Combination of sediment washing and bioactivators as a potential strategy for dredged marine sediment recovery

Dredging of potentially contaminated sediments from ports and waterways is an inevitable operation in order to maintain adequate depths for ship navigation. The fate of these sediments is an issue discussed worldwide due to their impact on human and environmental health. In this scenario, the aim of the present study is to provide an innovative eco-friendly and adaptable solution for dredged sediment decontamination and rehabilitation based on sediment washing followed by a biological treatment. The sediment washing, conducted at pilot scale, split the raw dredged sediment into two fractions of homogeneous particle size (silt-clay fraction and sand fraction). Sand fraction was characterized by a significant lower values of heavy metals and total petroleum hydrocarbons (TPH) with respect to the silt-clay and raw sediment samples. The biological treatment, carried out at mesoscale level, consisted in the addiction of a mixture of microorganisms (with hydrocarbon degrading ability), enzymes, and nutrients (bioactivator product) to the three matrices (raw sediment, silt-clay and sand). After three months, in raw sediment and sand fraction, the bioactivator product allowed a 46% and 55% removal of TPH, respectively; instead, in silt-clay fraction this treatment was not able to degrade significant amount of organic pollutants (reduction percentage of TPH lower than 5%). Culture-dependent analysis showed higher concentration of microbial cells immediately after addition of the bioactivator product and a general increasing of microbial biomass in both treated and untreated samples at the end of the experimentation. Moreover, PCR-DGGE analysis evidenced that the composition of microbial population varied in relation to the different granulometric characteristics of the sediment and to the application of the bioactivator product. Thus, the results here reported showed that bacterial and fungal communities responded differently to the bioremediation treatment. These results seem very promising considering the complexity of the material to be decontaminated and the apparent difficulty of creating acceptable habitat for the operation of a biological active system.