Critics say plan for drifting ocean trash collectors is unmoored

By Erik StokstadMay. 11, 2017 , 2:45 PM

It is undeniably an ambitious vision. Boyan Slat, a charismatic 22-year-old drop-out inventor, plans to clean up plastic trash circulating in the North Pacific Gyre by launching a fleet of floating trash collectors. Ocean currents would propel floating plastic trash into curved floating booms, which would funnel trash toward a central tank, to be collected monthly by ships. “We let the plastic come to us,” he says. The group hopes to eventually finance the operation by recycling the plastic and selling it as a branded product or raw material. Slat already has a pair of sunglasses made from recycled Pacific plastic.

Skeptics say the idea doesn’t make much sense and that collecting trash closer to shore would be more cost effective. “Focusing clean-up at those gyres, in the opinion of most of the scientific community, is a waste of effort,” says marine biologist Jan van Franeker of Wageningen Marine Research in the Netherlands. “It’s a lot of money to reduce something that disappears in 10 to 20 years, if you stop the input.” His research on seabirds showed a 75% decline of ingested plastic over 2 decades after reductions in industrial plastic entering the North Sea. Critics also worry that the high-tech clean-up project could distract from less glamorous efforts to lessen the use of plastic.  

Slat’s 4-year-old organization, The Ocean Cleanup, based in Delft, the Netherlands, is well on its way to launching its first unit. At an event tonight in the Werkspoorkathedraal—an industrial meeting hall in Utrecht, the Netherlands—Slat unveiled a new design that he says will allow The Ocean Cleanup to deploy its first collector in 2018, 2 years earlier than planned. It will also collect trash at twice the rate of earlier designs, he predicts.

Early encounter with plastic trash

Slat says he first experienced ocean plastic when he was 16. While diving in Greece, he recalls, he saw more plastic bags than fish. He designed a high school science project for cleaning up marine trash, and says he’s always been passionate about technology. “The act of creation, making something a reality, is one of the most fulfilling things you can do.” After a half-year of studying aerospace engineering (model rocketry was another early passion), Slat left university to found The Ocean Cleanup in 2013. Since then, and with the help of a TEDx Talk that has received 2.5 million views, The Ocean Cleanup has raised $31.5 million in donations—two-thirds of it since November 2016, with large amounts coming from silicon valley investor Peter Thiel, the chemical company Royal DSM, and other donors.

The Ocean Cleanup has about 65 engineers and other staff. While designing the collector, Slat’s team has also been studying plastic in the North Pacific. Most research vessels use 1-meter-wide trawls to sample plastic debris. In 2015, The Ocean Cleanup organized an expedition of some 30 ships, including a decommissioned National Oceanic and Atmospheric Administration research vessel, to measure larger pieces of debris. Last year, they also flew over the area to measure amounts of even bigger trash, including lost or discarded fishing gear called ghost nets. They plan to publish their findings this year.

In June 2016, the group tested a 100-meter prototype collector for structural integrity, placing it 16 kilometers into the North Sea. After 2 months the shackles connecting the booms to the mooring had begun to fail. Although the prototype experienced weather rougher than that typical of the Pacific, the test highlighted the long-standing challenge of how to secure the collectors to the seabed in water some 5 kilometers deep.

In a shift, engineers have come up with a new design. The approach is to use weights suspended a few hundred meters below the surface, where, according to the organization’s ocean circulation models, the currents are about one-fifth the surface speed. The weights consist of 12-meter-tall metal towers, shaped like a plus sign in cross section, that will drag in these slower currents. Because the surface water moves faster, plastic debris will collect on the drifting booms.

The organization also announced today it was downscaling the overall design. Instead of a few units each with two 100-kilometer-long arms, they will build multiple smaller collectors that are 1 kilometer long. This smaller scale should cut the per-unit cost to a few million dollars, Slat says, and also advance the production schedule by about 2 years, allowing deployment of the first unit in early 2018. Initial calculations suggested a moored design would collect about 40% of the plastic in the North Pacific Gyre within 10 years. The new design should be able to collect trash faster—by drifting into the denser accumulations of plastic—and remove half of the plastic within 5 years, once 50 units are at work.

Solution, or ineffective distraction?

So far, critics haven’t been impressed, listing technical limitations and concerns such as harm to marine life. “It’s not the best solution,” says Marcus Eriksen of the ocean nonprofit The 5 Gyres Institute, based in Los Angeles, California. “In fact, it’s a distraction from the work going on upstream.” Most environmental groups working on ocean pollution focus on reducing the amount of plastic that enters the ocean, and, ultimately, what Eriksen calls “the heavy lift of ending the one-time, throwaway culture.” Another issue is that researchers suspect much of the plastic that enters the ocean sinks to the sea floor, where it is inaccessible to floating trash-catching devices.

The open ocean may not be the best place to locate trash collectors. Computer simulations, published last year in Environmental Research Letters, suggested that collectors located near China and Indonesia would be more than twice as efficient at capturing microplastic—and collect fewer plankton—than ones located in the North Pacific. In streams and rivers, floating collectors can significantly reduce the amount of trash entering the ocean.

Slat replies that there is not an either-or solution. “We need to do both,” he says. “We need to intercept plastic before it becomes ocean plastic. And we need to clean up what is out there.” Eriksen says that plastic on the high seas is mostly lost or discarded fishing gear. Fishermen could be paid or encouraged to collect it, which he says has worked reasonably well in the North Sea. The rest will eventually break down. 

Source: Science Mag