Traitement des effluents piscicoles marins par lagunage a haut rendement algal

When facing the increasing development of aquaculture, farming in recycled water is an alternative to limit the impact on the environment: farming produces a lower amount of wastes but of higher concentration which can be treated. The goal of this thesis is to evaluate the efficiency of high rate algal lagooning/ponding (HRAP) for the treatment of marine fish culture effluents. Also, this study utilizes wastes from Dicentrarchus labrax grown in Ifremer's recycled waters station. The first step shows the particularities linked to recycled water farming effluents. They are characterized by low particle and organic substance concentrations as well as strong dissolved inorganic nitrogen (DIN) and phosphorus (DIP) concentrations. Furthermore, nitrogen is mainly present in nitrate form. When establishing an empirical model we can predict the evolution of DIN and DIP concentrations in recycled water farming effluents according to water renewal rate, fish growth and food rations. Next, nutriments absorption capacity was studied in laboratory using three macroalgae species cultivated in a highly concentrated nutriments environment. Among those algae, genus Ulva sp. seems to suit the purification of high concentrations of nutritive salts effluents. Using the HRAP treatment system promotes spontaneous development of this kind of Algae which biomass remained the greatest during the entire study. This treatment method improved physicochemical water state, for a potential reuse in farming systems. However, treatment efficiency is always superior to 50% for DIN and DIP figures, but still varies according to seasonal effects and nutriments flow coming through the lagoon area. The nutritive salts elimination rate helps to establish the size of a treatment unit according to fish biomass. Furthermore, the quality of treated waters seems to enable reclaiming into the farm's recirculation system (closed circuit farming).