Nissrine Loukili

In wastewater treatment, high molecular weight cationic polyacrylamides (CPAM) are widely used as flocculants due to their ability to form robust flocs and enhance both sludge thickening and dewatering. However, optimizing flocculation remains a major challenge, with significant financial, operational, and environmental implications. In this context, this study investigates flocculation mechanisms by examining the interplay between CPAM rheology and floc properties, including formation, morphology, and physical behavior, with the aim of anticipating their performance in sludge thickening and dewatering. This work demonstrates that CPAM are susceptible to degradation upon contact with metallic surfaces such as aluminum and stainless steel. This conclusion is drawn from pronounced changes in CPAM rheological properties during measurements with metallic Couette tools, where a shift from elastic to viscous behavior is evident. The low-shear viscosity drops drastically over time by several orders of magnitude, and the reptation time similarly decreases during this process. The second part of the study highlights the impact of this degradation on flocculation dynamics, as it shortens the sludge–polymer mixing time, accelerates the kinetics of floc structuring, and alters floc morphology. The flocs evolve from an initially branched and filamentous network to a more isotropic and dispersed structure, accompanied by a gradual reduction in size. Moreover, this mechanism significantly reduces the polymer dosage required to achieve complete flocculation. Beyond flocculation, the third part explores the influence of CPAM degradation on sludge thickening and dewatering applications. The results reveal that this phenomenon disrupts floc thickening, compromises solid–liquid separation, and reduces clarification efficiency, yet under pressure it enhances sludge permeability, thereby facilitating water release and improving dewatering performance. In conclusion, this thesis establishes a synergy between the rheological properties of CPAM, the flocculation mechanisms, and the physical characteristics of the resulting flocs. These findings provide novel insights into the origins of variability in flocculation performance and offer valuable guidance for operational strategies to improve wastewater treatment at the industrial scale.

Membres du jury

M. Yahya RHARBI
CHARGÉ DE RECHERCHE, CNRS, Directeur de thèse
M. Jean-Charles MAJESTÉ
PROFESSEUR DES UNIVERSITÉS, Université Jean Monnet, Rapporteur
Mme Cécile FORMOSA
CHARGÉE DE RECHERCHE, TBI - INSA Toulouse, Rapporteure
M. Pierre-Xavier THIVEL 
PROFESSEUR DES UNIVERSITÉS, Université Grenoble Alpes, Examinateur

Membres invités

Mme Nadia EL KISSI     -  DIRECTRICE DE RECHERCHE, CNRS
Mme Sabrina GUÉRIN  -  DIRECTRICE INNOVATION, SIAAP
M. Laurent JOSSIC       -  MAÎTRE DE CONFÉRENCES, Grenoble INP
M. Pascal GINISTY        -  DIRECTEUR SCIENTIFIQUE, IFTS
M. Yannick FAYOLLE    -  INGÉNIEUR DE RECHERCHE, INRAE