
Keywords :	soil; pollutant; perfluorinated compound; retention; transport; breakthrough curve; MRI (magnetic resonance imaging); computer simulation

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Detailed form :

Title : Transport and retention of fluorinated pollutants in soils: small scale experiments, magnetic resonance imaging and computer simulations