By adding grooves to the surface of a common oil-skimming device, researchers recovered up to three times as much oil as they did with smooth-surfaced devices. The improvement could reduce the environmental and economical costs of oil spills.
The Exxon Valdez incident spewed nearly 11 million gallons of crude oil into Alaska’s Prince William Sound in 1989. Although spills of that magnitude occur infrequently, smaller-scale spills are common. According to Jeff Brown of the National Response Center in Washington, D.C., nearly 100 spills of at least 1,000 gallons of oil and more than 10,000 smaller spills have been reported annually in U.S. waters in recent years.
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When a grounded tanker or burst pipeline releases oil into the sea, response teams first attempt to contain the spill with a large loop of plastic tubing that surrounds the oil. In most situations, responders next place skimmers shaped like drums or disks into the water. These skimmers rotate and pick up oil on their surfaces. An attached scraper removes the oil, which is later pumped into a storage tank.
Although effective, the skimmers work slowly. Their recovery rates range from 50 cubic meters per hour for heavy crude oil to 0.2 cubic meter per hour for diesel oil, which is lighter, notes Arturo A. Keller, an environmental engineer at the University of California, Santa Barbara.
Victoria Broje, now a spill-response specialist with Shell Global Solutions in Houston, had joined Keller’s lab with the goal of improving the efficiency of skimmer technology. She and Keller made several changes to a 25-centimeter-wide, drum-shaped skimmer. Their key innovation was V-shaped grooves, each 2.5 cm deep, on the aluminum drum, Keller says. The grooves increased the surface area of the drum and provided wells that collect oil.
The researchers tested their skimmer in pools of seawater under different temperatures, at different rotational speeds, and with oils of varying viscosities and in different oil slick thicknesses. The grooved drums skimmed up to three times as much oil as the smooth drums did, the researchers report online for the Dec. 15 Environmental Science & Technology. Under most conditions, the grooved drums picked up twice as much oil as the smooth ones did.
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“We knew it was going to be better, but we didn’t think it would be that much better,” says Keller. He adds that the technology has now been licensed to a company that manufactures oil-spill cleanup equipment.
It’s been a decade since such a “big improvement” in skimming technology has occurred, says Joseph V. Mullin, who manages oil-spill–response research at the Minerals Management Service, the federal agency in Herndon, Va., that funded the new work. “We look forward to this research being transferred to real-world operations.”