Environmental recovery of coastal areas: the bio-remediation study case of the industrial harbour of Marghera, Venice, Italy

We report on the experiment of in-situ bottom sediment oxygenation by forced aeration, in the industrial harbour of Marghera, with the aim of reducing heavy metal and organic pollutant content. Many of these are particularly resistant to biodegradation due to the presence of one or more aromatic rings in their molecular structure. In the presence of appropriate oxygenation conditions however, several species of bacteria rich in enzymes, known as "cyclo-oxygenase" can break the aromatic rings and use them for their energetic metabolism. With the aim of determining possible variations of heavy metal and organic pollutants concentration, five sets of three sediment cores, where collected before, during and after two oxygenation campaigns, in three different sites, with a 7 month interval of no aeration. Fast freezing of the cores, after extraction, was applied, in order to avoid adding any artificial sediment mixing, in particular for the top part of the sediment core that is very fluid and sediment mixing can easily occur. The comparison of the heavy metal concentration averages of the top 6 cm of each core collected before, during and after the aeration activities gave a good indication of the oxygenation effects, of their persistence in time and of the general reduction of the heavy metal concentration in the surficial sediments. The study has also indicated that bottom sediment mixing plays a very important role: where sediment reworking and mixing are strong the effect of oxygenation is very limited and irregular.