Containment and recovery
The aim of containment
and recovery operations is
to remove the pollutant from the sea surface, at sea and near the coastline, before it hits the shore.
In the open sea, these operations are restricted by
the sea conditions and the technical capacity of the available vessels. Specialised high sea oil recovery vessels are complex, very costly and are limited in their versatility. As the substance they recover contains several volumes of water for a volume of oil, these vessels must be able to store considerable quantities of oil-in-water emulsion onboard. Emulsions can be treated using an emulsion breaker to separate the hydrocarbons from the water and debris trapped in the emulsion, thus considerably reducing the extent of pumping operations and pollutant transfer. After settling, the volume of oil which needs to be eliminated can be significantly reduced and the settled water can be released into the environment.
Response means at sea: trawling a slick
Near the coast, in sheltered bays and port areas,
small barges, which can be transported by road or
air, can be used. Their marine performance is rela-
tively poor; however, their technical capacities of
selective oil recovery (with a minimal amount of
water) are good. They are often used in association with port storage barges or flexible tanks specifically designed for pollution response, ensuring continuous recovery.
Recovery at sea
Recovery of the fuel oil from the Prestige
These specialised vessels and barges are more effective on continuous thick slicks than on thin fragmented slicks. This method is often used on slicks which are contained by booms. The vessels are equipped with nets which can be used in dynamic mode (trawled by two boats) or in static mode (attached to fixed points).
Experience of the Prestige pollution in the open sea, involving
heavy fuel oil, demonstrated
the usefulness of fishing boats for the recovery of small dispersed slicks.
These vessels, of which hundreds may be made available in an emergency,
can cover far larger areas than the few dozen specialised response vessels
and barges existing in Europe. Equipped with simple recovery means, similar
to their usual work tools (nets, hand skimmers…), fishermen compensated
for the low individual recovery capacity by their large number and motivation
during response to the Prestige spill.
Polluted waste recovered during the Prestige spill (tonnes)
An exceptional performance
Response at sea to the Prestige spill lasted 6 months, compared to only 11 days in the case of the Erika spill, before a storm pushed the slicks onto the shore. Thirteen oil spill response vessels and more than 1,200 fishing boats participated in the response, each crew with their own experience and tools. They recovered 55,500 tonnes of emulsion, containing around 23,400 tonnes of fuel oil: an unprecedented performance in the history of oil spills. The combination of specialised vessels, which were efficient on fresh slicks (thick and concentrated), and fishing boats (which intervened later by skimming scattered patties and patches), is illustrated by the above diagram.
Recovery at sea