The effectiveness of wastewater treatment on the Emilia-Romagna coast: An analysis carried out by means of a three-dimensional hydrodynamical model

On the basis of the nutrient load measurements provided by local administrations and the managing organizations of the wastewater treatment plants, and given a description of the bathymetry of the coastal zone of the Emilia-Romagna region, a three-dimensional hydrodynamical model - which also accounts for salinity, temperature and nutrient diffusion - has been set up and calibrated. The model used is the 3D model by Leendertse, which integrates the mass and ntum differential equations, and uses the sub-grid-scale kinetic energy to compute the turbulent diffusivity coefficients which control the diffusion of temperature, salt and nutrients within the coastal waters. The scope of the modelling exercise was to analyze the effectiveness of the abatement of phosphorus and nutrients in wastewaters in relation to the particular summer conditions of the Emilia-Romagna coast where high temperatures and freshwater stratifications are associated with long periods of still waters, thus modifying the normal fall-winter washing out conditions. An attempt has also been made to prepare a graphical post-processor for the model output in order to allow decision-makers to visualize and synthesize the model results.