Theses in progress

The constructed wetlands are a natural treatment technology that significantly reduces  pollution. One of the main advantages of these systems is the low operation, maintenance, and  investment required. Among all the configurations, the French vertical  wetlands are widely spread in France, with more than 4,000 systems, and in 2015, they  represented more than 20% of all domestic wastewater treatment plants in France . However, the effluent’s discharge regulations in water bodies are restricted, especially  the nitrogen and phosphorus parameters, to avoid eutrophication. Therefore, some variants  were created and tested to overcome this problem, including the forced aeration.

The objective of the thesis project is to study and optimize an hybrid  vertical/horizontal flow treatment wetland system with forced aeration for treatment on demand purpose for reuse application. The specific objectives are:

• Study the link between oxygen transfers and the quality of the treatment in order to  define the conditions for controlling the treatment system (sequencing of aeration,  alternation of filters, etc.) in order to respect different levels of discharge with regard  to nitrogenous forms, in view of the quality constraints induced by the possible uses of  the treated water. 
• Evaluate the robustness and response dynamics of the treatment system with regard  to the variations in loads (organic and hydraulic) that a decentralized use in an urban  environment may produce. 
• Define the rules for controlling the treatment system based on on-line sensors  inserted in the treatment filter. 
• Propose simplified models allowing to determine the expected discharge levels and to  design the system in different contexts.

Caroline MIYAZAKI is supervised by Pascal MOLLE. The subject of her thesis is optimization and control of hybrid vertical/horizontal flow treatment wetland with forced aeration for wastewater reuse in an urban environment.

Context : Past and current water management practices will not meet future water needs. Water supply (pipelines) and wastewater treatment (sewage plants) infrastructures are ageing and need to be upgraded. In addition, raw material scarcity, water stress, population growth, climate change and biodiversity erosion pose new challenges. Decentralised urban water management to promote the circular economy (reuse of treated water) and make cities more resilient to climate change through Nature-based Solutions (NBS) appears to be an interesting alternative. NFS are actions or infrastructures that protect, restore and sustainably manage ecosystems to mimic and optimise natural processes to achieve target discharge levels, while promoting biodiversity and ensuring human well-being. A common NFS for wastewater treatment in France are planted filters, constructed wetlands designed to exploit natural processes to improve water quality. The thesis is part of the European research project MULTISOURCE. 

Objectives :  To study the dynamics of pathogen reduction and the operating limits of a horizontal flow planted filter system with forced aeration for treated water reuse purposes, on a pilot, under real conditions, in order to:

• study the link between oxygen transfers and the treatment efficiency of the various pathogens,
• evaluate the robustness, the resilience and the dynamics of the structure
• and propose simplified models based on process engineering 

In response to climate change, decentralised urbain water management constitutes a key lever to boost circular economy (treated wastewater reuse) and facilitate cities resiliency. Usage of nature-based solutions (NBS) in particular would answer these different environmental, and even economic and social issues. The diversity of contexts and technologies led ICRA (Catalan Institute for Water Research) to create a tool to ease decision-making process.

The thesis aims to improve the NBS pre-sizing model included within this tool. Pre-sizing is based on statistical-learning models that sometimes may lead to erroneous predictions. In order to overcome this issue, the quality and the quantity of the input data will be improved and models will be coupled (hydridation) with mecanist ones to ensure that resulting solutions will not move too far away from physically-likely solutions.

Goals :

• Enrich and improve the database
• Develop an ontology
• Identify the most adequate hybrid approach and implement it within the tool
• Evaluate the model performances
• Develop a process optimization algorithm for the combination of several technologies

The thesis is carried out in cotutoring between INRAE-INSA Lyon and ICRA-Universitat de Girona. It is integrated to the European MULTISOURCE project.

In the context of energy transition and the shift from wastewater treatment to resource recovery, the issue of treating and recovering secondary fluxes in wastewater treatment plants is crucial. These fluxes, mainly resulting from the dewatering of sludge after treatment, can contain significant quantities of nitrogen and phosphorus that need to be managed in the best possible way for :

• not negatively impacting the quality of the treated water
• and limit the cost of additional treatment.

The objective of the thesis is to make an inventory of the technologies proposed for treatment and valorization of effluents resulting from wastewater treatment plant sludge, including methanization. The first step is to establish protocols for characterizing these fluxes in order to provide the data required to inform the choice of treatment / recovery processes. These protocols will be implemented on two or three sites currently under study, and the results will be integrated into treatment plant operating models. Different scenarios will then be compared, using modelling, integrating the impact of the choices made on the overall performance of the installation and the associated costs (energy and reagents consumed).

In the context of the transition from wastewater treatment to resource recovery, domestic wastewater is increasingly considered as a resource rather than as waste. Innovative processes have been developed to rapidly capture organic matter at the head of the Wastewater Treatment Plant (WWTP) for recovery by anaerobic digestion. The optimization of carbon-capturing processes are still not well known. The interactions between polymers, secreted by microorganisms or injected, and colloidal matter in wastewater are very complex and still not well understood. However, they have a major impact on carbon capture performance in WWTPs, from the destabilization of charged particles through the creation of flocs, to decantation performance.

The objective of this thesis is to identify and characterize the different mechanisms and to specify the reaction kinetics related to the production of bio-polymers, or the use of bio-sourced polymers for carbon capture in WWTPs, and their interactions with colloidal organic matter. This research will also investigate the impact of bio-polymer production/reaction on the mechanisms of mineralization, biosorption, assimilation and storage of organic matter in WWTPs. This thesis will improve the understanding polymer/colloid interactions in WWTPs through metrology, monitoring interactions in pilot and full-scale units and modelling them.

In France, soil is considered a biological reactor or an outlet for treated domestic wastewater. In both cases, soil permeability remains one of the key parameters for establishing the infiltration capacity and indirectly the purifying potential of the soil. To date, there is no satisfactory technique for globally assessing the permeability of heterogeneous soil and its variability at field scale. Faced with this limitation, geophysical methods provide rapid answers on variations in the geophysical properties of the soil (electrical resistivity, electrical conductivity, wave velocity) over large volumes, but they do not directly measure our parameter of interest (permeability). The objective of the MISS project (Innovative Method for Spatialization of Properties in Soil) is to propose a methodology for Bayesian fusion of data from point measurements (Infiltrometer, penetrometer…) and 2D/3D geophysical methods. This methodology will allow to map in 2D or 3D the distribution of soil properties. This is essential for: 

• a better design of infiltration systems, by allowing the integration of distributed 2D/3D information into water transfer models,
• a follow-up of the efficiency of the these systems over time, in particular to characterize and determine clogging zones.

This thesis is carried out within the framework of an industrial partnership with the company Saur and backed by a collaborative project financed by the Rhone-Mediterranean-Corsica RMC Water Agency (Project CAPTURE). In the current context, domestic wastewater is increasingly considered as a resource rather than a waste. The ambition of the CAPTURE project is to develop two processes: 1) improved primary settling and 2) a highy-loaded activated sludge process (A process) to improve carbon capture and valorization by anaerobic digestion. The objective of this PhD thesis is to determine new knowledge on these two processes and to optimize their implementation in semi-controlled conditions to maximize carbon capture.

Specific research objectives:

Characterize and optimize the performance of both processes to maximize carbon capture.

• Characterize pollutant removal mechanisms in both processes in order to maximize methane production in the digestion step.
• Estimate the consequences of the set-up of these processes on downstream stages (sludge methanization, residual organic matter fraction, valorization of the nutrients in the sludge, nitrogen removal).

Methodology :

     1. steady-state tests under semi-controlled conditions

•  A-process: column scale (Vtot: 400 L) and pilot scale (Vtot: 3 m³);
• Improved settling: static (jar tests + settling columns) and dynamic tests (monitoring of a device including a 40 L settler).

    2. Analytical monitoring by analysis of organic matter fractionation and estimation of the contribution of each metabolic pathway (biosorption, storage and mineralization).

         3. Modelling of the results obtained in a dedicated software (mechanistic approach).