Bioremediation for Shoreline Cleanup: In Situ vs. On-Site Treatments

By the end of 2002, the shoreline of the Cantabrian Sea had been severely contaminated by the Prestige fuel oil spill. As a result, coastal sediments were affected with a heavy and viscous hydrocarbon mixture and, initially, waste was removed by hot pressurized water washing. However, some specific sites were considered for biotreatment where grain-size sediment and other factors made mechanical removal ineffective or inappropriate. Therefore, the aim of this work was to select bioremediation procedures for cobble and pebble sediments at Bahinas Beach (Asturias, Spain). Laboratory, pilot, and full-scale experiments were carried out to select nutrient sources, surfactants, and other bioremediation amendments to be applied as part of a novel on-site bioremediation approach vs. in situ bioremediation. Simple microbiological control and chemical determinations were made to monitor these two procedures. First, a classic approach of in situ bioremediation was tested with the direct application of S-200 (a new oleophilic fertilizer), which achieved hydrocarbon depletion higher than 30% of linear alkanes and aromatics after 60 days of cobble-pebble treatment. On the other hand, the design and subsequent implementation of on-site bioremediation achieved not only better results in shorter periods of treatment (40% of global hydrocarbon depletion after 30 days), but also reduced viscosity of the fuel residues adhering to the sediments, thereby enabling a secondary water washing to complete cleaning of cobbles and pebbles.