SEDI.PORT.SIL - Recovery of dredged SEDIments of the PORT of Ravenna and SILicon extraction

Abstract:

Background

Many European ports and harbours have a tendency to silt up over time in the face of natural environmental factors. Port authorities often have to remove deposited materials to maintain the needed depths in harbour channels and basins to meet the requirements of shipping and tourism. These materials then have to be disposed of appropriately.

The specific destination of dredged sediment in Italy is determined by its contamination levels as defined by national legislation. Confined Disposal Facilities (CDF) and landfills are the more common final destinations, due to limited availability of alternative techniques for treatment of pollutants.

An assessment undertaken within the SedNet European network found that the total amount of sediment dredged in Europe is between 100 and 200 million cubic metres per year. This material, together with the dredged water, is usually transferred into large fill-in basins. The polluted water is drained into wastewater systems, whilst polluted sediments are usually sent to landfill sites, incurring all the environmental risks associated with the management of dangerous waste.

Objectives

The SEDI.PORT.SIL project aimed to demonstrate an integrated approach for the sustainable management of sediment dredged from ports. It sought to demonstrate the efficiency of consolidated treatment technologies coupled with innovative techniques aimed at the recycling and valorisation of dredged material.

From a technical perspective, the project proposed an integrated cycle of actions to be applied to sediment - and associated water - immediately after dredging. It sought to reduce the environmental impact of dredged material and maximise the percentage of material suitable for recycling. It thus sought to turn a currently dangerous waste into an important resource.

Targeted uses for decontaminated sediment included as raw material in the infrastructure and environmental engineering sectors. The project also planned to investigate the potential for efficiently and effectively extracting valuable metallurgic silicon from polluted sediments. It targeted the elaboration of guidelines for treated sediment and raw material re-use, and to assess the feasibility and sustainability of a treatment plant at the port of Ravenna.

Results

The SEDI.PORT.SIL project successfully demonstrated a pilot treatment plant to valorise nearly the totality of dredged material samples from the Port of Ravenna in Italy. As well as showing the efficiency of the component parts of the treatment plant and the successful re-use of the material, the project assessed that the plant could be successfully scaled-up and applied in other European contexts.

The project constructed a prototype plant integrating three treatment stages: 1. Soil washing – decontamination techniques for contaminated soils and sediments, after which the latter are separated and classified according to different grain-size classes - gravel, sand and coarse solids. 2. Land-farming - a biological treatment based on biodegradation applied to the fine fraction of sediments, leads to a significant reduction of the concentration of organic compounds. 3. Plasma fusion - inertisation of the sediment followed by a plasma torch treatment to extract silicon metal.

It tested the plant on contaminated sediments dredged from the port of Ravenna, successfully demonstrating the possibility to turn 99% of the dredged volumes into secondary raw materials. It proved the efficiency of the plasma treatment in separating silicon - in particular valuable Ferrosilicon – from the sediment and the efficiency of the plasma torch for the decontamination of the finest fraction of dredged sediments which, after the thermal treatment, resulted inertised.

The project successfully explored the best possible re-uses of decontaminated sediment and extracted silicon. It notably demonstrated that the obtained materials could be reintroduced to the market in the infrastructure and environmental engineering sectors. Recovering products from the sediment waste means less natural raw material to be extracted and transported, less land consumption, less energy consumption, less land-filling and Confined Disposal Facilities.

Using the results of the tests, the team defined and planned an industrial-scale treatment plant for the Port of Ravenna. They evaluated the economic potential of material valorisation based on dredging of 11 million m3 of material in 3 years and identified possible new sources of sediment. They calculated that the plant would have a positive economic balance assuming a life cycle of 20 years.

The applicability of the process at the Port of Midia in Romania was successfully assessed and tested. This demonstrated the applicability of the treatment methodology in other European contexts. The project also published guidelines on the recovery and valorisation of treated sediment.