Abstract
In harbour areas and during dredging operations, polluted marine sediments can be resuspended in the water column and mobilized. This resuspension of polluted sediment poses a risk to the marine ecosystem surrounding the dredging site. There is therefore a need to limit the risks of pollution mobilization. Thus, an understanding of the mechanisms behind this mobilization is essential in order to better predict and thus better manage the processes occuring during dredging and the associated risks. In this context, the objective of this thesis was to identify and understand the parameters that can influence the mechanisms governing the mobilization of organic pollution more specifically that of Polycyclic Aromatic Hydrocarbons (PAH) during re-suspension events such as dredging. The experimental approach developed was therefore to study the parameters influencing sediment/PAH interactions at the molecular level, the phenomena of agglomeration/dispersion at the particulate scale (micro-mesoscopic scale) and the (re)sedimentation behaviour at the macroscopic scale.The work focused on the study of harbour marine sediments taken from a Mediterranean marina, the Grau du Roi. Morpho-granular, chemical and physico-chemical characterization of these real sediments allowed us to understand the complexity of their composition. After wet fractionation of the sediment, pollution levels, as well as the distribution of PAH in different granular fractions, were determined. It was found that PAHs were distributed in all granular fractions. For some sediments the highest PAH concentrations were found in fine granular fractions, as it is generally the case in the literature. However, for other sediments the highest concentrations of PAHs were found in coarse, low-organic fractions. The study on the adsorption of humic acid and pyrene by model materials reflecting the composition of marine sediments showed that, PAH (pyrene) can be adsorbed by MO and also by minerals (quartz and calcite). The laboratory-scale study of (re)sedimentation behaviour of PAH-polluted sediment helped determine the parameters that could have an impact in the event of re-suspension under dredging conditions. Parameters such as ionic force, fine particle content (< 20 µm), and density fraction have been identified as having an influence on sedimentation behaviour. Finally, it has been shown that the particle size of the sediments has an influence on the sedimentation mode, which also has an influence on the type of deposition formed. Formed deposit after the resuspension was constitute by two layers, including a fluid top layer, which may cause mobilization of pollution.