Theses in progress

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 : (i) not negatively impacting the quality of the treated water and (ii) 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).

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: i) a better design of infiltration systems, by allowing the integration of distributed 2D/3D information into water transfer models, ii) 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.

o    Characterize pollutant removal mechanisms in both processes in order to maximize methane production in the digestion step.

o    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).