Bioremediation Enhancement of Marine Sediments Contaminated by Crude Oil with Biogenic Pollutants Mobilizing Agents and Biosurfactants

One of the main limitations to the bioremediation of oil-contaminated marine sediments is the low hydrocarbons bioavailability. Aim of this PhD research project is to identify an environmental friendly approach to increase hydrocarbons bioavailability and biodegradation in oil-contaminated marine sediments. Several surfactants/pollutant mobilizing agents have been selected and applied to slurry microcosms: two microbial surfactants (sophorolipids and rhamnolipids), two types of cyclodextrins (hydroxypropyl- and randomly methylated- β-cyclodextrins; HPB-CD and RAMEB-CD), two commercial soy lecithin products (de-oiled and raw) and bile acids. Sophorolipids, cyclodextrins and to less extent, soy lecithins stimulated n-alkanes anaerobic degradation of actual oil-contaminated marine sediment from Gela (Sicily). Molecular analysis of 16S rRNA gene suggested that an Acidobacteria was probably responsible for the anaerobic biodegradation. Under aerobic condition, the same surfactants had inhibitor effects on n-alkanes degradation in Gela sediment, while HPB-CD and de-oiled soy lecithin were able to increase the degradation in crude oil-contaminated sediment from Ravenna. Increase of n-alkane bioavailability in oil-contaminated Gela sediment occurred in the presence of the two cyclodextrins and raw soy lecithin, both immediately after oil contamination as well as after the complete adsorption of hydrocarbons to sediment. Investigations of surfactant releasing formulations for the deployment of these agents to the sediments showed that HPB-CD could be efficiently encapsulated in agar hydrogels, while sophorolipids in polybutylene succinate (PBS) microspheres. The release rate of encapsulated HPB-CD was higher than encapsulated sophorolipids when formulations were incubated in marine water and similar in oil-contaminated sand slurries. Both encapsulated surfactants remarkably reduced adsorption of freshly spiked hydrocarbons to sand; conversely, only agar-encapsulated HPB-CD were able to desorb n-alkanes in weathered contaminated sand and increase their bioavailability and biodegradation similarly to free cyclodextrins. Therefore, encapsulation of HPB-CD in agar capsules might be the most promising solution for the enhancement of the bioremediation in marine sediment.