Topic of the practice
The aims of this practice is to test a new technique to recover the polluted seabed located in the industrial channel of the port of Livorno and to study a new process to re-utilise the dredged material for other purposes (raw material for building roads, yards, etc.)
Good Practice Information
The practice consisted of three phases.
1. Chemical characterization of the site. The channel has been divided in homogeneous sectors having an square-shaped area; the sectors along side had a surface of 33x33 m2 whereas the sectors in the middle of the channel had a surface of 66x66 m2. Sample of the sediments were probed in all the sectors and successively analyzed in the laboratories of the regional Agency for the protection of the environment (ARPA). The results of the analysis showed the distribution oh hydrocarbons and heavy metals (Cd, Zn, Cu, Ni, Pb, Hg, As, Cr) all along the channel so to have a three dimensional map of the pollutants distribution areas.
2. Removal of the sludge. The sludge on the bottom of the channel was transferred on land using a sucking pump operating under the surface of the sludge and a floating pipe.
The coarse material was riddled and separated from the sludge then the water was removed from the solid sediment by several methods (sedimentation, hydrocycling, clarifier and filter press) and, after being analysed and treated, the water was discharged into the sea if the contamination levels were under the limits set by the laws.
3. Treatment of the sludge. The choice of the best technique to adopt to treat the polluted sediments depends on several factors as the national and international environmental regulations, further analysis on the sludge to evaluate the efficiency of different methods, considerations about the feasibility to reproduce the test on larger scale. A final process, consisting of two stages, was proposed,: a) a basic washing with the extraction of the organic phase and b) an inactivation process.
Evidence of success
In general, dredging activities produce turbulence and torpidity increasing the pollution level in the site surroundings that have to be dredged. This secondary pollution could be strongly reduced using a sucking pump operating under the surface of the sludge as proposed by Livorno Port Authority.
The operative costs of the recovering and the treating process of the sludge were estimated in about 70 €/m3 whereas 520 €/m3 were necessary for the removal and disposal in a dumping site. Therefore, a good compromise between economic and environmental aspects was found.
Synergies with other ports in Europe were established to export the know-how and techniques carried out by Livorno Port Authority. Italian Port Authority of Catania, La Spezia, Marina di Carrara and Venice were quite interested into the results of this practice. Moreover, agreements with the “Office de la Marine Marchande et des Ports de Tunis” and the Dominican Republic were made in order to export these technologies.
Contact details to obtain further information on the practice
Ing, Giovanni Motta
Livorno Port Autority
Annex completed on: 04-05-2012