Ifsttar PhD subject

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Title : Reactive transfer modelling of metallic trace elements in stormwater infiltration basins

Main host Laboratory - Referent Advisor GERS - EE  -  BECHET Béatrice      tél. : +33 240845687

Director of the main host Laboratory PEYNEAU Pierre-Emmanuel  -

PhD Speciality Sciences de la terre et de l'environnement

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

Main location Nantes

Doctoral affiliation UNIVERSITE GUSTAVE EIFFEL

PhD school Matière, Molécules, Matériaux et Géosciences (3MG)

Planned PhD supervisor BECHET Béatrice  -  Université Gustave Eiffel  -  GERS - EE

Planned financing Contrat doctoral  - Université Gustave Eiffel

Abstract

1. Context and objectives
By 2050, 75% of the world's population will be living in urban areas, under the pressure of climate change (United Nations, 2012). Supported by regulations, optimised urban water management is one of the major challenges facing local authorities, particularly during intense rainfall events. They need solutions to limit the risk of flooding, but also to manage the flow of pollutants emitted by human activities (transport, heating, industry, etc.). Structures dedicated to the retention and infiltration of urban runoff are designed to protect the quality of surface water and groundwater (Eckart et al. 2017). Systems such as valleys and rain gardens make it possible to manage water flows on a small scale, alongside ponds designed to manage larger volumes of water. Over the last twenty years or so, various types of multi-functional alternatives to the 'all-pipe' system have been gradually incorporated into urban landscapes: a hydraulic function through the regulation of water flows, a landscape function through the frequent planting of created or spontaneous vegetation, an ecological function through the creation of wetlands, and a depollution function through decantation and infiltration into the soils of the structures (Keyvanfar et al. 2021).
Particular attention is paid to assessing the hydraulic and purification performance of structures, as they are fundamental to ensuring the sustainability and long-term effectiveness of stormwater management (Yang et al. 2021). However, as pointed out by Webber et al (2022), technical innovations (smart systems) essentially target the quantitative aspect of water management, and not the quality issue, which is controlled by the transfer of pollutants between the water, the sediments accumulated in the structures, and the underlying soil (Banc, 2021, Dang, 2023). Physical processes, chemical and physico-chemical processes and biological processes are the three main categories of processes that can affect the retention and mobilisation of pollutants. These processes are complementary to hydrological processes that react to surface water flows and hydrodynamic flows in sediments and soils. It is therefore understandable that the complexity of these systems has slowed down the development of integrated tools for assessing the risks associated with stormwater management. However, the issue of purification performance could benefit from research into coupled modelling between water flows and geochemistry (Simunek et al. 2006), with the aim of developing a tool to better understand the behaviour of micropollutants.

2. Scientific challenges
In the field of stormwater management, a large amount of experimental data has been collected in the literature to assess the purification capacity of various structures: ponds, ditches, filtering ditches, etc. (El Mufleh et al. 2012). Modelling the hydrological functioning of these structures has been the subject of a great deal of work at international level. In France, a platform has been developed within the Lyon urban hydrology observatory (OTHU) to provide hydrological simulation tools for operational staff (CANOE-HYDROTOP) (Asry et al. 2023). The flow of suspended solids in run-off water is described using fluid mechanics models. However, little modelling work has been carried out in the field of qualitative hydrology. While the literature is very rich in data on the quality of the water and sediments that accumulate at the bottom of structures, the understanding of transfer processes and the description of chemical speciation using hydrogeochemical models remains underdeveloped (Vezzaro et al. 2012). In recent years, laboratory experiments combined with geochemical modelling have made it possible to simulate the influence of pH on the release of trace and major elements (Drapeau et al. 2017, Banc et al. 2021), but a reactive transfer approach on the scale of the structure needs to be developed to complement the quantitative modelling component (Cannavo et al. 2018), based on existing work in the teams (Hanna et al., 2012).
The scientific challenges are threefold: 1) describing complex geochemical systems/is it possible to represent runoff and infiltrating systems in a simplified but sufficiently generic way? 2) determining the predominant static and dynamic interaction mechanisms and 3) adapting the available hydrology/contaminant transfer modelling tools.

3. Progress of the thesis
In order to contribute to the consideration of metal micropollutant transfer mechanisms in hydrodynamic and purification operating models, the proposed approach is based on the use of geochemical and/or hydrogeochemical modelling for the representation of stormwater infiltration system components and intra- and inter-component reactivity, combined with the use of experimental data from the literature for the calibration and validation of the predominant mechanisms.
The work will be organised into 5 phases:
1) Months 1 to 6: state of the art of modelling tools and approaches, collection of experimental data (in collaboration with the Urbis network teams in urban hydrology Paris/Lyon/Nantes)
2) Months 7 to 12: construction of geochemical models and mechanistic systems (run-off water, sediment, soil) after selection of two/three case studies
3) Months 13 to 24: calibration and validation of reaction systems based on experimental data
4) Months 25 to 28: testing the feasibility of coupling with a model describing the hydraulic/hydrological functioning of a structure.
5) Months 29 to 36: drafting of the manuscript and defence.

The data to be used is available in the literature or from partners. Several geochemical modelling software packages, such as Phreeqc2, are free and can be downloaded online. The main risk lies in data batches that are too partial, but the initial inventory should make it possible to provide concentration ranges for the various parameters required.
The PhD student will be based in Nantes, with short stays in Lyon to strengthen the geochemical modelling aspect.

4. Innovative character
The state of play to date and the discussions underway at national level in the Urbis network show that, while the tools for describing the hydraulic functioning of biofiltration structures are well developed, knowledge of the reactive processes is limited (a few articles, including one review). In order to develop the purification mechanics component, a geochemical approach to the systems appears to be complementary and highly innovative.
This thesis project will also provide an opportunity to exploit the inter-observatory data from the Urbis network. A review of the geochemical work carried out in recent years will highlight similarities, differences and future prospects. This project will be part of the SNO Observil 'hydrology and geochemistry' working group, so as to benefit from and contribute to the scientific activities.
It will also take advantage of existing literature to identify general trends (meta-analysis and statistical analysis). Finally, the innovation also lies in the intention to study the feasibility of coupling with a hydrodynamic modelling tool.

5. Expected results and exploitation
The expected results are of several types: 1) the production of one or more scientific articles. Objective 1 in terms of publications is a review article to conclude phase 1 of the thesis 2) presentations at international conferences (Novatech, ICUD), 3) the 3rd result is the assessment of the feasibility of developing a "geochemistry" module that is interoperable with hydrological/hydraulic models at the scale of the structure.

Keywords : stormwater management - trace metals - sediments - SUDS - reactive transfer model

Main host Laboratory - Referent Advisor	GERS - EE - BECHET Béatrice tél. : +33 240845687
Director of the main host Laboratory	PEYNEAU Pierre-Emmanuel -
PhD Speciality	Sciences de la terre et de l'environnement
Axis of the performance contract	3 - COP2017 - Planning and protecting regions
Main location	Nantes
Doctoral affiliation	UNIVERSITE GUSTAVE EIFFEL
PhD school	Matière, Molécules, Matériaux et Géosciences (3MG)
Planned PhD supervisor	BECHET Béatrice - Université Gustave Eiffel - GERS - EE
Planned financing	Contrat doctoral - Université Gustave Eiffel
Abstract 1. Context and objectives By 2050, 75% of the world's population will be living in urban areas, under the pressure of climate change (United Nations, 2012). Supported by regulations, optimised urban water management is one of the major challenges facing local authorities, particularly during intense rainfall events. They need solutions to limit the risk of flooding, but also to manage the flow of pollutants emitted by human activities (transport, heating, industry, etc.). Structures dedicated to the retention and infiltration of urban runoff are designed to protect the quality of surface water and groundwater (Eckart et al. 2017). Systems such as valleys and rain gardens make it possible to manage water flows on a small scale, alongside ponds designed to manage larger volumes of water. Over the last twenty years or so, various types of multi-functional alternatives to the 'all-pipe' system have been gradually incorporated into urban landscapes: a hydraulic function through the regulation of water flows, a landscape function through the frequent planting of created or spontaneous vegetation, an ecological function through the creation of wetlands, and a depollution function through decantation and infiltration into the soils of the structures (Keyvanfar et al. 2021). Particular attention is paid to assessing the hydraulic and purification performance of structures, as they are fundamental to ensuring the sustainability and long-term effectiveness of stormwater management (Yang et al. 2021). However, as pointed out by Webber et al (2022), technical innovations (smart systems) essentially target the quantitative aspect of water management, and not the quality issue, which is controlled by the transfer of pollutants between the water, the sediments accumulated in the structures, and the underlying soil (Banc, 2021, Dang, 2023). Physical processes, chemical and physico-chemical processes and biological processes are the three main categories of processes that can affect the retention and mobilisation of pollutants. These processes are complementary to hydrological processes that react to surface water flows and hydrodynamic flows in sediments and soils. It is therefore understandable that the complexity of these systems has slowed down the development of integrated tools for assessing the risks associated with stormwater management. However, the issue of purification performance could benefit from research into coupled modelling between water flows and geochemistry (Simunek et al. 2006), with the aim of developing a tool to better understand the behaviour of micropollutants. 2. Scientific challenges In the field of stormwater management, a large amount of experimental data has been collected in the literature to assess the purification capacity of various structures: ponds, ditches, filtering ditches, etc. (El Mufleh et al. 2012). Modelling the hydrological functioning of these structures has been the subject of a great deal of work at international level. In France, a platform has been developed within the Lyon urban hydrology observatory (OTHU) to provide hydrological simulation tools for operational staff (CANOE-HYDROTOP) (Asry et al. 2023). The flow of suspended solids in run-off water is described using fluid mechanics models. However, little modelling work has been carried out in the field of qualitative hydrology. While the literature is very rich in data on the quality of the water and sediments that accumulate at the bottom of structures, the understanding of transfer processes and the description of chemical speciation using hydrogeochemical models remains underdeveloped (Vezzaro et al. 2012). In recent years, laboratory experiments combined with geochemical modelling have made it possible to simulate the influence of pH on the release of trace and major elements (Drapeau et al. 2017, Banc et al. 2021), but a reactive transfer approach on the scale of the structure needs to be developed to complement the quantitative modelling component (Cannavo et al. 2018), based on existing work in the teams (Hanna et al., 2012). The scientific challenges are threefold: 1) describing complex geochemical systems/is it possible to represent runoff and infiltrating systems in a simplified but sufficiently generic way? 2) determining the predominant static and dynamic interaction mechanisms and 3) adapting the available hydrology/contaminant transfer modelling tools. 3. Progress of the thesis In order to contribute to the consideration of metal micropollutant transfer mechanisms in hydrodynamic and purification operating models, the proposed approach is based on the use of geochemical and/or hydrogeochemical modelling for the representation of stormwater infiltration system components and intra- and inter-component reactivity, combined with the use of experimental data from the literature for the calibration and validation of the predominant mechanisms. The work will be organised into 5 phases: 1) Months 1 to 6: state of the art of modelling tools and approaches, collection of experimental data (in collaboration with the Urbis network teams in urban hydrology Paris/Lyon/Nantes) 2) Months 7 to 12: construction of geochemical models and mechanistic systems (run-off water, sediment, soil) after selection of two/three case studies 3) Months 13 to 24: calibration and validation of reaction systems based on experimental data 4) Months 25 to 28: testing the feasibility of coupling with a model describing the hydraulic/hydrological functioning of a structure. 5) Months 29 to 36: drafting of the manuscript and defence. The data to be used is available in the literature or from partners. Several geochemical modelling software packages, such as Phreeqc2, are free and can be downloaded online. The main risk lies in data batches that are too partial, but the initial inventory should make it possible to provide concentration ranges for the various parameters required. The PhD student will be based in Nantes, with short stays in Lyon to strengthen the geochemical modelling aspect. 4. Innovative character The state of play to date and the discussions underway at national level in the Urbis network show that, while the tools for describing the hydraulic functioning of biofiltration structures are well developed, knowledge of the reactive processes is limited (a few articles, including one review). In order to develop the purification mechanics component, a geochemical approach to the systems appears to be complementary and highly innovative. This thesis project will also provide an opportunity to exploit the inter-observatory data from the Urbis network. A review of the geochemical work carried out in recent years will highlight similarities, differences and future prospects. This project will be part of the SNO Observil 'hydrology and geochemistry' working group, so as to benefit from and contribute to the scientific activities. It will also take advantage of existing literature to identify general trends (meta-analysis and statistical analysis). Finally, the innovation also lies in the intention to study the feasibility of coupling with a hydrodynamic modelling tool. 5. Expected results and exploitation The expected results are of several types: 1) the production of one or more scientific articles. Objective 1 in terms of publications is a review article to conclude phase 1 of the thesis 2) presentations at international conferences (Novatech, ICUD), 3) the 3rd result is the assessment of the feasibility of developing a "geochemistry" module that is interoperable with hydrological/hydraulic models at the scale of the structure.
Keywords :	stormwater management - trace metals - sediments - SUDS - reactive transfer model

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