Bioactivators as a potential strategy for dredged marine sediment recovery

Sediment dredging from harbors and water bodies in order to maintain the navigation is a necessity worldwide; however, the storage and treatment of sediments is a problem for harbor managers. Sediment decontamination could represent a sustainable approach for turning them into a new source of environmentally reusable material. To manage the sediments dredged from the Livorno harbour, several possible recycling techniques are being explored, including sediment washing and bioremediation. A combination of these two techniques can also be taken into consideration. This study examines the feasibility of an enzyme enhanced bioremediation technology used as it is, or in combination with the sediment washing. Specifically, we applied an enhanced bioremediation approach to both raw sediments and two derivate granulometric fractions separated by a pilot sediment washing facility: a silt-clay fraction (< 63 μm) and a sand fraction (>63 μm<200 μm). The preliminary sediment washing was effective in concentrating the organic and inorganic contamination into a smaller volume of fine sediment particles (silt-clay). The bioremediation experiment, carried out in triplicate at mesoscale level, consisted in setting up containers of about 0.2 m3 each, filled with the three matrices (raw sediment, clay-silt and sand fractions) treated and untreated (control) with bioactivators (a mixture of microorganisms, enzymes and synergists). The physical, chemical and biological properties of sediments were determined at the initial sampling time (t0) and after three months (t90) from the beginning of the experimentation. The bioactivator application, providing specialized microorganisms and stimulating the growth of indigenous microorganisms, determined the increase in microbial respiration and in hydrolytic enzyme activities in all the treated matrices, in particular in the siltclay fraction. However, this fraction both treated and untreated, has not been able to degrade significant amount of organic pollutants. This is probably due to the burial of contaminats in micropores making them inaccessible to microorganisms and extracellular enzymes. On the contrary, a significant reduction in total petroleum hydrocarbon was observed in sand and raw sediment matrices after three months from remediation strategy application (about 50%), indicating the efficiency of the bioremediation technology.