Camille Banc

"Tout au long de son travail Camille a mis sa détermination et sa motivation au service de son projet pluridisciplinaire. Par ailleurs il a étroitement collaboré avec le laboratoire Géosciences de l’Université de Rennes avec lequel il a créé de sa propre initiative une collaboration très fructueuse.
Son travail a donné lieu à plusieurs présentations orales en congrès internationaux renommés dans le domaine des
géosciences.Les très grandes qualités pédagogiques de Camille BANC et sa grande maîtrise du sujet ont d’ailleurs été unanimement saluées par le jury lors de la soutenance de thèse."
Mathieu Gautier et Rémy Gourdon, INSA Lyon

 

In water treatment systems described as "nature-based solutions" (i.e. constructed wetlands and infiltration basins), the retention of suspended solids can lead to the formation of a surface deposit layer. Both from the point of view of its capacity to interact with the pollutants during its presence on the treatment unit, and during its reuse, notably in land application after curing, pollutants speciation within the deposits and their prossess of remobilization are questioned. After removal, these deposits constitute an interesting resource, particularly in agriculture, due to the quantity of nutrients and organic matter they contain. The objectives of this work was to better describe the organo-mineral assemblage of these deposits and to provide a better understanding of the influence of colloidal phases on the remobilization of major and trace elements in order to be able to provide predictive models, both quantitative and qualitative, on the remobilization of pollutants from deposits subjected to pH variations.

A vertical flow constructed wetland sludge deposit was subjected to different pH conditions and the colloidal phases were studied. Remobilization of organic colloidal phases was found to be particularly sensitive to pH changes. In the acidic pH range, small organic molecules (<3 kDa) are predominantly remobilized from the deposits. For near-neutral and alkaline pH, large organic colloids (>30 kDa) prevail in solution. This release of organic matter seems to favor the remobilization of iron and aluminum oxides within organo-mineral colloids. The nature and quantity of the remobilized colloidal phases have a large influence on the release of major and trace elements from the constructed wetland’s sludge deposits. However, the affinity of the elements for these colloidal phases is also controlled by the chemical class of the element considered, its oxidation state and the pH of the solution.

The use of these experimental data allowed the development and calibration of a multi-surface geochemical model able to reproduce the release and speciation of a wide range of elements (Fe, Al, P, Ca, Mg, Cu, Cd, Cr, Zn, Pb, As) retained within a reed filter sludge. Due to the high concentration of organic matter measured in the sludge and their importance in the release and speciation of elements, the modeling of metal complexation on organic matter by WHAM-ModelVII has been the subject of numerous experiments. The modeling tests combined with the ultrafiltration results allowed to obtain a ratio of active organic matter allowing to improve the prediction of the elemental concentrations. In order to evaluate the robustness of the methodology used on this first sludge, the modeling strategy was applied to other samples (i.e. a second constructed wetland sludge and two infiltration basin sediments). The multisurface models developed in this thesis have all shown their efficiency in calculating the release of many elements whatever the pH conditions and despite very variable initial concentrations of major and trace elements. The information provided by this thesis have been fundamental in understanding the risks associated with the emission of trace metals in particular. In time these models could therefore be part of the decision supporting tools available to managers of these solid deposits.