The innovative ejectors plant technology for sediment management in harbours

More than 90% of global trade is carried by waterborne transport, constituting the most important means of transportation of goods. Therefore, global business critically depends on adequate ports, harbours, and navigation status (navigability). Preserving good navigability is challenging since port and harbour access and waterways are often hampered, as the vast majority of 10,000 ports and harbours worldwide suffer from sedimentation. Traditionally, the sediment that causes the problem is excavated, removed and relocated through maintenance dredging. Nevertheless, dredging is not effective in maintaining navigability over time. This objective may be reached through a higher frequency of dredging operations but would result in higher costs and complex authorization and permit procedures. Maintenance dredging also has considerable environmental impacts since dredging operations can: i) destroy or significantly modify underwater habitats and resident flora and fauna, ii) resuspend sediments and contaminants already present in the seabed, thus increasing the Suspended Solid Concentration in the water column with adverse effects for the ecosystem, iii) impact locally on greenhouse gas, pollutants and noise emissions, iv) generate a waste to be disposed, i.e. the dredged material. The University of Bologna has developed the “ejectors plant” technology as a sustainable alternative to maintenance dredging. It has been recently tested in two demo applications in the Marina of Cervia and Marina of Cattolica (Italy). The ejector is an open jet pump (i.e. without a closed suction chamber and mixing throat) with a converging section instead of a diffuser and a series of nozzles positioned around the ejector. Each ejector is placed on the waterbed and transfers momentum from a high-speed primary water jet flow to a secondary flow, a mixture of water and the surrounding sediment. The sediment-water mixture is then conveyed through a pipeline and discharged in an area where the sediment can be picked up from the natural water current or is not an obstacle for navigation. The paper aims to show the results produced by the two demo installation monitoring activities, suggesting that the technology is effective and efficient and that demo plant operation is accompanied by an improvement in several parameters related to the ecological status of the marine ecosystem in the area affected by ejectors within one year.