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Fishing for 142 billion kg of ocean trash

The 21-year-old Slat says at 16, he realised that he had encountered more plastic bags than fish while on a diving trip to Greece. For his school science project, he tried to understand why floating ocean plastic is so difficult to clean-up.

“I thought we could clean the ocean garbage patches. In late 2012, I presented this idea at a TEDx conference, and then spent several months with industry experts to compile a list of 50 questions that needed to be answered to confirm feasibility. In 2013 the idea went viral on the internet, which enabled me to raise funds and assemble a team of 100 people, with whom I’ve now published an extensive study indicating the concept’s feasibility,” says Slat.

Ocean Cleanup array

“Past concepts have been based on vessels with nets that would fish for plastic. Not only would this take billions of dollars and 79 000 years, but it would also create by-catch, where marine life isunintentionally trapped. Furthermore, the plastic rotates in the areas where the plastic is concentrated — it does not stay in one spot. So I wondered: why move through the oceans if the oceans can move through you? I came up with a passive system of floating barriers attached to the seabed and orientated in a V-shape. The barriers first catch and then concentrate the plastic, enabling a platform to efficiently extract the plastic once it arrives in the centre of the V,” he says.

As the project developed, the team grew to 100, most of whom were part-time volunteers. But now this inspired team has devoted thousands of hours to a project that faces feasibility concerns. And while Slat has succeeded in raising more than USD2-million for a cleaning device, critics say the high cost is misdirected. Last year, the project announced it had completed a survey that would pave the way for a June 2016 test of its prototype. With USD2.2-million in crowdfunding, Slat publicised plans to deploy 100km of floating barriers to clean-up 42% of the patch’s plastic pollution in 10 years.

Concerns voiced

Despite much online enthusiasm for the project, oceanographers are voicing concerns. They question whether the design will survive the open ocean and how it will affect sea life. Many are concerned about the lack of an environmental impact assessment prior to such a push for funding.

“We’re trying to achieve what has never been done before,” says Slat. “It’s 100 times bigger than anything that’s ever been deployed in the ocean. It’s 50% deeper, and 10 times more remote than the world’s most remote oil rig. So obviously there are challenges.”

In 2014, the Ocean Cleanup released a 500-page study, which Slat and his team used to determine the project’s feasibility. As described in the study, the passive system relies on wind, waves, and currents to push the plastic into screens that extend from the floating barriers like a skirt. The current passes beneath the screens to prevent by-catch of plants and animals. Since plastic floats, the barriers will capture ocean pollution between 35mm and 100mm in size. The V-shape of the array then concentrates the pieces at the centre, where they can be harvested. After the plastic is processed, it will be collected by boat to be sold as recycled material.

In the study, the Ocean Cleanup offers four possible designs, but Slat says they’re still working on finalising a concrete design of the collection platform.

Scientist andphysical oceanographer Kim Martini and biological oceanographer Miriam Goldstein aren’t convinced. After the feasibility study was published in 2014, they published their own review on where they say their concerns have remained unresolved.

Obstacles to overcome

Since the feasibility study, the Ocean Cleanup team has focused the most on the engineering and the design, according to Slat. Since 2014, he and his team have deployed two scale-model tests at water research centres. Based on the tests, the team is trying to better model how the structure will respond in the open ocean. Though Martini and Goldstein wrote that the study underestimated the forces of currents, Slat optimistically says, “The forces are a lot lower than we thought they would be”. Another issue is biofouling, which happens when marine life affixes itself to the structure, affecting its performance. “We’re testing different coatings to prevent biofouling,” says Slat.


“Why move through the oceans if the oceans can move through you?”


More resources

The Ocean Cleanup is continuing to test the concept. After the crowdfunding campaign in 2014, Slat hired 35 more employees “to tackle these challenges”.

The team has undertaken a series of six expeditions since 2013 to measure the depth and the size of ocean plastics within the gyre, the results of which will be published in a study that Slat says he will be submitting to a peer-reviewed journal. The next step he plans to take with his team is to deploy a prototype in the North Sea this summer. A 100m segment, or about 1/1000th of the planned array, will be set up about 20km offshore.


Slat says The Ocean Cleanup prepared for the next phase of testing with an environmental impact analysis with Royal HaskoningDHV. Early next year, the team plans to pilot the project off the coast of the Tsushima Island in Japan. But even after this, the uncertainties are numerous. The rope mooring systems cannot be properly tested off Tsushima, because the depth doesn’t match that of the open ocean. Slat admits that deploying something out in the middle of the ocean will be costly to fix if something had to go wrong.

Stop dumping plastic

“Even if the gyre clean-up were viable,” says Kara Lavender Law, research professor at the Sea Education Association, “it would be like mopping up the bathroom floor without turning off the tap to the bath”. Humans will continue to dump about 8.6 billion kilograms of plastic into the ocean each year. And as the larger pieces travel, they break down into microplastics that sink to the floor and are more difficult to clean-up.

Climate scientist and oceanographer Erik van Sebille has found it can take up to 50 years to reach the garbage patches. “Even if we would clean-up the garbage patches today, the garbage would return within a few decades,” he wrote.

Slat is undeterred. “The ocean garbage patches won’t disappear by themselves,” he says. “If you collect plastic closer to the source, the mass that you remove may be larger, and the influx to the gyres would be reduced. Our focus, however, is on the task of removing the plastic that has already reached the gyres.”

While it doesn’t have the same appeal as a giant passive structure that can help the ocean rid itself of plastic, Law notes that beach clean-ups that get people to tidy up their own shores (like the International Coastal Cleanup), do make a difference. In 2014, the initiative is reported to have collected more than 7.3 million kilograms of trash.

This is a shortened version of “Too good to be true? The Ocean Cleanup Project faces feasibility questions”, which originally appeared in The Guardian on 26 May 2016.



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