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Kévin Maciejewski



"Kévin a su développer une approche multi-échelles (terrain, pilote, laboratoire) et résolument pluridisciplinaire pour mener à bien ses travaux.(...) En association des laboratoires partenaires, une des innovations majeures de la thèse de Kévin a été de mettre au moint une démarche expérimentale associant des mesures (i) isotopiques de l'azote et (ii) des activités enzymatiques pour comprendre le comportement dynamique de l'azote dans les systèmes."
Mathieu Gautier et Rémy Gourdon, INSA Lyon


 




THESIS

Wastewater treatment in vertical flow constructed wetlands. Dynamic study of nitrogen in the stages of the process and denitrification constraints.

Abstract

Vertical flow treatment wetlands have experienced considerable growth in France over the last 20 years. The challenge today is to better control the performance of these systems and to optimise the treatment of nitrogen and phosphorus. To meet these objectives, variants to the classic systems have been developed, consisting in particular of immersing the bottom of the filters to create anoxic zones and/or integrating processes that promote oxidation (trickling filter, forced aeration) into the treatment chain. The work presented here concerns a system called AZOE® whose two main modifications in relation to the basic system are the partial immersion of the reed filters and the addition of a trickling filter at the head of the system. The objectives of this work are to deepen the understanding of the nitrogen treatment mechanisms in this system, in particular the link between carbon and nitrogen, and to test possible optimisations. The work was carried out on several scales, combining the exploitation of field data on a real scale with experimental tests on a pilot scale and, more marginally, in the laboratory. Particular attention was paid to the development of analytical methodology adapted to the particularities of these systems.

The results obtained have shown that in these processes, the carbon load is degraded by up to 50% on the trickling filter, while nitrification can reach 25% in certain cases. The trickling filter degrades the carbon load preferentially to the ammonia load. The first stage contributes 75% to nitrification and 60% to denitrification. Under normal conditions, the performance of the second stage is lower (20% and 5% for nitrification and denitrification respectively). The work as a whole confirmed that the lack of organic carbon on the second stage was the main limiting factor for denitrification and enabled us to better quantify the evolution of the carbon : nitrogen ratio throughout the treatment process.

One of the contributions of this thesis was to adapt and/or develop specific analytical approaches to improve the understanding of the processes. Firstly, an isotopic approach was developed in addition to hydraulic tracing to understand the dynamics of nitrogen behaviour during a system feed period. A tracing with labelled ammonium made it possible to highlight the reactivity of the nitrogen with the filter media and to follow the displacement and transformations of a batch over time. The experimental pilots were equipped with a specific installation allowing the sampling of filtering materials on which nitrification and denitrification enzyme activity analyses were carried out to provide information of each filter stage with a precision of about 5 cm within the horizons of the porous media.

In a final phase designed to optimise these systems with regard to the identified limitations, two organic carbon supply strategies were evaluated to overcome the carbon deficiencies limiting denitrification on the second stage. The diversion of a proportion of raw effluent to the second stage was tested on a pilot scale, coupled with the measurement of microbial nitrification and denitrification potentials, allowing a fine mapping of the horizons involved in nitrogen treatment in comparison with operation without diversion. Finally, in a prospective approach, laboratory tests were carried out on the choice and study of 7 materials whose volumes and methods of input to the second stage are discussed.

Key words

Reed filters, nitrogen, nitrification, denitrification, bacterial bed, isotope tracing, microbiology of water treatment

H2O'Lyon director of thesis

Rémy Gourdon, INSA Lyon

Thesis co-director

Mathieu Gautier, INSA Lyon

Doctoral school

ED 206 - Chemistry, Processes, Environmental

Laboratory

DEEP, INSA Lyon

Defence date

12 july 2022

Defence language

French and English

Thesis jury members

  • Diederik Rousseau, rapporteur
  • Yves Andrès, rapporteur
  • Cécile Delolme, examiner
  • Joan Garcia, examiner
  • Julie Mendret, examiner
  • Rémy Gourdon, thesis director
  • Mathieu Gautier, thesis co-director
  • Pascal Molle, thesis co-director
  • Philippe Michel, guest
  • Amélie Cantarel, guest
  • Patrick Jame, guest